Groundwater storage change estimation using GRACE data and Google Earth Engine: A basin scale study

Groundwater is the main source of drinking and irrigation water available in the majority of the Ghaghara river basin (GRB), which is a trans-boundary river basin and characterized by a sub-humid climate that possesses a lot of uncertainty due to non-precise measurement of water and energy flux. The basin is classified as an upper mountainous basin, geographical coverage of the GRB covers countries like China, Nepal, and India. The study is intended to estimate variation in groundwater storage based on satellite observations of the time-varying Earth's gravitational field from the Gravity Recovery and Climate Experiments (GRACE). In this study, soil moisture has been estimated from the TerraClimate data and rainfall from the Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) using Google Earth Engine (GEE).The long-term trends and spatio-temporal variation of groundwater have been analyzed from April 2002 to January 2017. The groundwater trend has shown a drastic decline in storage level. On an average 2.28cm of decline in groundwater storage per year and a total of 36.61 cm of decline in groundwater storage from 2002 to 2017 has been observed. The GRACE data showed that the southwest region of the GRB has a high storage level. The present research findings outline that implementation of suitable and a feasible water conservation scheme is necessary for improved management of water resources in the entire GRB. • GRACE & GEE were used for estimation of groundwater. • Validation has been carried out using pre- and post monsoon water table. • Groundwater trend has shown a drastic decline of storage level. • Average 2.28 cm of decline in groundwater storage per year. • Net groundwater storage has decreased by 36.61 cm from 2002 to 2017.