A recent study has shown that despite heavy rains in California in 2023, aquifers in the region were not fully recharged. The state, which has been facing a prolonged drought and excessive human pumping of groundwater, received a significant amount of rainfall in the form of atmospheric rivers and a hurricane, leading to a statewide precipitation level well above its 20th century average.
Los Angeles, a city prone to dry spells, relies on groundwater for about one-third of its water supply. The rainfall in the first three months of the year and the subsequent hurricane added over 90 billion gallons of water to surface reservoirs in the area. However, the study revealed that while the near-surface aquifers were almost completely recharged, deeper water-bearing layers saw minimal replenishment.
The research, led by William Ellsworth and his team at Stanford University, utilized seismic waves to assess the impact of the water infiltration on underground rock layers. By analyzing changes in the speed of seismic waves caused by water percolation, the researchers were able to determine that only about 25 percent of the water lost from the aquifers since 2006 was replenished by the 2023 storms.
The technique of using seismic waves to monitor water storage in aquifers over time has been hailed as exciting by experts like Roland Bürgmann from the University of California, Berkeley. While California benefits from a dense network of seismic instruments, other regions may be able to utilize underground fiber-optic networks with the right sensors to gather similar data.
Overall, the study highlights the importance of sustainable water management practices in the face of climate change and increasing water scarcity. By understanding how aquifers are recharged and depleted, policymakers and researchers can work towards ensuring a reliable water supply for future generations.
