Assessment of Hydroclimatological Changes in Eastern Himalayan River Catchment of Northeast India

This article focuses on the assessment of climate change impacts on the hydroclimatology of the Subansiri River basin, which is the largest tributary of the Brahmaputra River in the northeastern part of India. Three representative concentration pathway (RCP) emission scenarios, namely, RCP2.6, RCP6.0, and RCP8.5, of three general circulation models (GCM) archived by the Geophysical Fluid Dynamics Laboratory (GFDL), were utilized for the projection of climatic variables (such as precipitation and temperature). Long-term (2011–2100) projections of precipitation and temperature for different emission scenarios were made using the statistical downscaling technique. The soil and water assessment tool (SWAT) hydrological model was used for hydrological modeling of the river basin. The observed streamflow series for the period of 2002–2013 has been utilized for calibration and validation of the hydrological model. Parameterization, uncertainty analysis, and parameter sensitivity analysis of the model were performed using a sequential uncertainty fitting (SUFI2) program. The coefficient of determination ($R^2$) for the calibration and validation of the hydrological model on the monthly streamflow time series was found to be 0.86 and 0.80, respectively. Future projections of the precipitation and temperature suggest an increase in the annual average maximum temperature ($T\max$), annual average minimum temperature ($T\min$), and annual precipitation of the river basin. These projected climatic variables were used as the primary input in the hydrological model for the projection of the streamflow for the period of 2016–2100. The flow duration curve analysis of streamflow projections reveals an increase in the discharge for a particular percent of the dependable flow in the case of all the RCP scenarios. Water yield analysis also suggests an increase in the annual average water yield in all cases of emission scenarios.