Anthropogenic and Climate Contributions on the Changes in Terrestrial Water Storage in India

Despite the rapid depletion of groundwater and significant changes in surface water storage, the role of anthropogenic and climatic factors on terrestrial water storage (TWS) in India remains largely unexplored. Here, we provide a hydrologic framework based on the Variable Infiltration Capacity-SIMple Groundwater Model (VIC-SIMGM) and Gravity Recovery and Climate Experiment (GRACE) data sets to estimate the contribution of climate variability and anthropogenic groundwater pumping on TWS in the Indian basins. The VIC-SIMGM model was satisfactorily calibrated and evaluated against observed monthly streamflow and groundwater anomalies for the 17 river basins in India. The modeling setup combined with the GRACE data can be used for understanding the role of climate variability on surface and groundwater (shallow) storage in India. A significantly high correlation between TWS anomaly from GRACE (TWSA_GRACE) and the VIC-SIMGM (TWSA_VIC) was found in the majority of India except in northwest India. The negative correlation in northwest India is primarily due to considerable groundwater pumping for irrigation. Groundwater storage anomaly explains a significant variability of GRACE_TWSA in India, indicating the influence of anthropogenic groundwater pumping for irrigation. However, in the absence of anthropogenic influence, soil moisture is the major contributor to TWSA in the majority of India. The net anthropogenic depletion of TWS in north India is considerably higher than that estimated from the GRACE as the increase in precipitation has, during the recent decades, contributed to slowing down the declining rate of TWS.