Groundwater: scientists map how much water lies beneath the United States

Researchers used data from about 800,000 wells and a machine-learning model to produce the most detailed national map and estimate of U.S. groundwater, finding roughly 250 billion acre-feet across the country.

Researchers at Princeton University and the University of Arizona have produced a nationwide map estimating groundwater depth across the United States. They combined measurements from roughly 800,000 wells with a machine-learning model and geological data to estimate water-table depth down to nearly 1,300 feet. The study, published in Nature, provides the most extensive estimate of U.S. groundwater to date. Scientists say the map can help local decision-makers and researchers assess stressed aquifers and estimate depletion. Key findings: - The analysis used data from about 800,000 wells and a machine-learning approach to estimate groundwater depths across the country. - The researchers estimate roughly 250 billion acre-feet of groundwater nationwide, about 13 times the volume of the Great Lakes. - Groundwater depth varies widely: in some places water is a few feet below the soil and in others it can be hundreds to nearly 1,300 feet deep. - Data compiled by the study indicate the Colorado River watershed contains about as much groundwater as the Great Lakes, and California holds about 70% of that amount. - Declines in groundwater have already led to dry household wells, disappearing wetlands and streams, and land subsidence; the U.S. Geological Survey estimated the Central Valley lost about 128 million acre-feet as of 2019. Summary: The new map provides high-resolution information that researchers and water managers can use to locate deep and shallow groundwater and to assess where aquifers are stressed. Experts say the results complement satellite measurements, and that a national-scale network of deep monitoring wells would further improve tracking of quantity and quality down to bedrock.