| Abstract |
The aquifer recharge rate is pivotal in hydrology and water management and yet remains one of the most challenging hydrogeologic measures to estimate, especially in arid and semiarid regions, where rates of only a few millimeters per year are expected. Satellite-based methods offer the opportunity to assess integrated processes at a regional scale. Although averaged over large areas (103 to 106 km2), the hydrological quantities provided by satellite-based methods represent valuable general estimates for regional systems where exhaustive field measurements are unrealistic, too time-consuming, and too costly. In this respect, the gravity data provided by Gravity Recovery and Climate Experiment (GRACE), a satellite system launched in 2002 by NASA and German Aerospace Center, allow us to monitor the time variation of total terrestrial water storage (water masses in the upper crust). The use of GRACE data for basin scale water mass balance is gaining popularity in the hydrologist community. The Geothermal North Sahara Aquifer System (NSAS) supplies up to 90% of the water demand [OSS, 2008]. To satisfy growing needs, the global withdrawal rate in the aquifer increased from 0.5 to almost 3 km3 yr–1 from 1960 to 2010, causing an ongoing overall piezometric decline, especially since the 1970s. In this context, quantifying the recharge is crucial. |