Climate Change Impacts on Hydrology of a Small Watershed in a River Valley Project Catchment of Southern India

Abstract

The Kundhichira watershed is a sub-watershed of the Kabini river basin in Kerala. To simulate hydrological responses of the watershed, for observed as well as for the projected climate, hydrological model, Soil and Water Assessment Tool (SWAT) was used. The ASTER data derived DEM (30 m resolution) was processed to delineate stream network and ground verified by Google Earth provided digitized stream network. The land use map was prepared using Landsat-7 satellite imageries i.e. Enhanced Thematic Mapper (ETM+) and soil database was created from Govt. of India All India Soil and Land Use Survey (AISLUS) report. The model was calibrated and validated using sequential uncertainty fitting (SUFI 2) procedure through SWAT-CUP for the period 2003 to 2006 and 2007 to 2009, respectively with monthly observed runoff data. The modeling efficiencies (ME) during calibration and validation were 0.799 0.822 respectively. Monthly projections for the IPCC 3 SRES Scenario for 2020, 2050, and 2080 representing intermediate emissions (A2a) were used to simulate hydrological responses for future climatic change conditions. A substantial rise in temperature over the scenario and subtle change in rainfall may result in higher surface runoff rates (12.4% increases in 2080) and decreased base flow (7.4% decrease in 2050). The water yield may increase by 7% in 2020. The groundwater recharge components may increase by more than 90%. The crop yield in the face of increased temperature may reduce due to increased GDD (Growing Degree Days) negatively impacting the biomass yield as reflected in reduced evapotranspiration component (as low as 9.7% in 2050). The Climatic Net Primary Production of the study watershed is poised to have a limitation shift from precipitation to temperature.