Sediment transport in Indian rivers high enough to impact satellite gravimetry

Abstract. Satellite gravimetry is used to study the global hydrological cycle. It is a key component in the investigation of groundwater depletion on the Indian subcontinent. Terrestrial mass loss caused by river sediment transport is assumed to be below the detection limit in current gravimetric satellites of the Gravity Recovery and Climate Experiment Follow-On mission. Thus, it is not considered in the calculation of terrestrial water storage from such satellite data. However, the Ganges and Brahmaputra rivers, which drain the Indian subcontinent, constitute one of the world's most sediment rich river systems. In this study, we estimate the impact of sediment mass loss within their catchments on gravimetric estimates of trends in the local mass equivalent water height (EWH). We find that for the Ganges-Brahmaputra-Meghna catchment, sediment transport accounts for (4±2) % of the gravity decrease that is currently attributed to groundwater depletion. The sediment is mainly eroded from the Himalayas, where correction for the sediment mass loss reduces the decrease in EWH by 0.22 cm yr^-1, which is about 14 % of the EWH trend observed in that region. However, with sediment mass loss in the Brahmaputra catchment resulting to be more than twice that in the Ganges catchment and sediment mainly being eroded from mountain regions, the impact on gravimetric EWH data within the Indo-Gangetic plain, the main region identified for groundwater depletion, results to be comparatively small.