Calder_land Use Impacts on Water Resources

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Land Use and Wate r Resources Researc h

Land Use a nd Wate r Resource s Research1 (2000) 2.1-2.14 (http :// ww w.venus.co .uk/luwrr)

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1Based on the keynote paper presented at FAO Electronic-workshop on Land-Water Linkages in Rural Watersheds,

18 September to 27 October 2000. http://www.fao.org/ag/agl/watershed/

Land Use Impacts on W ater Resources1

Ian R Calder

Centre for Land Use and Water Resources ResearchUniversity of Newcastle upon Tyne, UK

Abstract

This paper aims to provoke discussion on land use and water resource impacts, particularly in relationto rural watersheds in developing countries, with a view towards surfacing key issues, identifyingresearch needs and, ultimately, towards developing guidelines on instruments to distribute costs and

benefits arising from land-use impacts on water resources amongst upstream and downstream stakeholdersin a watershed.

The paper is in three parts which address and question:l The adequacy of our scientific knowledge in relation to the environmental processes (biophysical/

climate) which determine land use impacts on water resources, summarising key points from theCGIAR SWIM paper 3 and the Earthscan publication: The Blue Revolution, (Calder, 1999; http://www.cluwrr.ncl.ac.uk/ ).

l The (often poor) connection between scientific knowledge and policy; the adequacy of the decision-

making and policy-making processes of national and international organisations in relation to landuse and water resources management; the self sustaining nature of pseudo science myths in relationto land use and water resources and the interdependence and interrelationships of stakeholders inrelation to land use and water resources.

l The adequacy of current management approaches and the need for consistent policies towards land-use and water resources management, development and poverty alleviation, which are applicablefrom the local to the global scale.

Introduction

It is argued that to deal satisfactorily with Land-Use impactson Water Resources requires an adequate scientificknowledge base, it needs this knowledge base to be connectedefficiently to the policy and decision making processes andit also requires the formulation of land-use and watermanagement policies which are not only upwardly anddownwardly compatible, from the local rural watershedscale to the global scale, but are also consistent with, and aredeveloped alongside, other global and local policies relatingto sustainability, climate change, biodiversity, trade, food

production and poverty alleviation.This paper seeks to open the debate on where effort is

still required to assist with the management of land-use andwater impacts in rural catchments.

The knowledge base - myth or reality

It has been argued (Calder, 1998, 1999) that the knowledgebase that is being used for land use and water resourcedecision making is often still based more on perceivedwisdom (myth) than science established reality. It issuggested that it is particularly necessary to purge the mythsrelating to forests and water because, arguably, not only doafforestation and deforestation activities account for thelargest area of land use change occurring on the planettoday, but they also account for some of the largesthydrological impacts. Seven mother statements relating toforestry and agroforestry issues are considered, as a meansto highlight issues and identify gaps in our knowledge:


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1 Forests increase rainfall ?2 Forests increase runoff ?3 Forests regulate flows ?4 Forests reduce erosion ?5 Forests reduce floods ?6 Forests sterilize water supplies improve water

quality ?7 Agroforestry systems increase productivity ?

Two additional, in some cases related, issues are also raisedin this paper as areas where our understanding of theunderlying processes and outcomes are uncertain:

8 Salinity control and downstream impacts;9 Land use and water related natural disasters

anthropogenic impacts and public perceptions.

The available literature and field experience related to theseissues is considerable. The titles referred to in the followingsections are just examples and by no means exhaustive. A

fuller account of the seven mother statements is given inearlier publications (Calder, 1998, Calder 1999) and only asummary is provided here together with relevant pointsmade during an informal internet debate, stimulated by theCGIARs Polex newsletter of December 1998 (contactDavid Kaimowitz [email protected]), makingreference to papers by Calder (1998) and Chomitz andKumari (1998).

1 Forests increase rainfall?H C Pereira (1989) states in relation to forests and rainfall:The worldwide evidence that high hills and mountainsusually have more rainfall and more natural forests than dothe adjacent lowlands has, historically led to confusion ofcause and effect. Although the physical explanations havebeen known for more than 50 years, the idea that forestscause or attract rainfall has persisted. The myth was createdmore than a century ago by foresters in defence of theirtrees The myth was written into the textbooks and becamean article of faith for early generations of foresters.

The overwhelming hydrological evidence supportsPereiras view that forests are not generators of rainfall. Yetthis myth, like many others in forest hydrology maycontain a modicum of truth that prevents it from beingtotally laid to rest. In earlier papers (Calder, 1998; Calder,1999) it was argued that there is some evidence for land-usecontrols on precipitation, but often the magnitude of these

effects are considerably less than is commonly imagined.Giambelluca and colleagues (Giambellucaet al., 1999) alsomake the important observation that many of the recentGlobal Circulation Model (GCM) predictions of reduced

precipitation following forest clearance are likely to beoverestimates because for the replacement vegetation groundsurface parameters relating to grass, rather than scrub orsecondary regrowth forest (the more usual vegetation coverfollowing forest clearance), have been used in the simulation.Giambelluca claims, in relation to forests in NorthernThailand, It is likely, therefore, that simulated reductions inprecipitation in the region due to deforestation will not beseen in model runs using more realistic scenarios of post-deforestation land cover characteristics.Perhaps the issue is best summed up by Bands et al.(1987),quoting from experience in South Africa: Forests areassociated with high rainfall, cool slopes or moist areas.

There is some evidence that, on a continental scale, forestsmay form part of a hydrological feedback loop withevaporation contributing to further rainfall. On the SouthernAfrican subcontinent, the moisture content of air masses isdominated by marine sources, and afforestation will havenegligible influence on rainfall and macroclimates. Thedistribution of forests is a consequence of climate and soilconditions not the reverseConclusion: Although the effects of forests on rainfall arelikely to be relatively small they cannot be totally dismissedfrom a water resources perspective.Research requirement: Further research is required todetermine the magnitude of the effect, particularly at theregional scale.

2 Forests increase runoff?Based on process studies and from catchment experimentscarried out throughout the world, a new understanding hasrecently been gained of the evaporative regime in forestsand the way forests influence, and generally decrease runoff

(contrary to widely accepted folklore), as compared withshorter crops.

The difference between forest and short crop evaporationis most marked in the extremes of both very wet and very dryclimates. In wet conditions interception losses will be higherfrom forests than shorter crops primarily because of increasedatmospheric transport of water vapour from theiraerodynamically rough surfaces. In dry (drought) conditionstranspiration from forests is likely to be greater because ofthe generally increased rooting depth of trees as comparedwith shorter crops and their consequent greater access to soilwater.

The few exceptions, (lending some support to thefolklore), are:

1 Cloud forests where cloud-water deposition may exceedinterception losses.

2 Very old forests. Langford (1976) showed that followinga bushfire in very old (200 years) mountain ash,Eucalyptus regnans, forest covering 48% of theMaroondah catchment, one of the water supplycatchments for Melbourne in Australia, runoff wasreduced by 24%. The reason for this reduction in flowhas been attributed to the increased evaporation from thevigorous regrowth forest that had a much higher leafarea index than the former very old ash forest.

Conclusion: Notwithstanding the exceptions outlined above

catchment experiments generally indicate reduced runofffrom forested areas as compared with those under shortervegetation (Bosch and Hewlett, 1982; Hamilton, 1987).Caveat: Information on the evaporative characteristics ofdifferent tree species/soil type combinations are still requiredif evaporation estimates with an uncertainty of less than30% are required. In both temperate and tropical climatesevaporative differences between species and soil types areexpected to vary by about this amount.

3 Forests regulate flows - increase dry season flows?Although it is possible, with only a few exceptions, to drawgeneral conclusions with respect to the impacts of forests onannual flow, the same cannot be claimed for the impacts offorests on the seasonal flow regime. Different, site specific,often competing processes may be operating and thedirection, let alone the magnitude of the impact, may be


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difficult to predict for a particular site.From theoretical considerations it would be expected

that:

1 Increased transpiration during dry periods will increasesoil moisture deficits and reduce dry season flows;

2 Increased infiltration under (natural) forest will lead tohigher soil water recharge and increased dry seasonflows;

3 For cloud forests increased cloud-water deposition mayaugment dry season flows.

There are observations (Robinson et al., 1997) whichindicate that for the uplands of the UK drainage activitiesassociated with plantation forestry increase dry season flows

both through the initial dewatering and in the longer termthrough alterations to the hydraulics of the drainage system.The importance of mechanical cracking associated withfield drainage and its effects on drainage flows has beenhighlighted by Robinson et al.(1985) whilst the work of

Reid and Parkinson (1984) indicates that landform and soiltype may sometimes be the dominant factors determiningsoil moisture and drainage flow response.

Bruijnzeel (1990) discusses the impacts of tropical forestson dry season flows and concludes that the infiltration

properties of the forest are critical in how the available wateris partitioned between runoff and recharge (leading toincreased dry season flows).

There are a number of observations from South Africawhich indicate that increased dry period transpirationfollowing afforestation with pine or eucalyptus species willsignificantly reduce low flows (Bosch, 1979; Van Lill et al,1980; Scott and Smith, 1997). Scott and Lesch (1997) alsoreport that on the Mokobulaan research catchments underEucalyptus grandis the streamflow completely dried up bythe ninth year after planting. When the eucalypts wereclearfelled at age 16 years perennial streamflow did notreturn for a further five years. They attributed this large lagtime as being due to very deep soil moisture deficits generated

by the eucalypts which required many years of rainfallbefore field capacity conditions could be reestablished andrecharge of the groundwater aquifer and perennial flowscould take place.Conclusions: Afforestation will not necessarily increasedry season flows. Competing processes may result in eitherincreased or reduced dry season flows. Effects on dry seasonflows are likely to be very site specific.

Caveat: The complexity of the competing processes affectingdry season flows indicates that detailed, site specific modelswill be required to predict impacts. In general the role ofvegetation in determining the infiltration properties of soils,as it affects the hydrological functioning of catchmentsthrough surface runoff generation, recharge and high andlow flows and catchment condition remains poorlyunderstood. Modelling approaches which are able to takeinto account vegetation and soil physical properties includingthe conductivity/ water content properties of the soil, and

possibly the spatial distribution of these properties, will berequired to predict these site specific impacts.

4 Forests reduce erosion?As with impacts on seasonal flows the impacts of forests onerosion are likely to be site specific, and again, many, andoften competing processes, are likely to be operating.

In relation to beneficial impacts conventional theory andobservations indicate that:

1 The high infiltration rate in natural, mixed, forestsreduces the incidence of surface runoff and reduceserosion transport.

2 The reduced soil water pressure and the binding effect oftree roots enhance slope stability, which tends to reduceerosion.

3 On steep slopes, forestry or agroforestry may be thepreferred option where conventional soil conservationtechniques and bunding may be insufficient to retainmass movement of soil.

Adverse effects, often related to forest managementactivities, may result from:

1 Bad logging techniques which compact the soil andincrease surface flow.

2 Pre-planting drainage activities which may initiate gully

formation.3 Windthrow of trees and the weight of the tree crop

reduces slope stability, which tends to increase erosion.4 Road construction and road traffic which can initiate

landslips, gully formation and the mobilization ofsediments.

5 Excessive grazing by farm animals which leads to soilcompaction, the removal of understorey plants and greatererosion risk.

6 Splash induced erosion from drops falling from theleaves of tree canopies, particularly if the litter layer andunderstorey are missing.

The effects of catchment deforestation on erosion, andthe benefits gained by afforesting eroded catchments will bevery dependent on the situation and the management methodsemployed.

Quoting Bruijnzeel (1990) In situations of high naturalsediment yield as a result of steep terrain, high rainfall ratesand geological factors, little, if any influence will be exertedby man. In the Himalayas, for example, there is evidencethat a large proportion of suspended sediments in the riversis contributed by big, deep, geologically induced landslideswhich occur on any type of land cover including forests(Galay, 1985). Also in situations where overland flow isnegligible, in drier land, little advantage will be gained fromafforestation. Versfeld (1981) has shown that at Jonkershoek

in the Western Cape of South Africa, land cover has verylittle effect on the generation of overland flow and soilerosion.

In more intermediate conditions of relatively low naturalrates of erosion and under more stable geological conditionsman-induced effects may be considerable. In these situationscatchment erosion may well be hastened by deforestationand there may also be opportunities for lessening erosion bywell-managed afforestation programmes. Even in thesesituations afforestation should not necessarily be seen as aquick panacea. In heavily eroded catchments, such as thoseon the slopes of the Himalayas, so much eroded material willhave already been mobilized that, even if all the maninduced erosion could be stopped immediately , it would bemany decades before there was any reduction in the sedimentload of the rivers (Pearce, 1986; Hamilton, 1987).

The choice of tree species will also be important in any


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programme designed to reduce erosion. Recent theoreticaldevelopments and observations (Hall and Calder, 1993;Calder 1999) confirm that drop size modification by thevegetation canopies of trees can be a major factor leading toenhanced splash induced erosion. These observationsindicate that tree species with larger leaves generallygenerating the largest drop sizes. The use of large leafed treespecies such as teak (Tectona grandis) in erosion control

programmes would therefore be ill advised, especially ifthere is any possibility of understorey removal taking place.Conclusions: It would be expected that competing processesmight result in either increased or reduced erosion fromdisturbed forests and forest plantations. The effect is likelyto be both site and species specific. For certain species, e.g.Tectona grandis, forest plantations may cause severe erosion.It is a common fallacy that plantation forests can necessarilyachieve the same erosion benefits as natural forests. Forestcover as such does not guarantee low rates of erosion, theforest quality (density of trees, quality of the lower canopylayers, the availability of surface litter) is an equally if not

even more important factor (Hamilton, 1987). Smyle (2000,pers. comm.) has suggested that the erosion rates inundisturbed natural forest might be considered to representa natural baseline or background erosion rate againstwhich the erosion rates from all other land uses could becompared. The use of such an index may well be of valuein land use management and the design of realistic erosioncontrol programmes.Caveat: Although conventional erosion modelling methodssuch as the Universal Soil Loss Equation (U.S. Departmentof Agricultural Research Service, 1961) provide a practicalsolution to many problems associated with soil loss fromagricultural lands it may not be adequate for the predictionof erosion resulting from afforestation activities. Processunderstanding of the erosive potential of drops falling fromdifferent tree species is not adequately appreciated and soil

conservation techniques related to vegetation type, soils andslope characteristics have not yet been fully developed.

5 Forests reduce floods?It is a widely held view, propagated by foresters and themedia, that forests are of great benefit in reducing floods.Disastrous floods in Bangladesh and northern India arealmost always associated with deforestation of theHimalayas; similarly, in Europe floods are often attributed

by the media to deforestation in the Alps. Howeverhydrological studies carried out in many parts of the world:America (Hewlett and Helvey, 1970), South Africa (Hewlettand Bosch, 1984), UK (Kirby et al., 1991; Johnson, 1995)

New Zealand (Taylor and Pearce, 1982) and Asia (Bruijnzeeland Bremmer, 1989; Ives and Messerli, 1989; Hofer, 1998A;Hofer, 1998B, show little linkage between land use andstorm flow and therefore do not support this view.Fromtheoretical considerations it would be expected thatinterception of rainfall by forests reduces floods by removinga proportion of the storm rainfall and by allowing the build

up of soil moisture deficits. These effects would be expectedto be most significant for small storms and least significantfor the largest storms.

The high infiltration rates under natural forests alsoserve to reduce surface runoff and flood response. Certaintypes of plantation forests may also serve to increaseinfiltration rates through providing preferential flow

pathways down both live and dead root channels. (Throughthe use of border trees around agricultural fields subject tosurface runoff generation there may be some prospect forrunoff and flood response mitigation whilst not introducingexcessive evaporative losses from wide expanses of trees.)However field studies generally indicate that it is often themanagement activities associated with forestry: cultivation,drainage, road construction (Jones and Grant, 1996), soilcompaction during logging, which are more likely to

Internet debate: Forests and landslips

Ian Cherret (FAO Honduras), on Hurricane Mitch:Calders comment on management activities is very relevant (That management activities associated with forestry such ascultivation, drainage, road construction, and soil compaction during logging are more likely to influence flood/erosion responsethan the presence or absence of the forests themselves.). This would be a good time to do field research in Honduras - CholutecaBasin - where first impressions are that extensive landslides that did so much damage ( a rough estimate of level of sediment carriedby flood waters running through Tegucigalpa at their height is 15-17%). The impression is also that landslides were concentratedwhere mature trees had been cleared (only shallow roots holding the saturated soil) or pine woods that had suffered extensiveburning last May (impoverished soils). This deserves investigating. Recent research by Texas A & M on an AID funded project

in the worst hit basin suggests that soil loss through landslides is at least as important in Central America as loss through run offand wind (Technical Bulletin No. 98-2 1998). And the key to landslide control is deep roots provided by large trees.Our experiences do not contradict the conclusions of Calder or Chomitz (relating to the importance of management activities) butthey do indicate that part of the need for further research requires unravelling relationships such as that of SOIL and vegetationalcover as opposed to TREES per se.

Jim Smyle (Natural Resources Specialist, Project RUTA, Costa Rica):The second topic (relating to lack of vegetation causing landslips) can be bit more thorny, as it can be governed by very local factorsand those factors may have little to do with vegetation. For example, the Choluteca basin had a tremendous amount of landsliding.It is also heavily deforested. It also appears to have a geology and soil type which makes it highly susceptible to land sliding. Deeprooted trees could be the answer...though in Hawaiis unconsolidated upland soils the weight of forest on hillslopes often makesthem MORE susceptible to sliding.

Ian Cherret (FAO Honduras), on Hurricane Mitch:In the watershed Lempira Sur in Rio Mocal, serious landslides occurred in the upper watershed on mount Celaque, the highest peak

(2900m) in Honduras, at over 2000 metres! they were deforested areas though - a thousand people have had to be relocated fromjust one landslide. Clearly the underlying geology has something to do with propensity to landslides. I believe that there is a needfor a more scientific study looking at factors such as slope, cover, geomorphology and rainfall pattern.


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required to resolve this issue but species impacts are probablynot as significant as often portrayed. Management activitiesare most likely to be paramount. At smaller spatial scalesthere is a greater likelihood of land use affecting both peakstorm flow and the time to peak.

6 Forests sterilize water supplies - improvequality?Forests were historically the preferred land use for watersupply catchments because of their perceived sterilequalities associated with an absence of livestock and anabsence of human activities. More recently the generallyreduced fertilizer and pesticide applications to managedforests and forest plantations compared with agriculturallands has been regarded as a benefit with regard to waterquality of runoff and recharge. Reduced soil erosion fromundisturbed or well-managed natural forests can also beregarded as a benefit.

Offsetting these benefits, management activities:cultivation, drainage, road construction, road use, felling,

are all likely to increase erosion and nutrient leaching.Furthermore, deposition of most atmospheric pollutants toforests is higher because of the reduced aerodynamicresistance of forest canopies compared with those of shortercrops. In high pollution (industrial) climates this is likely tolead to both long-term acidification of the catchment andacidification of runoff.Conclusions: Except in high pollution climates water qualityis likely to be better from forested catchments. Adverseeffects of forests on water quality are more likely to berelated to bad management practices rather than the presenceof the forests themselves.Caveat: Studies may still be required to determine themagnitude of the impacts for specific sites and the means tominimize adverse impacts.

7 Agroforestry systems increase productivity?Agriculturalists have long recognised the productivity

benefits that can be obtained from crops by avoiding resourceconstraints on growth particularly in relation to water andnutrients and also, in some situations, with regard to lightand carbon dioxide. Increasingly the tradeoffs betweenincreased production from irrigation schemes are beingassessed with respect to the costs to downstream users ofoften both reduced and poorer quality water resources.

Perhaps less well appreciated is that systems whichincrease productivity through crop mixtures and agroforestry,

are likely, if successful, also to have downstream impactsthrough increased resource (water resource) use. Arguablythere is a case for cost benefit analysis which takes intoaccount upstream- downstream benefits not only for forestryand irrigation systems but also for agroforestry systems,when these systems impact significantly on downstreamwater resources.

Farmers are well aware of the productivity benefits thatcan sometimes be gained by mixing different agriculturalcrops. When a crop such as pigeon pea is mixed withsorghum or maize much higher production can be obtainedcompared with pure crops of these species which occupy thesame total ground area. When productivity of the mixture issuperior to that of sole cropping it is regarded that themixture is overyielding and that complementarity hasoccurred. Requirements for complementarity are that thecrops, together in a mixture, make better use of resources

(water, light, nutrients and carbon dioxide) when supplies ofthese resources are limited.

It is thought that the increased productivity that has beenrecorded from mixtures of agricultural crops is largely theresult of temporal complementarity, especially when onecrop is an annual and the other a biennial, or a result of, forexample, nitrogen fixation or other factor or conditioncreated by one of the crops. Mixtures with pigeon pea,grown either as an annual or biennial legume, exhibits bothand has been found to show complementarity with manyspecies such as maize, sorghum, groundnut and cowpea(Ranganathan and de Wit 1996).

Agroforestry is built on the belief that mixtures ofagricultural crops and trees can also lead to increased

productivity, the belief that it is possible to find overyieldingmixtures of crops and trees which, when combined, wouldhave a higher yield than when grown separately on the sameland area.

However it is now becoming evident that the claims insupport of the beliefs, and the trials on which they are based,

are flawed. Ong and colleagues, from detailed studies ofresource capture between both intercropping and agroforestrysystems, carried out at the International Crops ResearchInstitute for the Semi Arid Tropics (ICRISAT) sites atHyderabad in India and the International Centre for Researchin Agroforestry (ICRAF) sites at Machakos in Kenya, havedeveloped a science framework and process understandingwhich is at variance with claims for increased biomass fromagroforestry systems. These experimental studies suggestthat with agroforestry systems often the best that can beachieved is near to neutral productivity.

Ong and colleagues (Ong et al., 1991, 1996), by theapplication of rigorous scientific reasoning, have alsoidentified some of the pitfalls that have trapped agroforestryresearchers into thinking that complementarity andoveryielding systems had been achieved. These have arisenmainly because the control plots containing the sole cropstands have not been under optimal conditions, so that themixture receives a favourable bias.

l One identified pitfall is that, for the convenience ofstatistical analysis, the same plant densities are used in

both the sole crops and the mixtures, although, to achieveoptimal productivity in the sole stand, higher densitieswould be required.

l A second is that the mixture and sole crop are managedidentically even though this management may result in

sub-optimal productivity in the sole crop. For example,pruning, which has been used in the mixture to reducecompetition from the trees and to return nutrients to thesystem, would not produce optimal productivity if appliedto the control plot.

l A third example is that plot sizes may be too small,allowing tree roots from the mixture or the sole tree plotsto penetrate into the plots of the sole agricultural cropand reduce their yields (van Noordwijk et al., 1996).Ong (1996) has shown from studies at Machakos, Kenya,that the roots of the tree Leucaena leucocephala canreduce the yield of maize 5m away within two years ofgrowth.

One of the fundamental differences between agroforestrysystems and intercropping systems is that the tree componentin an agroforestry system, after the initial establishment


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period, has a well-developed and deep root system.Opportunities for spatial complementarity of below groundresources are therefore limited because the tree roots tend toexploit the whole root zone.

Spatial complementarity of above ground resources,particularly in relation to light capture, is however achievablewith tree crop mixtures. Rao and colleagues (Rao et al.,1990) have shown that at the ICRISAT, Hyderabad site amixture ofLeucaena leucocephalaand millet increased thelight capture above that of a sole millet crop. Yet thisimproved light capture did not result in increased biomass

production of the mixture - the biomass produced by thetrees was essentially equal to the loss in biomass yield of thecrop. This lack of improvement has been explained (Cannellet al., 1998) in terms of the photosynthetic processesoperating in trees (all C3 type) which are less efficient intheir light to biomass conversion efficiencies than crops,such as millet, which are of C4 type and will have muchhigher efficiencies. Even though greater resource capture isachieved this does not translate through as higher total

productivity.It is now becoming apparent that trees in agroforestry

systems will generally lead to a reduction in biomass of theassociated crop (Ong 1996) and neutral total biomass

production is usually the best that can be expected.Modelling studies (Cannellet al., 1998) also support this

view. Cannell and colleagues, through the use of a processbased agroforestry model which takes into accountcompetition for light and water (but not nutrients), were ableto simulate the growth of a sorghum and tree crop mixtureunder different climatic conditions. Their conclusions can

be summarised as:

l at sites with less than 800 mm rainfall, maximum totalsite biomass production was obtained with a sole crop,without overstorey trees;

l at sites with 800-1000 mm rainfall neutral biomassproduction was obtained with a mixture;

l at sites greater than 1000 mm rainfall biomass productionwould be increased with a mixture provided the LeafArea Index (LAI) of the trees was greater than 0.25 - butthis increase in overall production would be at theexpense of a 60% reduction in sorghum grain yields;

l any decrease in crop yields due to tree competition willautomatically increase the frequency of years with pooryields and threaten food security.

Therefore, for low rainfall sites sole crops would clearly bethe best option and, even at higher rainfall sites, to achievehigher total biomass production, it would be necessary toaccept a huge, 60% reduction in the sorghum crop yield.Cannell and colleagues make the point that the biomass

produced by the trees must be of considerable value, relativeto that of sorghum grain, for this sacrifice in yield to beworthwhile.

The holy grail of agroforestry, a tree species which hasroots at depth which can exploit deep soil resources of waterand nutrients but with few roots in the surface layers to offercompetition to shallow rooted agricultural crops, is still

being sought. But, even if it ever were discovered, thespatial complementarity that would be achieved would not

be without costs. As for overyielding intercrops, theproductivity gains would be at the expense of increasedresource use and, when the resource is water, any increased

productivity gains would need to be assessed in relation tothe (marginal) cost of the extra water consumed.

These recent research findings discussed above have farreaching implications for the practice of agroforestry. Theyshow, contrary to the mother statements underlying muchof agroforestry practice, that there are in fact fewopportunities for gains in productivity by mixing trees withagricultural crops.Conclusions: Despite the claims made by over enthusiasticagroforesters there is little scientific evidence to show thatenhanced productivity can be achieved in agroforestrysystems. Growth of the woody component will virtuallyalways be associated with a decrease in biomass and valueof the associated annual agricultural crop. The hugeinvestment in the development and demonstration ofagroforestry systems purporting to increase productivitymight not have been wasted had more attention been paid bydevelopment workers to the indigenous knowledge of local

people. When high yielding crop systems are achieved itshould also be borne in mind that the productivity gains are

being achieved at the expense of increased resource useand, when the resource is water, any increased productivitygains should be assessed in relation to the (marginal) cost ofthe extra water consumed, and the impacts on downstreamusers of the water. These impacts need to be taken intoaccount for all high water using crop systems whetherforestry, agroforestry or irrigated agriculture.Caveat: Although it would be expected that close proximitycompetition from the woody component in agroforestrysystems would generally prevent productivity benefits theremight well be achievable synergies in agricultural crop andtree crop systems which rely on rotations or tree cropfallows. With these systems it is possible that the deeprooted nature of most trees may, although consuming deepsoil water reserves, bring to the surface through leaf fall,nutrients which are located at depths greater than annualcrops can access. A rotation with an annual crop may thenallow these nutrients to be utilised by the crop whilst thecrop itself, through having a less developed root system,will not be able to utilise all the rainfall, and some water will

be available to recharge deeper layers in the soil that the treecrop had previously depleted.

8 Salinity control in agricultural systems anddownstream impactsIt is widely recognised that salinity control and the avoidanceof waterlogging are important considerations, not only in

salinity prone dryland farming but also in the design ofirrigation schemes. The failure of salinity control measuresmay lead not only to land being rendered useless for

productive purposes but also to salinisation of watercourseswith consequent impacts on downstream users.

Deficiencies in our knowledge of the environmentalprocesses determining salinisation are probably not asignificant constraint in finding solutions to the problem.The quotation by Robertson (1996) salinity and itsavoidance or management has been an enigma in Australia.On one hand there has been a wide understanding of theinherently salty nature of the environment and theinevitability of salinity. On the other, there has been a highpropensity to ignore the problem and believe that for somereason salinity will not develop in any specific area.illustrates the frequently occurring situation world-widewhere, when land use and water resources decisions need to


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be taken promptly and where there is no lack of understandingof the processes, the issues are often fudged and deferred.Deferral of decision-making in these circumstances leads to

progressive salinisation of watercourses, destruction of theriver ecology and the lower reaches of river systems becomingunfit for human use or irrigation. Three types of optionshave been recognized as being beneficial in controllingsalinity problems in dryland agriculture and irrigationschemes: land management and engineering solutions, whichare discussed here, and economic/ policy instruments whichare discussed in the last section of the paper.

Land management approaches to salinity controlIn salinity prone dryland areas replanting tree and shrubs inthe recharge areas of a catchment will increase theevaporation, through increased interception and probablyalso increased transpiration, and reduce recharge andgroundwater levels. This will alleviate salinity problems inseepage areas by both lowering watertables and loweringthe level at which seepage takes place, hence reducing the

land area affected, and also by reducing the volume ofseepage waters. In areas where dryland salinity problemsare not extreme changes in cropping pattern have beenadvocated. In Australia research is now being conducted todetermine agricultural crop combinations which reducerecharge (Zhang et al., 1999) and, for areas where salinity

problems are more acute, combinations of agricultural andtree crops.

Land management has also been suggested as a methodfor salinity control in irrigation schemes. In situations wherewater rather than land is the primary constraint, landmanagement involving dry drainage has been suggested(Gowing and Wyesure, 1992) as an alternative to thetraditional engineering approach. The serious downside tothe dry drainage approach, which involves perhaps up toone half of the land area, rather than the watercourse,

becoming the sink for saline wastewaters, is that thissacrificed land becomes essentially lost to productive use.

On this sacrificed land surface evaporation allows thebuild up and concentration of salts in the soil profile. Inconjunction with the dry drainage approach the use ofshallow saline groundwater as a source of water for cropgrowth, rather than lowering groundwater tables through

pumping and then reapplying fresh water as irrigation waterfollowing traditional engineering practice, has beenadvocated as having additional benefits. The loss of land for

productive use clearly does not make the dry drainage

option particularly attractive and cannot be regarded as asustainable solution to land management. However,

perhaps in some circumstances, where salinisation hasalready occurred, the approach may have some benefits ascompared with costly conventional engineering solutions.Engineering solutions

Various engineering solutions have been proposed. Theseinclude the interception of saline groundwaters and thediversion of the excess water (returns) from irrigationschemes to evaporation pans or directly to rivers. Direct

pumping of groundwater to lower groundwater tables hasalso been advocated in both dryland agricultural areas andwithin irrigation schemes but a major problem with thesesolutions is the disposal of the saline effluents. Disposal torivers is the common option but often serves only to salinizethe vital water supply for the less fortunate users whohappen to be located downstream. If downstream users also

drain their field or pump groundwater in a similar fashionrivers will undergo progressive salinization until the ecologyof the river is destroyed and lower reaches become unfit forhuman use or irrigation. Piping the effluents for dischargeinto the sea has been considered in some locations but isgenerally thought to be not cost effective.

9 Land use and water related natural disasters anthropogenic impacts and public perceptionsMany development organizations have recently questioned

perceived wisdom in connection with the natural disasters,Hurricane Mitch and the floods in China. The type ofquestions asked were:

l Is there any evidence that the change in nature and/orfrequency of natural disasters has been caused by climatechange or environmental degradation?

l Is there any evidence that their impact has been greaterbecause of environmental degradation and if so, what

types of degradation?

Clearly these are important questions to address. Aidorganisations are called on to assist in the relief of naturaldisasters and funds allocated for preventive measures couldconceivably be a more effective use. The media often citeanthropogenic impacts as the cause of natural disasters,often reflecting the interests of one or other pressure groupswhose interests will be served by their solutions. TheFinancial Times article of 11/12March 2000 by VictorMallet argues in relation to the Mozambican flood of 2000that Drainage schemes, over-grazing and the spread ofconcrete in Mozambiques neighbours have destroyed theirlands ability to absorb heavy rains. The conversion ofwetlands to agricultural lands is also given as another reasonfor the flooding. At discussions at the World Water Forumin the Hague on the Mozambican floods (see http://www.worldwaterforum.com/news/frameset2.cfm) theDutch solution of dam building was evident: But most ofall its very important to get the help of people with expertisewho know how to build dams to prevent future flooding.A recent informal internet debate, stimulated by the CGIARsPolex newsletter of December 1998, making reference to

papers by Calder (1998) and Chomitz and Kumari (1998),involving representatives of the World Bank, CGIAR,international consultants and research organisations, hashighlighted not only the inadequacy in our scientific

knowledge in relation to the environmental processes andanthropogenic influences which may lead to and exacerbatenatural, water related, disasters but also another importantfactor: the public perception of disasters. Perhaps the public

perception of the increased frequency and severity of waterrelated disasters may be as much (if not more) related toincreased media coverage, higher world populations andhigher numbers of people at risk (particularly in relation tothe increased numbers of people living in flood plains andsubject to flood risk) as to climatic change or land usechange impacts? Understanding the role of indigenousknowledge may be a key factor in comprehending the public

perception of natural disasters (Barr, 1998). Commentsfrom this debate, which raised three new issues (or subissues), are given below with permission of the authors.


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Connecting science to policy

For land use related research to have any value it has to beconnected to the decision making and policy making process.Traditionally the culture of the research community, whichhas been fostered and is still being fostered by researchcouncils, is to publish research findings in tightly defineddisciplinary, peer-reviewed research journals the numberof research papers published and the number of citationsreceived determines the credit they achieve. Manyenvironmental research scientists still operate under thehappy delusion that once published their findings will alsoshortly be taken up and made use of in the development ofenvironmental policy. Sadly, this is not often the case. Thereaders of research journals are generally fellow researchers,not managers and decision makers. Decades may elapse,

particularly it seems in relation to land use and waterresource issues, before research findings trickle into policy.Arguably, addressing the reasons for this lack of connection

between science and policy, may be the single most effective

use of resources in furthering land use and water resourcesmanagement at all scales.

The problem is not just one of the developing world. TheUK Governments Rural White Paper on England (1995)called for a doubling of lowland forests, mainly for amenityconsiderations, without demonstrating any awareness of thewater resource implications of such a large change in landuse. Although the knowledge base for understanding thereasons for dryland salinity in Australia have been knownfor over 50 years (viz. the removal of forests reducesevaporation and saline water tables rise to produce salineseeps) forests are still being cut in the dryland areas and, toaggravate matters further, afforestation is occurring in theheadwater areas, thus reducing dilution flows. In Spainafforestation of the Pyrenees is being promoted by theSpanish Government to improve downstream waterresources. In Panama, Law 21, (with USAID support) has

been passed which promotes afforestation of the Panamacatchments as a means of enhancing flows and improvingthe functioning of the canal.

In respect to the need for water in order to increase thecapacity of the Panama Canal , it is estimated that if 1000ha per year of deforested land in the watershed was reforested,it would not be necessary to construct an additional damproposed for the Rio Ciri - Reported in: CEASPA. 1997.Panama: Evaluation of National Sustainability. Series:Panama Today No. 7. Pg.111 and taken from calculations

made by Nathan/Intercarib S.A., 1996, the consulting firmwhich developed the basis for Law 21.

Where does the problem lie?

l With the researcher for not making his results availableto a wider community of researchers operating in the differentdisciplines which all relate to environmental research anddecision making, and to the wider public and decisionmaking community?l With the research councils which still promote singledisciplinary research and where no impact factor is ascribedto any real world takeup of results in policy or decisionmaking?l With the managers and decision makers for not takingthe trouble to make themselves aware of new scientificdevelopments?

l With the media who are generally content with repeatingconventional wisdoms and pseudo science rather thanchecking authenticity?l With the scientific community who have a vested interestin assuring that no question is finally answered so thatresearch funding can continue?l With inadequacies in the structure and linkages betweenand within large organisations which hinder informationflows?l With the systems of economic incentives and penalties,and of regulation, which govern land management and

production practices?Probably all of these are responsible, and new

mechanisms, methods and research may be needed toovercome these constraints.

It has been argued (Calder, 1999) that another difficultyfaced in the task of connecting science to policy is themindset that has been generated in relation to someenvironmental issues. The perception that forests are alwaysnecessarily good for the water resources has become so

deeply ingrained in our collective psyches that it is usuallyaccepted unthinkingly. The view is routinely reinforced bythe media and is all-pervasive; it has become enshrined insome of our most influential environmental policydocuments. The report by the United Nations Commissionon Environment and Development (1992), states:

The impacts of loss and degradation of forests are inthe form of soil erosion; loss of biological diversity,damage to wildlife habitats anddegradation of watershedareas, deterioration of the quality of life and reductionof the options for development.

These simplistic views, particularly as they imply theinevitable link between the absence of forests anddegradation of water resources, have created a mindsetwhich not only links degradation with less forest butrehabilitation and conservation with more forest. Thismindset has caused, and continues to cause, governments,development agencies and UN organisations to commitfunds to afforestation or reforestation programmes in themistaken belief that this is necessarily the best or only wayto improve water resources. Clearly there are many validreasons for afforestation or reforestation programmes butwhere the objectives are to improve water resources they areunlikely to be achieved.

The mindset created by the old paradigm which inevitablylinks the absence of forests with degradation of waterresources, and more forest with improved water resources

has not yet been destroyed. Until it is replaced it willcontinue to cause governments, development agencies andUN organisations to commit and waste funds on afforestationor reforestation programmes in the belief that this is the bestway or only way to improve water resources.

An example would be the ODA-funded forestryprogramme in Sri Lanka where ODA in the early ninetiesinitiated a large scale forestry programme on the Mahawelicatchments in Sri Lanka based on the old paradigmassumption that pine reforestation would regulate flowsand reduce erosion to the catchments feeding the Victoriareservoir complex. It is now realised (Calder, 1992; Finlayson1998) that the pine afforestation is serving only to reduce

both annual and seasonal flows. Even if planted at thehighest altitudes, where there is still some remainingindigenous cloud forest at Horton Plains, recent researchindicates that afforestation would give no net benefit to


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flows; the measured interception losses from the forestexceed the enhanced cloudwater deposition. Furthermore,where the planting is generally taking place, on old,abandoned tea plantations, on-site soil erosion has virtuallyceased following the regrowth of pattana grasslands. Forestryoperations involved with planting and road constructionwill almost certainly be increasing on-site erosion.Understorey fires under the pines, a common occurrence inSri Lanka, also leave the soil exposed to splash inducederosion from the forest canopy. The forestry project istherefore having the opposite effect to that intended.

Furthermore, Stocking (1996) claims that even wherethere is bad on-site erosion on the Mahaweli catchment, anderosion from tobacco fields planted on steep slopes is

probably the worst source of erosion on the catchment, thisis not getting into the reservoirs. Recent sedimentationstudies reveal that there is, in fact, very little sedimentationoccurring in the reservoirs. Stocking claims that the on-siteerosion from the slopes is being deposited on the lowerslopes and flood plains and paddy field farmers are actually

benefiting from the sediment by incorporating it into theirpaddies.

The need for consistent policies

The need for land-use and water management policies thatare based on our best science rather than myth, that are notonly upwardly and downwardly compatible, from the localrural watershed scale to the global scale, but are alsoconsistent with other global and local policies relating tosustainability, climate change, biodiversity, trade, food

production and poverty alleviation, is surely undeniable.Perhaps nowhere is this need more acute than in relation

to forests and water policies. As discussed above, commercialforestry has often been promoted by developmentorganisations on its perceived environmental benefits. Yetscience based research has shown, and shown for a longtime, that many of the expected environmental benefits(which may in some cases be provided by natural forests)cannot be achieved through commercial plantations.Increasingly we are now becoming aware of theenvironmental dangers, rather than benefits that have beencaused by these plantations. Not only is there usually a highcost in terms of lost water associated with fast growingcommercial plantations but, as has been recognised by thegovernment of South Africa, there may also be dangers

associated with escaping plantation trees. The SouthAfrican Government, in the February 2000 budget, awardeda further R1,000,000,000 (over five years) to the Workingfor Water Programme (DWAF, 1996) for the purposes ofcontrolling and eradicating alien invading tree species. Theexpectation is that without this programme the invaderswould eliminate indigenous plant species and seriouslyreduce water resources. The programme also has, throughspecifically targeting the poorest in society for employment,a major poverty alleviation component. However, theexpectation is that the water resource and ecological valuesof the programme alone will justify the costs.

Although the alien invader issue has been recognised inRSA, the extent of this problem has not really been quantifiedfor the rest of the developed and developing world. Theextent to which past and present policies of developmentorganisations may have been responsible for introducing

and aggravating this problem - and are now morallyresponsible for helping with its resolution, is perhaps anotherquestion that needs to be broached.

As a means towards developing improved and moreconsistent land-use and water resource policies, applicable

particularly at the rural watershed scale in developingcountries, the following questions are raised for discussionregarding the adequacy of present approaches.

1 Compatibility of IWRM and SL approachesAre Integrated Water Resources Management, IWRM(resource focussed), and Sustainable Livelihoods, SL (peoplefocussed), approaches necessarily complementary or evencompatible at all spatial and temporal scales ?

The DFID White Paper on International Development,Eliminating World Poverty: A Challenge for the 21st Century,presents the concept of the stewardship of natural resourcesso that the needs of both present and future generations can

be met. The White Paper also promotes the concept ofsustainable livelihoods and this, together with the

management of the natural and physical environment isexpected to achieve the overall goal of poverty alleviation.DFID provides the following definition for a sustainablelivelihood:

A livelihood comprises the capabilities, assets (includingboth material and social resources) and activities requiredfor a means of living. A livelihood is sustainable when it cancope with and recover from stresses and shocks and maintainor enhance its capabilities and assets both now and in thefuture, while not undermining the natural resource base.Five types of assets, upon which individuals draw to buildtheir livelihoods, are defined: natural capital, social capital,human capital, physical capitaland financial capital (Carney,1998).

The Sustainable Livelihoods approach is still relativelynew and untested and the consequences for natural resourcemanagement of applying this new people-first povertyfocussed approach to sustainable development is not yetknown. There are concerns that poverty alleviationapproaches focussed at the microcatchment scale may resultin tragedy of the commons type impacts at larger scales.Conversely, it could be argued that IWRM approaches,although aiming to achieve net economic benefits to basininhabitants, may not be taking sufficient account of the

poorest in society.

2 Socio-economic impact of demand-management

approachesDo we fully understand the socio-economic implications ofapplying IWRM, demand-management, economicinstruments such as the registration and licensing of highwater using land uses (e.g. forests and sugar cane), water

pricing and tradable water rights? Is there a danger thatunless properly conceived the poorest sectors of society will

be disadvantaged? Here again there may be a conflictbetween IWRM approaches and poverty alleviation; inparticular the need to set water pricing at a level that thepoorest in society can afford. The South African Departmentof Water Affairs and Forestry (DWAF) now recognise thatthe primary goal of the Government of South Africa is thealleviation of poverty. Barbara Schreiner, Chief Director,Water Use and Conservation, DWAF, explains the issueeloquently:


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There are those for whom water resources managementappears to be an end in itself, and for whom the challengeis to perfect the science, perhaps even the art of waterresources management. For these people, economicgrowth is necessary in order to provide the necessarycontext for improved water resources management, asthough improved water resources management has someinherent and ultimate value in and of itself. Then thereare those for whom water resources management is atool, and not an end. There are those for whom waterresources management is one element in the struggle tobuild a socially and environmentally just society, notonly in South Africa but across the whole world. Forsuch people, and I number myself amongst them, theultimate purpose of what we do is to create a society inwhich there is no more poverty, to create a world inwhich all human beings have sufficient food and water,a place to live, a job, a clean and healthy environment,education, and a chance for a life of dignity and selffulfilment. (Schreiner, 1999)

3 Carbon sequestration benefits and water resourcedis-benefits of forestsWill the promotion of forestry as a land use in rural watershedsthrough carbon sequestration credits (Kyoto Protocol) reducedownstream water resources and aggravate downstreamwater resource conflicts ?

One of the difficulties in reconciling forest policy inrelation to both water and climate change is that there aretwo separate research communities addressing these issues.An example of this is given by the physical separation of thetwo communities into parallel sessions at the Forests andAtmosphere-Water-Soil Conferenceheld at Soltau, NorthernGermany in July 1999.

The recognition that forest carbon sequestration benefitsmay be at the expense of reduced water resources does notseem to have registered strongly in either community. Yet,even if the principles underlying the Kyoto Protocol areaccepted, there are important questions to be asked bycountries seeking carbon sequestration credits throughafforestation policies, in relation to the value of these creditsas compared with the value of the water that will be forgone.In monetary terms they may be quite similar. Taking(conservative) estimates of 250 and 400 mm per year as theaverage loss of water under deciduous hardwood and pines/eucalypts respectively (Bosch and Hewlett, 1982) and(conservative) average values for water for agricultural or

industrial water use as $100 per 1000 m3

( values as high as$4000 for industrial processes and nearly $2000 have beenquoted for some speciality crops) the loss in value of waterunder hardwood afforestation would be $250 per hectareand $400 under pines/eucalypts.

Aylward (Aylward 1998; Aylward et al. 1998) suggests,from studies in Latin America, that carbon sequestrationcredits arising from afforestation would amount to around$200-$500 per hectare with a price of $20/ton (amongst thehighest of the present carbon valuation) for carbon. Clearlyif there were higher value uses for water within a catchmentwhich were able to afford more than $100 per 1000 m3 onstrict economic arguments alone, forgetting the possiblesocio- economic downsides, there would be little merit in

pursuing carbon credits.

4 Increased production efficiencies at the expenseof downstream environmental problems

The fallacy of striving for increased irrigation efficiencyat the farm level which involves reducing the amount oflost return waters from the irrigation scheme has been ably

pointed out by Seckler (see Seckler 1996, http://www.cgiar.org/iwmi//reps.htm). At a larger basin scalethese return waters are not lost if they are being used forenvironmental or other downstream purposes. Similarly itshould perhaps be argued that where increased productionefficiencies of other high water using land uses, whetherirrigated farming, forestry or agroforestry, are achieved atthe expense of increased (water) resource use, the production

benefits need to be considered in relation to the marginalcost of the water to other downstream users and, wherenecessary, compensation mechanisms to downstream usersshould be considered.

For agroforestry systems we seem to have the particularly

curious situation that, irrespective of the downstream waterconsequences of increased productivity, increased

productivity from agroforestry systems as compared withnon mixed forestry and agriculture seems impossible toachieve. Research has established that through competitionfor resources, particularly water, the best that can normally

be achieved from agroforestry systems is the neutralproductivity condition (i.e. the presence of trees will, for allknown tree and agricultural crop mixtures, reduce the

productivity of the agricultural crop). Yet it would appearthat agroforestry is still being promoted by UN and otherdevelopment organisations as a means of increasing

production notwithstanding the extra labour requirementthat agroforestry systems usually entail. Is there a mismatch

between the knowledge base and policy in relation to thepromotion of agroforestry as a means of increasingproductivity?

5 Water subsidies to agriculture and increaseddownstream environmental problemsIn most countries government policies are such that irrigationwater is still provided, through subsidies, at an artificiallylow price. Increasingly it is being recognized that the use ofthese subsidised and low prices leads to inefficiencies inwater use which are direct contributory factors to bothwaterlogging and downstream salinity problems.

Increasing the price for irrigation water is one method

that has been adopted for encouraging efficient water use.Another method, which has been used in the USA andAustralia, is the Transferable Water Entitlement (TWE) ortransferable water right. This is a mechanism by which amarket for water can be achieved by allowing entitlementsto be bought and sold without the necessity of buying andselling the accompanying land. The use of the mechanism isexpected to increase efficiencies in a number of waysincluding the transfer of water to higher value uses andhigher valued crops. It is also expected to lead to theincreased adoption of water saving irrigation technologies,

because the saved water can then be sold. Decreased use ofirrigation on land which is poorly suited and where economicreturns are low, perhaps because of existing waterlogged orsalinized conditions, might also be anticipated.

Arguably combinations of three approaches: landmanagement, engineering solutions and economic


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instruments, may hold the best prospects for the managementof salinity and downstream environmental problems

6 Matching local land-use and water-resourcepolicies with global idealsThe Global Water Partnership (GWP) document TowardsWater Security, Framework for Action (http://www.gwpforum.org/Vision.htm#FFA) presents again themessages contained in the Dublin Statement and UNCED(UNCED, 1992) report of almost a decade earlier. Somehave questioned (see NGOs express serious concernshttp://www.worldwaterforum.com/news/frameset2.cfm ) thelack of progress that has been made over this decade andmost would agree that further development of the ideals,and the huge costs that this entails, is not what is required.What is required is action in terms of realistic policiesapplicable at the local level. Where this is happening, andthe case of South Africa, with a new water act, and with thedevelopment of new sectoral strategies being developed,may be the best example, perhaps we should be looking for

Best Management Practices, to see how such policies areperforming and to see how they may be applied, with anynecessary modifications, elsewhere in the world?

It may also be necessary to explore the GWP proposalsfor consistency and to ask questions such as are some ofthese Global approaches useful or meaningful at the local,rural catchment scale?, e.g. Is the GWP sending out anambiguous message in calling for achieving water-foodsecurity implying notions of national water-food securityand self sufficiency, when virtual water transfers throughfood trade may be a more efficient alternative?

A 30% increase in water productivity for food productionfrom rainfed and irrigated farming by 2015 is called for inthe GWP, Towards Water Security, Framework for Actionto meet future global food requirements. Are such projections

based on an adequate knowledge base? Are such exhortationsin anyway meaningful at a local scale? Do they mask theother economic and socio-political realities presentlyconstraining food production and water availability at therural catchment scale?

If it is agreed, during the conference, that some of theabove questions are valid and require an answer, perhaps afollow-up question that should be posed is: How can asolution be found, what more must we do to ensure consistent,integrated policies within watersheds of different scaleswhich deal with land use impacts on water resources, withthe impacts of upstream activities on downstream users,

which make use of appropriate economic, social and politicalmechanisms within watersheds and which are making bestuse of current scientific knowledge?

Acknowledgements

The author wishes to thank all those that contributed to theinternet debate that was reported here and to Thomas Hoferfor his valuable editorial comments on this paper.

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