Global assessment of the sensitivity of water storage to hydroclimatic variations

Observing basin water storage response due to hydroclimatic fluxes and human water use provides valuable insight to the sensitivity of water storage to climate change. Quantifying basin water storage changes due to climate and human water use is critical for water management yet remains a challenge globally. Observations from the Gravity Recovery and Climate Experiment (GRACE) mission are used to extract monthly available water (AW), representing the combined storage changes from groundwater and surface water stores. AW is combined with hydroclimatic fluxes, including precipitation (P) and evapotranspiration (ET) to quantify the hydroclimatic elasticity of AW for global basins. Our results detect consequential global water sensitivity to changes in hydroclimatic fluxes, where 25 % of land areas exhibit hydroclimatic elasticity of AW >10, implying that a 1 % change in monthly P-ET would result in a 10 % change in AW. Corroboration using a Budyko-derived metric substantiates our findings, demonstrating that basin water storage resilience to short-term water deficits is linked to basin partitioning predictability, and uniform seasonality of hydroclimatic fluxes. Our study demonstrates how small shifts in hydroclimate flux may affect available water storage potentially impacting billions globally.