Regional water balance analysis of glacierised river basins in the north-eastern Himalaya applying the J2000 hydrological model

The glacierised basins of the Northeast Himalayan region are highly vulnerable to climate-change impacts. The spatio-temporal hydroclimatic and physiographic variability impact the water balance of these glacierised basins across the region. This study assesses the glaciohydrological processes and dynamics in the data scarce region for the present as well future climate change scenarios by regional water balance analysis. The J2000 hydrological model was adapted to incorporate the frozen ground as well as glacier dynamics in a stepwise, nested basin calibration approach. The modelled ERA-Interim precipitation data cannot capture the high amplitude orographic and convective events. Therefore, Orographic correction factors were used to inversely correct the ERA-Interim precipitation data to account for the orographic as well as cyclonic precipitation in the region from reported glacier mass balance and evapotranspiration estimates. Monthly temperature lapse rate was adopted for correcting the ERA-Interim temperature dataset. The Beki basin was selected as the donor basin for model development and evaluation. The parameters from the Beki basin were regionalised to the receptor Lohit and the Noadihing basins by the Proxy-basin method. Multi-objective optimization criteria such as the Kling-Gupta efficiency (KGE) for temporal dynamics and flow distribution and Bias for overall water balance showed high to moderate conformity between measured and simulated discharge at the corresponding basin outlets. The variability in the water balance and runoff components among the three basins was primarily related to the spatio-temporal variation in the mean annual precipitation, runoff and evapotranspiration estimates. The impact of climate-change scenarios on the study basins indicated that water availability would sustain until the end of the century due to higher projected precipitation even though after the depletion of glaciers in the region.