As temperatures rise and water supplies drop, public policy could bolster municipal water provisions under pressure. But one policy prescription - pushing conservation - will likely be insufficient as a standalone fix to sustain some reservoirs, according to research led by scientists at Penn State.
The study, published in the journal Water Resources Research, centers on three western U.S. cities connected by the Colorado River: Denver, Las Vegas and Phoenix. Drawing from resident surveys and a new computational model, researchers found that reducing demand would be effective in buoying supplies under relatively mild climate change scenarios but have minimal impact in more dire circumstances.
If climate change brings more severe or prolonged dry conditions, managing customer demand "starts to fail as a way to maintain water availability," said Renee Obringer, assistant professor in the Department of Energy and Mineral Engineering in the College of Earth and Mineral Sciences (EMS).
"A lot of policymakers out West may be thinking that conservation policies might solve a lot of the problems - if they can just use less water and store the rest for emergency situations," said Obringer, the lead author on the paper. "We found that's not always going to be effective, especially given conditions across the drought-prone Colorado River Basin."
The work builds on Obringer's prior work in the region, where she and collaborator Dave D. White, director of the Global Institute of Sustainability and Innovation at Arizona State University, examined which groups are most likely to conserve. In another study, published in 2024, Obringer and White investigated how varying conservation attitudes might influence water availability in Phoenix.
A faculty associate of the Earth and Environmental Systems Institute and the EMS Energy Institute, Obringer said the recent study stems from her longstanding interest in the effectiveness of water-demand management. This latest collaboration includes Grace Peterson, a Penn State undergraduate majoring in environmental systems engineering.
As reported by the Public Policy Institute of California, Colorado River water use outpaces the river's annual supply by some 1 million acre-feet per year - an average established over the last quarter-century. Shortages are worsening amid higher temperatures and diminished snowpack, the institute noted.
That's a deepening concern for communities across seven states that depend on the river system for water since nearly 40 million people rely on it, according to the National Integrated Drought Information System.
"If a lot of people just simply don't care to follow demand-management protocols, recommendations or even mandates, then implementing those policies is not going to have any sort of real, lasting change," Obringer said.
In this research, the team estimated reservoir storage under a variety of climate change and demand-management scenarios in Denver, Las Vegas and Phoenix. All three cities receive drinking water from the Colorado River Basin and, because of a complex allocation system, have few ways to increase their supply.
The researchers sought to determine whether tempering demand through policy approaches - such as mandatory reductions - could sustain adequate water storage, especially amid drought. The region is predicted to have more and worse droughts because of climate change, Obringer said.
To assess the impact of policy changes in various scenarios, the researchers developed a model that incorporated hydrological data for the cities, including observations and simulations based on different climate possibilities. It also wove in data reflecting water consumption in each city and survey results that capture regional attitudes toward conservation.
Results differed among the cities. In Denver, the researchers found broader participation in water conservation could be a more significant, reliable counterbalance to climate-induced drawdowns of reservoir storage. Under one scenario there, the model showed the median reservoir level would be about 17% higher with conservation policies.
Variability appeared greater in Phoenix and in Las Vegas, where more robust conservation participation forecasted smaller bumps in reservoir levels. For Phoenix, demand-management policies may not be enough to counteract consequences of climate change, the researchers said.
Changing consumer attitudes can be effective for some cities up against water scarcity, but policymakers should integrate other approaches to ensure adequate supply, according to the research team.
"As the Colorado River is getting drier, attempts at interstate water management are struggling," Obringer said. "Demand reductions are not a catch-all; they're not going to do all the work. We still need to figure out other ways to moderate water use in the cities."
For the study in Water Resources Research, Obringer and her team received funding support through the National Socio-Environmental Synthesis Center under grants from the U.S. National Science Foundation. Additional funding came from the Department of Energy and Mineral Engineering, the Earth and Environmental Systems Institute and the Multi-Campus Research Experience for Undergraduates, all at Penn State. Obringer also is an affiliate researcher with the University's Institute of Energy and the Environment.
