Data from the Gravity Recovery and Climate
Experiment (GRACE) and outputs of
the CLM4.5 model were used to estimate recharge
and depletion rates for large aquifers,
investigate the connectivity of an aquifer’s
subbasins, and identify barriers and preferred
pathways for groundwater flow within an
aquifer system. The Nubian Sandstone Aquifer
System and its subbasins (Dakhla, Northern
Sudan Platform, and Kufra) in northeast
Africa were used for demonstration purposes,
and findings were tested and verified against
geological, geophysical, remote sensing, geochronologic,
and geochemical data. There are
four major findings. (1) The average annual
precipitation data over recharge areas in the
southern Kufra section and the Northern
Sudan Platform subbasin were estimated
at 54.8 km3, and 32.8 km3, respectively, and
knowing the annual extraction rates over
these two areas (~0.40 ± 0.20 km3), recharge
rates were estimated at 0.78 ± 0.49 km3/yr and
1.44 ± 0.42 km3/yr, respectively. (2) GRACEderived
groundwater depletion rates over the
Dakhla subbasin and the Northern Kufra
section were estimated at 4.44 ± 0.42 km3/yr
and 0.48 ± 0.32 km3/yr, respectively. (3) The
observed depletion in the southern parts of
the Dakhla subbasin is apparently caused
by the presence of the east-west–trending
Uweinat-Aswan basement uplift, which impedes
the south-to-north groundwater flow
and hence reduces replenishment from recharge
areas in the south. (4) A major northeast-
southwest–trending shear zone (Pelusium
shear system) is apparently providing
a preferred groundwater flow pathway from
the Kufra to the Dakhla subbasin. Our integrated
approach provides a replicable and
cost-effective model for better understanding
of the hydrogeologic setting of large aquifers
worldwide and for optimum management of
these groundwater resources.