REMOTE SENSING APPROACHES FOR ASSESSING GROUNDWATER RESOURCES AND ANTHROPOGENIC IMPACTS IN SOUSS BASIN, MOROCCO

Natural and human-induced impacts on water resources in North Africa continue to negatively affect the modern recharge, groundwater reserves, and alter the physical landscape. The increased exploitation of groundwater resources in the past half-century coupled with successive droughts has resulted in the depletion of the aquifer and acceleration of subsidence rates in the Souss Basin in Morocco. The primary groundwater aquifer (Plio-Quaternary Plain Aquifer), an unconfined aquifer, is being harvested by >20,000 wells at a rate of 650 MCM/yr, exceeding the rate of recharge by 260 MCM/yr. Intense development over the past 50 years has exposed the aquifer to a serious risk of groundwater table drawdown (0.5m-2.5m/yr), land subsidence, loss of artesian pressure, salinization, and deterioration of water quality across the watershed.

An integrated three-fold approach which combines satellite remote sensing, hydrologic models, and climate change scenarios was carried out in the Souss Basin, Morocco was utilized to quantify the current and projected changes in water resources and evaluate the impacts of groundwater extraction. First, current water resources were estimated using a combined field-based and satellite-based hydrologic model (SWAT) and GRACE RL05 data. Second, the projected climate change impacts were estimated using a 40-GCM ensemble using the IPCC AR5 data. Lastly, persistent scatterer interferometry (PSI) was conducted using SARscape with 250 ENVISAT and ERS1/2 SLC images to estimate ground subsidence induced by groundwater extraction.

Simulated (2000-2012) potential renewable groundwater resources obtained from SWAT are ~1.8 x 10⁹m³/yr. GRACE indicates a decline in total water storage of ~1.9 cm/yr, while the TMPA rainfall shows an increase in annual rainfall amounts which suggests human interactions as the underlying cause of depleting groundwater reserves. This is supported by the radar interferometry results of increasing land subsidence (-20mm/yr ±0.4mm/yr). The combined approach resulted in quantifying the amount of modern recharge, estimated the potential projected decreases in water resources in the future, measured the relative subsidence rates, and demonstrates the utility of satellite remote sensing data sets in developing management plans for modulating adverse impacts.