Assessment of Hydrological Responses to Climate Change in Himalayan Headwater Watershed

Assessment of hydrological processes to climate change, however not well understood, is crucial in Himalayan headwater watersheds since it is vital for developing suitable mitigation and adaptation strategies for sustainable water resources management. To assess headwater hydrology of Kali Gandaki Watershed (KGW) we used the Soil and Water Assessment Tool (SWAT) hydrological model to simulate streamflow and sediment yield based on input precipitation and temperature data. Annapurna and Dhaulagiri are high mountain peaks of the basin elevations > 8000 m that have 50% area with > 45% slope. To set up the model for simulation of KGW, 31 years (1979-2009) mean daily temperature and precipitation data was used from four meteorological stations. The model was calibrated utilizing 12 years (1979-1990) daily measured streamflow data and found surprising agreement between measured and model simulated values with r2 of 0.84 and Nash-Sutcliffe Efficiency (NSE) of 0.83. During calibration, snow processes, groundwater and soil moisture were found as the most influencing factors for determining streamflow of the headwater system. Our preliminary outcomes indicate that about 74% of the streamflow is contributed by the groundwater discharge seasonally. In addition, analysis of multi-temporal Landsat data showed that 6% of the basin is covered by glaciers and contributing approximately 15% as meltwater to streamflow. To assess future climate change, we used outputs from the ensemble means of temperature and precipitation from the General Circulation Model (GCM) for 2050 of the low, medium, and high emission scenarios developed by the Intergovernmental Panel for Climate Change (IPCC) as SWAT inputs for the KGW. Simulated stream discharge increased by 11%, 13% and 8% in low, medium and high emission scenarios respectively, with concomitant increases in sediment yield by 14%, 15% and 7%. Analysis of 32 years (1964-1995) data shows that 76% of the total streamflow occurs during monsoon season (June-September) and it coincides with 74% of the total precipitation in the basin. Future simulation indicates that daily average precipitation tends to increase by 9% causing to enhance the surface runoff by 12% mainly due to steep slopes of the basin. Groundwater storage is increased by 6% augmenting the groundwater discharge by 13% which indicates sustainability of its contribution to the streamflow. Increasing temperature also tends to increase mean daily evapotranspiration by 5% but in contrast snowmelt in the basin is decreased by 17% influencing hydrological processes of the basin.The hydrological impact analysis showed that mainly snowmelt processes may be affected by future climate with streamflow sustained by groundwater discharge.