Hydroclimate Elasticity of Accessible Water

Terrestrial water response to climate-induced acceleration of the hydrologic cycle underpins water management challenges, whereby water management in an increasingly uncertain climate must adapt to ensure sufficient resource availability to sustain global ecosystems while meeting societal water needs. Although hydrologic cycle intensification is expected through increased evaporation and precipitation, the unequal redistribution of water fluxes over terrestrial land remains unclear. Studies investigating hydroclimatic sensitivity of runoff assumed long-term steady-state basin storage conditions where P=ET+Q.  Steady-state assumptions neglect the role of groundwater, lakes and reservoirs as vital management resources.  Although hydrologic models have been used to measure sensitivity of basin responses attributed to climate, an assessment of observation-based data which captures temporal changes in basin storage can provide valuable insights to understand fundamental changes in water storage due to hydroclimatic factors.  Here, a sensitivity analysis using the Gravity Recovery and Climate Experiment (GRACE) satellite observations combined with auxiliary hydroclimate variables is investigated.  GRACE captures changes in water stores that result due to water management schemes to offset short-term (i.e., monthly) and long-term (i.e., annual) water deficits in addition to water budget changes driven by P and ET.  Accessible water (AW) represents the combination of groundwater and surface water storage anomalies derived from GRACE, water stores deemed accessible to fulfill water demands.  Results document the role of seasonality and storage potential with respect to hydroclimate elasticity.  Findings reveal that >1 billion people live in basins with elasticity magnitudes >10, meaning that small shifts in P-ET will be magnified 10-fold with respect to AW.