In situ and satellite-based estimates of usable groundwater storage across India: Implications for drinking water supply and food security

Groundwater use in India has been in the limelight in recent years due to its intensive and apparent unsustainable use that poses threats to water security, drinking water supply and food production. Here, we present estimates of usable groundwater storage, for the first time, at the state-level across all of India using both in situ and satellite-based measurements. Groundwater-level data are used from 3907 in situ monitoring wells across India and the total usable groundwater storage (UGWS) is estimated between 2005 and 2013. The UGWS estimates indicates high rates of depletion (> 5 km(3)/yr) of groundwater storage (GWS) in north-east India (i.e. Assam), even though increase in precipitation has been observed in that state. Satellite-based (Gravity Recovery and Climate Experiment, GRACE) estimates indicate that the development of recent GWS-depletion zones is concentrated in unconsolidated sediments or lithotype across the Indus, Ganges and Brahmaputra basins, in the states of Punjab, Haryana, Uttar Pradesh, Bihar, and West Bengal. In contrast, southern and central Indian states (such as Andhra Pradesh, Maharashtra, Gujarat, Tamil Nadu, and Chattisgarh), show replenishing GWS trends. We also find that the states with highest groundwater depletion rates are subjected to water-intensive cropping practices during the study period. We temporally downscale the UGWS with support from GRACE satellite-based measurements. We conclude that the approach we developed here can be applied in other parts of the world to devise management options for sustainable groundwater use.