Glacial changes over the Himalayan Beas basin under global warming.

We simulated and analyzed the glacier dynamics over the Beas basin (situated in the north-western Himalayas) for the present (1980-2015) and future climates (2006-2100) under RCP4.5 and RCP8.5 global warming scenarios. We first calibrated the Open Global Glacier Model over the study region and then conducted simulations for the present (forced by ERA-Interim) and future (forced by CMIP5 models) climates. For the present climate, the model simulations show that 50% of the total glacier volume (compared to 1980) is lost by 2011, with glacier area and volume showing a significantly decreasing trend, with higher fluctuations in the glacial area during recent decades. Future projections suggest 75% loss by 2040 ± 2.5 years and ~90% loss by 2094 ± 3.5 years under RCP4.5. Under RCP8.5, 75% loss is expected to occur by 2040 ± 3 years and ~90% loss by 2084 ± 8 years. Ensemble mean of the near-surface air temperature (both monthly mean and annual mean) shows a significantly increasing trend under both RCP4.5 and RCP8.5 for the entire 21 century. Ensemble mean of the total monthly precipitation shows no trend under RCP4.5, however, it shows a decreasing trend for months ODJFMA and an increasing trend for months JJ under RCP8.5. An increase in JJ precipitation does not increase glacier mass since this region does not receive snowfall during these months. Under RCP4.5, snowfall does not show any significant trend during NDJF, however, it shows a decreasing trend during October and March. Under RCP8.5, snowfall shows a significant decreasing trend for October through March. Overall, we find similar melting rates under RCP4.5 and RCP8.5 until ~2050, but the latter shows a higher rate afterward.