Groundwater over-exploited in agricultural regions, study finds

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Humans are over-exploiting underground water reservoirs in many large agricultural areas in Asia and North America, sucking up water faster than nature can replenish it, according to a recent inventory of global aquifer use.

In a study published Wednesday in the journal Nature, scientists mapped the “groundwater footprint” of 15 major agricultural regions, including California’s Central Valley. The analysis, which gave spatial representation to rates of water extraction, concluded that the global groundwater footprint was 3.5 times greater than the size of all aquifers combined.

The heavy consumption of groundwater was driven by a handful of areas, according to lead author Tom Gleeson, a civil engineering professor at McGill University in Montreal.

The areas included the Upper Ganges in India and Pakistan, western Mexico, northern Saudi Arabia, Iran, the High Plains of the United States and the North China Plain. Although 80% of the world’s aquifers had a calculated footprint that was smaller than their actual size, these major agricultural regions contributed to a global deficit.

Groundwater is a critical global resource that sustains billions of people, plays a central role in agriculture and directly affects many ecosystems. However, scientists have struggled to calculate precisely how its rate of use compares with its rate of replenishment.

The study sought to illuminate the matter by using data and models on water consumption and replenishment to calculate footprint size. The authors said that groundwater use could be better managed by mapping the size of footprints. For instance, relocating some crops grown in highly taxed aquifer areas to areas where groundwater was less exploited could reduce the overall global groundwater deficit. The study, however, did not factor in the quality of groundwater.

Although California’s Central Valley was included on the list of major agricultural areas and was found to have a footprint larger than its aquifer, its footprint was roughly a third smaller than in the High Plains and roughly nine times smaller than that of the Upper Ganges.