Washington, October 10 — Decades of groundwater monitoring by the United States Geological Survey (USGS) and satellite measurements from the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission reveal that aquifers across the American Southwest are being depleted at rates exceeding natural recharge. The USGS has maintained a national groundwater monitoring network since the mid-20th century, with long-term observation wells in Arizona, California, Colorado, Nevada, New Mexico, Texas, and Utah showing persistent declines in water levels.
GRACE-FO, launched in 2018 as a successor to the original GRACE mission (2002–2017), uses twin satellites to detect changes in Earth’s gravity field, allowing scientists to estimate changes in terrestrial water storage, including groundwater. Data from GRACE-FO indicate significant groundwater losses in the Colorado River Basin, particularly in southern California, Arizona, and New Mexico, where agricultural irrigation and municipal demand place heavy stress on aquifer systems.
In California’s Central Valley, USGS data show groundwater levels have dropped by more than 60 feet in some areas since the 1960s, with accelerated declines during drought periods such as 2007–2009 and 2012–2016. The High Plains Aquifer, also known as the Ogallala Aquifer, which underlies parts of eight states from South Dakota to Texas, has experienced cumulative storage losses of approximately 273 million acre-feet since predevelopment, according to USGS estimates published in 2017, with about 30% of that loss occurring since 2000.
Recharge rates in arid and semi-arid regions of the Southwest are naturally low, often less than an inch per year in many basins, making recovery slow even when pumping decreases. Climate projections from the National Oceanic and Atmospheric Administration (NOAA) suggest increasing temperatures and altered precipitation patterns may further reduce recharge potential in the region.
State water agencies in Arizona, California, and Texas have implemented groundwater management plans under legislation such as Arizona’s 1980 Groundwater Management Act and California’s 2014 Sustainable Groundwater Management Act (SGMA), which requires basins to achieve sustainability by 2040 or 2042 depending on priority. Despite these efforts, USGS scientists note that full recovery of deeply depleted aquifers may take centuries, if it occurs at all, due to the slow movement of groundwater through aquifer materials.
The combined use of ground-based monitoring and satellite remote sensing provides a critical tool for assessing long-term trends and informing water policy in one of the nation’s most water-stressed regions. The Ogallala Aquifer is a shallow water table aquifer surrounded by sand, silt, clay, and gravel located beneath the Great Plains in the United States. As one of the world’s largest aquifers, it underlies an area of approximately 174,000 square miles in portions of eight states (South Dakota, Nebraska, Wyoming, Colorado, Kansas, Oklahoma, New Mexico, and Texas).
It was named in 1898 by geologist N. H.
Darton from its type locality near the town of Ogallala, Nebraska. The aquifer is part of the High Plains Aquifer System, and resides in the Ogallala Formation, which is the principal geologic unit underlying 80% of the High Plains. Large-scale extraction for agricultural purposes started after World War II due partially to center pivot irrigation and to the adaptation of automotive engines to power groundwater wells.
Today about 27% of the irrigated land in the entire United States lies over the aquifer, which yields about 30% of the ground water used for irrigation in the United States. The aquifer is at risk of over-extraction and pollution.
Since 1950, agricultural irrigation has reduced the saturated volume of the aquifer by an estimated 9%. Once depleted, the aquifer will take over 6,000 years to replenish naturally through rainfall.
