A new study suggests that aquifers in the U.S. Southwest will be more severely impacted by climate change compared to those in the Pacific Northwest.

Climate models predict that the U.S. Southwest will face reduced rainfall due to global warming, while the Pacific Northwest will experience wetter conditions. However, researchers warn that groundwater pools in the Southwest are more vulnerable to climate variations than those in the North.

Modern aquifer data is not reliable for forecasting the effects of a warming planet due to extensive human extraction of groundwater. Therefore, scientists turned to ancient groundwater records from the last ice age (2.6 million to 11,700 years ago) to gain insights into potential future changes.

Lead author of the study, Alan Seltzer, an expert in marine chemistry and geochemistry at Woods Hole Oceanographic Institution, emphasized the significance of studying groundwater dynamics during the last ice age as a window into potential future scenarios.

Analysis of ancient groundwater from the Palouse basin aquifer beneath Washington and Idaho revealed clues about past water table depths through geochemical markers like dissolved noble gases. By examining isotopes of krypton and xenon from 17 wells in the aquifer, researchers reconstructed water table levels over a span of 9,000 years of global warming.

Comparing these findings with data from the San Diego aquifer in Southern California, the study showed that Southwestern aquifers experienced significant drops in water table levels during the last ice age, while Pacific Northwest aquifers remained relatively stable despite increased rainfall.

The study suggests that groundwater systems with shallow water tables, like the Palouse basin aquifer, are more resilient to climate changes as they can transfer water to neighboring soils more effectively. In contrast, aquifers with deep water tables, such as the San Diego aquifer, are highly sensitive to changes in precipitation and can rapidly dry out without sufficient rainfall.

Researchers validated their findings by comparing ancient groundwater data with an Earth system computer model, which yielded consistent results with the isotope measurements.