Click here to read this story in University of Arizona News by Mari N. Jensen
Click here to read this blog post by John Fleck
This post is about the release of a hydrology paper authored by Brad Udall and Jonathan Overpeck.
ABSTRACT: Between 2000 and 2014, annual Colorado River flows averaged 19% below the 1906-1999 average, the worst 15-year drought on record. At least one-sixth to one-half (average at one-third) of this loss is due to unprecedented temperatures (0.9°C above the 1906-99 average), confirming model-based analysis that continued warming will likely further reduce flows. Whereas it is virtually certain that warming will continue with additional emissions of greenhouse gases to the atmosphere, there has been no observed trend towards greater precipitation in the Colorado Basin, nor are climate models in agreement that there should be a trend.
Moreover, there is a significant risk of decadal and multidecadal drought in the coming century, indicating that any increase in mean precipitation will likely be offset during periods of prolonged drought. Recently published estimates of Colorado River flow sensitivity to temperature combined with a large number of recent climate model-based temperature projections indicate that continued business-as-usual warming will drive temperature-induced declines in river flow, conservatively -20% by mid-century and -35% by end–century, with support for losses exceeding -30% at mid-century and -55% at end-century.
Precipitation increases may moderate these declines somewhat, but to date no such increases are evident and there is no model agreement on future precipitation changes. These results, combined with the increasing likelihood of prolonged drought in the river basin, suggest that future climate change impacts on the Colorado River flows will be much more serious than currently assumed, especially if substantial reductions in greenhouse gas emissions do not occur.
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Colorado River losing essential water flow, new research shows
March 21, 2017 By Ty Betts
An increase in temperatures has the ability to reduce the flow of water in the Colorado River by 20 to 30 percent by mid-century, according to new research done by Colorado State University and the University of Arizona.
The research done by Bradley Udall, a senior water and climate scientist for CSU, and UA professor Jonathan Overpeck, found that loss of water is driven by higher temperatures arising from an increase in greenhouse gas emissions.
There are a number of reasons that increased temperatures are leading to less water in rivers, Udall said. The first is that there is now a longer growing season for plants to utilize water. The second is that plants demand more water with increased temperatures. Third, more evaporation is taking place on soil, reservoirs and rivers. Lastly, the atmosphere retains more moisture with higher temperatures.
The water in the Colorado River is relied upon by 40 million people, according to the Bureau of Reclamation. The Colorado River provides water to seven U.S. states and makes up half of the water consumption along Colorado’s Front Range, Udall said.
An assessment by the Bureau of Reclamation found that the Colorado River will face little to no change in levels because they anticipate an increase in precipitation to offset higher temperatures. Udall disagrees.
He said that the issue with their model is that they are combining a multitude of factors that are not necessarily certain. The bureau’s calculations combine warm and hot projected climates with precipitation decreases and increases as well as varied emission scenarios.
“When you come up with one number and you blend certain and uncertain outcomes, you can get a rosier picture than we think is warranted,” Udall said.
Udall and Overpeck’s research instead isolated these variables and achieved their estimates with confidence that temperature is increasing.
Udall said with changes in water levels expected, regulations will have to be adapted. The 1922 Colorado River Compact currently regulates the amounts of water that Colorado has rights to. Udall believes that with a 20 percent reduction in flow, it would be difficult for Colorado to meet the output requirements set in place by the act.
The seven states that make up the Colorado River basin – Arizona, California, Colorado, New Mexico, Nevada, Utah and Wyoming have to work together to negotiate new water agreements. Udall said that while negotiations usually take a lot of time, these states are good at coming to agreements.
“I would argue that this basin, perhaps compared to any other basin in the world, has a good track record of settling water disputes,” Udall said.
Other considerations Udall mentioned are that less water flow equates to less hydroelectric power. Hydroelectric power does not make up a large portion of total energy generation in the southwest, but is it essential to irrigation. Udall said farmers get inexpensive energy rates while using hydro-power generated from the Colorado River.
“Agriculture often runs on very small margins and increases in energy rates can cripple profits,” Udall said.
Udall said he believes new sources of water will not come easily or be feasible. California’s desalination work, or the process of extracting minerals from water, is too expensive for agricultural purposes. Furthermore, importing water into the Colorado River from other parts of the country is halted by high costs political push-back.
Udall and Overpeck’s research points to one solution to the problem: the reduction of greenhouse gasses.
“The water cycle is driven by heat,” Udall said. “When you add extra heat to the Earth as we are now doing because of greenhouse gas emissions, you change the water cycle in fundamental ways.”
