SR-5 : Forest influences on hydrological parameters

Abstract

The influence of forests on their environment forms part of a vast and complex relationship between environment and forest vegetation. Researchers have been trying for past several decades to ascertain the hydrological importance of forests. In this context, forests influences on various hydrological parameters, viz., rainfall, interception, infiltration, evapotranspiration, ground water, water yield, floods, water quality etc. have been described in this report which are based on studies conducted in India and abroad.

As regards to forest infouences on rainfall, the major of researchers have concluded that forests did not affect rainfall on a regional scale. Rainfall has been found to be affected by forests on local scale in some cases. In coastal belts, the forests have been found affecting rainfall by intercepting moist air masses. The interception losses in forested catchments are function of types of forests, precipitation characteristics and climate. The interception losses foresees do not have much importance during large rain storms but these are certainly important from soil conservation point of view. The evapotranpiration losses in forested catchments are higher than other types of land uaes. More studies are required to complete ET losses of different types of forests. The infiltration characteristics of forested

soils are better than other soils due to increased amount of organic matter and protection of soil by vegetal cover. Forest influences on ground water regime need to be studied carefully. There are opinions that due to deep rooting system and higher ET requirements the forests decline ground water table. The annual water yield from a watershed gets increased following forest removal due to reduction in ET losses. The effects of forests are limited to moderate and flash floods. The cutting of forests results in more soil loss which after getting deposited on stream and river beds and in reservoirs reduces their capacities and cause situations of floods. The quality of water gets deteriorated by coming into contact with trees in a forested ecosystem. More studies to this effect are required.

The studies which have been reported in this report have been done mostly on small watersheds and so the results obtained can not be directly extrapolated to large watersheds. More systematic studies are therefore required on large representative basins to ascertain hydrological behaviour of forests.