Hydrological functioning of forested catchments, Central Himalayan Region, India
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Central Himalayan forested catchments provide large quantities of fresh water supply and innumerable ecosystem services to millions of people. Hence, detailed understanding of the forest-water linkages is important to determine the availability of water at catchment scale. Therefore, the present study aims to understand the hydrological response of two forested catchments (namely, Arnigad and Bansigad) in the Central Himalayan Region. Three-years’ data (March, 2008 to February, 2011) were collected from meteorological and hydrological stations in these catchments. The annual hyetograph analysis revealed that the rainfall at both the catchments was highly seasonal, and wet-period (June-September) plays a key role in catchment functioning. Exceedance of rainfall threshold of ~200 mm (~10% of annual rainfall) significantly increased streamflow generation at both catchments. At Arnigad, the stream was perennial with a mean baseflow of ~83 mm per month (~6% of annual baseflow) whereas, Bansigad had greater seasonality due to lack of streamflow during the pre-wet-period (March-May). The forest ecosystem at Arnigad displayed healthier hydrological functioning in terms of reduced stormflow (82%), and enhanced baseflow (52%), soil moisture (13%), steady infiltration rate (22%) and lag time (~15 minutes) relative to Bansigad. These enhanced values indicated soil capability to store water at the forested catchment (Arnigad) and helped to understand the volume of water (discharge) that was available during dry-period. This study shows that rainfall during the wet-period was the main driver of hydrological functioning, whereas, forests provided substantial services by regulating water balance through different mechanisms of forest components at catchment-scale in the Central Himalayan region.
Key Words: Himalaya, threshold, stormflow, baseflow, soil moisture.