Hydrological Functioning of Forested Catchments, Western Himalayan Region, India.

Abstract

Background Forests, being the largest ecosystem and primary consumer of water, significantly affect the hydrological cycle at both global and local level and provide innumerable ecosystem services to humans. Western Himalayan forested catchments provide fresh water supply to millions of people. Hence, the understanding of linkages between forests and water is very crucial to recognize for availability and quality of water at catchment scale. Therefore, present study aims to understand hydrological response of two forested catchments (namely, Arnigad and Bansigad) in the Western Himalayan Region.Methods Three-year data (March, 2008 to February, 2011) were collected from meteorological and hydrological stations installed at Arnigad and Bansigad catchments. The present paper displays average hydrological response of forested catchments through detailed field investigation.Results The annual hyetograph analysis reveals that the rainfall at both the catchments were highly seasonal, and wet-period (June-September) plays a key role in catchment functioning. Exceedance of rainfall threshold of ~288 mm (~10% of annual rainfall) significantly increased streamflow generation at both the catchments. At Arnigad, stream was perennial with a mean baseflow of ~80 mm per month (~5% of annual streamflow) whereas, Bansigad had greater seasonality due to lack of flow during the pre-wet-period (March-May). Separation of hydrographs at Arnigad and Bansigad catchments i.e. stormflow (6% and 31%, respectively) and baseflow (50% and 32%, respectively) helps to understand the probability of flooding during wet-period and drought during dry-period. Forest ecosystem at Arnigad improves the hydrological functioning by: reducing stormflow (82%), and enhancing baseflow (52%), soil moisture (13%), steady infiltration rate (22%) and by increasing lag time (~15 minutes) relative to Bansigad. These enhanced values indicated potential for soil to store water at forested catchment (Arnigad) and helps to understand the volume of water that is available during dry-period. The decrease of denudation rate (at Arnigad) by 41% resulting in decrease of suspended sediment (18%) and bed load (75%) compared to Bansigad. Further, the enhancement of dissolved solids in stream resulted due to maximum organic matter generated in forest floor of Arnigad. Conclusion This study confirms the crucial role of forests in maintaining hydrological balances at catchment scale in the Western Himalayan region.