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Although the consequences of deforestation on rainfall are contentious and difficult to assess in quantitative terms at present, there appears to be rather more of a consensus of opinion on two adverse effects of forest clearance, namely an increase in storm intensity and the associated soil erosion. Dickinson (1980) states that in none of the numerical studies reviewed by him has the effect of deforestation on increasing temporal and spatial fluctuations between wet and dry conditions been examined. He feels that deforestation could increase the intensity and decrease the duration of tropical rainfall, enhancing runoff even if the mean rainfall were unchanged. If the intensity increases without a material change in the annual quantity, the result is accentuation of dryness and erratic spatial distribution. Circumstantial evidence of lasting and profound changes being initiated by forest clearing is provided by long-term observations on rainfall in private rubber plantations in Malaysia (Unesco 1978). After large-scale forest clearing, the number of rainfall incidents decreased, the rainfall intensity substantially increased, while the total rainfall appeared to remain unaffected. Meher-Homji (1980a, b) has shown, further, that large-scale deforestation has its effect more in the reduction of the number of rainy days than in the volume of rainfall. The result is soil erosion and, in turn, major disasters. If rainfall continues to be normal in amount but irregular, with occasional torrential falls, the consequences are floods and the silting of river beds. If successive drought years prevail, not only do streams and rivulets dependent on the gradual release of water from the soil dry up but dust becomes a problem. This may result in desertification of marginally subhumid zones. Even humid zones are in danger of becoming progressively drier if drought years continue to recur.

Many of the suggested effects of forests on rainfall in the literature remain to be tested by actual data from India. For instance, if tropical forest contributes only 3% to the global water cycle, what would the decrease be if the forests were cleared?


I wish to thank the organizers of the Workshop for having given me the opportunity to participate. My sincere thanks are due to Frank Thompson and Evan Reynolds for going through the manuscript and making useful suggestions.


Agrawal, P. C. 1976. "Variability and trend of annual rainfall in Chatisgarh region, Madhya Pradesh." Proc. Symp. Trop. Monsoon, Indian Inst. Trop. Met., Pune, pp. 465-470.

Angstrom, A. 1962. "Atmospheric turbidity, global illumination and planetary albedo of the earth." Tellus, 14: 435-454.

Bellan, M. F. 1987. Vegetation map of the Nilgiri Hills {India). Inst. Carte Intern. Tapis Végétal, Toulouse.

Biswas, B. C. 1980. "Effect of forest cover on rainfall distribution at Andaman and Car Nicobar Islands." Mausam, 31: 178-180.

Blanford, H. E 1888. "Influence of forests on rainfall." In Rainfall of India. India Met. Memoirs, vol. 3.

Blasco, E 1971. Montagnes du sud de l'Inde: Forêts, savanes, ecologic. Inst. Fr. Pondichery, Tr. Sect. Sci. Tech. 10 pp. 1-436.

Borisov, P. 1973. Can man change the climate? Progress Publ., Moscow.

Brooks, C. E. P. 1928. "The influence of forests on rainfall and run-off." Quart. J. R. Met. Soc., 54: 1-13.

Brunig, E. F. 1971. "On the ecological significance of drought in the equatorial wet evergreen (rain) forest of Sarawak (Borneo)." In J. R. Flenley, ea., The water relations of Malesian forests, pp. 66-79. Dept. of Geography Miscellaneous Series 11, Univ. of Hull, UK.

Bryson, R. A. 1974. "A perspective in climatic change." Science, 184: 753-760.

Bryson, R. A., and D. A. Baerreis. 1967. "Possibilities of major climatic modification and their implications: North-West India, a case study." Bull. Amer. Met. Sci, 48: 136-142.

Cadet, D. 1979. "Meteorology of the Indian summer monsoon." Mature, 279: 761-767.

Cadet, D., and G. Reverdin. 1981a. "Water vapour transport over the Indian Ocean during summer 1975." Tellus, 33: 476-487.

———. 1981b. "The monsoon over the Indian Ocean during summer 1975." Mon. Weal Rev., 109: 148- 158.

Chakravarti, A. K. 1978. "A case of droughts in the Sahara: The effect of the removal of natural vegetation on rainfall." Alternative 1978, pp. 55-56.

Charney, J. G., W. J. Quirk, S. H. Chow, and J. Kornfield. 1977. "A comparative study of the effect of albedo change on drought in semi-arid regions." J. Atmos. Sci, 34: 1366-1385.

Chief Conservator of Forests. 1971. Report of the Expert Committee on the effect of large scale planting of blue-gum on the rainfall in the Nilgiri district of Tamil Nadu. Chief Conservator of Forests, Madras.

Chowdhury, A., and V. P. Abhyankar. 1976. "An attempt to determine climatic shift in rainfall over Gujarat State." Proc. Symp. Trop. Monsoons, Indian Inst. Trop. Met., Pune, pp. 388-398.

Das, P. K. 1968. The monsoons National Book Trust, India.

Delannoy, H. 1982. "Introduction a ['etude des relations entre les temperatures des eaux océaniques et les precipitations côtières marocaines." Norois, 29: 535-545.

Desai, B. N. 1969. "Is it possible to increase rainfall in the semi-arid regions of Rajasthan by reducing quantity of dust suspended in the atmosphere?" Indian J. Met. Geophys., 20: 377-380.

Dickinson, R. E. 1980. "Effects of tropical deforestation on climate." In Blowing in the wind: Deforestation and long-range implications, pp. 411-441. Studies in Third World Societies, no. 14, College of William and Mary, Dept. of Anthrop., Williamsburg, Va., USA.

Escourrou, G. 1982. Quelques particularités des brises marines. Norois, 29: 577-584.

Fedorov, S. E, and A. S. Burov. 1967. "Influence of forest on precipitation." Soviet Hydrology.

Flohn, H. 1958. Monsoons of the world. Indian Met. Dept., New Delhi.

Fox, J. E. D. 1979. "The natural vegetation of Sabah, Malaysia." Trop. Ecol., 19: 218-239.

Gadgil, S. 1981. "Fluid dynamics of the monsoon." Proc. Indian Acad. Sci. (Engg. Sci.), 4: 295-314.

Garrat, J. R. 1978. "Flux profile relations above tall vegetation." Quart. J. R. Met. Soc., 104: 109-211.

Gaussen, H., P. Legris, M. Viart, and V. M. Meher-Homji. 1961. International map of vegetation and environmental conditions: Sheet Cape Comorin. Inst. Fr. Pondichéry, Tr. Sect. Sci. Tech. Hors Série No. 1, ICAR, New Delhi.

Green, S., and K. Minkowski. 1977. "The lion-tailed monkey and its south Indian rain forest habitat." In Primato conservation, pp. 289-337. Academic Press, New York.

Guilcher, A. 1982. "Problèmes climato-océanographiques du désert côtier d'Angola particulièrement la baie des Tigres (16035'S)." Norois, 29: 507-517.

Hewlett, J. D. 1965. "Summary of forests and precipitation session." Proc. Int. Symp. Forest Hydrology, Pennsylvania. Pergamon Press, Oxford.

Hughes, J. F. 1949. "The influence of forests on climate and water supply." Forestry Abstracts, 11 (2).

Hursh, C. R., and C. A. Connaughton. 1933. "Effects of forests upon local climate." J. Forestry 36 (9).

Jackson, R. D., and S. B. Idso. 1975. "Surface albedo and desertification." Science, 189: 1012- 1013.

Julian, P. R., and R. M. Chervin. 1978. "A study of the southern oscillation and Walker circulation phenomenon." Mon. Weal Rev., 106: 1433-1451.

Kaulin, V. H. 1962. "Effect of forest belts in Kamennaia steppe on precipitation." Meteorologia i Gidrologia, 6: 32.

Kittredge, J. 1948. Forest influences. McGraw-Hill, New York.

Klaus, D. 1981. Climalological and climato-ecological aspects of the drought in the Sahel. Franz Steiner Verlag, Wiesbaden, FRG, 260 pp.

Kung, E. C., R. A. Bryson, and D. H. Lenschow. 1964. "Study of a continental surface albedo on the basis of flight measurements and structure of the earth surface cover over North America." Mon. Weal Rev., 92: 543-564.

Legris, P., and F. Blasco. 1969. Variabilité des facteurs du climat: Gas des montagnes du sud de l'lnde et de Ceylan. Inst. Fr. Pondichéry, Tr. Sect. Sci. Tech. 8, pp 1-195.

Legris, P., and V. M. Meher-Homji. 1976. "Is rain in India on the wane? Biometeorological consideration." Int. J. Biometeor., 20: 190-193.

Lettau, H., K. Lettau, and L. C. B. Molion. 1979. "Amazonia's hydrologic cycle and the role of atmospheric recycling in assessing deforestation effects." Mon. Weal Rev., 107: 227-238.

Lockwood, J. G. 1980. "Some problems of humid equatorial climates." Malaysian J. Trop. Geogr., 1: 12-20.

Luna, R. K. 1981. "Do forests increase rainfall?" Sci. Reporter, 18: 472-474.

Manabe, S., and R. T. Wetherald. 1975. "The effect of doubling the CO' concentration on the climate of a general circulation model." J. Atmos. Sci, 32: 3-15.

Manabe S., and D. G. Hahn. 1977. "Simulation of the tropical climate of an ice age." 1 Geophys. Res., 82: 3889-3911.

Meher-Homji, V. M. 1980a. "Repercussions of deforestation on precipitation in Western Karnataka, India." Arch. f. Met. Geoph. Biokl., 28B: 385-400.

———. 1980b. The link between rainfall and forest clearance:Case studies from Western Karnataka. Trans. Inst. Indian Geographers 2, pp. 59-65.

———. 1982. "Do forests control climate?" Sci. Today 16: 37-42.

Mishra, A., and M. C. Dash. 1984. "Desertification around Hirakud reservoir." The Environmentalist, 4: 51-58.

Mitchell, J. M., et al. 1966. Climatic change. WHO Tech. Note 79, pp. 1-79.

Molchanov, A. A. 1960. The hydrological role of forests. Israel Programme for Scientific Translations, Jerusalem.

Mukherjee, A. K., S. K. Pradhan, and M. K. Rao. 1976. "Effect of change of topography for development of Bombay airport on rainfall of Santa Cruz." Proc. Seminar on Man and His Environment, Inst. of Sci., Bombay, pp. 55-57.

Mukherjee, A. K., and B. P. Singh. 1978. "Trends and periodicities in annual rainfall in monsoon areas over the Northern Hemisphere." Indian J. Met. Hydrol. Geophys., 29: 441-447.

Narayanan, P. P. 1980. "A case of inadvertent weather modification produced by fire." Mausam, 31 (3): 475.

Nicholson, J. W. 1929. Note on the influence of forests on c/imafe and water supply in Uganda. Suppl. to Kenya Forest Dept. Pamphlet No. 2.

Oguntoyinbo, J. S. 1970. "Reflection coefficients of natural vegetation, crops and urban surfaces in Nigeria." Quart. J. R. Met. Soc., 96: 430-441.

Otterman, J. 1974. "Baring high-albedo soils by overgrazing: A hypothesized desertification mechanism." Science, 186: 531-533.

———. 1981. "Satellite and field studies of man's impact on the surface in arid regions." Tellus, 33: 68-77.

Padmavalli, R. 1976. "Utilisation of major natural resources." Proc. Symp. Resource Development and Planning, Madras Univ., Dept. of Geography, Madras, pp. 1-19.

Pascal, J. P., S. Shyam Sunder, and V. M. Meher-Homji. 1982. Forest map of South India: Mercara-Mysore. Karnataka Forest Department, Bangalore, and French Inst., Pondicherry.

Pereira, H. C. 1973. Land use and water resources in temperate and tropical climates Cambridge, University Press, Cambridge, UK.

Pinker, R. T., O. E. Thompson, and R. E Eck. 1980. "The albedo of a tropical evergreen forest." Quart. J. R. Met. Soc., 106: 551-558.

Pittock, A. B. 1983. "The carbon-dioxide problem and its impact." Austral. Met. Mag., Feb. 1983.

Potter, G. L., H. W. Ellsaesser, M. C. MacCracken, and E M. Luther. 1975. "Possible climatic impact of tropical deforestation." Nature (Lond.) 258: 697-698.

Raju, K. V. S. 1981. "Forest and rain report on Uttara Kannada." In M. Gadgil, L. T. Sharma, and R. Sharma, eds., Major dams: A second look. Environ. Coll., Gandhi Peace Foundation, New Delhi.

Rakhmanov, V. V. 1962. Vodookhrannaya rol lesov (Water-conserving role of forests). Goslesbumizdat, Moscow, 236 pp.

Rama. 1980a. "Increasing the rainfall over India?" Mausam, 30 (2): 324-325. . 1980b. "Will rainfall over India increase?" Sci. Today, 14 (6): 6-7.

Ramaswamy, K. N. 1979. "Pollen grains: Nature's seeders of the clouds for the precipitation of rain." My Forest, 15 (3): 201-203.

Ranganathan, C. R. 1949. "Protective functions of forests." Proc. UN. Conference on Conservation and Utilisation of Resources.

Ripley, E. A. 1976. "Drought in the Sahara: Insufficient biogeophysical feedback?" Science, 191: 100.

Rockwood, A. A., and S. K. Cox. 1978. "Satellite inferred surface albedo over north-western Africa." J. Atrnos. Sci., 35: 513-522.

Rotty, R. M., and G. Marland. 1980. "Constraints on fossil fuel use." In W. Bach, J. Pankrath, and J. Williams, eds., Interactions of energy and climate. Reidel, Boston.

Rowntree, P. R. 1978. "Numerical prediction and simulation of the tropical atmosphere." In D. B. Shaw, ea., Meteorology over the tropical oceans, pp. 219-250. Royal Meteorological Society, Bracknell, UK.

Sagan, C., O. B. Toon, and J. B. Pollack. 1979. "Anthropogenic albedo changes and the earth's climate." Science, 206: 1363-1368.

Salati, E., A. Dall'Olio, E. Matsui, and J. R. Gat. 1979. "Recycling of water in the Amazon Basin: An isotopic study." Water Resources Res., 15 (5): 1250-1258.

Sarmah, S. K. 1976. "Some observations on the variations of monsoon annual rainfall in Assam." Proc. Syrnp. Trop. Monsoons, Indian Inst. Trop. Met., Pune, pp. 458-464.

Schnell, R. C. 1975. Biogenic ice nuclei removed by overgrazing, a factor in Sahelian drought. Final Report to Directors, Rockefeller Foundation, NCAR, Boulder, Colorado, USA.

Schubert, J. 1937. "Über den Einfluss des Waldes auf den Niederschalg in Gebiet der Letzlinger Heide." Zeitechr. f. Forst Jagdwesen, 69: 604-615.

Shukla, J., and Y. Mintz. 1982. "Influence of land-surface evapotranspiration on the earth's climate." Science, 215: 1498-1501.

Singh, S. N. 1978. "Is the climate of Hyderabad getting drier?" Indian For., 104: 263-269.

Sirinanda, K. U. 1982. "Rain-making (cloud-seeding) attempts in the tropics: The experience in south and southeast Asia." In M. M. Yoshino, l. Kayane, and C. M. Madduma Bandara, eds., Tropical environments, pp. 89-95.

Stidd, C. 1975. "Irrigation increases rainfall." Science, 188: 279-281.

Thompson, K. 1980. "Forests and climate change in America: Some early views." Climate Change, 3: 47-64.

Unesco. 1978. Tropical forest ecosystems. Unesco/UNEP/FAO, Paris.

Von Lengerke, H. J. 1977. The Nilgiris Weather and climate of a mountain area in South India. Franz Steiner Verlag, Wiesbaden, FRG, 340 pp.

Wadia, D. N. 1955. Deserts of Asia, their origin and growth in the Late Pleistocene thee. Second Sir Albert Charles Seward Memorial Lecture, Birbal Sahni Inst. of Palaeobot., Lucknow.

Walker, G. 1916. "Report on the evidence from meteorological records of any apparently permanent change in the amount and distribution of rainfall over the different large areas of India, and on the probable causes of such changes if and where they have taken place." In

M. Hill, Note on an enquiry by the Government of India into the relation between forests and atmospheric and soil moisture in India. Ind. Forest Bull. 33, Appendix 1.

Warren, W. D. M. 1974. "A study of climate and forests in the Ranchi plateau, Pt. 11." Indian For., 100: 291-314.

Winstanley, D. 1973. "Rainfall patterns and general atmospheric circulation." Nature (Lond.) 245: 190-194.

Woodwell, G. H., R. H. Whittaker, W. A. Reiners, G. E. Likens, C. C. Delwiche, and D. S.

Botkin. 1978. "The biota and the world carbon budget." Science, 199: 141-146.

Zon, R. 1927. Forests and water in the light of scientific investigation. U. S. Nat. Waterways

Comm., Final Report, App. V, 205-302. 62nd Cong., 2d sess. S. Doc. 469.


No doubt due to the variety of ways in which forest vegetation influences the rain climate, the alleged effects of forests on rainfall are not clearly revealed by changes in gross parameters. Indeed, annual values often obscure those features of the precipitation that produce ecological and agricultural responses. Meher-Homji has elucidated a series of parameters relating to the rainfall and to rainy days that might be supposed to be sensitive to specific mechanisms through which forest affects local climate. He regards trends of the majority of these with deforestation within an arbitrary 16 km radius of the meteorological station as signifying a proven effect, particularly where a control station in the region, with minimal deforestation, shows more equivocal trends in the parameters.

From these areas of the Indian subcontinent examples of the persistence of man's influence in deforesting the landscape demonstrate the subtleties of interplay between local exacerbation of drought, resultant fires, frost prevalence, and the production of a grassland subclimax.

It is to be hoped that the provision of a large number of references to the original literature, including many in French, will encourage development of these studies in a critical manner.

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