Researchers studying the historic strain on water supplies in the American West have found a simple solution that could put parts of the Colorado River basin on a more sustainable path.

A consortium of scientists and water experts, including Professor Peter Debaere of the University of Virginia’s Darden School of Business, recommends in a paper published today that closing the Free River Conditions gap in Colorado is an important first step in reducing water scarcity in the region.

“Closing this gap in Colorado’s water rights system could save millions of cubic feet of water. This would be the state’s modest contribution to solving the water shortage in the Colorado River basin,” said Debaere, an expert in water economics and water markets.

In Colorado, if the river has enough water to meet everyone’s needs, the Free River Condition allows anyone to take as much water from the river as they want, regardless of whether they own water rights or not.

The new article, “Closing loopholes in water rights systems to conserve water: The Colorado River Basin,” appears in the journal Water Resources Research, published by AGU, a global organization for earth and space sciences. Debaere is part of a consortium that includes researchers from UVA’s School of Engineering and Applied Science and other scientific and academic partners.

The 1,450-mile-long Colorado River is a lifeline for the American West, quenching the thirst of 40 million people in seven states, more than 25 Native American tribes, and parts of Mexico. It also irrigates some of the country’s richest farmland and generates hydroelectric power used throughout the region. The seven states that use the Colorado River’s waters are divided into two groups: Upper Basin (Colorado, Wyoming, Utah, New Mexico) and Lower Basin (Arizona, Nevada, California).

But this vital resource is under threat: The amount of water flowing into the Colorado is decreasing as rising temperatures increase evaporation and the snowpack that feeds the river shrinks, while demand from farms and cities is increasing.

This increasing strain on limited resources further highlights the problems associated with Colorado’s Free River Loophole.

The paper describes free-flow conditions as “an outdated relic from a time when water was relatively abundant” and suggests that this approach perpetuates the imbalance between supply and demand. That increases the likelihood that lower basin water users will make a “compact call,” essentially blaming the upper basin for not securing the amount of water required by law. Such a maneuver could lead to additional caps or restrictions on water use in the upper basin.

“Colorado can help prevent this by closing its Free River Gap,” the paper said.

The current challenges peaked in mid-2022, when water levels in Lake Powell and Lake Mead, the two major reservoirs on the Colorado River, dropped to the point where water withdrawals for hydroelectric power were at risk. The situation was so dire that the Biden administration had to intervene.

But further progress proved difficult, with California, Arizona and Nevada agreeing to major water cuts only in exchange for federal funding. Fortunately, an unusually wet winter in 2022-2023 and conservation efforts mitigated the immediate crisis.

Government officials said Lake Powell and Lake Mead were only 37 percent full as of Aug. 15. They were already nearly full in 2000.

Within each state in the Upper and Lower Basins, water users such as farms or cities have their own rights to a fixed amount of water, with previous users having higher demands.

In the event of shortages, users with older water rights have priority. They receive their allocation first and can demand water from users with newer rights, who then receive smaller amounts or no water at all.

This long-standing system is coming under increasing pressure from climate change. The strain is exacerbated by two factors: first, the river has been overused since the first Colorado River Compact was signed; and second, there is no explicitly agreed-upon cap on water use. In addition, the system lacks a cap that could adjust to changing water availability.

The seven states are currently negotiating how to share shrinking supplies, as some of the basin’s current water-sharing policies expire at the end of 2025.

“Finding a compromise among the seven states will be difficult, but blocking the Free River could be one way Colorado could contribute to the process,” Debaere said.

During the free-flowing river in 2017 – and despite problems with water downstream and falling water levels, for example – water users discharged an estimated 108 million cubic meters more than their water rights allowed them to, the new study says. That’s water that could have been stored in Lake Powell.

Debaere said that while the annual excess water withdrawal from free-flowing rivers is significant but not exorbitant, closing this gap is critical for other reasons.

It would better define water rights and prevent withdrawals beyond the legal limit. This is important for future reforms, such as limiting total water use or introducing field fallow programs. These efforts will not work if unlimited water access is granted occasionally.

By closing this loophole, Colorado could also help alleviate water shortages in the Colorado River basin, especially since the seven riparian states are having difficulty agreeing on reducing their overall water use.

“Removing the free-flow requirement will not only reduce water consumption but also prepare the water rights system for future reforms,” said Debaere.

In addition to Debaere, co-authors of the new document represent the following organizations: International Business School Suzhou, Xi’an Jiaotong-Liverpool University, Suzhou, China; B3 Insight, Denver; Department of Civil and Environmental Engineering, University of Wisconsin-Madison; Department of Civil, Design and Environmental Engineering, University of Alabama; Department of Civil and Environmental Engineering and Department of Systems and Information Engineering, University of Virginia; Sustainable Waters, Crozet, Va.