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A recent study from researchers at The University of Texas at Austin, along with collaborators from Arizona and Colorado, indicates that a combination of effective water management strategies has resulted in significant groundwater recovery in Central Arizona, despite ongoing challenges related to water scarcity in the region.
Efforts to recharge depleted aquifers in Central Arizona have been underway since 1980. A significant portion of this recharge relies on water sourced from the Colorado River, which constitutes 36% of Arizona’s water supply. This water is transported over 300 miles to the state through an extensive aqueduct network known as the Central Arizona Project.
Arizona has implemented various policies designed to encourage farmers to prioritize the use of surface water from the Colorado River instead of relying solely on groundwater. Additionally, certain initiatives direct river water toward aquifer recharge zones, promoting its infiltration into the groundwater system.
Published in Communications Earth & Environment, the study revealed that from 1989 to 2019, these policies facilitated the storage of approximately 10.5 cubic kilometers of groundwater in the active management areas of Phoenix, Tucson, and Pinal. Furthermore, an additional 14.2 cubic kilometers of groundwater has been attributed to unregulated surface-water irrigation, demonstrating the effectiveness of both planned and incidental water management strategies.
Collectively, these nearly 25 cubic kilometers represent about five times the annual water demand for the three major active management areas, which encompass agricultural zones larger than the state of Maryland.
Bridget Scanlon, lead author of the study and research professor at the UT Jackson School of Geosciences Bureau of Economic Geology, emphasized the importance of integrated management of both surface and groundwater resources.
The findings underline the success of Arizona’s groundwater recharge policies and suggest that such frameworks could serve as a model for other regions grappling with water scarcity. Nonetheless, the researchers caution that the sustainability of these gains may be at risk. The Colorado River has faced declining water levels, notably due to prolonged drought conditions. The two largest reservoirs in the U.S., Lake Powell and Lake Mead, have dropped from approximately 90% capacity in 2000 to about 30% capacity projected for 2025, largely due to reduced river flows exacerbated by climate change.
Co-author Kathryn Sorensen, director of research at Arizona State University’s Kyl Center for Water Policy, pointed out the implications of this evolving scenario, stating that while the groundwater recovery is commendable, the diminishing water availability from the Colorado River will lead to increased pressure on groundwater resources. “It’s a lot of water, and that’s great. We should celebrate that. But shortage on the Colorado River means we’ll have less water to boost our aquifers, and more pressure to pull groundwater out as a replacement supply,” Sorensen noted.
The Arizona aquifer research is part of a broader study assessing water levels in the entire Colorado River Basin over several decades. By utilizing data from GRACE satellites, regional models, and groundwater monitoring, the researchers have illustrated how water levels have fluctuated due to both natural cycles and human efforts.
In addition to confirming the value of proactive groundwater management policies, the study also highlighted the role of unintentional irrigation runoff in assisting aquifer recharge, particularly important for areas that experienced significant depletion from extensive groundwater extraction between the 1940s and 1970s, alongside periods of increased precipitation between the 1980s and 1990s.
Co-author Don Pool, a retired hydrologist at the U.S. Geological Survey’s Arizona Water Science Center, expressed skepticism about the likelihood of witnessing similarly wet conditions in the future, underscoring the importance of capturing and utilizing water during any available wet periods. “I don’t know if we’ll ever see a wet period like the 70s through the early 90s again, but we need to take advantage of those wet periods and get the water into the ground whenever and wherever we can,” he said.
Water distribution from the Colorado River is governed by a 1922 compact, with operational regulations set to expire in 2026. Stakeholders, including state leaders, indigenous groups, and representatives from Mexico, are gearing up to renegotiate water distribution agreements. Scanlon remarked that the comprehensive nature of the study can aid in planning for sustainable water usage from the river going forward, emphasizing the need to understand long-term trends in climate variability, irrigation practices, and overall water management.
“You can see how things have been changing over time,” Scanlon reflected. “And that’s important if you’re trying to understand climate variability, variations in irrigation pumpage, conjunctive management and put it into context.”
The study also includes contributions from Ashraf Rateb and Robert Reedy of the Bureau of Economic Geology, Brian Conway of the Arizona Department of Water Resources, and Bradley Udall of Colorado State University.
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