Mining Fossil Water: A Review of Groundwater Depletion, Recharge and Sustainable Management of the Nubian Sandstone Aquifer System

The Nubian Sandstone Aquifer System (NSAS), shared by Egypt, Libya, Sudan and Chad, is the largest fossil groundwater system on Earth, underlying about two million square kilometres of the eastern Sahara. Most of its water was recharged during humid periods of the Pleistocene and early Holocene and is effectively non-renewable on human timescales. Expanding abstraction for desert reclamation in Egypt's Western Desert and for Libya's Great Man-Made River has lowered water levels, dried artesian springs and raised pumping costs at major centres. This review synthesises hydrogeological, isotopic, numerical-modelling and satellite-gravimetry (GRACE) studies to assess the state of the aquifer. The literature agrees that large-scale transboundary drawdown is likely to be limited, but that local drawdown at pumping centres co-located with oases will become excessive, threatening oasis ecosystems, traditional agriculture and the economic viability of reclamation schemes. GRACE-based studies estimate depletion of about 4.4 km³ per year in the Dakhla sub-basin and show that modern recharge is episodic and limited to the southern and eastern margins during exceptionally wet years or high stands of Lake Nasser. The review discusses the economics of mining fossil water for low-value crops, the environmental impacts on oases, and the institutional arrangements of the Joint Authority for the Study and Development of the Nubian Aquifer, and proposes a framework for planned, transparent depletion management.