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.

KEYWORDS:

• NWSAS
• GRACE/GRACE-FO
• groundwater
• recharge
• water withdrawals
• gravity data inversion

Editor A. Fiori; Associate Editor M. Bianchi

Editor A. Fiori; Associate Editor M. Bianchi

Acknowledgements

This study was made possible using freely available satellite gravity and soil moisture data. GRACE/GRACE-FO Level 2B data products (RL06) were obtained from the GraVIS/GFZ website: ftp://isdcftp.gfz-potsdam.de/grace/GravIS/GFZ/Level-2B/. GLEAM datasets (v. 3.5) are available upon request from https://www.gleam.eu/#datasets.

Disclosure statement

No potential conflict of interest was reported by the authors.