米国の地下水源は過度に利用されているのだろうか

Current trends in potentially excessive groundwater drilling in the United States may be unsustainable, reports an Analysis in Nature Sustainability. The study provides a comprehensive look at how over-tapped this critical resource is.

Groundwater wells tap into aquifers across the US, which vary dramatically in size, shape and capacity, and provide an increasing proportion of the nation’s water used for drinking, agriculture and industry. The ways that people are responding to groundwater depletion are largely unknown due to the lack of data on the number, location and depth of groundwater wells that have been drilled over time.

Debra Perrone and Scott Jasechko compiled the first national database of groundwater wells, pulling together state-level data on nearly 12 million wells across the US. They found that deeper groundwater drilling is occurring in areas where there is already groundwater decline and that agricultural wells are often drilled deeper than those for domestic and drinking use. They indicate that as much as 89% of drilling sites in California’s Central Valley aquifer system and 73% in the Mississippi embayment aquifer system of the lower Mississippi River region show signs of well deepening and declining groundwater levels. The authors assert that drilling deeper groundwater wells is an unsustainable stopgap measure for increasing water availability in the long term.