Estimating the impact of climate change on streamflow in Bagmati Watershed, Nepal

Abstract. Observations show that the level of atmospheric greenhouse gas (GHG) has been increasing since the mid 19^th century. The Intergovernmental Panel on Climate Change (IPCC) estimated an increase of global GHG emissions by 25 to 90% between 2000 and 2030. As per IPCC estimate, the global average surface temperature will increase between 1.8 to 4.0°C and precipitation will increase by 5 to 20% over the period of 1990 to 2100. Understanding potential hydrologic influences to projected climate change is important for management of water resources. This study estimates the climate change impacts on hydrologic processes of Bagmati watershed in Nepal using the Soil and Water Assessment Tool (SWAT). Past climate data were obtained from Department of Hydrology and Meteorology. Digital Elevation model (DEM) and Soil data were obtained from free online server. The performance of the model was found to be good, both during the calibration and validation period. The performance statistics were better for monthly stream-flow as compared to the daily stream-flow. In order to study the impact of climate change, the outputs (i.e., temperature and precipitation) from global climate models (GCMs) are used to drive SWAT model. The GCM used in this study is from IPCC Fifth Assessment report. This study will demonstrate that the temporal differences in hydrologic responses to future climate changes in Bagmati watershed, Nepal. Uncertainty remains regarding the future hydrologic changes due to the uncertainty of future climate changes, especially precipitation patterns, the future dynamics of vegetation and land use, and partly due to the SWAT model processes uncertainty.