l'IFIQlfE DE LA HECHERCHEhorizon.documentation.ird.fr/exl-doc/pleins_textes/... · interrelated Tasks dealing with global change impacts on soil organic matter dynamics, soil degradation,

GC TE

GLOBAL CHA I~GE & TERRESTRIAL ECOSYSTEMS

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CENTRE NATIONAL

I DE LA HECHERCHE'1 SCIE!\l'IFIQlfE

IlProgramme enuironnemeni Il

29 - 30 - 31 March 1994 Paris

PLACEThe workshop on

"Erosion under Global Change"

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INTERVENANTS

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Dr. Albrecht A.labo Matière organique des Sols Tropicaux CentreORSTOM B.P. 800697259 Fort de FranceMartinique

Dr. Boudman J.Environmental Change UnitUniversity of OxfordMansfield ReadOXI 3TB Oxford

UKDr. Claude B.

Service des Sols Ministère de l'Agriculturedu Québec2700, rue EinsteinGIP 3W8 SAINTE·FOYQuébecCanada

Mr. favis-Mortlock D.Environmental Change Unit University of Oxford 1AMansfield RoadOXI 3TB OxfordOxonUK

Dr. Ingram J.GCTE Office. Dept of Plant Sciences University ofOxford SouthPark RoadOXI 3RB OxfordGrande-Bretagne

Prof. Kirkby M.J.School of GeographyUniversity of LeedsL52 9TJ LeedsGrande-Bretagne

Dr. Roth Ch.Inst of Ecology, Technical Univ. BerlinSalzufer11-1210587 BerlinGermany

Dr. Menaut J.C.laboratoire d'EcologieENS46. rue d'Ulm75230 Paris cedex 05France

Dr. Niclcs A.UUSDAAgricultural Research Service National AgriculturalWater Quality laboratoryP.O. Box 143074702 DurantOKUSA

Dr. Oldeman R.ISRICP.O. Box 3536700 AJ WageningenPays-Bas

Prof. Pla Senti 1.Apartado 1131 (Las Acacias)MaracayVenezuela

Prof. DR. Poaen. J.Geography. Lab... Exp•• Geom,K. U. LeuvenRedingenstraat 16bis3000 LeuvenBelgium

Dr. ~J.et M.University of Miami RosentielSchool of Marine and Atrnospheric Science4600 Rickenbacker CausewayFL-33 149-1098 MiamiUSA

Mr. Sanden D. W.FAOViale delle Terme di Caracalla00 100 Romeltaly

Dr. SlaymaJcar O.Univ. of British Columbia1984 W. MAll British ColumbiaV65 IGICanada

Dr. Slddmore E.Erosion Research USDARSKansas State University, Waters Hall66506-4006 ManhattanKansasUSA

Dr. Imeson A. C.Inst. Physical GeolographyUniversity of AmsterdamNieuwe Prinsengracht 1301018 vz. AmsterdaMPays-Bas

Dr. Valentin Ch.ORSTOM B.P.11416 NiameyNiger

Dr.Wilcox P••Wilcox. B.Environmental Science Group los Alamos NationallaboratoryEES-15 MSJ 495 NM87545 los Alamos New MexicoUSA

Dr. Yu BofuFacu/ty of Environmental Sciences Griffith University4109 NathanQLD4111Australia

Dr. ZabecJcUsda-Agriculture Research Sery1294 FM RoadLubbeekUSA

SOMMAIRE

SESSION V: CURRENT MODELLING PROGRAMMES

SESSION VII: PARAllEl WORKING GROUPS AND REPORTING

EPle-water eroslon favis-Mortloclc, UK ...............................................................................••....................•..•.....43-

SESSION III: CURRENT EXPERIMENTAL AND MONITORING PROGRAMMESRainfaLl pattern changes and erosion Roth, Ge:rmany .••••••.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 17 ...Wind regime changes and erosion Prospero, USA ..............................................................•...•..•..............•...•......... 19Global change induced vegetation changes and erosion Slaymalcer, Canada ...................................•......•...........•...........21.Global change induced SOM changes and erosion Albrecht, Martinique ..................•...•......•...........•.....•.•............•.......23--CUTTent erosion monitoring programmes Boardman, UK 25

CREAMS/GLEAMS Model Application Under Global Change Niclcs, USA 41·

SESSION IV: OTHER. RELEVANT INTERNATIONAL PROGRAMMESInternational Board for Soil Research and Management networks (lBSRAM) Valentin, Niger 2,9--Global (Assessment ofSoil Degradation-UNEP/ISRIC) Oldeman, ISRlC•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••31 .Impact of c1imate change on the erosional response of Mediterraneanecosystems along a c1imatological gradient in SE Spain.Crete œtd Israel (ER.MES) Imuon, Netherlands 35The GCTE Transects Menaut, france.....•••••••••••••••••••.•••.••••••••.•..•......••••.•••••••••••••••••••••••••••••••••••••••••.•••••••••••••••••••3~

RWEQ-Revised wind erosion equation Zobeclc, USA ..............................................................•...•................•.•..........47WEPP . A new generation soil troslon model. Wilcox, Bradford, USA .....................................•...••..................•.•........49

EPIC-wind eroslon Skidmare, USA ....................................................................•............•......••.......•.....•••.•.........45

EUROSEM Morgan, UK ..••••.••....................••••........•...........•.•..•........•........•.•.•..........•••••.•.••.•••...•....•..••••••••••.•.•.51MEDALUS modtLs for soil œtd vegetation change Kirlcby, UK ......................................................•.....•...........••..........53.

Existing Data and Monitoring Working Group. leader: Pouen, Belgium 61Experimental Working Group leader: Boardman. UK. 63Modelling Working Group leader: favis-Mortlock. UK .....................................•..•..•................•.•••.•.............•.•••••••......64 .

SESSION VIII: OTHER fORMS Of SOll DEGRADATIONMediterranean desertification and land use (MEDALUS) Pouen. Belgium 69FAO's priorities Sanders, fAO 71

SESSION VI:PROPOSAL fOR A GCTE SOll EROSION MODElLiNG/EXPERIMENTAl NETWORKThe GCTE crop networks: an example of the GCTE network approach Ingram, WC •••••••••••••••••.•••••••••••••••••••••.•••.••••••••••••••57

ISSS priorities Pla Sentis, ISSS 73

1111 SESSION 1: INTRODUCTION

GBP. GCTE. Focus 3 & Soil Activity overviews and meeting objectives Ingram, UK•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••3 .1 :~:~:~o:ll:e:~:~o~:: initial ideas Valentin, Niger 5~Recent techniques for the study of long term erosion Claude Bernard, Marc Laverdière, Canada•••••••~••••••••••••••••••••••••••••••••9

1 Long-term variations in Regional Rainfall. Exarnple in Australia Yu, Australia 11Long-term variations in regional rainfall and in land degradation. example in West Africa Valentin, Niger 13 --

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IGBP. GCTE. Focus 3 & and the Soil Activityoveroiews and meeting objectives

Ingram. John

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The International Geosphere Biosphere Programme (IGBP) hasbeen developed to improve our knowledge of the dynamics of thebiosphere influencing, and influenced by. global environmentalchanges. It was Jaunched in the mid 19805 under the aegis of theInternational Council of Scientific Unions. and has given rise tosix Core Projects. One of these, Global Change and TerrestrialEcosystems (GCTE), has the overall joint aims of:

(i) Predicting the effects of changes in c1imate,atmospheric composition and land use on terrestrialecosystems, including

a) agriculture. forestry and soils, andb) ecological complexity, and

(ii) Determining how these effects Jead te feedbacks to theatmosphere and the physical c1imate system.

GCTE is divided into four major themes (Foci); Ecosystemfunction; Ecosystem structure and compositioni Global changeimpact on agriculture. forestry and soils; and ecologicalcomplexity. Broad outlines of the research agenda for each Focusare published in the GCTE Operational Plan (IGBP Report No. 21).

GCTE Focus 3 contains five Activities. three dealing withmajor food production systems and managed forests, and twodealing with the cross cutting issues of pests, diseases and weeds.and soils. This last Activity (Activity 3.3) contains threeinterrelated Tasks dealing with global change impacts on soilorganic matter dynamics, soil degradation, and soil biology. Thisworkshop is designed te launch the second Task (Task 3.3.2) andto prepare a detailed research agenda for its initial. predominantaspect. soil erosion under global change.

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SOIL EROS/ON UND ER GLOBAL CHANGE 3

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------------14 Erosion under Global Change

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IIII The CCTE soil degradation Task - initial ideas

Valentin Chistian

Ipropitiously conducted at various scales from the plot to the watershed.and possibly to larger scales. should be combined. to remote sensing dataand integrated into GIS.

ModellingThe broad range of data covering the space-time domain can be used

to calibrate. initialize. and validate models..We need models that shouldbe concurrently highly sensitive to climatic and land use changes andsufficiently flexible to be relevant under the largest range of conditions.The recent soil erosion process-based model. WEPP (Water ErosionPrediction Process; lane and Nearing, 1989). is highly sensitive toprecipitation (Nearing et al., 1990). However. considerable developmentsare ahead in linking global climatic models with more detailed erosionmodels accounting for interactions between physical and human factors.Some attempts have being made in this direction. Physically basedsimulation models such as the erosion productivity impact calculator(EPIC; Williams et al. 1984) allow us to linkclimate with other factors toestimate erosion and to examine the impact on cropyields. Skidmore andWilliams (Skidmore and Williams. 1991) developed a wind erosioninterface with EPIC. Approaches as Expert Systems may be an effectivealternative to these models that are data-intensive in nature. (Boardman etal. 1990). The rules generated by the. Expert System may be, used topredicterosion rates at a different scale acrossthe landscape undervaryingclimatic conditions..There is a need to develop decision support systemsthat facilitate the transferof scientific knowled.~ to land management

ConclusionI Even though the climatic models are still inaccurate. sufficient

information has been collected to make some assessmentof thelikely effect of climate and land-use induced changes on soilerosion.

2 This requires a better integration of long-term monitoring.experimental and modelling programmes at different scales bothin time and space.

3 A network should be inaugurated to test the existing models interms of sensitivity and flexibility and to implement theexperiments necessary to provide lacking inputdata.

4 Another goal to meet the dual GCTE's objectives is theassessment of potential feedbacks of soilerosion to the physicalclimate system. Changes in albedo resulting from denudation.crusting 'and erosion make necessary a multidisciplinaryapproach at a regional scale. permitting linkages to GeneralCirculation Models (GeM). This requires a close collaborationwith other programmes like BAHC (Biospheric Aspects of theHydrologic Cycle).

S Soil erosion results from complex interactions of physical andhuman factors. Theselatter are potentially more damaging thanthe direct effectsof climate change on soils. Stronglinksshouldbe therefore established with HDP (Human DimensionsProgramme of Global Environmental Change), notably withLUCC (land Use and Cover Change).

In accordance with GCffs objectives. the first objectives of the SoilDegradation Task's could be:

- To design and undertake experimental and monitoring programmes toprovide a predictive understanding of the impacts of changes inclimate and land use on soil erosion.

• To refine and adaptcurrent erosion models for use in global changestudies from the plot to the region.

ObjectivesOne of the major threat for sustainable land management is soil

erosion that has been identified as the major type of human-induced landdegradation in a global perspective. Nearly one sixth of the world usableland has been already degraded by water or wind erosion (Oldeman et al.,199 I). The GCfE soil degradation task will therefore initially concentrateon soil erosion the severity. frequency and extentof which are .likeJy to bealtered by expected changes in rainfall amount and wind intensity.interlinked and exacerbated by human activity.

I Possible approaches.

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Despite the numerous current and past experiments conducted on the

I factors affecting soil erosion. some uncertainties remain. An internationalset of collaborative experiments could be specifically designed to copewith changingenvironmental conditions. This research could concentrateon the impact upon soil losses of rain and wind storm profiles. of soil

I surface structure as related to soil organic matter status and faunalactivity. Another pivotal issue should be the integration of erosionalprocesses. i.e.. sealing. wind and water erosion. Such field experiments.

Past data

I Even though the lack of knowledge over the precise climate in the, future renders predictions uncertain. it is crucial to anticipate the

consequences of possible future scenarios. This has to be consideredregarding data currently available on presenterosion. In this respect one

I must be aware that the already large archive of air-photos and satellitedata has not been yet sufficiently used as a retrospective basis forpredicting models. New techniques like radioactive fallout 137Cs

Imeasurements could also provide information on recent erosion rates.Additional information on longer time-span erosion. related to climaticchanges. could be derived from the numerous data on late Quaternary.Pollen. charcoal. chemical, physical. magnetic mineral and radiocarbon

I dating (14C) along with archaeological record. and local documentaryevidence could be interpreted in the light of models of climatic change.However helpful as theyare. the use of paleoclimatic analogues should bepursued with care as it is not clear that they are realistic for the midI twenty-first century.

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Long-term monitoring andexperimental programmesSince erosion processes are commonly threshold exceedance related.

I emphasis should be put on the determination of such thresholds. onreversibility of processes. and on soil resilience. low-frequency climaticevents. like heavy storms. typhoons. etc.. can trigger severe erosionunpredictable from short-term records. Monitoring erosion in the long run

I is therefore essential to observe possible transient and not equilibriumresponses to climatic and land use changes.

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ISOIL EROSION UNDER GLOBAL CHANGE

16SEPT. 1994

References

Boardman, J., Evans, R., favis-Mortlock, D. T.; Harris, T. M, 1990. Climate change and soil erosion on agricultural land in England and Wales.Land degradation & rehabilitation. 2(2): 95-106.

Lane, LJ.• Nearinr, M.A. (eds). 1989. USDA-Water Erosion Prediction Projeet profile model documentation. NSERL Report n02. West Lafayette,253 p.25.

Nearing,. M.A., Deer-Ascougb, L., LaDen, J.M•. 1990. Sensitivity anaJysis of the WEPP hiUslope profile erosion model. Transactions of the A5AE,33(3):839-849.

Oldeman, LR., Halckeling,. R.T.A., Sombroek, W.G., 1991. World map of the status of human-induced soil degradation: an explanatary note.ISRIC, Wageningen. UNEP, Nairobi, 34p.

Slcidmore, f.L, WilUuu, J.R.. J991. Modified EPIC wind erosion mode!. in: Modeling plant and soil systems. ASA-eSSA-SSSA. AgronomyMonograph n031 :457-469.

Willluu, J.R., Jones, C.A., Dyke, P.T•. 1984. A modeJing approach ta determining the reJationship between erosion and soil productivity. Trans.ASAE, 27: 129-144.

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6 Erosion under Global Change 11

1111111111 SESSION Il: PAST DATA

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Recent techniques for the study of long term erosionThe use of radioisotopes

Claude Bernard1 and. Marc R. Laverdière2

net soillosses. as runoff plots do. but make possible the. distinction of theareas of soil loss from those of soil deposition. their extent. theirdistribution in the landscape and the assessment of the. magnitude ofthese soil move.ments. Besides soil move.ments may be. e.stimated trom asingle sampling visit. making long-terrn monitoring of the. studied sitesunnecessary. Finally. Cs-137 having a half-life of30.2 years. the amountsstill present are e.asily detectable and will remain so for many years.

Since the pioneering work done in the USA in the mid-1960·s. the useof Cs-137 for erosion studies has spread over the world. It has been usedin North America. Europe. Africa. Asia and Oceania. The reported studiescovered a Jarg spectrum ot soil types. slope parameters (length. gradient.fonn). crops and cropping practices. Some authors simp/y e.stimated netsoil loss rates. while others used. the Cs-137 signature. to document thesoil movement patterns and their relationship with the topographiefeatures of the experimental unit The are.a of the studied sites was alsoquite variable. Most of the published studies were condueted at the fieldleve!. However. some researahers compared soil and. Cs-137 losses onnunoff plots whiJe others altempted to establish sediment budgets at thewatershed scale. It may also be used to assess. soil erosion in long tem soilquality rmonitorint programs. The variety of conditions under which theCs-137 technique has been used demonstrates its versatility.

Soillosses are e.stimated from Cs-137 data by comparing the total arealactivity (Bq mol) of a cultivate.d site to that of an uneroded one(pemanent pasture. forest). whe.re Cs-137 depJetion may be attributed tonatural decay only. Three main types of matghematical expressions havebeen proposed to translate Cs-137 losses into soil lossees. Manyauthorsconsidered a proportional relationship. which assumes that the soil Jossrepresent a fraction of the plow layer identicaJ to that of the Cs-137 loss.However. Soil erosion is a selective process. When compared to the soilthey originate from. eroded sediments are currently enriched in clay.organic matter. nutrients and Cs-137 as weil. Some logarithmic expressionshave then been proposed. However. many of these. expressions weredeveloped from field and plot data covering a short time span and maygenerally be considered as site specifie. The Iinear and logarithmicrelationships iynore the fact that soil erosion. Cs-137 accumulation andloss are time variable processes. To take these aspects in consideration.accounting models s where suggested. These models calculate thevariation of the Cs· 137 inventory of the plow layer. on an annual basis. asa function of the annuai deposition of Cs-137. the annual soil loss. thedilution of fallouts by tillage and the enrichment of eroded soil in Cs-137.The use of either type of relationship may lead to ddifferent soil lossestimates. Consequently. this point is probably the aspect of the Cs-137technique that need the most to be investigated. Neve.rtheJess. Cs-137data can already be used with confidence to establish pattems of soilmovements in the landscape and to estimate the relative rates of thesemovements. For the derivation of soil erosion rates. one should keep ln

mind the limitations of the various types of relationships. knowing thatthe difference between the proportional method and the other ones growswith the percentage of Cs-137 loss and becomes important over a 40%loss approximateJy.

Soil erosion is rightfully considered as a major component of the soiland water degradation process. Not only does erosion reduce the soilproductivity of affected fields but it also impairs the quality of adjacentwater bodies by turbidity. sedimentation and the introduction ofsignificant amounts of nutrients and pestiades. However. in mostcountries. many questions related to erosion remain unanswered. e.g. thecurrent rates of erosion. its geographical distribution. the topographies andagricultural systems most vulnerable. its contributlion to nonpointpollution loadings. etc.

The measure of soil erosion on conventional runoff plots is a time andresource consuming approach. It must be carried over many years tointegrate the natural variability of c1imate and produce representative data.Besides. the number of plots may increase very quickly if erosion hazardsare to be assessed under a variety of soils. crops and agricultural practices.The capacity of plots of a few tens of m2 to realistically represent thewhole erosive prooesses taking place in fields of many hectares has alsobeen questioned by some authors.

ln this context. the use of persistent tracers becomes an attractivealternative. For erosion studies. a good tracer should be fimly retained bysoil partides and its movements ln the environment should reflect thoseof the tagged soil. Different isotopes have been tested: P-32. Sc-46. Fe-59.Co-60. Zn-65. Sr-90. Ag-IIO. Cs-134. Cs-137. Ba-140. However. most ofthese isotopes have short half-lives of less than one year. precluding theiruse for the derivation of long terrn erosion rates. Besides. soil tagging hasto be done for ail ofthem. but Sr-90 and Cs-137. Since this is possible forsmall volumes of soil only. their use is thus limited to plot or laboratorystudies. Some of them. like Sr-90. are vulnerable to leaching and areuptaken by plants in significant amounts. For these reasons. caesium-137has outclassed the other isotopes for soil movement tracing.

1

1 Cs-137 originated from nuclear weapon testing in high atmosphere inthe late 1950's and early 1960·s. It fell back on earth with precipitationsand dry deposits. The major fallouts occurred around 1963, with anothersmaller. yet important, peak in 1958. Regionally. the magnitude of thefallouts was approximately proportional to the total annual precipitation.ln many parts of Europe. the Chemobyl accident. in 1986, introducedvariable amounts of this isotope. depending on the importance of local1 precipitations in the days following the accident

Cs-137 is a very interesting indicator of soil movements under manyaspects. The fallouts were universal. making possible its use anywhere in

1 the world. at different scales ranging from plots to whole watersheds.Since the fallouts started in the mid-1950·s. long terrn erosion rates can beobtained. Arter reaching the soil surface. Cs-137 is strongly adsorbed byclay particles. Except for minute amounts. it is neither leached nor uptaken

1 by crops. Any further redistribution in the environment is thereforeconsidered to take place in close association with soil movements. Thesoi! loss data derived frorn Cs-137 measurements include the snowmelt

1 runoff contribution. which may be responsible for an important fraction oftotal annual soil losses under northem c1imates but is difficult to measurewith conventional runoff plots. The Cs-137 measurements reveal not only

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SOIL EROS/ON UNDER GLOBAL CHANGE 9

Consequent/y. this point is probably the aspect of the Cs-137 techniquethat need the most to be investigated. Nevertheless. Cs-137 data canaJreacly be used with confidence to establish patterns of soil movements inthe landscape and to estimate the relative rates of these movements. Forthe derivation of soil erosion rates. one should keep in mind thelimitations of the various types of relationships. knowing that thedifference between the proportional method and the other ones growswith the percentage of Cs-137 loss and becomes important over a 40%loss approximately.

1 Ministère de l'Agriculture. des Pêcheries et de l'Alimentation du Québec.Service des Sols. 2700 rue Einstein, Sainte Foy. Québec. Canada. G1P 3w8

2 Université Laval, Département des Sols. Sainte-Foy. Québec. Canada. GI K7P4

ln conclusion. although the relationship between Cs·137 and soilmovements stiJl needs to be investigated. this isotope offers the potentialta document quicldy and quite economicaJ/y the soil movements of thelm 35 years and their reJationship with different cJimatic. agronomic andtopographic factors.

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10 Erosion under Global Chanre 11

1111 Long-term Variations in Regional Rainfall. Example in Australia

Yu Safu

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Barring Antarctica. Australia is the driest continent on the Earth with amean annuai rainfall of only 420 mm. North and north-east of thecontinent has a marked summer wet season. Southern Australia. espciallythe south-west corner of the continent. has a pronounced wintermaximum. Much of the south-east has relatively uniform rainfall. Notonly rainfall on average is low. but rainfall in Australia is highly variabletemporally and rather uneven spatially.

rainfall total is known to have decreased significantly over the last seventyto eighty yeaTS. there has been no corresponding decrease in highintensity rainfall for the same period (Yu and Neil. 1993). Using seerninglyquite different methods. Lough (199/) notecl that no significant change inhigh-intensity rainfall had occurred in Queensland. and Nicholls andKariko (1993) also found that high-intensity rainfall for a number ofrepresentative stations in eastem AustraJia did not show any significantchange over time in the twentieth century.

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Early studies of the long-term rainfall variation in Australia include thatof Deacon (1953) and Kraus (1954). who noted an increase of rainfall insoutheastem Australia since the Jate 1940s. Wright (1974a. b) reported adecreasing rainfall trend for southwest Western Australia since the 1920s.Subsequent investigations. for example. Pittock (1983) using districtrainfall averages and Nicholls and lavery (1992) using high-quality rainfalldata for individual stations. have confirmed these earlier investigations.Proxy records. especially the water level at Lake Ceorge (Jacobson and

1 Schuett. 1979) and the magnitude and frequency of flood events in theHunter and Hawkesbury basins (Bell and Erskine. 1981; Erskine andWamer. 1988). have strongly indicated that rainfall has increased rather

1 abruptly around 1947-48 for much of southeastem AustraJia. These longterm rainfall variations have been used to develop c1imate changescenarios in relation to the enhanced'greenhouse effect' (Pittovk. 1988).

1 While rainfall total is one of the most relevant variables to consider inthe context of cJimate change. high-intensity rainfall is more importantthan raifall total as far runoff and soil erosion are concerned. Recent

1 investigations in Australia have shown that long-term variations of highintensity rainfall do not necessarily follow the same pattern of variation forrainfall total. On the Southem TabJelands in southeastern Australia. for

1 example. Yu and Neil (J 991) were able to dernonstrate that while rainfalltotal hag increased since the late 1940s. the high-intensity rainfall has adistinct maximum in the 1920s. In southwest Western Australia where

1 References

Secular variation of rainfaJl. especially that of high-intensity rainfall haslong been recognised as an important factor in land degradation processes(e.g. Leopold. 1951). More recently. Balling ant Wellg (1990) haveidentified a period of higher-than-present rainfall intensity around the turnof this century as one of the primary causes of arroyo (gully) incision andlatter infilling in the southwestern United States.. The effect of highintensity rainfall would be particularly significant if its occurrencecoincides with periods of below-average rainfall total as is the case withthe Southem TabJeJands in southeastem Australia.. Long-term variation ofhigh-intensity rainfall therefore warrants separate and special examinationfor the evaluation of soil erosion under global change. because highintensity rainfall does not necessarily follow the same trend for the rainfalltotal.

ln summary. rainfall has signiftcantly decreased over the last seventyto eighty years in southwest Western Australia where winter rainfalldominates. In southeastern Australia. with relatively uniform rainfall.rainfall is significantly higher for the latter part of this century incomparison with that for the first haIf of the century. There has been noobserved change of rainfall e1sewhere in Australia.. High-intensity rainfall.on the other hand. does not seem te follow this pattern of increasing anddecreasing rainfall trends. and ail evidences at hand suggest thatsignificant change has not occured as yet te high·intensity rainfall.

1 Bailing. Le.. Jr. and Wells. S.G.. 1990. Ann. Assoc. Amer. Geogr.. 80:603-617.Bell. F.C. and &sane. WD•. 1981. Search. 12:82-83.Deacan. LL. 1953. Aust j. Phys.. 6:209-218.Jacobson. G. andSchuett. A.W.. 1979. BMRj. Aust Geol. Geophys.. 4:25-32.

1 Leopold. LB•. 1951. Trans. Amer. Geophys Union. 32:347-357.LoUlh. J. M.. 1991. Int j. CHm.. 11:745-768.Kraus. E. B.. 1954. Q. j. R. Meteorol. Soc.. 80:591-601.

1NlchoUs. N. and Lavery. B. 1992. Int j. CHm.. 12;153-163.Nlcho/Is. N. and Karilco. A.. 1993. j. Clim. 6: 1141-1 152.Pittodc. A. B.. 1983. CHm. Change. 5:321·340Pittock. A.B.. 1988. Greenhouse: Planning for c1imate change. Pearman. G.!. (ed.). CSIRO. Melbourne. 35-51

1 Wright. P.B.. 1974a. Mon. Wea. Rev.. 102:219-232.Wright. P.8•. 1974b. Mon. Wea. Rev.. 102:233-243.Yu. B. and Nell. T. D•. 1991. Int j. Clim.. Il :653-661.Yu. 8. and Neil. T.D•. 1993. Int. J. Clim., 13:77-88.

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Long-term variations in regional rainfall and in landdegradationExample in West Africa

Valentin Christian

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Droughts

I Three main periods can be distinguished during the 20th century: (I)from the beginning of the century to the late 40·s. annual variability ofrainfall is high. Thehigher or below average periods are limited to 2 or 3consecutive years. In particular. three severe drou ghts occurred in 1911-

I 1914. 1941-1942 and 1947-1949. (2) from 1950 to 1968: this time-serieswas continuously exceeding average. (3) since 1969. annual rainfallremains below average with two major droughts in 1972-1974 and 1983-

I1985. The recent drought has resulted ina pronounced southward shiftofthe isohyets. particularly in the already driest zone.

Rainfall. intensityBased on daily rainfall records from 20stations in Burkina Faso over a

I period of nearly 50 years. daily rainfall higher than 40 mm shows asubstantial decrease since 1969. However. no concurrent decrease wasobserved. neither for high intensity rainfall nor for the depth of the daily

I rainfall of decennial frequency (AlbergeJ. 1986). In some locations. thisrainfall depth has even increased (Fig. I).

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Runoff productionOne of the most significant changes in land-use patterns have been

the dramatic shortening of the fallow period to meet increasing dernandfor agricultural land. Another striking feature is the clearing of marginalland. especially the plateaux or the stripes of land alongthe water courses.This expansion of cultivated surface tend to balance. the. decreasing yield.or income in the case of commercial crops subject to external marketfluctuation. The combination of these processes. with no change inexceptional precipitation. has led to a pronounced increase in runoff in theSaheJian zone. a slight increase in the SaheJo-Sudan zone.. and a minuteincrease in the Sudan zone (Fig. 2). Such results. suggest that any furtherdecrease in precipitation in the most arid zone would induce a furtherincrease in runoff production.

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Fig. 2. Changes in runoff production between the 50'sand the 80's in three watersheds of Burkina Faso offew /0-m2 for an unchanged ten-year return periodrainfall (afterAlbergel. /987).

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Soil erosionIn such a region. it is difficult to study the effect of kinetic energy

upon erosion in isolation from the structural change of the soil surface.Comparing the effect of a variety of intensities and kinetic energies for agiven rainfall depth. ColJinet (1988) showed in northern Burkina Faso thatany increase in kinetic energy led to a decrease in erosion in dayey soilsand to a very slight increase in sandy soils. This must be ascribed to thecomplex interactions between kinetic energy. surface degradation anderosion. For clayey soils. the rainfall impact results in a compacted anddenser plasmic seal (or "erosion crust") which tends to protect the soilunderneath from further erosion. at least temporarily. contrary to sievingcrusts formed on sandy soils.

95

98

94

93

97

96

99

92 .j----/o--1---1--+--+--+-+---+--+--t---t1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985

Year

101

100

Fig I. Fifteen-year running average of decennial dailyrainfall in Ouagadougou for the period /934-/983(after Albergel. /986).

IntroductionThe savanna zone of West Africa has been stricken by severe

recurrent droughts in the last two decades. In the nine states of theSahelian zone. the population has doubled over the period 1960-1988.The combination of these two processes has worsened erosion problemsin the region. This presentation will focus on the evolution of rainfallintensity. runoff production and erosion.

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16 SEPT. 1994

SOIL ERaS/ON UNDER GLOBAL CHANGE 13

ln a Burkinabe watershed within less than 25 years, the surface ofcultivated land has doubled, fallow land was halved. shrub savannah wasreduced from 80% to 45% while severe/y eroded patches increased 20fold (Albergel and Valentin, 1988). In a less densely populated region ofBurkina Faso bare and crusted patehes increased 6-fold within 28 years(Serpantié et al., 1991).

ConclusionDecreased precipitation does not invariably impJies reduced water

erosion.

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References

Albergel J•• 1986. Evolution de la pluviométrie en Afrique Soudano-Sahlienne. Exemple du Burkina-Faso. in: Colloque International sur la révision desnormes hydrologiques suite aux incidences de la sécheresse. CIEH. Ouagadougou. 17p.

Albercel. J.• 1987. Genèse et prédétermination des crues au Burkina Faso. Du m2 au Km2. Etude des paramètres hydrologiques et de leur évolution.Ph.d. Univ. Paris VI. 336 p.

AlberCel. J•• Valentin. c.. 1988. "Sahélisation d'un petit bassin versant soudanien : Kognere-Boulsa au Burkina-Faso. in :. B. Bret (edit). "Les hommesface aux Sécheresses", Nordeste brésilien - Sahel africain. EST/IHEAL. Collection Travaux et Mémoires. n0 42. pp. 179-191.

ColUnet. J•• 1988. Comportements hydrodynamiques et érosifs de sols de l'Afrique de l'Ouest Ph.d.. Univ. Strasbourg..521 p.Serpantie. G•• Tezenu du Montcel,. L. Valentin. C.. 1991. La dynamique des états de surface d'un territoire agropastoral soudano-sahélien sous

aridification climatique: Conséquences et propositions. in : L'aridili: une contrainte pour le développement ORSTOM. coUectionDidactiques. 419-447.

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14 Erosion under Global Chanee 11

SESSION III: CURRENT EXPERIMENTALAND MONITORING PROGRAMMES

1111111111liiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii

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Rainfall pattern changes and erosion

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SOIL EROS/ON UNDER GLOBAL CHANGE

Roth,. Germany

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Erosion under Global Change

Dr. Albrecht AlainLab. Matière organique des Sols TropicauxCentre ORSTOMB.P. 800697259 Fort de FranceMartiniqueTél. : (596}63D6D9 Fax: (596}71 73 16

Dr. Ambouta K. j.M.Université LavalPavillon Paul ComtoisSainte FoyQuébecCanada G1K7P4

Dr. Bernard ClaudeService des SolsMinistère de l'Agriculture du Québec2700. rue EinsteinGIP 3W8SAINTE-FOYQuébecCanadaTél: (418) 644-6818 Fax: (418) 644-6855

DR. Boardman johnEnvironmental Change UnitUniversity of OxfordMansfield RaadOXI3TBOxfordUKTél : 0865281180 Fax: 0865281 181

M. Boli Baboulé Z.IRABP 163 FoumbotCamerounTél: . Fax: 237 44 Il 01

Dr. Bresson j.M.INAPG78850 Thiverval GrignonTél : 33 30 81 54 29 Fax: E-Mail : [email protected];fr

Prof. Bullock PeterSSLRCCranfield UniversitySilsoe BedsMK45 4DT SilsoeGrande BretagneTél : oo44/(0}525/860428 Fax: 0044/(0}528/86 1147 E-Mail: [email protected]

DR. Druilhet A.Laboratoire d'aérologieUniversité Paul Sabatiier118. route de Narbonne31 062 ToulouseTél : 61 55 69 48 Fax: E-Mail:

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Dr. Gomes l.U.S.A.Université Paris. 7 et Paris 12Unité. de recherche. Associée au. CNRS 1404Faculté des. Sciences61 av. du Général de Gaulle940 10 Créteil cedexFrance

MR. Favis-Mortlock DavidEnvironmental Change UnitUniversity of Oxford1A Mansfield RoadOXI3TBOxfordOxonLlKTél :( + 44) 865 281189 Fax: (+ 44) 865 281181 E-Mail. :DAE%JSA@ECU OX AC UK

Dr. Imeson Anton C.Fysisel Geografisal en Bodemkundig Lab.University of AmsterdamNieuwe Prisengracht 1301018 V2. AmsterdamPays-BasTél: 31205257451 Fax: 31 205257431 E-Mail: [email protected]

Dr. Ingram j.GCTE Office. Dept of Plant SciencesUniversity of OxfordSouth Park RoadOX 13RB OxfordGrande-BretagneTél : 865275079 Fax: 44865275060 E-Mail: [email protected]

Prof. Kirkby M.j.School of GeographyUniversity of LeedsL52 9TJ LeedsGrande-BretagneTél : (44)-532-333310 Fax: (44)-532-336158 E-Mail: [email protected]

Dr. Le BissonnaisSESCPF/INRAArdon45160 OlivetFax: 33 38 41 78 79

Prof: Morgan R.P.C.University CranfieldSilsoe BedsMK 45 4 DT SilsoeGrande Bretagne

DR. Nicks ArlinUUSDA-Agricultural Research ServiceNational Agricultural Water Quality LaboratoryP.O. Box 143074702 DurantOKUSATél: (405-924-5066 Fax: 405-924-5307 E-Mail: !A03ADNICKS Internet

Dr•. Oldeman RoelISRICP.O. Box 3536700 AJ WageningenPays-BasTél: (31)-(0)8370-71711 Fax: 31-8370-24460 E-Mail.: [email protected]

Prof. DR. Paesen JeanGeography, Lab., Exp.. Geom.K. U. LeuvenRedingenstraat 16bis3000 LeuvenBelgiumTél : 32 16 22 69 20 Fax: 32 16 29 33 07 E-Mail: (KGECAO [email protected])

Prof. Pla. Sentis 1.Apartado IlOLMarcayVenezuela

Dr. Prospero Joseph MichaelUniversity of Miami Rosentiel Schocl of Marine. and Atmospheric Sciencee4600 Rickenbacker CausewayFL-33 149-1098 MiamiUSATél: 305 361 4789 Fax: 305 361 4891 E-Mail: [email protected] (Internet)

Prof. Quiton J:University CranfieldSilsoe BedsMK 45 4 DT SilsoeGrande Bretagne

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Dr. Planchon O.ORSTOM B.P. 182OuagadougouBurkina. FasoTél. : 226 31 03 85 Fax:

Dr. Rajot J.l.ORSTOM B.P. 11416NiameyNigerTél : 227 75 28 04 Fax:.

Mr. Sanders D. W.FAOViale delle. Terme di Caracalla00 100 RomeItaly

Prof. Sidorchuk A.Geographical FacultyMoscow State UniversityMoscow. 119899

E-Mail :planchon@ouaga. orstom. r

E-Mail:[email protected]

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DR.. Skidmore. EdwardErosion ResearchUSDARSKansas. State University, Waters Hall66506-4006 ManhattanKansasUSATél : 913 532 6726 Fax: 913 532 6528 E-Mail: [email protected]

Dr•. Slaymaker OlavUniv•. of British Columbia1984 W. MALLBritish ColumbiaV65 IGICanadaTél : 604 822 5159 Fax: 604 822 3134 E-Mail : olav [email protected]

Nsc. Sterk GeertWageningen Agricultural UniversityIrrigation and Soil and Water ConservationNieuwe Kanaalll6709 PA WageningenHollandeTél : 31-8370-48778 Fax: 31-8370-48759

Prof. Tinker BernardDepartment of Plant SeiencesOxford UniversitySouth Parks RoadOXI3RBOxfordLlKTél : (+ 44) 865 215019 Fax: (+ 44) 865 215060 E-Mail. :INGRAM@VAX OX AC UK

Dr. Torri DinoCentro Genesi Suolopjazzale Caseine 1550144 FirenzeItalieTél: 39 55 360517 Fax: 9 55 321148

Dr. Turenne J.F.ORSTOM70 route d'Aulnay93143 BondyFrance

Dr. Valentin ChristianORSTOM B.P. 11416NiameyNigerTél. : 227.75 28 04 Fax: ..... E-Mail :[email protected]

Prof. Stanilas. WicherekCentre de Biogeographie-EcologieENS Fontanay Saint Cloud Le ParcUra 1514 CNRS922 11 Saint-CloudFranceTél : 47719111 Fax: 46023911

E-Mail:

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Dr.. Wilcox B. P.Environmental Science GroupLos Alamos National LaboratoryEES-15 MS] 495NM 87545 Los AlamosNew MexicoUSATél : (505) 665-6044 Fax: (505)665-3866 E-Mail: [email protected]

DR. Yu BofuFaculty of Environmental. SciencesGriffith University4109 NathanQLDAustraliaTél: 07 875 5258 Fax: 07 875 7459 E-Mail: [email protected]

DR. Zobeck Ted M.United. States. Department of AgricultureAgriculturaJ Research ServiceRoute 3. Box 21579401 LubbockTXUSATél: (806) 746-5353 Fax: (806) 744-4402 E-Mail: [email protected]

DR. Middleton N. j.Schocl of GeographyUniversity of OxfordxMansfield. RoadOXI 3TBOxfordGrande-BretagneTél. : 44 865 271 929 Fax:

DR. Struwe S.Dept of General MicrobiologyUniversity of CopenhagenSolugade 83H1307K CopenhagenDanemarkTéi : 45 35 322040 Fax: (806) 744-4402 E-Mail: [email protected]

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Wind Erosion Modeling and Application to Climate Changeby

Edward L. SkidmoreUSDA Agricultural Research Service, Manhattan, Kansas USA

Presentation abstract for Workshop on "Erosion under Global Change"

Problem. Wind erosion ravages agricultural lands. Each erosion season millions of ha of landare moderately to severely damaged which results in a significant decline of the productivity ofthe region's soils. Sorne soil from damaged land is suspended and becomes part of theatmospheric dust load. Dust obscures visib-ility, pollutes the air, causes automobile accidents, andimperils human and animal health. Blowing soil fills road ditches; reduces seedling survival; andcontributes to transmission of sorne plant pathogens. Historically, wind erosion has been highlysensitive to variations in climate. Thus, predicted climate change will modify the conditionsconducive to wind erosion.

Wind erosion equation (WEQ). A model proposed by Woodruff and Siddoway (1965), titleda wind erosion equation, has been used extensively with various modifications during the pastquarter century. The model was developed as a result of investigations to understand themechanics of the wind erosion process, to identify major factors influencing wind erosion, andto develop wind erosion control methods. Soil erodibility index and climatic factor were the twomost important dependent variables.

Solving the functional relationships of the wind erosion equation as presented by Woodruff andSiddoway required the use of tables and figures. The awkwardness of the manual solutionprompted a computer solution and later the development of a slide-rule calculator. Thecomputer solution not only predicted average annual soil loss, but solved the equation todetermine the field conditions necessary to reduce potential soil loss to a tolerable amount. Itallowed the user to look at many combinations of wind erosion control practices for particularfield and climatic conditions. Later Colè et al. adapted the model for simulating daily winderosion as a submodel in the erosion productivity calculator(EPIC) developed by Williams et al.

Wind erosion prediction system (WEPS). Although WEQ was used widely it had many faults.Therefore the US Department of Agriculture initiated the Wind erosion prediction system(WEPS), multidisciplinary project to develop improved technology to predict wind erosion.WEPS is designed to use a weather generator to drive other submodels which simulate soil, crop,and residue conditions of a field scale using a daily time step-step. On days with erosion, theerosion is calculated on a sub-hourly basis.

The structure of WEPS is modular, consisting of a main supervisory program; a user interfaceinput section; an output control section; and seven submodels (WEATHER, SaIL,HYDROLOGY, CROP, DECOMPOSITION, MANAGEMENT, and EROSION) along with theirassociated data bases.

Revised wind erosion equation (RWEQ). Several issues regarding the present Wind ErosionEquation (WEQ) were identified as needing attention in order to support soil conservationprograms from now until the wind erosion prediction system (WEPS) now under development(Hagen, 1992) is fully implemented. In order of significance these issues were identified as: 1)the climatic factor is unrealistically high in arid climates and is perceived to be too low in humidclirilàtes and does not account for irrigation. 2) The soil erodibility index does not account fortemporal variation of aggregate status as influenced by management, weather, etc. 3) WEQ doesnot account for temporal variation in other model factors like climate, roughness, growing cropand crop residue. 4) Small grain equivalent is difficult to communicate to the person in the field.5) Random roughness is not presently recognized in WEQ. 6) Spatial variability is not presentlyrecognized in WEQ. Persons were assigned to address each of the above listed issues and revisethe associated factors of the wind erosion equation. Then deliver a revised wind erosion equation(RWEQ) for use until WEPS is implemented.

Wind erosion and climate change. Research is proposed to evaluate the impact of predictedclimate change on wind erosion and associated soil and environmental degradation in the USAGreat Plains. Questions to be examined include: how predicted climate change will affect 1)wind erosion climatic erosivity, 2) wind erosion protection afforded by vegetation as influencedby growth of major agronomie crops in the region, 3) residue decomposition of main residueproducing crops, 4) soil properties that are related to susceptibility to wind erosion, and 5) thetotal field soil loss partitioned among saltation-creep and suspension components.

The new advances in wind erosion prediction technology from the Wind Erosion PredictionSystem (WEPS) will be used to quantify the impact of predicted climate change on the climatic,vegetative, and soil factors that control wind erosion. The HYDROLOGY submodel of WEPSwill be used to evaluate soil wetness at the soil-atmosphere interface as influenced by modifiedclimate. The CROP and DECOMPOSITION submodels will be used to quantify the effects ofclimate change on the growth of major agronomie crops and the decomposition of their residues.The SOIL submodel of WEPS will be used to evaluate the influence of climate change on soilerodibility by wind. Furthermore, the EROSION submodel will be used to predict field soil lossand deposition.

The proposed research will contribute valuable knowledge for assessment of the wind erosionpotential and associated soil and environmental degradation as a result of climate change. It willaid in the development of sound conservation and environmental planning. Therefore, thefindings from the research will improve the scientific basis to formulate policy and legislativeactions to best serve the long-term needs of society forcoping with change.

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Wind regime changes and erosionProspero J. M.

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1111 Global change induced vegetation changes and erosion

Slaymaicer Olav

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There are at least three approaches to the prediction of vegetation anderosional changes that may result from climate change. They axe:empirical/y established c1imate-process relations: paleoreconstruction ofecologic and geomorphic parameters using analogues: modelling andsimulation of process-response systems. The latter approach is exploredhere in terms of the qualitative relations between c1imatic. hyctrologic.ecological and erosional processes. Seven ecoclimatic regions in westernCanada. covering about 3.5 million km2. are considered. as follow: PacificCordilJeran. Interior Cordilleran. Eastern CordilJeran. Prairie Grasslands.Boreal Forest. Arctic Lowlands. and Subarctic Cordilleran zones. Globalc1imate under conditions of doubled atmospheric concentration of C02 byA.D. 2050 in the 50°-60° N latitude band will likely average 4.2°Cwarmer in winter and 2,4°C warmer in summer. In the 60°·700 N latitudeband. winter temperatures may be about 8.5 oC warmer and summertemperature will be less than 1°C warmer. As the error bands aroundthese estimates are 3°C. it is c1ear that generalisations have to be couchedwithin a framework of uncertainty. The majority of models also predictsome inaeased winter precipitation but precipitation predictions are lessconsistent than temperature predictions.

A series of lagged responses to this order of c1imate change can beenvisaged as changes in permafrost and glacier behaviour. vegetationcover. soil erosion. debris flow. torrent. landslide frequency and sedimentyield output The Pacific Cordilleran vegetation zone may expand byabout 12% (25.000-280.000 km2): the Interior Cordilleran zone mayexpand by over 18% (ssO.000-6s0.000km2): the Eastern Cordilleran zonemay be reduced by about 325% (200.000-lsO.000km2): the PrairieGrasslands may expand by about 28% (3s0.000-4s0.000km2); the BorealForest may expand by about 12% (1.200.000- J.3s0.000km2): the ArcticLowlands ecoclimatic zone may be reduced by over 37% (400.002s0.000km2); and the Subarctic CordilJeran zone may be reduced byabout 33 % (600.0ll0-400.000km2).

The key regional changes which deserve ecoJogicaJ and erosionalemphasis are:

1 .In the Pacific Cordilleran zone. warmer and moderate/y wetterwinters may activate debris torrent activity and glacier icedynamism;

2. In the Interior Cordilleran zone. signigicantly warrner andwetter winters may lead ta glacier expansion and increasedfrequency of snow avalanche:

3. In the Eastern Cordilleran zone. significantly warmer and wetterwinters may generate increased fluvial erosion and sedimenttransport;

4. In the Prairie Grasslands. significantJy warmer winters andreduced summer precipitation may promote extensive gul/yingand soil erosion:

5. In the Boreal Forest. significantJy warmer winters will lead tagreater variability of river flow and to fluwial erosion: in thenorthern part of this region permafrost degradation will besevere:

6. In the Arctic Lowlands zone. very much warmer temperatureand permafrost degradation are like/y ta occur;

7. In the Subarctic Cordilleran zone. very much warmer winterswill fead to active permafrost degradation.

The big unanswered question is the speed with which the ecologyadjusts. and hence the timing of the subsequent erosional responses todimate change.

The possible implications of the above changes for soil erosion. fluvialerosion. and large mass movement activity are reviewed. Examples aredrawn from Saskatchewan. Alberta. Northwest Territories. Yukon Territoryand British Columbia.

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IIII Global change induced SOM changes and erosion

Albrecht Alain

I from a field station, with these different land uses. are studied; thevariation of SOM content in the surface soil (o-San layer) was tro 1.5 to4.0 gClIOOg soil . Soil aggregation, characterized by the MWD (meanweight diameter) after head-over-head agitation in water. is related toSOM.

Using a small field rainfall simulator. it is possible to characterized soildetachment under different rainfall intensities and different types of soilsurface for the nine studied situations. All the field experimentations aredone in wet soil conditions; so because vertisols. have the property ofswelling. it is possible to workin the same conditions of watererosion:same rainfall intensity and same runoff intensity. Three soil surfaces. aretested for all the situations: herbaccous. bare, hand-ploughed (seedbedtype).

Themain results of thisstudyare:• Soil surface type is the most important element regulaling soil

detachment exprimed bythe runoff waterturbidity.• SOM influences soil detachment only in the case of the most

credible soil surface situation (hand-ploughed)• Organic carbon in the runoff water turbidity is in higher

concentration as SOIM for all. the soil surface situations excepthand-ploughed and CIN ratios are systematically lower thatSOM ClN ratios,

• Organic carbon and nitrogen exportations are not related toSOM.

• Rainfall intensity increasing acts a factor of an increasing of soildetachement for the situations under hand-ploughed surfaceand particularly thoseWilh less SOM.

This paper viII present (i) a quick review about Global change inducedSOM changes and (ii) resulls of an experimental programme in MartiniqueI about relationships between SOM andsoil detachment

Global. change induced SOM changesElevalion of atmospheric C02 andclimate changes (specially elevation

I of temperature) can, theorically, act onc carbon cycle alnd so, on soilorganic matter dynamics. It exits only few references on this subject andtheir conclusions are not really effective. Laboratory experiments; on theeffects of elevation of atmospheric C02 have showed that organic matter

I produced under high concentration of carbon dioxide had higher CINratios. Carbon cycle models under different scenarii of climate changes inthe intetropical areas showed that the variation of soil organic matter

I(SOM} storage was very low and that this variation could be positive ornegative. That is no comparison withSOM stock variations under differentland uses. It is usual to note a decrease of 40% of SOM stocks for thesulrface soil after long-term annual plants cultivation

I Land use, SOM, soil aggregation and soil detachment: anexample. ill Martinque. (F.W.I.) olllithomorphic vertisols

IThe Martinique, in thc Caribbean, is a tropical mountainous volcanic

small-sized island. In the South East of the island. vertisols aredeveloppedon compact volcanic rocks under 1300 mm rainfall perannuum with a dryseason (4/5 months). Land uses on these soils can be divided into two

Imain categories: pastures (planted with Digitaria decumbens) and longterm market-gardening or food crop cultivation.

Long-term Gropping, different situations of crop rotations or pasturesI would differenciate the SOM status of these vertisols. Nine siluations.

IIIIIII SOIL EROSION UNDER GLOBAL CHANGE 23

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Current erosion monitoring programmesBoardman J.

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1define erosion monitoring as field-based measurement of erosionaland/or depositionaJ forms over a significant area (e.g > 10 km2 and for aperiod >2 years. Sorne of the aims of monitoring erosion are:

1. to understand processes responsible for erosion at a field scale:2. to assess quantitatively the contribution of processes such as

sheetwash. rilling and ephemeral gullying to total erosion:3. to estimate rates of erosion for parts of the landscape. specific

soiJs. or crops etc.4. to provide data for. and to test the valldity of. models:s. to identify areas at risk of erosion (e.g. produce hazard maps)

Field-based monitoring exercises are particularly important for severalreasons:

1. Many erosion models perform poorly in field situations. Thereare many reasons for this but a principal one is that they havebeen developed using data from plots which do not replicatefield conditions. Field measurements provide a valuable chekon model predictions.

2. There is Iittle reliable information on rates of erosion. Theseare difficult to assess. Most published rates are based oneither sediment yield data from rivers or smalll experimentalplots. There is a need for rates based on field measurement .

3. Erosion rates vary spatially within the Jandscape: they also varytemporally. There are many problems with using averagevalues and often it may be as important to know variationsfrom the average. Field monitoring of erosion is important inorder to assess this variation.

4. Unless we understand and can predict present day rates oferosion. it will not be possible to predict the effect of futureland use and climate change on erosion.

There are few examples of field-based monitoring of erosion: thoseknown ta the author are Iisted in Table 1.

One may speculate on reasons why monitoring has not been widelyattempted:

1. it is often regarded as 'unscientific' in comparison withcontrolled experiments in the labaratory or on the plot:

2. problems of sampling;3. probJems of securimg long-term funding.

Better undergtanding of erosional processess will come about bystudies at many scales - the laboratory. the experimentaJ plot and the field.The latter should not be neglected.

1 Table 1 Field-based erosion monitoring exercises

severaJ papersby Evans e.g.e.g. 1992. 1993

17 localities inEngland and Walesc. 826 km2

Soil Survey of Englandand Wales (1982-86)

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1 1----------------------r--------------------------r-----------------------Ministry of Agriculture: 13 localities. : Chambers et al..

1 1(UK) (1989-93) : 10-179 ha each : 1992

1 1----------------------r--------------------------r-----------------------South Downs (UK) : c. 36 km2 : several papers(1982-91): : by Boardman

: : e.g. 1990.19931 1______________________ L L _

1 1

Southern Sweden : 90 km2 : Alstram & Bergman(1986-88): : -Akerman (1992)

1 1----------------------T--------------------------r-----------------------Cenntral Belgium : 86 fields : Govers (1991)

1 1

(1982. 1984 & 1985) : :1 11 11 1

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------------ 126 Erosion under Global Change

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SESSION IV: OTHER," RELEVANTINTERNATIONAL PROGRAMMES

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International Board for Soil Research and Management networks (/BSRAM)Valentin Christian

I A comparison between different experimental plots indicate that thereare strong differences in erosion rates from site to site. These differencesare related to the rainfall. the slope. or the soil cover; but the major soil

ConclusionIBSRAM Networks on sloping lands might be regarded as beyond the

scope of Soil Erosion under Global Change since they are primarily soilconservation oriented and do not seem to be much concerned with soilerosion processes and modelling. However. the data collected on soilerosion should not be overlooked for several reasons:

- Only few data areavailable in the wet tropics on watererosion.- Theconservation techniques being tested byfarmers. at the scale

of their own fields. can reflect possible changes in land use inthe not too remote future.

- These networks represent one of the first International attempt tocoordinate experimentation and datacollection. really integratingInternational Agricultural Research Centers {IARCs}. NARs.Institutes of higher education from the developed countries.extension officers andfarmers.

Consequently appropriate links should be forged between the SoilDegradation Task of GCTE and IBSRAM.

effect on erosion is through aggregate stability. In Chiang Dao. Thailand.on an Alfisol developed on shales. the soil loss was limited. and a simplemulch formed from crop residues was sufficient to reduce losses to anacceptable level. On Inceptisols developed on volcanic material inPhilippines and Ultisols developed on sancistones in Indonesia. contourbarriers were essential to ensure that soil loss was kept within acceptablelimits. ant the erosion control measure adopted in this instance led to theformation of terraces. On Ultisols developed on granite in Chiang Rai,Thailand. hillside ditches were adopted as the preferred method oferosioncontrol. Thefact that three different solutions were used makes the pointthat soil conservation measures need to be adapted to the. site. Soilconservation has a price which will vary according to the erodibility of thesite. andifthe price is too high agricultural development is precluded.

In particular. IBSRAM has initiated programmes on sloping lands inAsia and in South Pacific. It integrates information obtained from withinand between sites belonging to thesetwo networks.

The main interest of these networks concerning Erosion under GlobalChange consists in the valuable data related to the impact of changes inland use uponsoil losses in a variety ofsoil andclimate conditions.

IntroductionIBSRAM was created in 1983 with a view of promoting soil

management research within national agricultural research systems{NARS} in developing countries. Through it network approach. it hasforged links with some thirty NARS in Africa. Asia and the South Pacific.and has assisted interactions between developing countries in these areasand institutions in thedeveloped word.

The Management of Sloping Lands networksTable I presents some characters of the projects of the two networks

related to sloping lands in Asia and South Pacific (IBSRAM. 1993)

IIII

Some resultsIn most cases soil conservation techniques are highly effective in

I reducing soil losses {Table 2}. However. during years with strong-rainfallevents. very erodible soils require mechanical measures such as hillsideditches or terraces {IBSRAM. 1992}. Results obtained in Indonesia.

IPhilippines andThailand clearly showed that the use of fertilizer decreasedthe soil/oss by more than 50%. In most case. however. this reduction inerosion rates is notsufficient to maintain the sustainability of the system.

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References

IBSRAM. 1992. Highlights. IBSRAM. Bangkok. 48 p.

IBSRAM. 1993. Highlights. IBSRAM. Bangkok. 48 p,

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SOIL EROSION UNDER GLOBAL CHANGE 29

11

Country : Number of Sites : State of Project 1993: Treatments-------------1---------------------~-----------------------------~--------------------------------------

China 2 Second year Farmer's practice, Ailey croppingIndonesia 3 Fifth year Farmer's practice, Ailey croppingPapua New Guinea 1 First year Sweet patataVanuatu 1 Second year Sweet potataMalaysia 2 Fifth year Farmer's practice, Rubber + corn + peanut.

Rubber + pineapple.Rubber + cornlpeanut+ pineapple

Philippines 3 Fifth year Farmer's practice, Ailey cropping (Iow input),Ailey cropping (high input). Banana hedgerow(high input)

Thailand 3 Fifth year Farmer's practice. Ailey cropping, Bahia grassstrips. Hillside ditches

Vietnam 3 Fourth year Farmer's practice. Ailey cropping (Iow input).Ailey cropping (high input).

Fidji Second year Gingerltaro. CassavaWestern Samoa Second year Taro

Table 1

Table 2

Progress in the sloping lands nelWork in Asia and South Pacific.(after IBSRAM. 1993)

Effect of soil conservation practices on soil loss in the sloping lands nelWork in Asia belWeen 1990 and 1992.(after IBSRAM. 1993).

111111111

Site : Slope (%) : Treatment : Soil 1990 : Loss 1991 : (t ha- I ) 1992 1--------~--------------~----------------------------~--------------~--------------~----------------China

Indonesia

Malaysia

Philippines

Thailand

Vietnam

30-46

8-18

10-15

15-25

20-50

5-7

Farmers'praticeAiley croppingFarmers'praticeAiley croppingFarmer's practiceRubber +corn + peanutRubber +pineappleRubber +cornlpeanut + pineappleFarmers'practiceAiley cropping (Iow input)Ailey cropping (high input)Banana hedgerow (high input)Farmer's practiceAiley croppingBahia grass stripsHiliside ditchesFarmer's practiceAiley cropping (Iow input)Ailey cropping (high input)

27.012.051.838.289.614.597.02.01.02.0

68.713.817.210.03.32.22.2

57.840.688.011.09.0

13.51.12.5

18.40.20.10.1

224.389.164.615.92.20.60.6

84.014.955.08.00.7

20.50.84.5

56.1ND*ND*ND*146.541.7

7.13.51.00.50.5

11111

30

ND* : not detectabel

Erosion under Global Change

1111

1

The project Global Assessment of Soil Degradation (GLASOD). which

1 was formulated by UNEP. was coordinated by the International SoilReference and Information Centre (ISRlq in close cooperation with adiverse group of more than 200 soil scientist and evironmental experts

1worldwide and with expert advice from members of the InternationalSociety of Soil Science (ISsS).

The GLASOD map serves as a tool to strengthen the awareness ofpolicy-makers nd decision makers of the dangers resulting from

1 inappropriate land and soil management. It can lead to a basis for theestablishment of priorities for action programmes. in particular forrehabilitation in areas affected by human-induced soil degradation.

1Content of the World Map of Human-induced SoilDegradation

l in order to ensure uniformity in reporting and delineating On maps theseriousness of various soi1degradation processes a simplified geographicbase map was provided and general guidelines were developed for the

1assessment of the status of human-induced soil degradation (ISRIC. 1988).The cooperators were asked to indicate on the map regions where thebalance between the attacking forces of climate and the natural resistanceof the terrain against these forces has been broken by human intervention.

1resulting in a decreased currrent and/or future capacity of the soils tosupport life. The present status of soil degradation was to be characterizedby the degree to which the soil is presently degraded and by thepercentage of the mapped area that is affected by soil degradation. Only

1 soil dogradation occurences which took place since 1945 were to beconsidered. Also the kind of physical human intervention that has causetdsoil deterioration had to be indicated.

11111

Introduction

31

Global Assessment ofSoil DegradationOldeman L. R.

soil degradation is defined as a process that describes human·inducedphenomena which lowen the current and/or future capacity of the soil tosupport human life. The GLASOD map does not indicate the presentand/or future rate of degradation processes and the potential hazards thatmay occur under human influence. It delineates the present status ofhuman-induced soil degradation. which can be defined by the type, thedegree. and the areal extent of the degradation process

Two categories of soil degradation processes are recognized. The firstgroup relates to displacamantof soil materaI. The two major soildegradation types in this category are soil erosion by water forces or bywind forces The second group deals with soil deterioration in-situ. Thiscan either be a chemical or physical soil degradation process.

Water erosion1. Loss ofTopsoil (surface wash or sheet erosion)2. Terrain deformation (nUs and gullies)

Wind erosionThree types of wind erosion are recognized by GLASOD:

1. Loss of topsoil (a uniform displacement of the topsoil)2. Terrain deformation (an uneven displacement of soil material.

leading to deflation hollows and dunes)3. Ouerblowing (the coverage of the land surface by wind-caned

particles)

Chemical degradation

The following chemical degradation processes are distinguished:1. Loss of nutrients and/or organic matter2. Salinization (a change in the salinity status of the soil)3. Acidification4. Pollution

Physical degradation

Three different types are identified:1. Compaction. cruting and sealing2. Waterlogging3. Subsidence of organic soils

The degree to which tghe soil is presently degraded is related in aqualitative manner to the agricultural suitability of the soil, to it declinedproductivity. to its possibilities for restoration to full productivity and inrelation to its original biotic functions. The foUowing four degrees of soildegradation were specified:

1. Light. The terrain has a somewhat reduced agricultural suitability.but is suitable in local farming systems. Restoration to fullproductivty is possible by modifications of the management.Original biotic functions are large/y intact.

2. Moderate. The terrain has a great/y reduced productivity. but is stillsuitable for use in local farming systems. Majorimprovements are required to restore the terrain to fullproductivity. which are beyond the means of local farmers indeveloping countries. Original biotic functions are partiallydestroyed

SOIL ER.OS/ON UNDER. GLOBAL CHANGE

The intense amd increased pressure on lamd and water resources.leading to degradation and pollution of those resorces. and leading to apartial or complete loss of the productive capacite of soil caUs for anapproach that strengthens the awareness of users of these resources onthe dangers of inappropriate management and at the same timestrengthens the capability of national soil/land resou rces institutions todeliver reliable. up-to-date information on land resources in an accessiblefonnat to a wide audience.

Although soif degradation is recognized as a serious and widespreadprobJem. ib geographiccal distribution and tlhe total areas being affected isonly very roughly known. Sweeping statements that soi 1 erosion isundermining the future prosperity of mankind do not help planners. whoneed to know where the problem is senous and were not (Dregne, 1986)

The United Nations Enviromnent Programme (UNEP) expressed theneed to produce. on the bassis of incomplete knowledge. a scientifical/ycredible global assessment of soil degradation in the shortest possible time."Political/y it is important to have an assessment of good quality nowinstead of having an assessment of very good qualiy in 15 to 20 yearsfrom now" (ISSS. 1987).

1

1

111

11

13. Strong. The terrain has virtually lost its productive capacity and is

not suitable for use in local farming systems. Majorinvestments and/or engineering works are required torehabiJitate the terrain. which are often heyond the means ofnational govemments in developing countries. Original bioticfunctions are large/y destroyed.

4. Extreme. The terrain is unreclaimable and beyond restoration. It hashecome human-induced wasteJand. Original biotic functionsare fully detroyed.

These general descriptions are qualitative and judgements made by theexperts in the field are subjective.

At the chosen scale of the GLASSOD map it will not be possible toseparate each type of soil degradation as individual events. The expertswere asked to give their best estimate of the frequency of occurrence ofeach type of soil degradation within each mapping unit as a percentage ofthe surface area affected.

The concept of human-induced soil degradation implies by definition asocial problern. No person will intentionally destroy this precious naturalresource. But increasing pressure on the land. the increased desire forbetter living conditions. and higher standards of living. the search for landto survive etc. etc. have resulted in sorne kind of physical humanintervention that has caused the soil to degrade. The GLASSOD approachdistinguishes the following types of causative factors:

1. Deforestation or rem.oual of the natural uegetation2. Ouergrazing3. Agricultural actiuities4. Ouerexploitation of the uegetation for domestico use5. Bio-industrial and indutrial actiuities

water and wind erosion are of almost equal importance. In South Americanutrient decline is more important than wind erosion. A1most 50% of the 1land that is affected by salinization is Jocated in West Asia • whiJe itocupies almost equal areas in South East Asia and Africa . Compaction isa major type of soil degradation in Europ (50% of the compacted soiJs 1worldwide). Although pollution is worldwide a type of soil degradationoccupying only 22 M. ha. it is important to note that 19 M ha of thesepolluted soil are located in Europe Over 300 Mha -about the size of lndia-is degraded to such an extent that restoration. to its. original productivity 1can only be achivied through major investrnents. This terrain has virtuallylost its productive capacity. Around 40% of his strongly degraded land islocated in Africa. while 25 % is found in South East Asia A much largerportion -910 M. ha- has a moderate degree of soil degradation. This terrain 1is characterized bya serious decline in productivity. but can he restored. Ifno efforts are undertaken to rehabilitate this moderately degraded land.one may fear that a. major portion will further deteriorate to the pointwhere it may become unreclaimable. Around 25% is found in South East 1Asia 20% in Africa.

Overgrazing of the pasture land. mismanagement of the agriculturalland. and deforestation of the forest and woodlands are the major causes 1of soil degradation. Overgrazing is of particular importance in Africa andAsia. deforestation is of serious concem in Aia and South America. whileagricultural practices have affected the soils negatively on ail continents. 1but particularly in large areas in South East Asia and Africa.Overexploitation of the vegetative coyer is mainly a probJem in West Asiaand Aifrica. Industrial activities are of obvious. importance in Europ.

Further details on areas by type and by degree for the various 1continents can he found elsewhere (Oldernan. Hakkeling and Sombroek1991).

1111

1

11

1

1Conclusion

The GLASOD map and the derived statistic on human-induced soildegradation should be considered as a first attempt to arrive at a global 1picture of the status of human-induced soil degradation. Themethodology is subjective and based on a qualitative expert estimate ofthe present conditions of the stantus of the soils. There is an urgent needto follow-up these estimates by more detailed studies and a. better 1quantification of the status of soil degradation. which can best beaccomplished through the development of SOTER (World Soils andTerrain Database) (Oldeman and Van Engelen. 1993).

Since t1he map was first published in 1990. ISRIC has received manycomments. both supporting the results as weil as criticizing details of themap. At the same time. many requests were received for more detailed 1information on the status of soil degradation for specifie countriies. Wehave categorically denied such requests. since GL ASOD was meant forproviding these details. Last year the Group of Soil Conservation expertsof the Council of Europe requested to prepare an up-date of the Europeansection of GLASOD. Also tho Asian Network of Problem Soils hasrecommended the preparation of a detailed assessment of human-inducedsoil degradation at country level. using uniform methodologies asdeveloped for the GLASOD map.

Erosion under Global Change32

The. Extent of Human-induced Sail Degradation

Since the surface area of each mapped unit on the GLASOD map couldbe calculated separately once the map was digitized. an estimate wasmade of the area within each mapped unit that is affected by humaninduced soil degradation. Although the mapped scale of the GLASOD mapdoes not allow to make areal estimates on a country-by-country basis.statistics for the world and for continents can be given. Asimmarized dataset is given in Table 1.

The summation of the surface areas of ail GLASSOD mapped units leadto a total land area of 13013 M ha (million hectares). which comparesfavourably with FAO's estimate of 13069 M ha (FAO. 19 90). Humaninduced soil degradation worldwide has affected 1965 Mha or 15 % of thetotal land area The total land area however includes large portions of theearth that are not influenced by men. A more realistic figure would be toconsider the total area under agriculture. permanent pasture and underforest and woodland. These are the areas affected by human-induced soildegradation. Based on FAO statistics this land surfaces ig around 8735 M.ha. of which 22% is degraded as a result of human intervention.

Water erosion is the most important type of soil degradation (55 %)followed by wind erosion (28%). nutrient decfine (7%). salinization(4%) and compaction (3%). In ail continents water erosion is the mostimportant type of soil degradation. except for West Asia and Africa. where

References

Dregne. HE.• 1986. Soil and Water Conservation: A Global Perspecive. Interciencia Vol. 2 n° 4 FAO. 1990. FAO Yearbook 1989. Production. FAOStatistical Series n° 94. Vol. 43. FAO. Rome

ISRIC. 1988. Guidelines for Ceneral Assessment of the Status of Human-induced Soil Degradation. OIdeman L.R. (ed.) Working Paper & Prepint 88/4.ISRIC. Wageningen. (in English and French)

1555. 1987. Proceedings of the Second International Workshop on a Global 50ils and Terrain Digital Database ('18-22 May 1987. lINEP. Nairobi). Vande Weg. RF (ed.) Soter Report 2. ISSS Wageningen.

Oldeman. LL. L T.A. Haldceling and W.G. Sombroek. 1991. World Map of the Status of Human-induced Soil Degradation: An explanatorynote. Second revised edition. Wageningen. International Soil Reference and Iformation Centre Nairobi. United Nations EnvironmentProgramme. 27 pp + 3 maps.

Oldeman. L.R and V.W.P. Van Engelen. 1993. AWorld 50ils and TerrainDigital Database (SOTER) - An Improved Assessment of Land Resources.Geoderma 60: 309 325.

111111

Table 1 The extent of the status of human-induced soil degradation by type. degree and causative factor for the world and majorcontinents or regions. expressed in million hectares

2

+

+1

+

9642

12838

8316

Oceania

8448641

21+

42963

Degradation TypeWaterWindNutrient decJineSalinizationPollutionAcidificationCompactionWaterloggingSubsidence org. soils

11

World SE Asia W. Asla Africa: SeN. Europe1 1 1 1 : America 1 America 1 America 1 1

-----------------~------~-------~--------,-------~----------~---------~----------~---------,----------1 1 1 1 1 1 11 1 1 J 1 11 1 r 1 1 1

: 1094 322: 118: 227: 123 46 1 60 1\4:1 1 1 1 1

: 548 88: 134: 187: 42 5 35 42:: 135 10: 4: 45: 68 4 3 :: 76 17 1 36 1 15: 2 2 4 :: 22 1 1 +: + 19 :: 6 4 0 2: + +:: 68 + 10 18: 4 + 1 33:1 1 1

: 1\ + 0 +: 4 5 ':: 5 2 0 : 2 :1 1 1 1 1 1 1----------------ï------ï--------ï--------ï-------ï---------ï---------ï-----------ï---------ï----------

Total : 1965: 444: 303: 494: 243: 63: 96: 218: 1021 1 1 1 1 1 1 r 1________________T ~---_----~----_---~-------l_---------~---------~----------,---------~----------

• 1 1 1 1 1 1 1 1 1

Degradation Degree: : : : : : : : :üght : 1749: 151: 144: 173: 105: 2: 17: 60:Moderate : 910: 214: 130: 192: 113: 35: 78: 144:Strong : 296: 79: 29: 124: 25: 26: 1: 10:Extreme : 9: : +: 5: : : : 4 :

1 1 1 1 ; 1 1 1 1________________ ~ ~ ~~ L ~ ~ ~ _

Causative factors: : : :: :1 1 1 1 1

Deforestation : 579: 219 79: 67: 100 14 :Overgrazing : 678: 67 131: 243: 68 9 :Agric. mismanagement: 552: 157 47: 121: 64 28 :Overexploitation : 133: 46: 63: 12 11 :Industrial Activities : 23: 0: +: + :

1 1 1 1 11 1 1 1 11 1 1 r 1r 1 1 1 1

1

1

1

1

11

1

11

111111


Erosion under Global Change34

1111111111111111111

------------11

11111

Modellingg and Projecting the impact of climate change on soilerosion along climatological gradients

Imeson A. C. and LaveeH.

11111111111111

A methodology for modeling the impact of dimate-change onecosystem and land degradation is being developed as part of aninterdisciplinary research project (ERMES) The project consist of studies atthree locations that from a transect across the Mediterranean. Theselocations are on similar limestone and mari sites in Israel, Crete andValencia The hwork includes field. laboratory and modelling investigationof soil erosion. The approach is to study conditions at reference locationsalong c1imatological gradients. Relations between dimate and processesare being analyzed to see how changes in climate would influence keyprocesses at the reference transects. The work focusing on processes that

affect water and sediments storage and movement. on hill sJopesThe work reported will descnbe the soil erosion investigation at the

transect in Israel that runs from the Galilee via Jerusalem to the Dead SeaIt was found that erosion under and conditions is greatly influenced bythe dynamics of salt Above about 700 mm of rainfall. so much organicmatter is produced that the soil erodibility is always Jow. At intermediateelevations erosion is very sensitive to drought and land use practises.Along ail of the gradients studied it is condued that often erosion isgreatest at sites which have the highest biomass production. This isbecause fire and grazing are prevalent at such locations.

11


1111111111111111111


1

1111 The GCTE Transects

ValentinCh.

example of the idealised IGBP terrestrial transect SALTs primary objectivesare: To develop a predictive understanding of functional and dynamicchanges in West African savannas under present and expeeted c1imaticand human pressures.To provide scientific background for decision makingin land use management in the face of

future cJimatic and human constraintsSub-objectives are: To identifyand analyse ecosystem responses to natural and anthropogenicconstraints; to charaeterise savanna-atmosphere and landscape interactionsat different scales (feedback effects on atmospheric properties); tointegrate ecological processes from Jocal to regional and continentalscales; ta build scenarios of long term evolution of savanna systems.SALTis based on an integrated study of the processes Iinking energy and matterflows to species and vegetation dynamics.

The project is based on process studies conducted on eight majorsites in C te d'Ivoire. Burkina Faso. Mali. Niger and Senegal, and on anumber of secondary sites. spanning a I.OOO-km long transect from C ted'Ivoire to Mali, and on the use of remote sensing data ta extrapolate theresults of the site studies. The following processes are measured, analysedand modelled in SALT: primary productivity. organic matter and nutrientcycling; soill vegetation/atmosphere interactions; soil surfacecharacteristics (crusts) and erosion processes; vegetation structure anddynamics; ecosystem response to disturbances (e.g.. fire. grazing.cultivation); and changes in the hydrology of smail catchments.

Analysis of these processes of these processes will lead ta a genericmodel of savanna functioning and dynamics at different spatial andtemporal scales, incJuding responses ta cJimatic and human constraints.

Integrating processes at larger scales are based on the establishment ofrelationships between remote sensing data and field measurements:

1- Identification and classification of land cover types.2- Biomass, phenology and primary production.3- Detection of fires and monitoring burnt areas and biomass

through space and time.4- Integrating processes over scaless- Atmospheric turbidity: particuJate transport and corrections of

algorithms (subproject PHOTONS).This project involves many African and European research institutions.

Relations with the Soil Degradation TaskThe Soil Degradation Task should collaborate with these GCTE

Transect programmes for several reasons :- They should provide in the long terrn valuable data on soil erosion

factors, notably concerning the changes in c1imate and land use.- They collect relevant data in terms on erosion (e.g.• atmospheric

turbidity. remote sensing data on surface features).- They develop models on possible changes in ecosystems which

could be incorporated in erosion models.

This project is conducted by six Australian research institutions.

SALT (Savannas in the Long Term)SALT is the most advanced of the transects, and provides a good

11

1

1

1

NATT (Northem AustraUa Tropical Transect)NATT is a joint IGAC-GcrE project. Its specifie objectives related to

GCTE are: To determine the C02. N20, CH4. CO, NMHC and NOxemissions from important tropical savanna and coastal wetland systems,

l and to deterrnine the human-jnduced cornponent in relation to the cyclingand storage of carbon and nitrogen in those systems; ta develop a generic,predictive model of change in tropical ecosystems, from humid woodlandsto semi-arid shrubland, in response ta human disturbance and c1imatic

1 change; to determine the effect of soils and vegetation on the exchange ofmass (water and trace gases). energy. and momentum between the landsurface and the atmosphere; and the impact of c1imatic extremes and

1human activities (especially the effect of fire) on these exchanges.

The transect is located in tropical northem Australia along a line fromDarwin to north-west of Tennant Creek. This area includes ecosystemsranging from tropical ocean, coastal floodplain. monsoonal savannawoodland and semi-arid shrubland. Its primary c1imatic gradient isprecipitation, which ranges from f565 mm per year in the north to 470mm per year in the south. There are several secondary gradients in soil

1type and intensity of land use (cattle grazing, fire).

The ecological aspects are divided into four tasks:- Vegetation and plant functional types. The classification is based

on a combination of remote sensing and site-basedmeasurements.

- Models at the Patch Scale.- Extension of Models to Regional Scale.- linkage to Global Models.

1Objectives

GCTE has initiated the establishment of IGBP terrestriaJ transects forglobal change research. Each transect is comprised of a coherent set ofresearch sites along a gradient of a major global change driving force (e.g.,temperature. precipitation. intensity of land use). The transects are usedwithin IGBP to study change in biogeochemistry. surface energyexchange. and vegetation structure and dynamics. and ta serve as studyareas for model development and as test beds for the use of remotesensing data in global change science. They will contribute to research in

l a number of core projects in addition to GCTE. including IGAC(International Global Atmospheric Chemistry), BAHC (Biospheric Aspectsof the Hydrologie Cycle). LUCC (land-use and Cover Change).

1 The first two IGBP transects -Savannas in the Long Term (SALT WestAfrica) and the Northem Australia Tropical Transect (NATT) have beenaccepted into the GerE Core Research Programme.

1

1

Sources

1 CiCTE, 1994. Core Research: 1993 Annual Report. GCTE, Canberra, 135 p.Men.ut (J.C.). Saint (Ci.). Valentin (C.). 1993. SALT. Les Savanes Long Terme. Analyse de la dynamique des savanes d'Afrique de l'Ouest: m

canismes sous-jacents et spatialisation des processus. Lettre du Programme Environnement, CNRS, n 10:34-36.

1 SOIL EROS/ON UNDER GLOBAL CHANGE 37

1

1111111111111111111


1

1111111111 SESSION V: CURRENT MODELLING PROGRAMMES

iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii

11111111111

1111111111111111111


1

111

CREAMS/GLEAMS Madel Application Under Global Change111111111

The CREAMS (Chemicals, Runoff and Erosion, from AgriculturalManagement Systems) model (Knlise!, 1980) was developed to addressthe issues raised by giidelines established by the Clean Water ActAmendments of 1972, Public Law N° 92500 by providing a tool toevaluate sources of nonpoint pollution. CREAMS is a continuous dailysimulation model wilh three separalted stand alone components.hydrology, crosion/sedimentation, and chemistry. Each component can berun separately by incfuding appropriate input files required by thecomponent.

For hydrology the inputs are a daily precipitation file and a parameterfile containing field size, siope, soil characteristics. mean monthlytcmperature. solar radiation and crop leaf area curves. Output form thismode! is then passed to the erosion component by a pass file containingthe daily climate elements, precipitation, temperature. and radiation, andalso the runoff volume. peak flow. rainfall erosivity index for each storm.plant water uptake. soil evaporation. and the amount of percolation.

A parameter file is required for the erosion component containing thetillage dates, depths, and types, the soil loss ratios for tillage sequences.sediment particle size distributions. number of channels. types. widths andslopes. A pass file is constructed by the erosion component for input intothe chemistry mode!s containing ail the elements of the hydrology passfi 1e with the addition of soil loss mass and enrichment ratio.

Nielcs A. D.

characteristics of the compounds appJied such as half-life. water solubility.and partition coefflicient for soil and Iiquid phase.

The GlEAMS (Groundwater loading Effects of AgriculturalManagement Systems) model (Knisel. 1993 and Leonard, et al. 1987) is anextension of the CREAMS mode! with improved hydrology and nutrientcomponents and an added component for vertical flux of pesticides.Because GlEAMS is a continuation of CREAMS much of the materialdescribing the model is the same as given in the original CREAMSdocumentation.

The hydrology component of GlEAMS has been modified to allow for2 evapotranspiration options. The first, used in CREAMS. is the Prestly·Taylor method which uses daily air temperature and solar radiation forestimating potential evapotranspiration. The second method is thePenman-Montheith method which utilizes addition al daily windmovement and relative humidity inputs. Therefore. additional cfimateinput files are required for the latter optlion. A daily mean temperature fileis an optional input for the Penman-Montheith evapotranspiration option.

Other modification to the hydrology is the division of the plant rootzone into minimum of 3 to a maximum of 12 computational layers. Soilphysical properties required for each layer for hydrologie, erosion andpesticides are included in the bydrology parameters.

The chemistry component is really two models that are run separately.

1 First a nutrient component for predicting the amount of nitrogen andphosphorus in the runoff. percolation, and attached to soil particfes.Secondly, the pesticide mode!s predicts the amount of applied or residual

1 chemicals that are lost in the runoff and attached to soil particfes.Themodels are run with the erosion pass file and parameter files for eithernutrients or pesticides.

1 Nutrient parameters are derived from application rates. dates andmethods of application. Pesticide parameters are derived from the chemical

1

The erosion component of the GlEAMS model remains unchangedfrom that of the CREAMS mode!.

The nutrient and pesticide components of GlEAMS have been modifiedextensively fom those of the CREAMS mode!.

Both the CREAMS and GLEAMS models can be adapted to GlobalChange scenarios applications. However. GlEAMS would seem to be themore appropriate model to use because of tbe additJonal options andimprovements incorporated in to the mode!.

111

References

Leonard. LA•• W.G. lCnisel. and D.A. Still. 1987. GlEAMS: Groundwater loading Effects of Agricultural Management Systems. Transactions ofthe American Society of Agricultural Engineers, 30(5): 1403 1418.

lCnisel. W. G•• editor. 1993. Gleams: Groundwater loading Effects of Agricultural Management Systems. University of Georgia Costal PlainsExperiment Station, Biological and Agricultural Engineering Department Publication No. 5. 260 pp.

lCnisel. W.G. editor. 1980. CREAMS: A Field-Scale Model for Chemicals. Runoff. and Erosion from AgriculturaJ Management Systems. U.S.Department of Agriculture. Conservation Report No. 26. 640 pp.

11

saIL EROS/ON UNDER GLOBAL CHANGE 41

1111111111111111111

----=-=-42------------ 1Erosion under Global Change

1

1111 EPIC-water erosion

Favis-MortlocK D.

,111111111111111

The EPIC mode! shares a common ancestry with CREAMS. It wasdeve!oped by the USDA-ARS to estimate the long-term impact of soilerosion on US crop productivity for the 1985 Resources Conservation Actappraisal. The model is composed of physicaHy-based components whichsimulate erosion and crop growth: submodels additionally deal withhydrology. weather. nutrients. soil temperature. tillage. economics andplant environment control on a daily basis. A stochastic weather generatormay be used to produce synthetic sequences of daily weather data eitherwhere measured data is sparse or fo c1imate change studies. A recentenhancement to EPIC permits modelling of the direct effect:s of inereasedatmospheric C02 on crop growth. A catchment version of EPIC iscurrently beimg deveJoped.

EPIC simulates erosion on a small hillsJope area (around 1 ha). Soilproperties are assumed to be homogeneous on this area. but up to 10 soillayers may be defined. THe user may choose one of three basic erosionequations (USLE. Onstad-Foster or MUSLE). Rili and inter-rill erosion arenot separately considered. nor are non-uniform slopes.

The model's data requirements are considerable. THe US user canaccess databases of meteorological. pedologicaL crop and managementinformation via a companion data entry program. Outside the US thisoption is not available for weather and soil profile data: also the databasesof crop and management details may require modification for localconditions. The mode! has manny default settings for mssing data items.however these must be used with caution in a non-US context.

The model has been used for estimation of contemporary erosionand/or crop yield in the US. France. Australia. Argentina and the UK. andfor climate change impact studies in the US and the UK. Earlier impactstudies were confined to consideration of c1imate scenarios differing fromthe present only in long-term monthly mean values of precipitation.temperature and C02 content. Tillage and crop details remainedunechanged from the present However. current work has also begun toconsider chage in rainfall frequency and agricultural management.together with temporal shift in rainfall and temperature means.

11

SOIL EROS/ON UNDER. GLOBAL CHANGE 43

1111111111111111111

----=--=-44----------- 1Erosion under Global Change

1

111111111111111111111


EPIC-wind erosionSkidmore E.

4S

111111111·1111111111


1

1111

Reuised wind erosion equation united states department of agricultureAgricultural Research ServiceFryrear O. W., Zobeck T. M.

111111111111111

The Wind Erosion Equation (WEQ) developed by Dr. W. S. Chepil.Neil Woodruff. and Dr. F. H. Siddoway in 1965 has been revised toincorporate new technology.

ln WEQ. the factors important in the erosion process were relatedthrough a "functional" relationship using tables and figures to determinethe amou nt of erosion. In the RWEQ. the factors are expressedmathematically as the product of parameter values to estimate winderosion on a daily, bimonthly or any time period using a personalcomputer.

The RWEQ assumes that the magnitude of the wind force will limitthe quantity of soil that can be eroded and transported by wind. Thevelocity of the wind above a threshold value is cubed to quantify theimpact of wind. In addition. the density of the air during the specifieerosion period will influence the magnitude of the wind force.

Soil conditions are represented with the following parameters:1. Sail erodibility. This term reflects the portion of the surface

soil less than 0.84 mm diameter. It can be determined fromcompact rotary sieve analyses. or computed from soilproperties.

2. Sail roughness. The impact of soil surface roughness isreflected with an oriented (ridge) roughness coefficient andwith a random roughness coefficient. When the wind isperpendicular to the soil ridges and furrows. both orientedand random roughness values are important. When wind isparallel to ridges and furrows. only the random roughness isimportant. RWEQ will decay roughness with rainfall, buteach type of roughness is decayed separately.

3. Sail wetness. When the surface soil is saturated, soil erosionwill be controlled, but the surface millimeter of soil will dryvery rapidly. Consequently. soil erosion can occur the sameday it rains. The influence of soil wetness is providedthrough an equation which includes potentialevapotranspiration and rainfall.

4. Sail crust. When raindrops impact the soil surface. surfaceparticles may be reconsolidated into a surface crust. For finetextured soils, the resulting crusted soil may effectively resistwind erosion. For coarse-textured soils, the crusted soil mayhave a layer of loose sand grains on the surface. These loose

sand grains may easily be moved by wind because theraindrops also leave an aerodynamically smooth surfacecompared to a freshly tilled surface. Immediately after tillagethere is no surface crust and this parameter has no effect.Surface crusts are not included in the RWEQ until at least10mm of precipitation has fallen.

ln some regions, crop residues are the major component of aneffective wind erosion control system. The importance of crop residues isreflected with the following crop inputs:

1. Flat residues. If a significant portion of an erodible soil surfaceis covered with fiat. nonerodibJe plant residues. wind erosionwill be controlled untH the residues decay.

2. Standing residues. Wind tunnel tests and field observationssupport that standing residues. even thin or sparsely spacedplants, will be about 9 times more effective in reducing winderosion than the same quantity of plant material lying fiat onthe sail surface. In RWEQ. the standing residues will decayuntil the plant falls to the sail surface. After it falls to thesurface. the residue is decayed as fiat residue.

3. Crop canopy. Crop canopies can greatJy reduce the force ofthe wind on the soil surface. Young plants will providepartial protection for the sail surface.

4. Wind barriers. Wind barriers are a series of plants arranged inrows perpendicular to the predominant wind direction toreduce wind force on the sail surface. The effectiveness ofsuch barriers will depend on the density (or porosity) of thebarrier, the spacing between adjacent barriers. the veJocity ofthe wind. and the roughness of the soil surface.

These soil and crop parameters act to reduce the wind force on thesoil surface. Each parameter has a value between 0 and l, reflecting theamount of erosion reduction. A parameter value of 1 indicates no effecton erosion and a value of 0 indicates total control.

The success of any new model is dependent on how weil winderosion predicted by the model agrees with measured wind erosion. InRWEQ, erosion was measured at Sidney, Nebraska: Elkhart. Kansas: andBig Spring. Texas. The mean predicted to measured erosion ratios were0.59, 1.02. and 1.14 for Sidney, Elkhart. and Big Spring. respectively.

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WEPP-Water Erosion Prediction ProjectAnew generation soil erosion model

Wilcox P. Bradford

Four input files are needed te run the modeJ:. 1) c1imate file. 2) slopeprofile file. 3) soil file. and 4) a management file. As already discussed thec1imate input file is generated by ClIGEN. The slope file provided generalinformation about the s10pe profile. including the number of overland f10welements (area of similar soils and management). steepness. shape andaspect Information on texture. albino, thickness. erodibility and hydrauliccharacteristics of the soil is provided for up te ten soil layers in the soilfile. There are two management options. A crop management file is usedfor farming lands and a rangeJand management file is used for rangelands.The management file is the most complicated te build. A file builder hasbeen developed to help construct the file. Information in the cropmanagement file includes the crop type. irrigation system. tillage practice.contouring. residue management etc. The rangeland management filerequires physiological characteristics of the dominant shrubs andunderstory plants in the rangeland plant community so that above andbelow ground growth may be characterized. In addition information ongrazing management. burning frequency. and use of herbicides is alsoinput.

A major challenge in the use of process-based modeJs such as WEPP,is proper parameterization. Parameter values such as effective conductivityand soil erodibility require extensive field measurements. This is c1earlyunrealistic for most model users. Much effort has gone into thedeveJopment of parameterization procedures that allow estimation ofparameters based upon easily measured characteristics. such as soiltexture. These parameterization procedures have meet with only Iimitedsuccess and work continues in this area. Even if field determined valueswere available for each parameter, success is not insured. Typically.physically-based hydrologie models have required calibration for reliablepredictions. Calibration is clearly impossible in most cases given theIimited number of locations world wide with measurements of runoff anderosion.

The development of a model such as WEPP has been an ambitiousand noble task. It goes a long way teward meeting the need for a modelthat can predict hydrologie and erosion phenomena for ungaged basins.yet remain flexible enough te be used te evaluate the impact of land useand environmental change. A model such as this is ideally suited forevaluating the impact of global change to soil erosion.

WEPP is a process-based soil erosion model that incorporatesfundamentals of infiltration theory. hydrology. soil physics. plant science.hydraulics and erosion mechanics. Major advantages of the WEPP modelover the Universal Soil loss Equation is that it is (1) capable of estimatingspatial and temporal distributions of soil loss and (2) since the model isprocess-based. it can be applied to a broad range of conditions.Development of the modeJ is headed by scientists in the United StatesDepartment of Agriculture. AgriculturaJ Research Service. and has beenongoing for almost a decade. A version will be released for public use inMarch of 1995. In my summary of WEPP. 1 have relied heavily onmaterial provided in the modeJ documentation.

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The model can be divided into six major components: climategeneration. hydrology. plant growth. soils. irrigation. and erosion. The

1 climate generator. ClIGEN. generates daily values for rainfall amount.duration. intensity and time te peak intensity; maximum and minimumtemperature; solar radiation; wind speed and direction; and dew point

1 temperature. The hydrology component calculates infiltration. runoff,evapotranspiration and deep percolation. Infiltration is simulated using theGreen and Ampt infiltration equation. The kinematic wave equations areused te simulate runoff. The plant growth component simulates changes

l in vegetation coyer throughout the year. The soils component of themodel allows many of the hydrologie and erosion parameters te changewith time as a result of farm practices, soil freezing. compaction.

1 weathering, and history of precipitation. The model is capable ofsimulating a wide range of irrigation regimes. Erosion prediction is basedupon the steady State sediment continuity equation. Soil detachment in

1interrills and delivery of sediment to rills is estimated as a function ofrainfall intensity and slope. Rill erosion is predicted if the hydraulic shearstress of the f10w is greater than the critical f10w shear stress for the soil.and the sediment load already in the f10w is less than the f1ow's transport

1 capacity. If sediment Joad is greater than the capacity of the f10w thendeposition occurs. The effects of canopy coyer. ground coyer and buriedresidue, which are continuously calcuJated by other components of the

1model, are incorporated inte soil detachments calculations. The modelalso simulates the sediment size distribution for the eroded sedimentleaving the profile. This calculation is based upon the original size

1distribution of the soil and the assumption of preferential deposition oflarger particles along the profile.

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1The scaling-up process between the three models involves model

complexity. time steps and spatial units. As an example of the cascade of

1 Kirkby Mike

complexity. the catena model directJy solves the unsaturated f10wequations for a number of soil layers. and for a number of soil columnscorresponding to positions within the microtopographic and vegetationdistribution. For the large catchment mode!. individual slope catenas arestill represented. but the soil is represented by single unsaturated andsaturated stores. while the microtopography is parameterised as a normaldistribution. Flow through the unsaturated store is accumulated at theleve! of hourly rainfalls. while subsurface f10w is lumped using a varianton TOPMODEL At the global scale. local topographie factors are givenless importance. and the hydrology is represented by a single store relatedto vegetation and soif characteristics. Iinked to a distribution 0 dailyrainfalls for each month.

Spatial scaling from the catena to the catchment scale is achieved bydivision into up te 500 sub-eatchments and the choice of representativecatenas or fJow strips for each sub-catchment. The size of subcatchments is varied. with smaller areas (1-5 km2) in headwater areasand larger areas (10-20 km2) downstream. Sub-eatchments are linked bya linearised routing algorithm for both water and sediment. Channelpattern and f100dplain geometry may respond dynamically to changingconditions by empirically relating erosion rates to hydraulic geometry.

ln the catena modeJ. time steps are as short as. are required by themost demanding process. which is ususally overland f10w when relevant.and data is taken from autematic weather station data on a. 5-15 minutetime base. For the catchment modeJ. rainfall etc. is. taken in hourly todaily steps. and sub-hourly distributions treated as a fractally generateddistribution. For the global modeJ. distributions of daily rainfall are usedon a monthly basis.

Sub-eatchments are delineated from DEMs based on 1:50.000 maps.which also provide data on catchment plan-form and elevationdistribution. These data are respectively used to define the planconvergence and divergence of f1ow-lines.. and te define average profileform. A representative flow strip is assigned plan and profilecharaeteristics. and used as the basis for explicit simulation of hydrology.vegetation and net change for its sub-catchment. Distributions oftopography within the sub-eatchment can then be linked back, whenrequired. te sub-eatchment and catchment wide distributions of landslidehazard and large scale vegetation change, allowing recognition of plantmigration issues and landscape scale disturbance. principally through fireand landuse change.

At present. the mod.eJs are primarily focused on uncultivated areas.although they will also be modified for agricultural areas. includingterraced landscapes. Landuse changes may be imposed. or interaet withvegetation growth. for example with grazing. Socio-economic impactsmay currently be imposed as external constraints. although we hope teintegrate them more completely. through interactive feedbacks betweeneconomic and physical models.

MEDALUS models for soil and vegetation change

The MEDALUS project involves co-operation by over 20 (1991-92) to40 (1993-94) groups to work on Mediterranean desertification through

(i) field work at seJected sites in Greece ltaly. Spain. Portugal andFrance.

(ii) modeJling of physical processes. socio-economic processes.c1imate change and remoteJy sensed fanduse.

(iii) application and remedial action with respect to particularproblems of salinisation. groundwater and erosion

(iv) collaborative application to large catchment areas of greaterthan 1000 km2 in the Agri. Pescara (Italy) and Guadalentin(Spain) catchments.

Within MEDALUS. innovative simulation models for soil degradationare being deveJoped at three distinet scales. Within MEDALUS 1. detailedmodeJs were deveJoped for single hillslope catenas. in close collaborationwith work at individual field sites. In MEDALUS II. these models are beingscaled up to catchments of 1-5.000 km2. These modeJs are explicitJydriven by c1imatic and landuse variables. and have also been applied in asimplified form at a global scale. currentJy to provide c1imatic indices tosoil erosion risk for uncultivated and agricultural areas. Although thesedifferences in scale profoundly affect the approach adopted and thedominance of different processes. we have adopted common conceptsand tried to explicitJy link between scales. so that the modeJs may beregarded as a mutually consistent suite.

The MEDALUS modeJs are explicitly nntended to address the issuesof degradation and change over time periods of up to a century or more.This requires an explicit simulation of vegetation growth. under cultivatedor uncultivated regimes. and inclusion of dynamic interactions betweenvegetation. soil, the soil surface and the atmosphere (throughevapotranspiration). These interactions are central to simulatong longterm change. and provide one important and distinctive component ofthe MEDALUS mode!s.

Our models for soif degradation are built upon the underlyingphysical principles. and their most important common denominator istheir hydrological basis. In ail modeJs the dominant soil erosion process isrillwash by concentrated overland f1ow. A central core at all scales istherefore concerned with hydrological models which simulate thegeneration of overland f1ow. its frequency distribution and accumulatederosional effect and. as appropriate at the various scales. its routing overthe landscape. In detail. an important and novel approach in the modeJsis the explicit treatment of microtopographic roughness. which influencesthe spatial pattern of infiltration and overland f1ow. and may itself evolve

l over time. For uncultivated Mediterranean areas. this pattem is associatedwith a concentration of perennial vegetation on topographic highs. andof erosion in the intervening lows.

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1 ReferencesK.J. Beven and M-J. Kirlcby. 1979. AphysicaJly~ variable contributing-area model of catd1tnenthydrology. Hydrological Scienœ Bulletin 24(1). 43-09.M-J. Klrkby. A.J. Baird. j.Ci. Lodcwood. M.D. McMahon, P.j. Mitchell, j. Sh.D, j.E. Sh.ehy, j.B. Thorn.. & F.I. Woodward, 1993.

1The~~CiiEmrrai:t a~tmrllJtXES5 rn:xEIb"~. e:xi:lwcnilinlà:fIa:lâu i'èrclJi:i lS. i'l Mtlit"allJlbliiai,ucnilinl use (J.B.Thmescni~ Br.nlt Eœ)~1D theCICal the MIDl\I..US IlJOjtt Ca1lr.M:t t\b EPCC-erooœI4-(SMl\). R87-139.

M-J. Kirlcby and N.j. CDX, in press. A c1imatic index for soil erosion potential (CSEP) including seasonal and vegetation factors. Catena Supplement

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SESSION VI: PROPOSAL fOR A GCTE SOIL. EROSIONMODELLING/EXPERIMENTAL. NETWORK

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IGBP, GCTE, Focus 3, and the Soil ActiuityIngram. John

The International Geosphere Biosphere Programme (IGBP) has been1 deveJoped ta improve our knowledge of the dynamics of the biosphereinfluencing. and influenced by. global environmental changes. It waslaunched in the mid 1980s under the aegis of the International Coundl of1 Sdentific Unions. and has given lise ta six Core Projects. One of these.Global Change and Terrestrial Ecosystems (GCTE). has the overall jointaims of:

1 .Predicting the effects of changes in climate. atmosphericcomposition and land use on terrestrial ecosystems. including

a) agriculture. forestry and soils. and

l b) ecological complexity. and2 - Determining how these effects lead to feedbacks to the

atmosphere and the physical c1imate system.

1 GCTE is divided into four major themes (Foei); Ecosystem function:

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Ecosystem structure and composition; Global change impact onagriculture. forestry and soils; and ecologica1 complexity. Broad outlines ofthe research agenda for each Focus are published in the GCTE OperationalPlan (IGBP Report No. 21).

GCTE Focus 3 contains five Activities. three dealing with major foodproduction systems and managed forest:s. and two dea/ing with the crosscutting issues of pests. diseases and weeds. and soils. This last Activity(Activity 3.3) contains three interrelated Tasks dealing with global changeimpacts on soil organic matter dynamics. soil degradation. and soilbiology. This workshop is designed. ta launch the second Task (Task3.3.2) and ta prepare a detailed research agenda for its initial. predominantaspect. soil erosion under global change.

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Mediterranean desertification and land useSoil degradation research in the framework of MEDALUS

Poesen Jean

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As a result of the human land degradation and the threat of impendingc1imatic changes. the European Union has set up a multi-disciplinaryproject, MEDALUS. in order

- to investigate the physical. biological and socio-economicprocesses leading ta and continuing ta cause desertification in theMediterranean regions of Europe:

aggregate stability. soil erosion in stony soils. the. effects of rainfallexclusion and the impact of different modes of cultivation of commonMediterranean crops on runoff and erosion processes. This work has beencarried out at eleven main field sites throughout the Mediterranean inPortugal (Alentejo). Spain (Almeria. Murcia and Guadelentin). France (Varand Roussillon). ltaly (Sardinia. Basilicata and Abruzzi) and Greece (Spataand Petralona).

1 This presentation will only deal with soil erosion measurements in thefield (in the framework of MEDALUS). MEDALUS models for soil andvegetation change are discussed by Prof. M. Kirkby.

ln addition ta work individual ta each site. the field sites are also beingused ta collect data. ta a standard format, for modelling purposes (corefield programme. MEDALUS model). These data include weather data onan hourly basis: dynamic soil and soil erosion data on il storm-event basis:and vegetation on il monthly or seasonal basis. In addition staticproperties. such as soil texture. topography and aspect have beendescribed. The co-ordination and assembling of field data is beingundertaken by the University of Amsterdam (Prof. A.lmeson).

One of the field studies deals with the effects of rock fragments on soilerosion by water. Results from this study reveals that the effects. of rockfragments on sediment yield depends on the spatial scale considered.While a mesoscale interrill area shows a variety of contrasting effects ofrock fragment covers on sediment yield. sediment yield was found todecrease with rock fragment cover at the microscale and the macroscale(interrill and rill erosion). Results from field work extended the analyses ta

the catena-sized megascale and proved that rode fragment cover increaseslogarithmically with slope gradient along catenas and megatransects in SESpain. This indicates that in serni-arid areas some important erosionfactors. such as rock fragment cover, vary systematicaJly in the landscape.This allows prediction of rock fragment cover and soil erosion frominformation easily obtained from maps or DTM's.

- ta modeJ these processes with a view ta projecting the impact ofc1imatic changes and changes in socio-economic activities.especially the European Union policy. on the landscape system ofthe Mediterranean:

- ta identify possible mechanisms for mitigating these effects.

MEDALUS 1 commenced in january 1991 and the first phase wascompleted by December 1992. The second phase. MEDALUS Il.commenced in january 1993 and will continue until Decernber 1994.Research for MEDALUS is conducted by 19 teams working in nationalinstitutes and universities throughout Europe under the co-ordination ofProf. j. Thomes. King's College London.1

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ln order ta understand the physical processes of desertification, runoffgeneration, soil erosion and vegetational processes are studied at the localscale through detailed field investigations. This involves special studies of

1 plant physiological response, the relation between vegetation cover andsoil erosion under Mediterranean conditions, the evolution of soil

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The world's population had double over the last centaury and isexpected te grow te about Il billion before it stabilizes. Studies by FAO

1 indicate that the world's land resources are sufficient te meet the likeJyincreased demands for food and other agricultural product but on/y if theproductivity of the land is maintained.

l A recent study by ISRIC shows that some 1.9 billion ha of land arenow averseJy affected by "human-induced soil degradation". Erosion is themost important cause of land degradation with 56 percent of the degradedland being affected by water erosion and 27 percent by wind erosion. The1 question facing us now is how te overcome this problem.

Although a considerable amount of time and money has been spenton soil conservation since the 1930s. the situation is getting worse rather

1 than better. There are a number of reason for this and they indude thefact that more marginal. erodible land is being brought inte production inthose countries which have rapid/y growing populations. It also includes

1the fact the some present day pricing structures and farming policies areencouraging bad land use and management. But. perhaps moreimportant/y. it is due te the fact that past approaches te soil conservationwere faulty: land users were not interested in most of technologies wich

1were advocated because they were often cost/y te app/y and did not ofterthe quick retums that are needed by those trying te make a living fromthe land. This last fact is now becoming generaJ/y accepted and there is amovement away from the traditional soil conservation programmes . wich

1 relied upon mechanical erosion control measures. and a movementtewards productive systems of land use which increase productivity whileredudng the risk of erosion.

1 FAO has been concerned with the problem of erosion since itsinception in 1945 and over the years it has aided many countries throughsoil conservation projects. In the past these projects concentrated onintrodudng modem technologies from the USA and other technological/y

1advanced countries. Projects usually aimed at demonstrating thesetechnologies - which were usually physical erosion control measureswhich did not direetly increase farm production - in pilot areas and intraining local staff. It was assumed that at the end of the projects that the

1local staff would continue the work and that it would spread te otherareas. However. in practice this did not work weil and so FAO's prioritiesand activities have been changing.

1 It was realized that wide-scale conservation could not be broughtabout without govemments adopting the right sort of long-term policies.FAO therefore introduced the WorJd Soil Charter in 1981 which provides1a framework of principles and guidelines for any country wishing to

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FAO's prioritiesSanden D. W.

deveJop a long-term programme to overcome land degradation. As afollow-up te this. FAO is now assisting countries deveJop their individualnational soil poJides and guiding them in the formulation of strategies andprogrammes.

No region of the world is more averseJy affected by soil erosion thanAfrica so in 1990 FAO launched a special programme: the InternationalScheme for the Conservation and Reclamation of African Lands. Underthis scheme. countries are offered assistance in deveJoping national soilconservation programmes which are tailored te there own particularrequirements. A feature of the scheme is a mechanism which allowscountries to deveJop their own programmes but in close. collaborationwith those donors. NGOs. financing institutions and technical assistanceagencies which are needed te help implement the programmes.

While work of this scheme is still in the e.ar/y stages•. FAO has decidedte expand it to other areas and a Special Action Programme for landConservation and Reclamation was approved in late 1993 which willincorporate the African scheme and at the same time deveJop similarschemes for the Asia and Pacifie and latin America. and Caribbe.an regions.

FAO is not a research organization but in the. field of soil conservationa priority is to identify problems which are of common concern and thente promote the required rese.arch. As a result of this. a network has beenestablished of institutes which are now investigating the effects of erosionon soil productivity.

FAO's resources are smal!. Priority is therefore. given te establishingand maintaining contacts with leading soil conservation institutions indifferent parts of the world so that it has re.ady access te the most up tedate data and deveJopments and is in a position te quicldy cali upon thebest expertise and information.

With the growing importance of land degradation. FAO's priorities arelikely to remain focused on assisting governments to establish soundconservation policies and in formulating the necessary strategies andprogrammes. Its approach te conservation is likeJy te remain based on therationale that land can on/y be effectively conserved and rehabilitated on alarge scale by the land users themselves. For this te happen. conservationpractices must be developed and advocated which not on/y conserve thesoil but which also provide the land user with sorne immediaterequirement such a better crop yield. a reduced risk of crop failure or areduction in labour requirements. Without this. conservationprogrammes will continue to prove costly and to be of limitedeffectiveness.

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1111 Soil erosion under global change ISSS priorities

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It is known that the population explosion. OOgether with the increaseduse of sourcces of energy and technologies producing increasing amountsuf gases Iike C02. CH4. N20 and others•. are Jeading te temperatureincrase on the eartJi surface due 00 the absorption of infrared radiation bysuch "grsenhouse gases". It is previewed that such temperature rise couldlead te changes in the amount. intensity and distribution of rainrfall.which may increase the risks and severity of water eresion in manyregions of the world.

Although the emission of C02 due 00 deforestation and buming offorests and savanas. and due to 1oses. and. decomposition of the soilorganic matterduring the soil degradation processes•. is only 1/300 1/4 ofthe C02 emitted due 00 the use of fuel derived from petroleum. theirrelative contribution has a tendency te inaease. More important is therole that appropiate agricultural systems and soil management practices.designed te prevent the degradation of soil qualities and to assuresustainable Productivity. may play in sequestering the C. and. inneutralizing the increase in greenhouse gases mainly C02•. from othersources. In any case. the existing c1imatic models. are still not able 00predict with certainty which would be the possible effects. of c1imaticchanges on soil degradation processes. But at the same time. the changesin soils affected by degradation processes due 00 inaeased human activity.specially in the tropics. are faster and more severe than the effects thatcan be attributed 00 c1imate chanses.. In order 00 prevent bath effects. thepresent and future strategies in the management of soil and waterresources has to concentrate on the increase in efficiency andintensification of agricultural production in the lands alreeady cropped.more than in the extension and overexplotation of newer. and generallymore fragile lands.

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The main objectives of Subcomission C ("Soil Conservation andEnvironment" of the International Society of Soit Science (ISSS) is tePromote the conservation of the natural resource soil. by means ofsustainable management practices to insure an increasing agriculturalproductivity. bath for the presont and future generations. white preservingthe environmentaJ quality. To fulfill those objectives. the Subcomission Cof ISSS sponsor and collaborate in the organigation of congresses.workshops. symposia. training activities. etc. in the general topic ofsoilconservation. and in the publication of Ibooks and other printedmaterial promoting such conservation. and showing results derived ofresearch and studies of application of different management andconservation practices. In this period (1990-94). the Subcomission C ofISSS was one of the sponsors of the 12th International Soil ConservationConfrence of ISCO (Sydney. Australia. September 1992) and the Ilworkshop of the Latinamerican Network of Conservation Tillage (REIACO)in Guanare (Venezuela. November 1993). and the main organizer of anInternational Workshop on "Soit Erosion Processes on Steep Lands.Evaluation and Modelling" (Merida. Venezuela. May 1993) . During thenext 15th Intemational Congress of Soil Science (Acapulco. Mexico. July1994 ) it has the responsability of a Symposium on "Assessment of longterm soil degradation and rehabilitation. Field methodology and modeling"and of the plenary lecture on "Soil degradation and climate-induced risks

1 of aop production in the tropics". and participates in the Symposia on"Alternatives te slash and bum agriculture" and "The role of soil scientistin the design and development of soil conservation policies". In ail of

1 them the main topis were the evaluation and Prediction of soildegradation processes. mainly water erosion. and the test and use ofmanagement practices capable of preventing further degradation. and Ifor

1reclaiming soils and lands already affected by degradation processes.Soiceconomic and political issues. which are generally the indirect causesbehind any soil degradation. were also covered.

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Documents

l'IFIQlfE DE LA HECHERCHEhorizon.documentation.ird.fr/exl-doc/pleins_textes/... · interrelated Tasks dealing with global change impacts on soil organic matter dynamics, soil degradation,