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Jointly estimating recharge and groundwater withdrawals of the NWSAS by inverting GRACE/GRACE-FO gravity data

ABSTRACT A new approach is proposed for estimating groundwater recharge and withdrawals in the North Western Sahara Aquifer System (NWSAS) by inverting 18 years of Gravity Recovery and Climate Experiment (GRACE/GRACE-Follow-On) data. In this study, only the groundwater component was found to contribute to GRACE-based terrestrial water storage change. By considering the inter-zone heterogeneity of potential recharge and water withdrawals in the groundwater balance equation, total recharge and water output rates are estimated at both the grid-cell level and on the scale of the whole NWSAS. The total recharge and water-output rates were found to be 1.9 and 5.2 km3/year, respectively, corresponding to −3.3 km3/year of depletion. After subtracting from the total recharge both artificial and assumed-Quaternary recharges, 1 km3/year was found for actual recharge, similar to what is reported elsewhere. For water withdrawal, the estimated rate is 4.75 km3/year, higher than the rates published in other studies. The agreement of our results with those of other authors validates our approach.