The Colorado River System is At Risk From Climate Change
The Colorado River basin, which drains just under 250,000 square miles of land in the Western United States, is the tenth largest river system in North America as ranked by drainage area, which is less than one-seventh the size of the massive Mississippi River basin, which dominates the eastern two-thirds of the United States. Nonetheless, the Colorado River, which originates in the La Poudre Pass Lake at an elevation of more than 10,000 feet in the Rocky Mountain National Park, and drains into the Pacific Ocean through the Gulf of California, is very economically important because it is the major surface water source for agricultural, industrial, and municipal use across the region. The Colorado River and its major tributaries provide water to portions of seven states (Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming, as well as to the northwestern Mexican states of Sonora and Chihuahua), along its 1,450 mile length.
It is estimated that between 70 and 80 percent of the Colorado River’s water is used to serve the western agricultural sector, both for irrigated cropland and large livestock feeding facilities. Water from the river irrigates about 5.7 million acres of cropland and pastureland, both within the basin and areas just outside it, such as in California’s Imperial Valley at the southern end of the state. Much of this irrigated land is used to raise alfalfa, hay, and other forage crops intended for cattle feeding, not row crops. Additional water is consumed directly by livestock, as both beef and dairy cattle drink an estimated 30 gallons of water per day per animal.
Outside of the agricultural sector, water from the Colorado River system also provides drinking water to an estimated 40 million people living both within and just outside the basin, such as in Denver, CO. Hydroelectric dams throughout the system generate an estimated 4,200 megawatts of power, and the system supports an economy with 16 million jobs. All of these activities are at risk due to the worst drought seen in the region in the last 1,200 years, driven largely by a lack of winter precipitation in the Rocky Mountains and thus a reduction of snowmelt water driven by climate change.
Starting in 1922, allocation of water from the Colorado River system was governed by the Colorado River Compact, which guaranteed every state within the basin a certain amount of water. A 1944 agreement with the government of Mexico allocated an additional 1.5 million acre-feet of Colorado River water per year to our southern neighbor. However, that compact envisioned sharing average natural water flow of 15 million acre-feet per year within the Colorado River system at that time, while today, due to drought and reduced snowmelt, that natural flow is now estimated to be about 12.5 million acre-feet per year.
In March 2019, the seven states formally agreed to a set of plans to manage the flow of water in the Colorado River system to minimize the impact of the ongoing drought and reduced flow. The plans put forward by the lower basin states of Arizona, California and Utah were quite detailed, while the other four upper basin states provided only an outline of what steps they would take. They reached that deal under pressure from the U.S. Bureau of Reclamation (an agency in the Department of the Interior), which threatened to take over allocation of Colorado River water if the states failed to reach an agreement.
In recent years, some municipal areas in the West have been able to reduce their water use through conservation efforts, and in some states have purchased water rights from farmers who agree to give up their water and idle some of their cropland in exchange for large payments. For example, in 2003, the San Diego County Water Authority in California purchased rights to 200,000 acre-feet of water from farmers in Imperial County with an annual payment of about $94 million. In Arizona, about 93 percent of the water that enters the Greater Phoenix waste stream can be reclaimed and treated for potable use in the city’s modern water treatment facilities.
As part of the Colorado River system, the federal government has constructed massive reservoirs/dams over the decades to store water in to help maintain a stable flow year-round. At a maximum, the system has the capacity to store about 34 million acre-feet of water, or roughly twice the annual flow. However, the multi-year drought has reduced the total amount of water stored in the system to historic lows, especially in Lake Mead and Lake Powell, which are the main storage facilities in the lower Colorado River Basin. At this time in the early fall of 2022, both reservoirs have receded to levels which are close to requiring shutdown of the hydroelectric power generation capacity. As of late July, Lake Mead was only at 27 percent of full capacity, and Lake Powell was at 26 percent as of late August.
At the beginning of this summer, the Bureau of Reclamation urged the seven states to reach an agreement to make additional reductions in water usage of between two to four million acre-feet to address this problem. When that interstate process failed to reach a solution, the Bureau announced on August 16th that it was imposing cuts under its own authority. Due to the decline in water stored in the Lake Mead reservoir, the Bureau’s Commissioner Camille Touton has declared a Tier 2 shortage there, thus prompting an announcement that water allocations from the Colorado River system would be reduced by 21 percent in Arizona, 8 percent in New Mexico, and 7 percent for Mexico.
More information about some of the steps that Arizona and New Mexico farmers might have to take to respond to the water allocation cuts can be found in a blog I co-wrote in July 2021 with Skip Hyberg.
