our recent collected dating groundwater samples. Nubian Sandstone Aquifer System (NSAS) of northeast Africa is believed to have been recharged in previous wet climatic periods in the Quaternary Period. However, the isotopic (O & D) signatures of the groundwater samples show that the aquifer is still receiving modern recharge in some regions (central and north Sudan, the Eastern Desert and Sinai). These regions have a rainfall that feed the aquifer during the current dry climate. The groundwater source
Recovery and Climate Experiment (GRACE) and climatic model (CLM 4.5) outputs were conducted over the southern part of the Nubian Sandstone Aquifer System (NSAS) (area: 835 × 103 km2) in Sudan and Chad to estimate the natural recharge rate. The Nubian Sandstone Aquifer System (NSAS) is shared by Egypt, Libya, Chad, and Sudan, and is one of the largest (area: ~ 2 × 106 km2) groundwater systems in the world. Findings from the study include: (1) average annual precipitation was estimated at 77.5 mm (65 km3);