Satellite-derived surface and sub-surface water storage in the Ganges–Brahmaputra River Basin

Study region: The Ganges–Brahmaputra (GB), a major river basin of the Indian Sub-Continent (ISC), is the host of more than 700 millions people. Study focus: In addition to monsoons and strong climate variability, GB is facing growing demands for freshwater availability by a continually growing population and rapidly developing of agricultural and industrial sectors. The management of water resources is thus of highest priority and, in the context of current over-abstraction of groundwater, accurate estimates of terrestrial freshwater storage are essential. We propose a multi-satellite approach to estimate surface freshwater storage (SWS) and subsurface water storage (SSWS, groundwater + soil moisture) variations over GB. New hydrological insights: Basin-scale monthly SWS variations for the period 2003–2007 show a mean annual amplitude of ∼410 km3, contributing to about 45% of the Gravity Recovery And Climate Experiment (GRACE)-derived total water storage variations (TWS). During the drought-like conditions in 2006, we estimate that the SWS deficit over the entire GB basin in July–August–September was about 30% as compared to other years. The SWS variations are then used to decompose the GB GRACE-derived TWS and isolate the variations of SSWS whose mean annual amplitude is estimated to be ∼550 km3. This new dataset of water storage variations represent an unprecedented source of information for hydrological and climate modeling studies of the ISC.