Assessment of total water storage and other variables over the Indus, Ganga, and Brahmaputra River basins

In the present study, assessment of the abating total water storage (TWS) in the three river basins viz Indus (IRB), Ganga (GRB), and Brahmaputra (BRB) and its associated changes in precipitation across the Indian Himalayan Region (IHR) are examined. Time lead and lag relationship among TWS and other contributory factors viz., precipitation, evaporation, runoff, snow water equivalent (SWE), soil moisture, groundwater, etc., are assessed. In the present study precipitation dataset and TWS available from Global Precipitation Measurement Mission (GPM) and Gravity Recovery and Climate Experiment (GRACE) is used respectively while other variables were extracted from ERA5. Mann-Kendall and Theil Sen estimator test is used for calculating trend of precipitation and TWS during different seasons (winter, pre-monsoon, monsoon, post-monsoon). Our study supports, there is a decreasing trend of TWS over the Indus Ganga Brahmaputra (IGB) basin, though all the basins are drying but slower during monsoon. IRB shows maximum decrease in TWS in postmonsoon whereas over GRB and BRB it is observed in premonsoon. In all seasons, heat flux distributions suggested drying, especially over the higher reaches of the IHR and certain areas of the IRB. The changes in temporal and spatial distribution of TWS over IRB indicate a rapid drop in monsoonal moisture flux. More evaporation and runoff during the monsoon season reduce the TWS process. Present work will be of utmost importance for the policy or planning for state-level governance for societal benefit.