As discussed in Chapter 14, groundwater usage in some areas of the world is well above recharge rates (the rate at which water used is replaced). Indeed 15% of aquifers are being used unsustainably, most notably aquifers in western Mexico, the High Plains and California’s Central Valley in the United States, Saudi Arabia, Iran, northern India and parts of northern China. These aquifers are particularly crucial to agriculture.
Researchers from Canada and the Netherlands have shown, by using global groundwater usage data and models of underground water resources, that for these few aquifers the overextraction rates are so large as to offset the efforts of sustainable management in other areas. Or in other words for the globe, water use, on average, is higher than recharge rates.
There are also fears that largely untapped underground water reserves under the driest North African countries like Libya, Algeria, Egypt and Sudan may be unsustainably managed. Mapped by a team from the British Geological Survey and University College London in April these reserves could be a huge buffer against future drought but schemes are already in place in some countries that could undermine this potential. In Libya, for example, the $25 billion Great Manmade River project, implemented under Colonel Gaddafi is planned to provide water to residents of Tripoli, Benghazi and Sirte. The provision of water is planned to be higher than the rate it can recharge itself. At these rates water resources are expected to last about 60 to 100 years.