MONITORING AQUIFER DEPLETION FROM SPACE: CASE STUDIES FROM NUBIAN SANDSTONE AQUIFER IN EGYPT AND THE SAQ AQUIFER IN SAUDI ARABIA

In arid and semi-arid regions of the world the demand for fresh water resources is increasing due to increasing populations and scarcity of fresh water supplies. Examples of these regions include the Middle East countries where the scarcity of fresh water is contributing to political instability, disputes, and conflicts. Many of these countries are blessed by having large amounts of fresh water stored in non-renewable and widely distributed aquifers. The majority of these aquifers remain poorly investigated for the following reasons: (1) their locations in the less-developed parts of the world, (2) the general inaccessibility of many of these regions, and (3) difficulties in collecting background information. Given the previous reasons, we developed an integrated approach to investigate the hydrologic setting of two main fresh water aquifers, the Nubian Sandstone Aquifer System (NSAS; area: 493 x 10³ km²) in Egypt and the Saq Aquifer System (SAS; area: 489 x 10³ km²) in Saudi Arabia. Specifically, we are addressing aquifer response to natural climatic and anthropogenic effects. Monthly (01/2003 – 09/2012) Gravity Recovery and Climate Experiment (GRACE) data was processed (destriped, Gaussian smoothed, and soil moisture removed) and used in conjunction with other relevant datasets to investigate aquifer depletion rates. Results indicate: (1) both NSAS and SAS are experiencing declining GRACE trends, (2) time series analyses show a negligible changes between GRACE before and after removing soil moisture indicating that the main drivers for GRACE anomalies are the groundwater extraction activities, (3) areas with negative GRACE trends are highly spatially correlated with irrigated areas, (4) the annual depletion rates based on GRACE data for the NSAS and SAS is estimated at 1.8 x 10⁹ m³ (3.6 mm/yr) and 2.3 x 10⁹ m³ (4.8 mm/yr) respectively, and (5) GRACE results are consistent with the reported groundwater extraction rates for both aquifers. Given the available temporal monthly GRACE solutions for the past eleven years, the global coverage of this data set, and the plans underway for the deployment of a GRACE follow-On and GRACE-II, we suggest that within the next few years, GRACE will probably become the most practical, informative, and cost effective procedure for monitoring aquifer depletion rates across the globe.