Impacts of climate change on water availability in snow dominated river basins in Bhutan

Climate change may have profound implications on water availability in the snow-dominated river basins in Bhutan. Changes in water availability under the projected future climate can have implications for hydropower production and agriculture among others in Bhutan. In this study, we examined the impact of the projected future climate on streamflow of five river basins (Amochhu, Wangchhu, Punatshangchhu, Mangdechhu, and Drangmechhu) in Bhutan. Streamflow for each basin was simulated using the Soil and Water Assessment Tool (SWAT) for the observed and projected future climate after calibration and evaluation at a number of gauge stations. The analysis for the projected future climate was performed for near (2011-2040), mid (2041-2070) and end (2071-2100) periods of the 21st century using the downscaled and bias-corrected precipitation and temperature forcing. Daily precipitation and temperature data for Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios were obtained from six General Circulation Models (GCMs) included in the Coupled Model Intercomparison Project phase five (CMIP5). The 1 gridded dataset were downscaled and bias-corrected using Princeton University dataset using the equidistance quantile mapping technique. Apart from the use of the elevation bands, parameterizing sub-basins separately with the help of multiple gauge stations in a basin helped in improving the SWAT model calibration. It was found that streamflow in all the five river basins is projected to increase in the 21st century with a higher increase under the RCP 8.5 than that under RCP 4.5 scenario. The increase in mean annual streamflow during the end period with respect to the historical reference period (1981-2010) was estimated to range between 10.76 % (16.74 %) and 43.26 % (26.29 %) under the RCP 4.5 scenario in the five river basins. The increase in streamflow under the RCP 8.5 is ~1.5 times higher than the projected increase in streamflow under the RCP 4.5 at the end of 21st century. Projected increase in streamflow in the snow dominated river basins might have implications for floods, landslides, reservoir operation, and hydropower production in Bhutan.by Prakash GautamM.Tech