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.
Groundwater is Earth's largest reservoir of fresh, liquid water. Accounting for more than 20% of water usage worldwide and 43% of irrigation water (Earman & Dettinger, 2011;Fetter, 2001;Zektser & Everett, 2004), groundwater serves as the primary source of freshwater for over 2 billion people across the globe (Alley et al., 2002;Famiglietti et al., 2011;Gleeson et al., 2012; WWAP, 2015). Its contributions are expected to increase with rising global population and changing climate, as surface water becomes a less reliable resource (FAO, 2005; OECD, 2011; WWAP, 2015). It is estimated that by 2050, 2 billion additional people will need to be fed, increasing demand on agricultural land use for improved rates of food production (OECD, 2011; WWAP, 2015). As climate change continues to alter patterns of drought and regional recharge dynamics, groundwater will continue to establish itself as an increasingly critical component of the water cycle, as groundwater variability directly impacts surface water (
<p>Coastal regions are home to more than 40% of the world&#8217;s population and often depend on fresh groundwater resources to sustain economic, residential, and recreational activities. However, coastal groundwater is under threat from saltwater intrusion (SWI), due in part to rising sea level and climate change. In this work we provide, for the first time, a global assessment of SWI and SWI vulnerability due to regional differences in sea level rise and predicted changes in recharge, leveraging NASA datasets of recharge, seawater density, and IPCC AR6 sea level rise. We show that climate-driven recharge changes drove 45% of watersheds to experience SWI, while SLR drove 92% of watersheds to experience SWI. By synthesizing various global datasets within an analytical framework, the work provides the first step towards evaluating the coastal impacts of saltwater intrusion in a changing climate.&#160;</p>
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