Groundwater Depletion in California’s Central Valley Accelerates During Megadrought

Groundwater provides nearly half of irrigation water supply, and it enables resilience during drought, but in many regions of the world, it remains poorly, if at all managed. In heavily agricultural regions like California’s Central Valley, where groundwater management is being slowly implemented over a 27-year period that began in 2015, groundwater provides two-thirds or more of irrigation water during drought, which has led to falling water tables, drying wells, subsiding land, and its long-term disappearance. Here we use nearly two decades of observations from NASA’s GRACE satellite missions and show that the rate of groundwater depletion in the Central Valley has been accelerating since 2003 (1.86 km3/yr, 1961-2021; 2.41 km3/yr, 2003-2021; 8.58 km3/yr, 2019-2021), a period of megadrought in southwestern North America. Results suggest the need for expedited implementation of groundwater management in the Central Valley to ensure its availability during the increasingly intense droughts of the future.

地下水可为全球近半数的农业灌溉提供水源，在干旱时期能够保障供水韧性，但全球多数地区的地下水管理仍十分薄弱，甚至几乎未得到有效管控。在加利福尼亚中央谷这类农业高度发达的区域，自2015年起，当地地下水管理计划正以27年的周期缓慢推进；而在干旱时期，该区域三分之二及以上的灌溉用水均依赖地下水，由此引发了地下水位下降、水井干涸、地面沉降，乃至地下水长期枯竭的一系列问题。本研究借助美国国家航空航天局（NASA）重力恢复与气候实验（GRACE）卫星任务近二十年的观测数据，分析发现自2003年以来，中央谷的地下水枯竭速率持续加快：1961-2021年间年均枯竭量达1.86立方千米/年，2003-2021年间增至2.41立方千米/年，2019-2021年间更是达到8.58立方千米/年；这一时期正值北美西南部特大干旱期。研究结果表明，为保障未来愈发严峻的干旱时期地下水供应，中央谷亟需加快推进地下水管理工作。