In 2023, California experienced heavy rainfall, but it didn’t significantly recharge the state’s aquifers that have suffered from years of drought. A new study highlights this ongoing issue.
Los Angeles relies on groundwater for about a third of its water supply. The first part of 2023 saw over a dozen atmospheric rivers, which are long weather systems filled with moisture, bringing rain to the West Coast. This was followed by Hurricane Hilary, which poured even more rain on Southern California. Overall, the state received more than double the average precipitation for the 20th century, adding over 90 billion gallons of water to surface reservoirs in the Los Angeles area.
Researchers found that while the moisture helped recharge near-surface aquifers, deeper aquifers remained largely unaffected. William Ellsworth, a seismologist from Stanford University, alongside his team, conducted this research. They published their findings in the journal Science.
To understand how water impacted aquifers, the team analyzed how water infiltrating rock layers affected seismic wave speeds. They harnessed existing seismic noise—from natural events and human activity—to map underground features. Ellsworth mentioned that this seismic noise provides valuable information about the earth that researchers can utilize.
By examining vibrations at different frequencies, the team detected water levels down to hundreds of meters below ground. They found that only about 25% of the water lost from the aquifers since 2006 was replenished by the rains in 2023.
Geophysicist Roland Bürgmann from UC Berkeley expressed excitement about visualizing water storage in aquifers over time. While this method shows promise, many areas lack the dense seismic networks found in California. However, researchers hope to adapt this technique using underground fiber-optic networks equipped with suitable sensors, which could provide more insights elsewhere.
