Global Cooling - science do 2 - Earth & Environmenthomepages.see.leeds.ac.uk/~lecsjed/huiyi/GCdossier7.pdfclimate. These are tested on past decades to show that they are competent

The Global CoolingProject

ScienceDossier

Edited by Ray Taylor21-07-07

This dossier brings together evidence supporting cooling impact ofa large scale rainwater harvesting project, to be put into action inthe tropics in four continents, with the priority on West Africa.

The work was supported by Professor Peter Cox of the UKMeteorological Office, Dr Sietse Los of the University of Wales andDr Richard Harding from the Centre for Ecology and Hydrology,Oxfordshire. Peer-reviewed articles are referenced and somearticles are included in full.

www.TheGlobalCoolingProject.com0845 058 0537

+44 845 058 0537

Cover illustration by Ashleigh Gordon ([email protected])

RAINWATER HARVESTING

↓MORE SOIL MOISTURE

↓MORE CLOUDS

↓GLOBAL COOLING

"The climate crisis .... offers us the chance to experience what very few generations in history have had the privilege of knowing: a generational mission; the exhilaration of a compelling moral purpose; a shared and unifying cause; the thrill of being forced by circumstances to put aside the pettiness and conflict that so often stifle the restless human need for transcendence; the opportunity to rise."

Al Gore

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Contents

A. Introductory material:

(1) Summary and purpose of this dossier 5

(2) Acknowledgements 7

B. Evidence sections:

I. More low altitude clouds → more global cooling 10

II. More soil moisture → more low altitude clouds 32

III. Rainwater harvesting → more soil moisture 42

C. Copies of key references and maps 46

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This publication is copyleft: it may be reproduced and quoted freely to promote the concept of global cooling through land-atmosphere interaction, though permission must be obtained from original authors for publication of articles and illustrations.

If using any of the material in this dossier, please send information about any quotation or reproduction to [email protected]

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Part A

Introductory Material

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Summary

The Global Cooling Project proposes large scale rainwater harvesting (RWH) in semi-arid tropical countries to increase soil moisture in periods of low rainfall, thus improving vegetation cover and cloud cover.

This dossier brings together scientific evidence of critically important impacts of strategic rainwater harvesting (SaRaH) for regional and global climate. It comprises comprehensive peer-reviewed evidence for the beneficial role of strategic/large scale rainwater harvesting in semi-arid tropical countries in:

• global cooling

• regional cooling

• increased regional rainfall and prolonged rainy season

This is to be undertaken on a large scale in 4 continents, with a initial priority on West Africa. For full details of the project see the separate document: "The Global Cooling Project - outline".

While global cooling may be important and helpful, it is through impact on regional temperature and rainfall the the greatest benefit is likely to accrue to human beings and ecosystems.

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RAINWATER HARVESTING in semi-arid tropical regions

↓MORE SOIL MOISTURE

after end of usual rainy season ↓MORE CLOUDS

low altitude clouds and cumulo-nimbus

↓GLOBAL COOLING

The evidence in this dossier comes in four forms:

A. Historical evidence - based on ground level observations over many years, showing the impacts of human and other "forcings" on the regional and global climate. These often compare two regions (eg one where deforestation has occurred, with another where it hasn't).

B. Model evidence - studies using computer models to simulate the regional and global climate. These are tested on past decades to show that they are competent to model future climates.

C. Satellite evidence - satellite data which shows how present time differences in climate are linked to present time differences in (eg) surface vegetation

D. Causative/process evidence - e.g. studies which demonstrate factors causing increased cloud formation: eg the role of trees in increasing dry season water vapour and in producing aerosols and turbulence.

Section III shows how various techniques of rainwater harvesting can be used to increase year-round soil moisture and tree survival. Material on techniques of rainwater harvesting is included in Part C.

Section II shows how an increase in soil moisture or forest leads to more cloud formation and rainfall.

Section I shows how an increase in low-altitude and convective cloud has a global cooling impact. It also describes modelling studies showing links between tropical vegetation and forest and global cooling. The impacts of soil moisture and forest on regional rainfall are also demonstrated.

NB It is not claimed that this project removes the need for reductions in CO2 and methane emissions - the best hope is that the global cooling project will buy more time to prevent runaway global warming.

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Acknowledgements

I would like to acknowledge the help and support of Dr Michal Kravcik, Dr Sietse Los, Dr Richard Harding, Dr Milo Shott, Mr Juraj Kohutiar, Mr Brian Nobbs, Ms Ashleigh Gordon and Professor Peter Cox.

Financial and moral support from Scotland Unlimited, Will Miles, and Christian Waetjen is gratefully acknowledged.

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Part B

EVIDENCE SECTIONS

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The Kogi tribe of Colombia describe themselves as "Elder Brothers" and white Europeans as "Younger Brothers":

The Elder Brother survived, high on the mountain, but the progress of the conquest ground steadily on. And now .... the Younger Brother is pressing on into this final refuge. And as he does so, he completes his process of plunder, ripping apart the world for profit. Cutting down trees, ripping out gold, minerals and oil, heating up and drying out the world. 'We know what you have done. You have taken the clouds. You have sold the clouds!'

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SECTION B I

More low altitude clouds → more global cooling

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I.1 Clouds and the Earth's heat balance

Clouds in the tropics cool the planet in 3 ways:

(A) by reflecting the incoming UV and light radiation from the sun (their contribution to planetary albedo or reflectivity

(B) by storing heat radiation trapped in the atmosphere and emitting some of it out to space in the form of longwave radiation

(C) by taking energy from the land surface, in the form of water vapour/heated air/etc, and carrying this great distances, ultimately into the upper atmosphere, where it can again be emitted from the top of the atmosphere, as longwave radiation.

Earth's radiation budget - IPCC 2001

As illustrated above, immediate reflection by clouds (along with aerosol etc) immediately reflects out into space 22.5% of incoming radiation. (A)

19.6% of incoming energy is absorbed by the atmosphere (including clouds) before reaching the surface of the earth. (B)

Of the 49.1% which reaches the surface, water vapour evaporated and transpired accounts for almost half (22.8%) transferred back into the atmosphere. (C)

When B and C are combined with other, smaller inputs to the atmosphere the energy emitted as longwave radiation from the top of atmosphere is over 45% of the total incoming solar radiation.

This means that clouds/evapotranspiration are involved in 22.5 + 45 = 66.5% of the total cooling of the planet. Any change in cloud cover is therefore likely to have a major impact on the earth's radiation budget, all other factors staying the same.

Low altitude tropical clouds are particularly good for (A) and (B), and convective (thunderstorm) clouds are particularly good for (C). Low altitude clouds at mid-latitudes can also have large cooling impacts.

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By raining and increasing soil moisture in semi-arid regions, clouds also provide water needed by plants and trees, enabling them to fix CO2, and thus reduce atmospheric greenhouse gas totals.

In the late 1980s, the NASA Earth Radiation Budget Experiment (ERBE) proved conclusively that on average, clouds tend to cool the planet. The classic study is by V Ramanathan et al1. Quoting from the paper: "For the April 1985 period, the global shortwave cloud forcing [-44.5 watts per square meter (W/m2)] due to the enhancement of planetary albedo, exceeded in magnitude the longwave cloud forcing (31.3 W/m2) resulting from the greenhouse effect of clouds. Thus, clouds had a net cooling effect on the earth." In other words, the cloud reflection of sunlight back to space dominates over the clouds' greenhouse effect. Similar results have been obtained from the European ScaRaB project2.

To prove that extra clouds for SaRaH will cause increased cooling, further evidence from observation and model studies will be described, but first it will be necessary to clarify the difference between cloud feedback and cloud forcing.

1 Cloud-Radiative Forcing and Climate: Results from the Earth Radiation Budget Experiment V.RAMANATHAN et al (6 January 1989) Science 243 (4887), 57

2 http://www.cgd.ucar.edu/cms/wcollins/papers/bullams_1998_v79_p765.pdf

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Cloud feedback vs cloud forcing

The Global Cooling Project is mainly concerned with cooling produced by an increase in cloud radiative forcing. Cloud feedback is just the result of other changes. For example, increases in greenhouse gases lead to the type of clouds that tend to exacerbate the warming produced by the greenhouse gases in the first place - this is positive feedback and amplifies the warming effect. Cloud forcing, on the other hand, is the effect of an active change in cloud formation, caused by factors outside the normal atmosphere system e.g. volcanoes or human beings3. Positive forcing increases the temperature of the planet and negative forcing decreases it. This whole section on the cooling effect of SaRaH clouds refers to the negative forcing effect of clouds. (SaRaH clouds are clouds produced by strategic rainwater harvesting). Given our present climate, this is a helpful effect tending to restore equilibrium to a planet that is warming at a dangerous rate.4

Of course, given the changing state of our climate, there could be a possibility that things could change so that cloud forcing could have a warning rather than a cooling effect at some point in the future. In a personal communication with Dr Anthony Del Genio (NASA Goddard Institute), I have confirmed that the most recent models show that the cooling effect of low altitude clouds applies above land with both present and future climate scenarios.

When examining the cooling role of clouds, it is found that not all clouds are equal. The best clouds for reflecting solar radiation are low-altitude clouds in the tropics in the daytime, and high altitude cirrus clouds even have a warming effect. Before examining the cooling impact of particular cloud types, we will first identify the types of clouds produced through strategic rainwater harvesting and increased soil moisture / vegetation.

3 For an excellent summary on feedbacks and sensitivity, see this web entry by Brian Soden: http://www.realclimate.org/index.php/archives/2006/08/climate-feedbacks

4 From a philosophical point of view, if human beings were considered to be part of the ecosphere, they could be seen as being agents of helpful (stabilising) negative feedback through rainwater harvesting in response to global warming. This has a more attractive ring to it than "negative forcing", but could become very confusing when discussing the science. In general I will refer to the "cooling effect" of "SaRaH clouds" or "RWH clouds", for the sake of clarity.

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I.2 Types of clouds produced by SaRaH(strategic rainwater harvesting)

a. Deep convective5

b. Shallow convective clouds / boundary layer cumulus clouds 6, 7 (fair weather, non-precipitating)

c. Monsoon clouds8, 9 (including strato-cumulus)

d. Low altitude stratus10 / mist and fog / forest cloud11(given the right orography/other factors)

Cloud formation will be discussed more fully in Section II. The main point to note here is that most cloud formation secondary to rainwater harvesting is going to be convective cumulus cloud. These clouds will from now on be referred to as SaRaH clouds.

deep convective clouds

5 Pielke, Sr, R. A. (2001) Influence of the spatial distribution of vegetation and soils on the prediction of cumulus convective rainfall. Rev. Geophys. 39, 151–177.

6 Chen, F., and R. Avissar, 1994: Impact of Land-Surface Moisture Variability on Local Shallow Convective Cumulus and Precipitation in Large-Scale Models. J. Appl. Meteor., 33, 1382–1401.

7 Freedman, J.M., D.R. Fitzjarrald, K.E. Moore, and R.K. Sakai, 2001: Boundary Layer Clouds and Vegetation–Atmosphere Feedbacks. J. Climate, 14, 180–197.

8 Sen, O. L., Wang, Y. & Wang, B. Impact of Indochina deforestation on the East Asian summer monsoon. J. Climate 17, 2004

9 Tang, X., and B. Chen (2006), Cloud types associated with the Asian summer monsoons as determined from MODIS/TERRA measurements and a comparison with surface observations, Geophys. Res. Lett., 33,

10 http://www.meted.ucar.edu/topics_aviation.php

11 Lawton, R. O., Nair, U. S., Pielke, R. A. & Welch, R. M. (2001) Climatic impact of tropical lowland deforestation on nearby montane cloud forests. Science 294, 584–587.

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deep convective clouds from space

I.3.1 Evidence for the global cooling impact of SaRaH clouds

This section addresses the impact of clouds on the total energy absorbed or lost from the earth, the earth's radiation budget. To follow the warming or cooling of the planet, the radiation budget (and ocean temperatures) tell us much more than changes in surface air temperature. Although global impacts are important, regional change (covered in the next section) may be much more important for human beings and continental ecosystems.

a. RADIATIVE IMPACT / ALBEDO / CLOUD FORCING

Key work on this was done by Dennis Hartmann and Maureen Ockert-Bell12: "On a global average basis, low clouds make the largest contribution to the net energy balance of the earth, because they cover such a large area and because their albedo effect dominates their effect on emitted thermal radiation. High, optically thick clouds can also very effectively reduce the energy balance, however, because their very high albedos overcome their low emission temperatures."

Wielicki et al13 looked specifically at tropical clouds: "We present new evidence from a compilation of over two decades of accurate satellite data that the top-of-atmosphere (TOA) tropical radiative energy budget is much more dynamic and variable than previously thought. Results indicate that the radiation budget changes are caused by changes in tropical mean cloudiness."

12 Hartmann, D.L., M.E. Ockert-Bell, and M.L. Michelsen, 1992: The Effect of Cloud Type on Earth's Energy Balance: Global Analysis. J. Climate, 5, 1281–1304.

13 Bruce A. Wielicki et al: Evidence for Large Decadal Variability in the Tropical Mean Radiative Energy Budget Science 1 February 2002: Vol. 295. no. 5556, pp. 841 - 844

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Baijun and Ramanathan established that low clouds exert a negative radiative forcing of about 220 Wm2 at the surface as well as in the atmosphere14.

In a very detailed study looking at total cloud forcing Chen, Rossow and Zhang15 establish that "on average, the dominant contributions to the negative total net [cloud forcing] come from the nimbostratus and deep convective clouds". They also state: "If all of the clouds had the properties of deep convective clouds, the overall effect would be a strong cooling, appearing mostly at the surface and offset by some atmospheric heating. If all clouds were cumulus, a weak surface cooling at lower latitudes is reinforced by weak atmospheric cooling, whereas weak surface heating at higher latitudes is offset by stronger atmospheric cooling, to produce a weak net cooling of the earth at all latitudes. Finally, if all clouds were stratus, strong surface cooling is reinforced by atmospheric cooling, which is weaker near the equator than at the Poles, to produce strong cooling of the earth."

Net surface radiation decreases with any increase in cloud amount. Eltahir and Humphries16 use surface observations on short and long wave radiation from the Amazon forest to infer the role of clouds in the surface radiation balance at the monthly timescale.

Net solar radiation decreases by about 1.7 W/m2 per 1% increase in cloudiness; net long wave radiation increases by about 0.7 W/m2 per 1% increase in cloudiness. As a result of this cancellation, the impact of clouds on net surface radiation is somewhat weakened; net surface radiation decreases by about 1.0 W/m2 per 1% increase in cloudiness. They state that this conclusion, which is based on observations, is consistent with the results of several modelling studies.

b. HEAT TRANSPORT BY CONVECTIVE CLOUDS

Cumulonimbus clouds showing strong updrafts

14Tian B. and Ramanathan, V. 2002: Role of Tropical Clouds in Surface and Atmospheric Energy Budget. AMS 2002

15 Chen et al 2000 Radiative Effects of Cloud-Type Variations J O U R N A L O F C L I M A T E American Meteorological Society

16 Eltahir et al: The role of clouds in the surface energy balance over the Amazon forest, International Journal of Climatology, vol. 18, Issue 14, pp.1575-1591

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file:///wiki/Cumulonimbus_cloud

Boundary layer cumulus clouds (fair weather nonprecipitating cumulus) play a crucial role in modulating the exchange of radiation, heat, and moisture within and above the planetary boundary layer17. This means that convective clouds can cool the planet both through their impact "where they are" and also through their ability to convey heat/moisture from the tropics to higher latitudes (from where the heat can be radiated into space5).

Ackermann et al18 and Machado et al19 have shown that the ‘‘anvil’’ clouds in tropical mesoscale convective complexes produce large vertical heating rate gradients that enhance convective instability, alter upward energy and water transports in the tropics, and may help sustain these larger systems over more than one diurnal cycle.Futyan et al have showed that in summer months in the convective regions of Africa the cloud radiative forcing is strongly negative20. Balachandran and Rajeevan have showed the same for the Asian monsoon21.

Quoting from Pielke's work on the impact on climate of agriculture22 (included in Part C):

"elevated dewpoint temperature and moisture fluxes within the PBL [planetary boundary layer] can increase convectively available potential energy (CAPE), promote atmospheric instability, and enhance daytime cloud cover ...... While land covers less than 30% of the Earth’s surface, its effect on global climate can be disproportionally large ...... Thunderstorms, for example, predominantly occur over land (by a 10:1 ratio).....This preference for deep convection over land is because energy for deep cumulus clouds, or CAPE, is typically larger over land. It has also been shown ....... that much of the the energy transported upwards in the tropics and then poleward, occurs because of these thunderstorms which are the starting point for the major, global-scale, circulation cells such as the Hadley and Walker cells. These studies demonstrated that 1500–5000 thunderstorms, which they refer to as ‘‘hot towers’’, are the conduit to transport heat, moisture, and wind energy to higher latitudes. Since these thunderstorms occur mostly over land, any change in their spatial patterns due to land use/ land-cover change, including vegetation, or anthropogenic aerosols would be expected to have global climate consequences. Indeed, this human-caused change in thunderstorm patterns caused by the diverse regional climate forcings identified in this paper may have a greater effect on the climate system than the radiative effect of doubled CO2."

17 Stull, R. B., 1988: An Introduction to Boundary Layer Meteorology.

18Ackerman, T. P., K. N. Liou, F. P. J. Valero, and L. Pfister, 1988: Heating rates in tropical anvils. J. Atmos. Sci., 45, 1606–1623.

19 Machado, L. A. T., and W. B. Rossow, 1993: Structural characteristics and radiative properties of tropical cloud clusters. Mon. Wea. Rev., 121, 3234–3260.

20 Futyan, J M., Russel, J. E. and Harries, J.E.: Cloud Radiative Forcing in Pacific, African, and Atlantic Tropical Convective Regions

21 S. Balachandranand M. Rajeevan, 2007: Sensitivity of surface radiation budget to clouds over the Asian monsoon region. J. Earth Syst. Sci. 116, No. 2, April 2007, pp. 159–169

22 Roger A. Pielke Sr.: A new paradigm for assessing the role of agriculture in the climate system and in climate change. Agricultural and Forest Meteorology 142 (2007) 234–254

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c. EFFECTS ON CO2 BALANCE

An increase in cloudiness can lead to an increase in rainfall and soil moisture, and in semi-arid regions this change from dry to moist soils leads to an increase in vegetation i.e. a carbon sink. Devdutta Niyogi23 has examined this effect using a process-based model, showing that the impact is significant, through an impact on greenhouse gas absorption.

Freedman et al24 showed that the presence of boundary layer cumulus clouds enhances net carbon uptake, as compared with clear days.

Against this we must off-set the impact of an increase in lightning. Lightning produces ozone and nitrox gases, which are both greenhouse gases (though they have a shorter half-life in the atmosphere than CO2). So an increase in convective clouds, and therefore lightning, may produce a small and potentially significant impact in greenhouse gases in the short term. (In the longer term, increased absorption of carbon by plants will lead to a reduction in greenhouse effect.) The proposed Global Cooling Project will need to quantify this impact, in the pre-implementation phase.

23 Niyogi, D.S: Biosphere-atmosphere interactions coupled with carbon dioxide and soil moisture changes, Thesis (PhD). North Carolina State University, Jun 2001.


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I.3.2 Evidence for the impact of land use / forest on regional temperature and rainfall

For human well-being the local and regional effects of any global cooling project are going to be more significant than global effects, at least in the short and medium term. In Africa, the most important consideration is likely to be the impact on rainfall. This section will demonstrate that an increase in soil moisture and vegetation leads to more rainfall. It will also be seen that there are certain parts of the planet that show a particularly strong coupling between land surface conditions and atmospheric conditions (eg the Sahel). If wetter land can produce more rainfall and more rainfall produces wetter land, a virtuous circle can be set up in otherwise semi-arid regions. There is evidence that some of these regions can switch over long term to a greener state (which produce more SaRaH clouds). This can be seen as geo-engineering, but I would prefer to see it as restoration or mimicking of the natural state. Since the increase in soil moisture produced by rainwater harvesting will be greatest just after the end of the rainy season, the most important impact is a prolongation of the rainy season, giving a longer growing season for farmers.

Hypothesis of the influence of land cover change - after Roger Pielke Snr. (full article included in Part C)

a. IMPACT OF OVERALL CHANGES IN VEGETATION COVER

Los et al25 looked at the Sahel and used satellite evidence and models to establish that vegetated areas can increase rainfall by as much as 30% as compared to non-vegetated areas.

Using a coupled plant and meteorological model, Eastman et al26 have shown that land-

25 Los et al: An observation-based estimate of the strength of rainfall-vegetation interactions in the Sahel, GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L16402, doi:10.1029/2006GL027065, 2006

26 Eastman,et al: `The effects of CO2 and land-scape change using a coupled plant and meteorological model’, Global Change Biology 7, 797-815

Fig. 4. Hypotheses of the influence of land-use/land-cover change on regional climate.

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"[With land use change] The effect of enhanced atmospheric concentrations of CO2 on plant growth on a seasonal time scale is shown to have a greater influence on the region’s radiative effect of enhanced atmospheric CO2. The non-linear effect of vegetation-atmospheric feedback on this scale results in a complex spatial and temporal pattern of response. Not only is there a teleconnection of atmospheric conditions to locations distant from where the land feedback occurs, but the landscape at distant locations itself is influenced by the altered weather. In other words, even in regions where no direct landscape change occurs, the feedback and transport of the atmosphere response due to a landscape change influences vegetation and soil processes at large distance from where the surface disturbance occurred. In manipulative vegetation experiments where carbon dioxide concentrations are arbitrarily increased, for example, this nonlinear feedback between the atmosphere and land surface is missed since there is no feedback to the regional weather (with greater vegetation cover resulting in greater summer rainfall and cooler maximum surface air temperatures)."In Florida the draining of marshes and cutting down of forests with replacement by agriculture has been shown by Marshall et al27 to reduce rainfall and increase temperatures at the surface:"In essence, these results provide evidence that the advent of agricultural production on the Florida Peninsula may have contributed to a significant decrease in warm-season rainfall across the region during the 20th century."

b. TROPICAL DEFORESTATION

A comprehensive review of the importance of land use including tropical forests has been done by Roger Pielke28, and is included in Part C:

"Observational studies, spanning several decades, and numerical modelling studies both show that tropical deforestation influences cloud formation and rainfall .... Observational studies ..... report a wide range of changes in rainfall associated with deforestation (1–20% decrease) ...... Regional-scale modelling results show that the eastern Asian summer monsoon is sensitive to deforestation in the Indochina region .......

"In general, observations and modelling studies agree that [afforestation and reforestation] would decrease near-surface temperature ....."

Freedman29 agrees:"...... observation and modeling studies suggested that forests may be responsible for a large percentage of convective clouds and rainfall in the Tropics ......."

In Florida the replacing of wetland and forest by agriculture has been shown by Marshall et al30 to reduce rainfall and increase temperatures at the surface: "In essence, these results

27 Marshall, C.H., Pielke Sr., R.A., Steyaert, L.T., Willard, D.A., 2004a. The impact of anthropogenic land-cover change on the Florida peninsula sea breezes and warm season sensible weather. Mon. Wea. Rev. 132, 28–52.

28 Pielke, R. A: Impacts of regional land use and land cover on rainfall: an overviewr, Climate Variability and Change—Hydrological Impacts, November 2006, IAHS Publ. 308, 2006.


30 Marshall et al: The impact of anthopogenic land-cover change on the Florida peninsula sea breezes and

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provide evidence that the advent of agricultural production on the Florida Peninsula may have contributed to a significant decrease in warm-season rainfall across the region during the 20th century." On average there was a 10% decrease in rainfall.

Narisma and Pitman31 investigated at the effect of land cover change (1788 and 1988) on the Australian regional-scale climate using a mesoscale model. They looked at air temperature, rainfall, latent heat flux etc. Results showed that the impact of land cover change on local air temperature is statistically significant at a 99% confidence level. There were also statistically significant changes in rainfall, which agreed with observations. They conclude that these results provide further evidence of large-scale reductions in rainfall following land cover change.

Zhao, Pitman and Chase32 used an NCAR climate model to investigate the impact during a 17 year period of a change from forest to grass. They found regional reductions in temperature and increases in rainfall.

Defries et al33, used the IMAGE 2 model to look at future climate change between 2007 and 2050. They found that deforestation, by decreasing latent heat fluxes, could in increase regional surface air temperatures by 1-2C.

Sen et al34 looked at local and regional effects of deforestation in South-East Asia:

"Far-reaching effects in summer include a weakening of the monsoonal flow over east China, near the Tibetan Plateau, and a strengthening over the neighboring seas to the east. These changes yield sandwich-type drier and wetter bands that are elongated along the main flow path of the east Asian summer monsoon. A comparison of the modeled changes with the observed rainfall trends suggests that the deforestation in the Indochina Peninsula could be one of the major factors causing changes in the climate of the region."

c. CHANGES DUE TO IRRIGATION

In, "A new paradigm for assessing the role of agriculture in the climate system and in climate change35" (included in Part C), Roger Pielke looked in detail at changes in land use in the USA and their impact on regional (and global) weather and climate. He reviewed numerous studies showing that irrigation had led to a reduction in regional maximum temperatures and an increase in rainfall. A study by Williams and Murfield36 showed that

warm seson sensible weather. Mon. Wea. Rev. 132, 2242-2258

31 Narisma, G.T., and A.J. Pitman, 2003: The Impact of 200 Years of Land Cover Change on the Australian Near-Surface Climate. J. Hydrometeor., 4, 424–436

32 Zhao et al: The impact of land cover change on the atmospheric circulation. Climate Dynamics, Volume 17, Issue 5/6, pp. 467-477 (2001)

33 Defries et al: Human modification of the landscape and surface climate in the next fifty years, Global Change Biology 2002 8:5 438


35 Pielke et al: A new paradigm for assessing the role of agriculture in the climate system and in climate change, Agricultural and Forest Meteorology 142 (2007) 234–254

36 Williams, J.H., Murfield, S., 1977. Agricutural Atlas of Nebraska. University of NE Press, pp.215

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http://adsabs.harvard.edu/cgi-bin/author_form?author=Chase,+T&fullauthor=Chase, T.&charset=UTF-8&db_key=PHYhttp://adsabs.harvard.edu/cgi-bin/author_form?author=Chase,+T&fullauthor=Chase, T.&charset=UTF-8&db_key=PHYhttp://adsabs.harvard.edu/cgi-bin/author_form?author=Chase,+T&fullauthor=Chase, T.&charset=UTF-8&db_key=PHYhttp://adsabs.harvard.edu/cgi-bin/author_form?author=Chase,+T&fullauthor=Chase, T.&charset=UTF-8&db_key=PHY

Nebraska would have a midsummer maximum temperature 3.4C higher without irrigation.

De Ridder and Galle37 found significant increases in convective rainfall in southern Israel associated with irrigation and intensification of agricultural practices, while De Ridder 38 found that dense vegetation produces a positive feedback to precipitation.

d. PATCHY LANDSCAPE CHANGESeveral studies show that disturbances due to patchy landscape change have the potential to modify cloudiness - see section B II (5).Weaver and Avissar39 found that that diurnal, thermally induced circulations occur during summer over a 250x250 km region in Oklahoma and Kansas. They found that the force behind these circulations is the landscape heterogeneity resulting from differential land use patterns, that such atmospheric phenomena are characteristic of surfaces with this type of heterogeneity and not limited to infrequent days when unusual wind or other meteorological conditions prevail, and that the net effect of these motions is significant, not only locally, but also at the regional and global scales.

Baidya and Avissar40 looked at deforestation in Amazonia using a model and found that coherent mesoscale circulations were triggered by the surface heterogeneity; synoptic flow did not eliminate the circulations but advected them away from the location where they were generated. This was substantiated by satellite-derived cloud images.

Souza et al41 proposed a theory about patchy landscape based on the thermodynamics of heat engines. The predictions made by the theory were confimed by observation in the Amazon basin.

In his review, "Land Use/Convection/Regional Climate", Pielke states:

"....... heterogeneity strongly influences the ability of mesoscale flows to concentrate CAPE within local regions so as to permit a greater likelihood of stronger thunderstorms. ...This focusing of CAPE is analogous to what occurs with round islands...... Dalu et al42 used a linear model to conclude that the Rossby radius defined as Eq. (A41) in Pielke (2001) is the optimal spatial scale for landscape heterogeneities to produce mesoscale flows."

37 De Ridder, K., and H. Galle, 1998: Land surface-induced regional climate change in southernIsrael. J. Appl. Meteor., 37, 1470-1485.

38 De Ridder, K., 1998: The impact of vegetation cover on Sahelian drought persistence. Bound.-Layer Meteor., 88, 307-321.

39 Christopher P. Weaver and Roni Avissar: Atmospheric Disturbances Caused by Human Modificationof the Landscape, 2001 American Meteorological Society

40 Baidya Roy, S. & Avissar, R. (2002) Impact of land use/land cover change on regional hydrometeorology in Amazonia. J. Geophys. Res. 107(D20), doi:10.1029/2000JD000266.

41 Souza, E. P., Rennó, N. O. & Silva Dias, M. A. F. (2000) Convective circulations induced by surface heterogeneities. J. Atmos.Sci. 57, 2915–2922.

42 Dalu, G.A., R.A. Pielke, M. Baldi, and X. Zeng, 1996: Heat and momentum fluxes induced by thermal inhomogeneities. J. Atmos. Sci., 53, 3286-3302.

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This will help to plan ideal patterns for rainwater harvesting in The Global Cooling Project.

In the same review, Pielke describes what amounts to a regional version of the Gaia hypothesis:

"Emori43 shows, using idealized simulations, how cumulus rainfall and soil moisture gradients interact so as to maintain a heterogeneous distribution of soil moisture. Taylor et al44 concluded that such a feedback occurs in the Sahel of Africa which acts to organize cumulus rainfall on scales of about 10 km. Simpson et al45, 46 have shown that cumulus clouds that merge together into a larger scale produce much more rainfall.

See also section section II.3.5 on cloud formation in patchy landscape.

e. SPECIALLY SENSITIVE REGIONS

Several studies show that in some regions there is specially strong "coupling" between land and atmosphere i.e. changes on the land surface have a big impact on the atmospheric conditions and vice versa. Other studies show that forests on islands have a specially strong impact on regional and global climate. These two kinds of region will be prioritised for the Global Cooling Project.

Molen et al47 looked at long term field studies of changes with deforestation. They found that tropical deforestation has larger impacts on local, regional and global climate when it occurs under maritime conditions rather then under continental conditions.

"At the local scale, we compare results from a field experiment in Puerto Rico with other long-term studies of the changes in surface fluxes after deforestation. Changes in surface fluxes are larger in maritime situations because a number of feedback mechanisms appears less relevant (e.g. the dependency of soil moisture on recycling of water and the larger reduction of net radiation in the wet season due to clouds in continental regions). Pastures may evaporate at similarly high rates as forests when soil moisture is sufficient, which has a strong reducing effect on the sensible heat flux after deforestation. At the regional scale ....model simulations show that the meso-scale sea breeze circulation under maritime conditions is more effective in transporting heat and moisture to the upper troposphere than convection is in the continental case. Thus islands function as triggers of convection, whereas the intensity of the sea breeze-trigger is sensitive to land use change.

43 Emori, S., 1998: The interaction of cumulus convection with soil moisture distribution: An idealized simulation. J. Geophys. Res., 103, 8873-8884.

44 Taylor, C.M., F. Saїd, and T. Lebel, 1997: Interactions between the land surface and mesoscale rainfall variability during HAPEX-Sahel. Mon. Wea. Rev., 125, 2211-2227.

45 Simpson, J., N.E. Westcott, R.J. Clerman, and R.A. Pielke, 1980: On cumulus mergers. Arch. Meteor. Geophys. Bioklimatol. Ser. A., 29, 1-40.

46 Simpson, J., T.D. Keenan, B. Ferrier, R.H. Simpson, and G.J. Holland, 1993: Cumulus mergersin the maritime continent region. Meteor. Atmos. Phys., 51, 73-99.

47 M.K. van der Molen et al: Climate is affected more by maritime than by continental land use change: A multiple scale analysis, Global and Planetary Change, v. 54, iss. 1-2, p. 128-149. 11/2006

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At the global scale, using satellite-derived latent heating rates of the upper troposphere, it is shown that 40% of the latent heating associated with deep convection takes place in the Maritime Continent (Indonesia and surroundings) and may be produced mostly by small islands. Continents contribute only 20% of the latent heating of the upper troposphere. Thus, sea breeze circulations exert significant influence on the Hadley cell circulation. These results imply that, from a climate perspective, further deforestation studies would do well to focus more on maritime conditions. "

The following extract is from a major paper by Koster et al48:

"The Global Land–Atmosphere Coupling Experiment (GLACE) is a model intercomparison study focusing on a typically neglected yet critical element of numerical weather and climate modeling: land–atmosphere coupling strength, or the degree to which anomalies in land surface state (e.g., soil moisture) can affect rainfall generation and other atmospheric processes. The 12 AGCM groups participating in GLACE performed a series of simple numerical experiments that allow the objective quantification of this element for boreal summer. The derived coupling strengths vary widely. Some similarity, however, is found in the spatial patterns generated by the models, with enough similarity to pinpoint multimodel “hot spots” of land–atmosphere coupling. For boreal summer, such hot spots for precipitation and temperature are found over large regions of Africa, central North America, and India; a hot spot for temperature is also found over eastern China."

48 Koster et al: GLACE: The Global Land–Atmosphere Coupling Experiment. Part I: Overview. J. Hydrometeor., 2006, 7, 590–610.

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Kleidon49 and Claussen50 did work with similar conclusions. Quoting from Kleidon:

"Sensitivity of the vegetation-climate system: Our results are in qualitative agreement with the sensitivity study by Claussen ......, who investigated the equilibrium of vegetation-atmosphere system using different initial conditions (similar to our ‘desert world’ and ‘green planet’ simulations) with a coupled biome-climate model. Claussen found that the equilibrium state of the vegetation-atmosphere system depended on the initial distribution of biome type in the Sahara region and Central Asia and concluded that these regions are most sensitive to changes in vegetation cover. Our results agree with this conclusion. However, we find a much more pronounced response which can be explained by the differences in rooting depth/soil water storage capacity that we considered in our simulations and the resulting intensification in the water cycle. In addition, we find that other arid regions are equally as sensitive, for instance Australia and South Africa."

Koster et al51 ran a global circulation model over very long time scales and found that amplification of precipitation variance by land–atmosphere feedback is most important outside of the regions (mainly in the tropics) that are most affected by sea surface temperatures. The strength of land–atmosphere feedback in a given region is controlled largely by the relative availability of energy and water there and foreknowledge of land surface moisture state contributes significantly to predictability in transition zones between dry and humid climates.

f. OTHER STUDIES

Xue and Shukla52 found that soil moisture reduction not only brought forward the end of the rainy season in West Africa but also delayed its onset.

Bounoua et al53 used a coupled bioshere-atmosphere model to look at the impact of realistic changes in vegetation on global and regional surface temperatures and rainfall. They found that an increase in vegetation produced an increase in surface albedo in the tropics, and a decrease in surface temperatures (0.5 and 0.8C in January and July respectively).

49 Kleidon and Fraedrich: A Green Planet Versus a Desert World: Estimating the Maximum Effect of Vegetation on the Land Surface Climate Climatic Change 44, 4, 471, 2000-03-01

50 Claussen, M. 1998. On Multiple Solutions of the Atmosphere-Vegetation System in Present-Day Climate. Global Change Biology 4, no. 5: 549-59.

51 Koster, R.D., M.J. Suarez, and M. Heiser, 2000: Variance and Predictability of Precipitation at Seasonal-to-Interannual Timescales. J. Hydrometeor., 1, 26–46.

52 Xue, Y., and J. Shukla, 1993: The Influence of Land Surface Properties on Sahel Climate. Part 1: Desertification. J. Climate, 6, 2232–2245.

53 Bounoua, L., G.J. Collatz, S.O. Los, P.J. Sellers, D.A. Dazlich, C.J. Tucker, and D.A. Randall, 2000: Sensitivity of Climate to Changes in NDVI. J. Climate, 13, 2277–2292.

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I.3.3 Evidence for the global cooling role of vegetation/forest in the tropics

Land cover change affects the global heat balance through albedo (reflectivity) and the effect of transpiration, aerosols etc on cloud formation, aswell as via the greenhouse effect.

In the last section it was easy to establish a link between forests and substantially lower regional surface air temperatures. On the other hand, model studies show only a small drop in global average surface temperatures when comparing a world with extensive tropical forests to a world with none. If forests are producing their own clouds, and clouds have a strong global cooling impact, why isn't there also a direct link in the models between forests and global surface air temperatures? There are various reasons for this, but two have implications for the global cooling project:

(1) Forests are dark - if they're not covered with cloud, they absorb solar radiation, and not all forests in the tropics will necessary produce clouds. The Global Cooling Project is a rainwater harvesting proposal aiming mainly for an increase in soil moisture . It will not focus on reforestation, except in locations where trees add to turbuence/transpiration etc in a way that augments cloud formation. Also, strategic locations, with or without forest growth potential, will be chosen where cloud formation in response to increased soil moisture is maximised.

(2) Temperature and heat are not the same thing. A small decrease in average air temperatures doesn't actually tell you much about how much heat is being lost (information on the radiative impact of clouds tells you more about that - see section I.3.1). In fact, higher upper atmosphere temperatures are one of the best ways for a planet to lose heat to space (much as a patient with a fever loses heat from their skin in order for their core temperature not to overheat). So even though global surface air temperatures may only go down a little with a ful scale global cooling project, it can still be the case that the planet as a whole is being cooled and runaway global warming is being delayed, giving us time to work on reducing human-induced greenhouse warming.

Papers in this section will address the following questions about the global cooling role of tropical vegetation/forests:

(a) Does forest/vegetation really have a cooling role?

(b) What are the mechanisms?

(c) Can distant effects (teleconnections) be demonstrated?

a. DOES FOREST/VEGETATION REALLY HAVE A COOLING ROLE?

Roger Pielke54 summarises recent research:

"There is accumulating evidence that land-cover changes, including those due to agriculture, may have significant effects on .....circulation regimes..... Chase et al. noted, using general circulation model experiments, that agricultural and other land modifications result in large and significant changes in large-scale circulations such as the major jet streams, Hadley cells, and monsoon. These shifts in circulation allow the effects of land-


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cover change on agriculture, and on other regions, to be experienced far from regions where the land-cover changes occur and therefore can be considered surface-induced teleconnection patterns.55, 56 Other examples are given in Chase et al57. Results from more recent experiments have supported the idea that human agricultural land-cover changes can have strong and quite distant effects (Zhao et al58 Feddema et al59).

The above paper is included in Part C.

In another review60 looking at the link between surface moisture and heat fluxes and cumulus convective rainfall Pielke states:

"The spatial structure of the surface heating, as influenced by landscape patterning, produces focused regions for deep cumulonimbus convection. In the tropics, and during midlatitude summers, deep cumulus convection has apparently been significantly altered as a result of landscape changes. These alterations in cumulus convection teleconnect to higher latitudes, which significantly alters the weather in those regions. The effect of tropical deforestation is most clearly defined in the winter hemisphere. In the context of climate, landscape processes are shown to be as much a part of the climate system as are atmospheric processes."

Werth and Avissar61 were able to show the impact of deforestation on local and global climate, particularly a reduction in rainfall, using a sophisticated approach to models, which cut out the effect of "noise".

McGuffie et al62 used an NCAR model and found that the modification of atmospheric circulation patterns over deforested tropical regions prompts climate responses distant from the disturbance. Impacts of tropical deforestation include a disturbance of the Asian monsoon and small but statistically significant changes in climate in the middle and high latitudes.

55 Chase, T.N., Pielke Sr., R.A., Kittel, T.G.F., Nemani, R.R., Running, S.W., 1996. The sensitivity of a general circulation model to global changes in leaf area index. J. Geophys. Res. 101, 7393–7408.

56 Chase, T.N., Pielke Sr., R.A., Kittel, T.G.F., Zhao, M, Pitman, A.J., Running, S.W., Nemani, R.R., 2001. The relative climatic effects of landcover change and elevated carbon dioxide combined with aerosols: a comparison of model results and observations. J. Geophys. Res., 106, 31, 685–631, 691.

57 Chase, T.N., Pielke Sr., R.A., Avissar, A., 2005. Teleconnections in the earth system. Encyclopedia Hydrol. Sciences. Wiley Publishing, pp. 2849–2862.

58 Zhao, M., Pitman, A.J., Chase, T.N., 2001. The impact of land cover change on the atmospheric circulation. Climate Dyn. 17, 467–477.

59 Feddema, J et al: A comparison of a GCM response to historical anthropogenic land cover change and model sensitivity to uncertainty in present-day land cover representations Climate Dynamics 25, no. 6, pp. 581-609. Oct 2005.


61 Werth, D., and R. Avissar (2002), The local and global effects of Amazon deforestation, J. Geophys. Res.107(D20), 8087, doi:10.1029/2001JD000717.

62 McGuffie, K., Henderson-Sellers, A., Zhang, H., Durbidge, T. B. & Pitman, A. J. (1995) Global climate sensitivity to tropical deforestation. Global and Planetary Change 10, 97–128

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Claussen63 et al were able to compare the relative importance of biogeochemical effects ( CO2 / greenhouse gases) and biogeophysical effects in a model study, and still found that tropical forests would cool the planet: "Our sensitivity studies show that tropical deforestation tends to warm the planet because the increase in atmospheric CO2 and hence, atmospheric radiation, outweighs the biogeophysical effects."

b. WHAT ARE THE MECHANISMS?

The albedo effect does not seem to be the main mechanism by which tropical forests cause cooling, because the high albedo caused by cloud production is balanced by the low albedo of the dark tree leaves64.

In an article pointing to both the global and regional role of irrigation and natural forest, Douglas et al65 looked at vapour and energy fluxes across India comparing natural tropical forest, unirrigated agricultural land and irrigated land. They found an increase in latent heat flux of 9 W m-2, largely due to irrigation. Natural tropical forest, however, had an even higher latent heat flux. This shows how surface/soil moisture and vegetation can have a major impact on the atmosphere. Baidya and Avissar66 looked at deforestation in Amazonia using a model and found that coherent mesoscale circulations were triggered by the surface heterogeneity; synoptic flow did not eliminate the circulations but advected them away from the location where they were generated. This was substantiated by satellite-derived cloud images. These circulations affected the transport of moisture and heat at the synoptic scale and can affect climate.

c. CAN TELECONNECTIONS BE DEMONSTRATED?

Zhao, Pitman and Chase67 used an NCAR climate model to investigate the impact during a 17 year period of a change from forest to grass. They found regional reductions in temperature and increases in rainfall, not always in the immediate vicinity of the changes in vegetation.

Chase et al68 undertook a 10-year global circulation model experiment comparing the modelled global outcomes of present day land use to that of "natural" (more forested)

63 Claussen, M et al: Biogeophysical versus biogeochemical feedbacks of large-scale land cover change GEOPHYSICAL RESEARCH LETTERS, VOL. 28, NO. 6, PAGES 1011-1014, MARCH 15, 2001

64 G. Bala et al: Combined climate and carbon-cycle effects of large-scale deforestation PNAS, April 17, 2007, vol. 104, no. 16, 6550-6555

65 Douglas et al: Changes in moisture and energy fluxes due to agricultural land use and irrigation in the Indian Monsoon Belt. ‘Natural Hazards’ (Special Issue on Monsoons) July 20, 2005

66 Baidya Roy, S. & Avissar, R. (2002) Impact of land use/land cover change on regional hydrometeorology in Amazonia. J. Geophys. Res. 107(D20), doi:10.1029/2000JD000266.

67 Zhao et al: The impact of land cover change on the atmospheric circulation. Climate Dynamics, Volume 17, Issue 5/6, pp. 467-477 (2001)

68 Chase, T. N., Pielke Sr, R. A., Kittel, T. G. F., Nemani, R. R. & Running, S. W. 2000 Simulated impacts of historical land cover changes on global climate in northern winter. Climate Dynam. 16, 93{105.

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http://adsabs.harvard.edu/cgi-bin/author_form?author=Chase,+T&fullauthor=Chase, T.&charset=UTF-8&db_key=PHYhttp://adsabs.harvard.edu/cgi-bin/author_form?author=Chase,+T&fullauthor=Chase, T.&charset=UTF-8&db_key=PHYhttp://adsabs.harvard.edu/cgi-bin/author_form?author=Chase,+T&fullauthor=Chase, T.&charset=UTF-8&db_key=PHYhttp://adsabs.harvard.edu/cgi-bin/author_form?author=Chase,+T&fullauthor=Chase, T.&charset=UTF-8&db_key=PHY

landscape: "These results also suggest that teleconnection patterns due to anthropogenic land cover changes which have already occurred are capable of affecting the temperature and precipitation distributions worldwide and may have already done so. Such effects are traditionally unaccounted for in global climate trend analyses."

Importantly, these impacts on global circulation deriving from regional changes in surface fluxes are non-linear feedbacks and so could be very large.

d. PATCHY LANDSCAPE CHANGE - GLOBAL IMPACT

See section I.3.2 d and section II.3.5

e. OTHER STUDIES

In a major study, Bounoua et al69 used a coupled bioshere-atmosphere model to look at the impact of realistic changes in vegetation on global and regional surface temperatures and rainfall. In almost all cases in both July and January, an increase in vegetation produced a decrease in temperature, both regionally and globally.

Pielke in "Land Use/Conection/Regional Climate" lists 34 other papers with results supporting the concusion that there is a significant effect on the large-scale climate due to land-surface processes:

This weight of evidence would appear adequate to support the contention that land surface changes affect the climate.

69 Bounoua, L., G.J. Collatz, S.O. Los, P.J. Sellers, D.A. Dazlich, C.J. Tucker, and D.A. Randall, 2000: Sensitivity of Climate to Changes in NDVI. J. Climate, 13, 2277–2292.

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The biography of Christopher Columbus by his son Ferdinand states that

"on Tuesday, July 22d [1494], he departed for Jamaica.... The sky, air, and climate were just the same as in other places; every afternoon there was a rain squall that lasted for about an hour. The admiral writes that he attributes this to the great forests of that land; he knew from experience that formerly this also occurred in the Canary, Madeira, and Azore Islands, but since the removal of forests that once covered those islands they do not have so much mist and rain as before."

Satellite image of SW France which clearly shows increased cloud formation over the Le Landes forest.

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SECTION B II

More soil moisture → more low altitude clouds

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Link between soil moisture/vegetation and cloud form ation

The references in this section prove that in some parts of the earth, especially those parts of the tropics which are dry for part of the year, an increase in soil moisture and/or vegetation will affect the climate by increasing evaporation/transpiration and cloud cover. Many of the references in this section were identified through the work of Roger Pielke Snr.

II.1 MECHANISM

There are studies of the regional importance of spatial and temporal variations in soil moisture and vegetation coverage (e.g., Fennessy and Shukla70). Delworth and Manabe 71 discuss how soil wetness influences the atmosphere by altering the partitioning of energy flux into sensible and latent heat components. They found that a soil moisture anomaly persists for seasonal and interannual time scales so that anomalous fluxes of sensible and latent heat also persists for long time periods.

Jones et al72 discuss how surface heating rates over regional areas are dependent on surface soil wetness.

Eltahir73 proposed a mechanism by which increased soil moisture causes increased rainfall from convective cloud and demonstrated this mechanism through field observations in Kansas.....

"..... under wet soil moisture conditions, both [latent and sensible] components of net radiation are enhanced, resulting in a larger total flux of heat from the surface into the boundary layer. This total flux represents the sum of the corresponding sensible and latent heat fluxes. Simultaneously, cooling of surface temperature should be associated with a smaller sensible heat flux and a smaller depth of the boundary layer. Whenever these processes occur over a large enough area, the enhanced flux of heat from the surface into the smaller reservoir of boundary layer air should favor a relatively large magnitude of moist static energy per unit mass of the boundary layer air." More static energy means more convective rain."

70 Fennessy, M.J., and J. Shukla, 1999: Impact of initial soil wetness on seasonal atmospheric prediction. J. Climate, 12, 3167-3180.

71 Delworth, T., and S. Manabe, 1989: The influence of soil wetness on near-surface atmospheric variability. J. Climate, 2, 1447-1462.

72 Jones, A.S., I.C. Guch, and T.H. Vonder Haar, 1998: Data assimilation of satellite-derived heating rates as proxy surface wetness data into a regional atmospheric mesoscale model.

73 Eltahir, E. A. B.: 1998. ‘A Soil Moisture-Rainfall Feedback Mechanism. 1. Theory and Observations’, Water Resour. Res. 34, 765–776.

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A number of researchers have established that elevated moisture fluxes within the planetary boundary layer can enhance daytime cloud cover.74, 75, 76, 77, 78

Of course, it's not only soil mositure that correlates to increased mositure flux. In his review of the influence of land use (which is included in Part C) Roger Pielke79 states:

"Observational ....... and several modelling studies ...... [show] that tree plantation establishment may affect the hydrological cycle."

II.2. MODELLED IMPACT OF SOIL MOISTURE

Chen and Avissar80 used a high resolution model to look at the impact of land surface moisture. They found that it significantly affects the timing of onset of clouds and the intensity and distribution of precipitation.

"In general, landscape discontinuity enhances shallow convective precipitation. ..... interactions between shallow cumulus and land-surface moisture are highly nonlinear and complicated by different factors, such as atmospheric thermodynamic structure and large-scale background wind. This analysis also showed that land-surface moisture discontinuities seem to play a more important role in a relatively dry atmosphere, ...... A general trend between the maximum precipitation and the normalized maximum latent heat flux was identified..... In general, large values of mesoscale latent heat flux imply strongly developed mesoscale circulations and intense cloud activity, accompanied by large surface latent heat fluxes that transport more water vapor into the atmosphere."

In a multi-model analysis, Guo et al81 found that the existence of areas of strong land–atmosphere coupling is because of the coexistence of a high sensitivity of total evaporation to soil moisture and a high temporal variability of total evaporation.

74 Holt, T.R., D. Niyogi, F. Chen, K. Manning, M.A. LeMone, and A. Qureshi, 2006: Effect of Land–Atmosphere Interactions on the IHOP 24–25 May 2002 Convection Case. Mon. Wea. Rev., 134, 113–133.

75 Douglas et al: Changes in moisture and energy fluxes due to agricultural land use and irrigation in the Indian Monsoon Belt Geophysical Research Letters 2006, jul, 33, 14403

76 Pielke Sr., R.A: Influence of the spatial distribution of vegetation and soils on the prediction of cumulus convective rainfall. Rev. Geophys. 2001, 39, 151–177.

77 Stohlgrenet al: Evidence that local land use practices influence regional climate and vegetation patterns in adjacent natural areas. Global Change Biol. 1998, 4, 495–504.

78 Alapaty, K., Pleim, J.E., Raman, S., Niyogi, D.S., Byun, D.W., 1997. Simulation of atmospheric boundary layer processes using local and non-local-closure schemes. J. Appl. Meteor. 36, 214–233.

79 Pielke, R. A: Impacts of regional land use and land cover on rainfall: an overviewr, Climate Variability and Change—Hydrological Impacts, November 2006, IAHS Publ. 308, 2006.


81 Guo, Z. et al 2006: GLACE: The Global Land–Atmosphere Coupling Experiment. Part II: Analysis. J. Hydrometeor., 7, 611–625.

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Koster, Suarez and Heiser82 ran a global circulation model over very long time scales and found that amplification of precipitation variance by land–atmosphere feedback is most important outside of the regions (mainly in the tropics) that are most affected by sea surface temperatures. The strength of land–atmosphere feedback in a given region is controlled largely by the relative availability of energy and water there and foreknowledge of land surface moisture state may contribute significantly to predictability in transition zones between dry and humid climates.

In a model study Blyth et al83 showed that with forest cover there was a 30% increase in rainfall compared with a bare-soil domain. Half of this increase was from positive feedback of the intercepted water that re-evaporates. The high roughness length of the forest, with its associated physical and dynamical effects, accounted for the rest of the increase in rainfall and for the accompanying increase in soil moisture. This is important because it show how a virtuous circle or cascade effect can develop between soil moisture, forest cover and downwind soil moisture (leading to a natural spread of forest).

Dirmeyer84 found that interannual variations of soil wetness are large enough to influence climate GCM simulations.

Delworth and Manabe85 discuss how soil wetness influences the atmosphere by altering the partitioning of energy flux into sensible and latent heat components. They found that a soil moisture anomaly persists for seasonal and interannual time scales so that anomalous fluxes of sensible and latent heat also persists for long time periods.

Yeh, Wetherald and Manabe86 modelled the effect of large-scale irrigation. They found that rainfall increased not only in the irrigated region but also in adjacent regions.

82 Koster, R.D., M.J. Suarez, and M. Heiser, 2000: Variance and Predictability of Precipitation at Seasonal-to-Interannual Timescales. J. Hydrometeor., 1, 26–46.

83 Blyth, E. M., A. J. Dolman, and J. Noilhan, 1994: The effect of forest on mesoscale rainfall: An example from HAPEX–MOBILHY. J. Appl. Meteor., 33, 445–454.

84 Dirmeyer, P.A., 1999: Assessing GCM sensitivity to soil wetness using GSWP data. J. Meteor. Soc. Japan, 77, 1-19.

85 Delworth, T., and S. Manabe, 1989: The influence of soil wetness on near-surface atmospheric variability. J. Climate, 2, 1447-1462.

86 Yeh, T.C., R. Wetherald, and S. Manabe, 1984: The Effect of Soil Moisture on the Short-Term Climate and Hydrology Change—A Numerical Experiment. Mon. Wea. Rev., 112, 474–490.

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II.3.ACTUAL CLOUD FORMATION

II.3.1 Deep convective and boundary layer cumulus

Quoting from Roger Pielke Snr 87:

".... an increase in irrigation or surface wetness reduces sensible heat flux while increasing physical evaporation and transpiration. The resulting additional moisture flux can enhance the moist static energy within the convective boundary layer (CBL) and consequently become thermodynamically more conducive to an increase in rainfall (Betts et al88; Segal et al89)....."

Strato-cumulus

Cumulonimbus

87 Roger A. Pielke Sr: Influence of the spatial distribution of vegetation and soils on the prediction of cumulus convective rainfall. Reviews of Geophysics, Vol. 39, Number 2, 151-177, MAY 2001

88 Betts, A.K., Ball, J.H., Beljaars, A.C.M., Miller, M.J., Viterbo, P., 1994. Coupling between land-surface boundary-layer parameterization and rainfall on local and regional scales: lessons from the wet summer of 1993. Preprints, Fifth Conference on Global Change Studies, Nashville, TN. Am. Meteor. Soc. 174–181.

89 Segal, M., Avissar, R., McCumber, M.C., Pielke Sr., R.A., 1988. Evaluation of vegetation effects on the generation and modification of mesoscale circulations. J. Atmos. Sci. 45, 2268–2292.

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Again quoting Pielke90: "elevated dewpoint temperature and moisture fluxes within the [planetary boundary layer] can increase convectively available potential energy (CAPE), promote atmospheric instability, and enhance daytime cloud cover ...... This preference for deep convection over land is because energy for deep cumulus clouds, or CAPE, is typically larger over land." (See Part C for full article.)

Freedman et al91, in an article focussed on boundary layer cumulus clouds, state:

".....Boundary layer cumulus clouds (fair weather non-precipitating cumulus) play a crucial role in modulating the exchange of radiation, heat, and moisture within and above the planetary boundary layer .... Moreover, the presence of boundary layer cumulus clouds ....... is strongly associated with the type and quantity of underlying vegetation, through this energy exchange."

II.3.2 Low altitude stratus / mistTropical montane cloud forests (TMCFs) depend on predictable, frequent, and prolonged immersion in cloud92. Clearing upwind lowland forest alters surface energy budgets in ways that influence dry season cloud fields and thus the TMCF environment. Landsat and Geostationary Operational Environmental Satellite imagery show that deforested areas of Costa Rica's Caribbean lowlands remain relatively cloud-free when forested regions have well-developed dry season cumulus cloud fields.

In other words, lowland deforestation and associated increases in the Bowen ratio lead to elevation of the orographic clouds forced by terrain downwind .......leading to changes in the direct harvesting of cloud water by montane vegetation.



92 Lawton, R. O., Nair, U. S., Pielke, R. A. & Welch, R. M. (2001) Climatic impact of tropical lowland deforestation on nearby montane cloud forests. Science 294, 584–587.

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II.3.3 StratusAviation training manuals tend to have the best information on the factors influencing the formation of low-altitude stratus clouds and fog, for obvious reasons. They show the role of soil moisture and forests in increasing the likelihood of fog and low stratus.

The following guidelines are given for making stratus forecasts are given93 :

" Local and mesoscale influences can make or break your fog or stratus forecast. Influences of local water bodies, terrain, vegetation, soil characteristics, and coastal features on the lower atmosphere can play a vital role in the development, duration, and intensity of these events. This module will examine several of these influences and discuss how they enhance or inhibit a fog or stratus event. The features and processes discussed in the lesson [are listed in the box below]:

Stratus top-cloud, Cape Town

Sun through stratus

93 http://www.meted.ucar.edu/topics_aviation.php

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• Terrain Influences • Mountain valley

breeze • Upslope/blocked

flows • Downslope flow

• Sea/Land Transition • Onshore flow (sea

breeze) • Offshore flow (land

breeze) • Coastal shape • Local upwelling

• Local Surface Influences • Soil moisture • Surface

characteristics • Surface state

• Parcel-Scale Processes • Parcel mixing • Turbulence and heat

transfer • Cloud condensation

nuclei "

II.3.4 Effect on monsoonsSen et al94 looked at local and regional effects of deforestation in South-East Asia:

"Locally, the effect could be described as increases in wind speed and temperature, and as a decrease in water vapour mixing ratio from the surface up to about 850 mb. Furthermore, the deforestation tends to enhance the rising motions, and, hence, tends to reduce surface pressure and geopotential height up to about 850 mb over the deforested area. The local landscape changes tend to increase rainfall on the downwind side and decrease it on the upwind side.

Sud and Smith95 modelled deforestation in India and found a major weakening of the monsoon.

Monsoon cloud types are deep convective, cirrus, cirro-stratus and stratocumulus. In the East Asian monsoon region, the most frequently occurring cloud type is stratocumulus.

monsoon cumulo-nimbus

II.3.5 Patchy landscape and cloud formation

Several studies show that heterogeneity-induced mesoscale circulations (i.e. disturbances due to patchy landscape change) have the potential to modify cloudiness96, 97, 98 .


95 Sud, Y. C. & Smith, W. E. (1985) Influence of local land surface processes on the Indian monsoon: a numerical study. J.Climate Appl. Met. 24(10), 1015–1036.

96 Souza, E. P., Rennó, N. O. & Silva Dias, M. A. F. (2000) Convective circulations induced by surface heterogeneities. J. Atmos. Sci. 57, 2915–2922.

97 Silva Dias,et al. (2002) Cloud and rain processes in a biosphere-atmosphere interaction context in the Amazon region. J. Geophys. Res. 29:10.1029/2000JD000335.

98 Baidya Roy, S. & Avissar, R. (2002) Impact of land use/land cover change on regional hydrometeorology

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Pielke99 showed that the spatial structure of the surface heating, as influenced by landscape patterning, can and does produce focused regions for deep cumulonimbus convection. (In the tropics, and during midlatitude summers, deep cumulus convection has apparently been significantly altered as a result of landscape changes. )

In a study of Central America, Ray et al100 showed that surface air over deforested areas tends to get warmer and drier, and when these winds flow over forested patches they impact the cloud formation processes and rainfall. They also found that during the driest month (March) forest vegetation accessed deep soil water, which vegetation in deforested regions did not.

Chen and Avissar's 101 detailed work on the role of land surface moisture is very helpful:"Numerical experiments using a state-of-the-art high-resolution mesoscale cloud model showed that land-surface moisture significantly affects the timing of onset of clouds and the intensity and distribution of precipitation. In general, landscape discontinuity enhances shallow convective precipitation. Two mechanisms that are strongly modulated by land-surface moisture—namely, random turbulent thermal cells and organized sea-breeze-like mesoscale circulations—also determine the horizontal distribution of maximum precipitation. However, interactions between shallow cumulus and land-surface moisture are highly nonlinear and complicated by different factors, such as atmospheric thermodynamic structure and large-scale background wind. This analysis also showed that land-surface moisture discontinuities seem to play a more important role in a relatively dry atmosphere, and that the strongest precipitation is produced by a wavelength of land-surface forcing equivalent to the local Rossby radius of deformation. A general trend between the maximum precipitation and the normalized maximum latent heat flux was identified. In general, large values of mesoscale latent heat flux imply strongly developed mesoscale circulations and intense cloud activity, accompanied by large surface latent heat fluxes that transport more water vapor into the atmosphere."

Deforestation in the Amazon has taken place in a fish bone pattern around main roads. Cutrim et102 al showed that shallow cumulus form over deforested areas in the dry season .

See also section I.3.2 on patchy landscape change.

in Amazonia. J. Geophys. Res. 107(D20), doi:10.1029/2000JD000266.


100 Ray et al: Impact of Deforestation on Clouds and Rainfall On the Northern Part of the Proposed Mesoamerican Biological Corridor. American Geophysical Union, Fall Meeting 2004, abstract #B11A-0134


102 Cutrim, E.; Martin, D.W.; Rabin, R., Enhancement of cumulus clouds over deforested lands in Amazonia. Bulletin of American Meteorological Society, 76(10), 1801-1805, 1995.

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SECTION B III

Rainwater harvesting → more soil moisture

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What is rainwater harvesting?

Rainwater harvesting is a well-established set of techniques, ancient and modern, strongly supported by UNEP (United Nations Environment Programme). In essence it consists of "catch and hold" or "catch and store" technologies, ranging from simple mulching practices to underground dams and aquifer replenishment.

Eastern and Southern Africa, Brazil, India, Slovakia, Syria, Australia and other regions all have particular experience and competences in RWH. This is an areas where there is relatively little published material in mainstream scientific journals, as most of the work has been done by farmers and development organisations, such as the members of the SEARNET (the Southern and Eastern Africa Rainwater Network). UNEP (United Nations Environment Programme) has supported rainwater harvesting globally and has very produced very useful maps showing rainwater harvesting potential in Africa. Some are included in Part C.

Stylised representation of Katumani pits in plan (a and b) and cross sectional views (c) (Simiyu et al., 1992103).

Fuller descriptions of RWH methods are included in Part C.

103 Simiyu, S.C., E.M. Gichangi, J.R. Simpson, and R.K. Jones 1992. Rehabilitation of Degraded Grazing Lands Using the Katumani Pitting Technique. In: M.E. Probert (Editor), A Search for Strategies for Sustainable Dryland Cropping in Semi-arid Eastern Kenya. ACIAR Proceedings No. 41, 138 p.

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Rainwater harvesting increases soil moisture and supports tropical regreening and reforestation

While it is obvious that irrigation and rainwater haresting will increase soil moisture in the short term, this section will prove that RWH can lead to soil moisture changes sufficiently long-lasting to have an impact on vegetation (and therefore transpiration and climate).

Stephen Ngigi104 has written engagingly on the potential of RWH in global farming:

"Rainwater harvesting is a promising technology for improving the livelihoods of many inhabitants of the vast dry regions of the world. RWH can be viable in areas with as low as 300mm of annual rainfall (Kutch, 1982). However, Pacey and Cullis (1986) gave a more conservative range of annual rainfall, 500-600 mm. But, Kutch (1982) further stated that annual rainfall is not the most important criterion. Nevertheless, the technology has been used to sustain food production in the Negev desert of Israel with meagre annual rainfall of about 100mm (Shanan and Tadmor, 1976). Ironically, most of the famine stricken areas of Africa receives much more than 100mm of rainfall."

Ali and Yazar105 have shown that RWH increases soil moisture and improve shrub establishment in areas of low rainfall.

Boers106 has shown that RWH can be used to speed up tree establishment and deep root development, and to reduce mortality rates in arid and semi-arid zones.

Ali et al107 analysed RWH experience in Syria, Pakistan and Egypt. In Syria thy found that RWH established fodder shrubs with 3-7 fold growth improvement and 27 to 90% survival rate. In Pakistan, low-cost structures reduced terrace damage and improved field soil moisture.

In Mehasseh in Syria (120 mm annual rainfall) Oweis108 found the shrubs having less than

104 Ngigi, S. N: What is the Limit of Up-Scaling Rainwater Harvesting in a River Basin? 3rd WaterNet/Warfsa Symposium 'Water Demand Management for Sustainable Development', Dar es Salaam, 30-31 Oct 2002

105 Akhtar Ali and Attla Yazar: Effects of microcatchment water harvesting on soil-water storage and shrub establishment in the arid environment, International Journal of Agriculture and Biology 2007/09-2-302-306

106 Boers, T.H.M: Rainwater Harvesting in Arid and Semi-arid Zones. PhD dissertation Wageningen Agriculture University, the Netherlands

107 Ali et al: Water harvesting options in the drylands at different spatial scales, Land use and water resources research 7 (2007) 1-13

108 Theib Y. Oweis: Coping with Increased Water Scarcity in Dry Areas: Increased Water Productivity, International Center for Agricultural Research in the Dry Areas Aleppo, Syriahttp://www.unu.edu/env/land/Aleppo/08%20-%20Oweis.doc.

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http://www.unu.edu/env/land/Aleppo/08 - Oweis.doc

10% survival rate normally had over 90% survival rate with RWH.

G. N. Gupta109 conducted a field experiment at the Arid Forest Research Institute, Jodhpur to study the influence of different systems of water harvesting and moisture conservation on soil moisture storage, growth, biomass accumulation and nutrient uptake by three tree species. Water harvesting significantly improved their growth of three species (height by 58%, 35% and 40%, collar circumference by 73%, 56% and 63%, and crown diameter by 111%, 51%, and 131%, respectively). Biomass accumulation by A. indica and T. undulata increased 3-8 fold and 4-6 fold and root mass 4-5 fold and 3-8 fold, respectively. Tree roots in water harvesting plots were deeper and had several times larger spread than the control. Nutrient uptake by these tree species increased several-folds as a result of the different water harvesting and moisture conservation treatments.

Yeh, Wetherald and Manabe110 modelled the effect of large-scale irrigation. They found that soil moisture created by irrigation can persist for at least several months due to increased evaporation and precipitation.

Johan Rockstrom is a major figure in tropical hydrology and agriculture. In an article with P. Fox111, he states, "Surface run-off dynamics in the Sahel have in a number of studies proven to be of considerable magnitudes. Rainwater harvesting into small ponds for supplemental irrigation during intra-seasonal dry-spells during crop growing seasons could therefore prove to be a viable solution. During an on-farm study carried out in semi-arid Burkina Faso, supplemental irrigation during dryspells increased sorghum harvests by 41%, and in combination with added fertilization, by 180 %."

In a spectacular demonstration close to the Dead Sea in Israel, Geoff Lawton112 was able to both support tree growth and reduce effective soil salinity. On 10 acres, 1.5km of swale (ditches on contour) were dug. When full, these swales hold 1million litres of water and they fill several times over a winter. Intensive mulching and the planting of hardy desert trees and fruit trees were carried out. Within 4 months there were fig tees with figs on! The soil was tested and it was found that salt levels were dropping. At first it was thought that the salt was being washed through. Later it was found that the salt was being chelated and rendered insoluble.

109 Gupta G.N:Rain-water management for tree planting in the Indian Desert,Journal of Arid Environments, 31,October 1995

110 Yeh, T.C., R. Wetherald, and S. Manabe, 1984: The Effect of Soil Moisture on the Short-Term Climate and Hydrology Change—A Numerical Experiment. Mon. Wea. Rev., 112, 474–490.

111 P. Fox and J. Rockström: Water-harvesting for supplementary irrigation of cereal crops to overcome intra-seasonal dry-spells in the Sahel Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere, Volume 25, Issue 3, 2000, Pages 289-296

112 http://permaculture.org.au/?p=230

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Part C

Articles

48

WATER HARVESTING - PAST AND FUTURE

DIETER PRINZ

Universität Karlsruhe (TH)Institut für Wasserbau und Kulturtechnik

76128 Karlsruhe

ABSTRACT. Water harvesting, defined as the collection of runoff and its use for the irrigation of crops,pastures and trees, and for livestock consumption, comprises six different forms, primarily defined by theratio between collecting and receiving area: (1) Roof Top Water Harvesting, (2) Water Harvesting forAnimal Consumption, (3) Inter-Row Water Harvesting, (4) Microcatchment Water Harvesting, (5)Medium-sized Catchment Water Harvesting and (6) Large Catchment Water Harvesting. The commongoal of all forms is to secure water supply for annual crops, pastures, trees and animals in dry areaswithout tapping groundwater or river-water sources. In the past, water harvesting was the backbone ofagriculture in arid and semi-arid areas world-wide. After a decline, it gained new interest during pastdecades. Its future role will be as a linking element between rainfed agriculture, soil and water conser-vation and irrigated agriculture, still using untapped water resources in arid lands, alleviating slightly thestress on drought-ridden farmers and communities.

Introduction

As long as mankind has inhabited semi-arid areas and cultivated agricultural crops, it has practised somekind of water harvesting. Based on "natural water harvesting" the use of the waters of ephemeral streamswas already the basis of livelihood in the arid and semi-arid areas many thousands of years ago, allowingthe establishment of cities in the desert (Evenari et al. 1971). Presumably millions of hectares of land in the dry parts of the world were once used for water harvest-ing but a variety of causes has brought about a steady decline. The European expansion, especially the technological development since 1850, lead to a steady increasein area under "classical" irrigation techniques with preference to large schemes. Small-scale irrigation andtraditional irrigation techniques received inadequate attention. The latter include the various techniques ofwater harvesting and supplementary irrigation. During recent decades the interest in water harvesting has increased and national as well as internationalbodies have launched programmes to investigate the potential of water harvesting and to expand its area.

The sustainability of water harvesting systems was in the past based on the 'fitting together' of the basicneeds of the farmers, the local natural conditions and the prevailing economic and political conditions ofthe region. The preconditions for a positive future development of water harvesting will be the very same(Prinz 1994).

1 Basic Concepts and Characterization of Water Harvesting

1.1 GENERAL CONCEPT

Water harvesting is applied in arid and semi-arid regions where rainfall is either not sufficient to sustain agood crop and pasture growth or where, due to the erratic nature of precipitation, the risk of crop failure isvery high. Water harvesting can significantly increase plant production in drought prone areas byconcentrating the rainfall/runoff in parts of the total area. The intermittent character of rainfall and runoff and the ephemerality of floodwater flow requires somekind of storage. There might be some kind of interim storage in tanks, cisterns or reservoirs or soil itselfserves as a reservoir for a certain period of time (Finkel and Finkel 1986). Water harvesting is based on the utilisation of surface runoff; therefore it requires runoff producing andrunoff receiving areas. In most cases, with the exception of floodwater harvesting from far awaycatchments, water harvesting utilizes the rainfall from the same location or region. I does not include its

2

conveyance over long distances or its use after enriching the groundwater reservoir. Water harvestingprojects are generally local and small scale projects.

1.2 DEFINITION, GOALS AND PARAMETERS

There is no generally accepted definition of water harvesting (Reij et al. 1988). The definition used in thispaper covers "the collection of runoff and its use for the irrigation of crops, pastures and trees, and forlivestock consumption" (Finkel and Finkel 1986). The goals of water harvesting are: ? Restoring the productivity of land which suffers from inadequate rainfall. ? Increasing yields of rainfed farming ? Minimizing the risk in drought prone areas ? Combating desertification by tree cultivation ? Supplying drinking water for animals. In regions with an annual precipitation between 100 and 700 mm, low cost water harvesting mightprovide an interesting alternative if irrigation water from other sources is not readily available or toocostly. (In summer rainfall areas the minimum precipitation for water harvesting is around 200 mm/year).In areas with more than 600 - 700 mm annual rainfall water harvesting techniques can prolong thecropping season. In comparison with pumping water, water harvesting saves energy and maintenancecosts. These advantages are countered by the problem of unreliability of rainfall, which can partly beovercome by interim storage (cisterns, small reservoirs etc.). Modern hydrological tools (e.g. calculationof rainfall probability and water yield) allow a more precise determination of the necessary size of thecatchment area. As mentioned before, the central elements of all water harvesting techniques are:- a runoff area (catchment) with a sufficiently high run-off

Documents

Global Cooling - science do 2 - Earth & Environmenthomepages.see.leeds.ac.uk/~lecsjed/huiyi/GCdossier7.pdfclimate. These are tested on past decades to show that they are competent