The Colorado River, seen here at Horseshoe Bend in northern Arizona, supplies drinking water to 40 million people and irrigates 5 million acres of farmland across the southwestern United States, 30 tribal nations, and parts of Mexico. Credit: Pexels via Pixabay
When the seven states of the Colorado River Basin first divided water rights in the 1920s, they handed out more than the river could reliably deliver, especially during periods of drought. Today, the basin supplies drinking water to 40 million people and irrigates 5 million acres of farmland across the southwestern United States, 30 tribal nations, and parts of Mexico.
Climate change has exacerbated shortages, with studies indicating that recent Colorado River flows are near their lowest in at least 2,000 years. That has had severe consequences for fish: Of the 49 fish species native to the Colorado River Basin, 44 are already threatened, endangered or extinct.
Standing agreements governing Colorado River management among states and between the U.S. and Mexico are set to expire after 2026. New research led by University of Washington water policy expert Philip Womble found that a market-based approach to managing water could provide more reliable supplies for farmers, communities and industry. The right market design and a little extra investment could also help threatened fish species.
Philip Womble, assistant professor in the Evans School of Public Policy & Governance
The study, published June 20 in Nature Sustainability, details a new system for leasing rights to water from the basin while reallocating some water to imperiled habitats. Among the paper's most substantial findings, researchers estimate that strategically spending 8% more than under the cheapest water conservation program could nearly triple the ecological benefits.
"There's already a lot of money spent on water conservation agreements. Spending a little bit more money, especially in headwaters, could have outsized ecological impact," said Womble, who started this research as a graduate student and postdoctoral fellow at Stanford University and is now a UW assistant professor in the Evans School of Public Policy & Governance.
Rights to the river's water have been divided by a complex and contentious set of agreements. Under the 1922 Colorado River Compact, states in the river's Upper Basin (Colorado, New Mexico, Utah and Wyoming) agreed that they would not cause the river's flow towards the Lower Basin (Arizona, California and Nevada) - just below the nation's second-largest reservoir, Lake Powell - to be depleted below a 10-year rolling average of 7.5 million acre-feet per year.
As the climate crisis intensifies and a historic megadrought has lowered the amount of water in the river, a legal debate has erupted over how much water the Upper Basin states can use and how much they must leave to the Lower Basin states. The possibility of litigation before the U.S. Supreme Court looms.
In an effort to avoid the risk of sudden cutbacks, water users in the Lower Basin states have created systems for voluntary water market transactions. Some Upper Basin states, meanwhile, have explored a water market designed to reduce water consumption and keep water flowing to Lake Powell. But existing programs generally do not prioritize water for critical fish habitats.
To quantify the cost of strategically improving fish habitat, researchers developed a model to simulate transactions and ecological impacts in Colorado's headwaters, which contribute nearly a quarter of the river's natural average annual flow into Lake Powell.
In the proposed market model, water sellers - including farmers, irrigation organizations, and cities - would lease senior water rights to governments and non-governmental environmental organizations to protect threatened fish habitat. Those senior water rights are critical for environmental protection because they are fully allocated before newer, junior water rights receive any water.
"One key characteristic of water law across the western U.S. is our 'use it or lose it' principle," Womble said. "That can be a disincentive to water conservation."
The team evaluated six scenarios to understand potential outcomes in a future drought year. They compared a "protected" market - where newer water users are legally barred from diverting restored flows - to an unprotected market with no legal flow protections.
Simulations showed that without reductions in water consumption, fish populations could face dire conditions for at least one month of the irrigation season along nearly the full length of the river. In contrast strategic transactions that reduce water use would benefit more than 380 miles of restorable river reaches. This includes hundreds of the most ecologically significant miles, which could see at least partial restoration of fish habitats.
"Instead of only reducing water consumption, strategic environmental water transactions would simultaneously reduce water consumption and preserve fish habitat at the lowest cost to the buyer," the authors write.
Additional modeling results suggest that moderate cuts to water use could be achieved with $29 million spent in a protected market. Aggressive reductions might cost approximately $120 million. Comparable reductions would cost about 12% more in an unprotected market.
The model indicates the most stringent market design - with aggressive water-use reductions and legal protections for conserved water - is 29% more cost effective than a less formal option.
"By strategically directing river water to the right places, even under drought conditions, fish can be saved with targeted restoration at nominal additional cost," said Steven Gorelick, a Stanford professor of Earth system science who is a senior author on the study.
Other authors include Barton "Buzz" Thompson, a Stanford professor of natural resources law and of environmental social sciences, and J. Sebastian Hernandez-Suarez, who participated as a postdoctoral scholar at Stanford.
Gorelick and Thompson are also senior fellows in the Stanford Woods Institute for the Environment. Gorelick directs the Global Freshwater Initiative and Thompson is faculty director of the Water in the West program.
This research was funded by the Stanford Woods Institute for the Environment, Walton Family Foundation, the Stanford Doerr School of Sustainability's Emmett Interdisciplinary Program in Environment and Resources (E-IPER), a Stanford Interdisciplinary Graduate Fellowship, Ishiyama Family Foundation, Babbitt Center for Land and Water Policy, Robert and Patricia Switzer Foundation, a Landreth Family Grant, and a McGee/Levorsen grant from the Stanford School of Earth, Energy & Environmental Sciences.
Adapted from a press release by Stanford University.
