Quantifying temporal variations in water resources of a vulnerable middle eastern transboundary aquifer system

Freshwater resources in the arid Arabian Peninsula, especially transboundary aquifers shared by Saudi Arabia, Jordan, and Iraq, are of critical environmental and geopolitical significance. Monthly Gravity Recovery and Climate Experiment (GRACE) satellite-derived gravity field solutions acquired over the expansive Saq transboundary aquifer system were analysed and spatiotemporally correlated with relevant land surface model outputs, remote sensing observations, and field data to quantify temporal variations in regional water resources and to identify the controlling factors affecting these resources. Our results show substantial GRACE-derived terrestrial water storage (TWS) and groundwater storage (GWS) depletion rates of -9.05 +/- 0.25mm/year (-4.84 +/- 0.13km(3)/year) and -6.52 +/- 0.29mm/year (-3.49 +/- 0.15km(3)/year), respectively. The rapid decline is attributed to both climatic and anthropogenic factors; observed TWS depletion is partially related to a decline in regional rainfall, while GWS depletions are highly correlated with increasing groundwater extraction for irrigation and observed water level declines in regional supply wells.