Summer Monsoon Drying Accelerates India's Groundwater Depletion Under Climate Change

Groundwater in north India remains a vital food and water security resource for more than one billion people. Both summer monsoon drying, and winter warming pose considerable challenges for rapidly declining groundwater. However, their impacts on irrigation water demands and groundwater storage under the observed and projected future climate remain unexplored. Using in situ observations, satellite data, and a hydrological model that considers the role of irrigation and groundwater pumping, we show that summer monsoon drying and winter warming accelerate groundwater depletion in north India during the observed climate, which will continue in the projected future climate. Summer monsoon precipitation has significantly (P-value = 0.04) declined (similar to 8%) while winters have become warmer in north India during 1951-2021. Both satellite (GRACE/GRACE-FO) and hydrological model-based estimates show a rapid groundwater depletion (similar to 1.5 cm/year) in north India with a net loss of 450 km3 of groundwater during 2002-2021. The summer monsoon drying followed by winter warming cause a substantial reduction in groundwater storage due to reduced groundwater recharge and enhanced pumping to meet irrigation demands. Summer monsoon drying and winter warming will continue to affect groundwater storage in north India in the future. For instance, summer monsoon drying (10%-15% deficit for near-far periods) followed by substantial winter warming (1-4 degrees C) in the future will further accelerate groundwater depletion by increasing (6%-20%) irrigation water demands and reducing groundwater recharge (6%-12%). Groundwater sustainability measures including reducing groundwater abstraction and enhancing the groundwater recharge during the summer monsoon seasons are needed to ensure future agricultural production. Groundwater in north India is facing rapid depletion due to summer monsoon drying and winter warming. The decline in summer monsoon precipitation and warmer winters have led to major droughts, resulting in a massive loss of groundwater between 2002 and 2021. Summer monsoon drying coupled with winter warming climate will increase irrigation water demands and reduce groundwater recharge. This necessitates the implementation of groundwater sustainability measures to ensure future agricultural production during monsoon droughts. Examined the role summer monsoon drying and winter warming on groundwater storage in India Rapid groundwater depletion (similar to 1.5 cm/year) resulted in a net loss of 450 km3 of groundwater during 2002-2021 Summer monsoon drying followed by substantial winter warming under the warming climate will further accelerate groundwater depletion