A boat navigates the Colorado River near Horseshoe Bend on April 18, 2023, in Page, Ariz. (LE Baskow/Las Vegas Review-Journal) @Left_Eye_Images} The Colorado River meanders in the Glen Canyon National Recreation Area near the bridge Hite Crossing on April 22, 2023, in Hite, Utah. (LE Baskow/Las Vegas Review-Journal) @Left_Eye_Images Rowers make their way down the Colorado River north of Moab, Utah, on April 19, 2023. (LE Baskow/Las Vegas Review-Journal) @Left_Eye_Images The Colorado River rises from Lake Powell to Glen Canyon Dam on April 18, 2023, in Page, Arizona. (LE Baskow/Las Vegas Review-Journal) @Left_Eye_Images Late-day sun illuminates a campground and the Eagle River, which feeds into the nearby Colorado River, on April 19, 2023, in Gypsum, Colo. (LE Baskow/Las Vegas Review-Journal) @Left_Eye_Images Visitors look down on dwindling Lake Powell, fed by the Colorado River, on April 18, 2023, in Page, Ariz. (LE Baskow/Las Vegas Review-Journal) @Left_Eye_Images Water flows from the Roller Dam along the Colorado River on April 21, 2023, in Palisade, Colo. (LE Baskow/Las Vegas Review-Journal) @Left_Eye_Images
Rising temperatures due to climate change have depleted more than 10 trillion gallons of water from the Colorado River in the past two decades, enough water to completely fill Lake Mead from top to bottom, according to a new study by UCLA researchers. .
Both scientists and water managers have long pointed to climate change as one of the main causes of the decline in the flow of the Colorado River. But the new study, published in the journal Water Resources Research, gives us a clearer picture of the extent to which human-induced climate change has depleted the flow of the river that supplies water to some 40 million Americans in the Southwest. country.
“The fact that warming has removed as much water from the basin as the size of Lake Mead itself during the recent megadrought is a wake-up call about the climate change impacts we are currently experiencing,” he said in a press release. Benjamin Bass, a UCLA hydrologic modeler and lead author of the study.
If it weren’t for climate change, scientists say, the reservoir would most likely not have dropped to the levels that triggered the first-ever federal water shortage in 2021.
The models the scientists used showed that the Colorado River basin has warmed by about 2.7 degrees from 1880 to 2021, and that the warming trend has accelerated since the 1980s.
That warming trend has caused a 10.3 percent reduction in the flow of the Colorado River since 2000, and the researchers say it will only get worse if temperatures continue to rise in the future. The researchers calculate that every 1.8 degree Fahrenheit increase in temperatures can cause a 6.8 percent decrease in flows in the Colorado.
“Going forward, we may have some natural variability, wet or dry oscillations, but this study highlights that there has been a downward trend in runoff. In the long term, it is likely to continue if greenhouse gas emissions are not reduced,” Bass said.
Complementary research
The UCLA study builds on previous research showing similar losses in the river system due to climate change, by including the effects of carbon dioxide on vegetation.
The researchers used land surface models capable of analyzing how rising levels of carbon dioxide in the atmosphere influence the amount of water that plants and other vegetation take in and release as water vapours.
The harsh winter has given a boost to the river system, and the current level of Lake Mead is more than 20 feet higher than it was in early August of last year. But even a good winter season isn’t enough to make up for more than two decades of drought on an already overburdened river, and Lake Mead was only at 32 percent capacity Monday.
The seven states that depend on the Colorado River have agreed to a series of proposals to reduce water use along the river in Nevada, Arizona and California over the next three years.
Meanwhile, the federal government began the process this summer to rewrite long-term plans to govern the river after the current guidelines expire in 2026.
Sarah Porter, director of the Kyl Center for Water Policy at Arizona State University, said the study provides another way to look at the well-known problem of the Colorado River having less water, which will be useful as those negotiations progress. after 2026.
“Another way to measure the impact of climate change is to analyze the actual flows of the river. And the conclusions of that study are pretty much in line with what the basin has experienced,” Porter said.
Match demand to supply
The original 1922 compact that has governed allotments along the river assumed flows of about 15 million acre-feet per year. Since the current drought began around 2000, flows have averaged close to 12.5 million acre-feet, but withdrawals from the river have remained relatively the same, compounding the problem over the years. the basin and has driven its Lake Mead and Lake Powell reservoirs to record lows last year.
But states must be prepared for things to get worse, said Eric Kuhn, a retired former CEO of the Colorado River Water Conservancy District.
“This study adds to the body of evidence that shows the need to be fully prepared for less water than we have allocated,” Kuhn said.
Another study published in June, co-authored by Kuhn, showed that states would have to reduce their collective use by 1.5 million acre-feet a year just to keep the system from collapsing further. To refill the reservoirs, states would have to cut up to 2.5 million acre-feet a year, or nearly the amount of water Arizona is entitled to receive from the river.
According to Kuhn, basically all basin states recognize the need to cut back at least 1.5 million acre-feet of collective use each year. But deciding which states to cut, and by how much, remains the main hurdle.
“I’m optimistic for the long term, but I don’t know how many lawsuits or crises there will be before that solution is reached,” Kuhn said.
2023-08-03 19:36:12
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