The Colorado River's top climate expert is worried

Politico

11-07-2025

With help from Alex Nieves, Mike Lee, Marc Heller and Miranda Willson
INCONVENIENT SCIENCE: President Donald Trump may be erasing the words 'climate change' from federal websites and moving to shut down climate science programs, but he can't ignore the problems climate change is causing along the Colorado River.
With current rules governing how states split the river's water for farming and drinking set to expire at the end of next year and states at loggerheads over new ones, the West's most important waterway is handing the Trump administration its first climate crisis as its levels have reached critical lows.
No one knows that better than Brad Udall, a senior water and climate research scientist at Colorado State University's Colorado Water Institute. Udall has studied the Colorado River for three decades and made it his mission to explain the science in a way that works for policymakers.
(The name might ring a bell: His father was Mo Udall, the Arizona congressman and Democratic presidential candidate who lost the 1976 primary to Jimmy Carter. His brother is former Colorado Sen. Mark Udall, former New Mexico Sen. Tom Udall is his cousin, and his uncle, Stewart Udall, was John F. Kennedy's Interior secretary.)
'It's hard to describe just how bad this is,' Udall said of the trajectory for the Colorado River, which supplies 40 million people, including nearly half of Californians and the agricultural engine of the Imperial Valley. Already the river has shrunk 20 percent since 2000 as temperatures have risen.
After more than a year of cross-border verbal sparring and threats of litigation, the involved states, which include California, Colorado, Arizona and others, are now contemplating a new approach that would tie water deliveries to the amount of water actually flowing down the river. It's a framework that could be more adaptable to climate change, but negotiators have yet to resolve the biggest sticking points, including just how deeply the states will agree to cut their usage.
Udall spoke with POLITICO about how bad things could get along the Colorado River, whether the states and federal government are preparing for worst-case possibilities, and what Trump's assault on scientific work means for efforts to keep the taps running.
This interview has been edited for length and clarity.
Just how dire is the climate situation along the Colorado River?
I use the term, 'beyond awful.' This year we had pretty good snowpack, almost 95 percent of normal snowpack, and we're going to get 45 percent of normal runoff out of that snowpack, which is stunning.
With respect to temperature, we know if it warms, all forms of evaporation increase, and we put that decrease at about 10 percent of the flow for every degree Celsius that warms.
It's far more challenging to figure out what's going on with precipitation. What's been disturbing in the basin is we have seen modest precipitation declines, especially in summertime, that seemed to translate into large reductions in flow the following year because of reduced soil moisture that serves as a buffer from one year to the next. Basically, if it's dry in the summer, the soils dry out and the next spring, when the snow pack goes to melt, instead of that water flowing over land into rivers and creeks, as it did historically, it now goes to recharging the decimated soil moisture from the previous year.
So what does this all mean for overall flows?
We have seen a 20 percent reduction in flows over the first 26 years of this century, and at least half of that — and potentially the whole amount — is due to human-caused climate change.
If you want to be really pessimistic, we could double that. We could see a 40 percent reduction in flow by 2050, which is about a 10 million acre-foot per year average [as compared with the 16.5 million acre-feet that were promised to states and Mexico under current compacts and treaties.]
So put that in the context of the negotiations right now. Are the states and the federal government contemplating the full range of climate scenarios that you think the science demands?
The two initial proposals — one out of the Upper Basin [states of Colorado, Utah, Wyoming and New Mexico] and one out of the Lower Basin [states of California, Arizona and Nevada] — contemplated up to 4 million acre-feet of reductions. And that's close. But it's such a closed process, so nobody knows what exactly is going on.
There's been a long history of states doing deals and then having to come back every few years for another round of negotiations when there's another crisis. How do you think the Trump administration's stance on climate change will affect how states craft rules that would hold up in doomsday scenarios?
Back during work on the 2007 agreement [for the current rules governing the Colorado River], Reclamation pulled together six different climate scientists to put together an appendix to the environmental impact statement which talked about the climate challenges in the basin. To my knowledge that was the first time a major EIS incorporated climate science, and that was under a Republican — the Bush administration.
There are really conservative states in the basin, both Wyoming and Utah. Even though people maybe can't mention the climate change word, they see what's going on here. It's impossible to deny what's happened in this space — it's happening in front of our eyes. So maybe that constrains future reductions that I'd like to see people plan for. But there's no pretending that we're going back, that we're going to see 15 million acre-feet.
What else should be on people's radar right now?
I worry about the administration's complete anti-science bent. Cuts to NOAA, cuts to the USGS, cuts to Reclamation on, frankly, very important science that is our eyeglasses to the future. — AS
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BUCKLE UP: Get ready for a jam-packed week of energy policy debate in the Capitol, including the first hearing for a sweeping bill to overhaul gas regulations.
Lawmakers will hear SB 237, a proposal backed by Senate Pro Tem Mike McGuire, for the first time on Wednesday in the Assembly Utilities and Energy Committee.
That bill lost its most controversial provision — a proposed cap on low-carbon fuel standard credits — last night after Senate Democrats nixed the concept in the face of opposition from state officials, fuel producers and environmental groups. But it could still make major changes, like transitioning California away from its unique, lower-emission gasoline blend to a West-wide standard in an effort to stop supply shortages.
Both chambers will also hear their representative cap-and-trade reauthorization proposals in the Assembly Natural Resources and Senate Environmental Quality committees. Negotiations over the future of the program remain a work in progress, but the hearings should offer an opportunity for both sides to lay out their top priorities.
Also on the schedule: Assemblymember Cottie Petrie-Norris and Sen. Josh Becker, chairs of each chamber's energy and utility committee, will hear each other's energy affordability bills. And Becker's SB 540, a bid to move California towards a Western regional energy market, is also up in Assembly Utilities and Energy. — AN
DON'T HOLD YOUR BREATH: California shouldn't count on the Trump administration to help fight wildfires this year.
Forest Service Chief Tom Schultz told lawmakers during a congressional committee hearing Thursday that he doesn't know how much, if any, financial assistance the agency can provide communities to defend against wildfires for the remainder of the year, Marc Heller reports for POLITICO's E&E News.
Schultz defended the administration's current and proposed cuts to programs that assist local fire departments, saying that they haven't told these departments that they wouldn't receive support. 'We're saying we're still in discussions on that,' he told lawmakers.
Schultz said the Forest Service announcements about what local grants will be dispersed are coming 'probably within the next couple of weeks,' ahead of an Aug. 15 deadline. That response drew a rebuke from California Sen. Alex Padilla, who said it should be a 'big red flag for all of us.'
'We're a month out, and you're still finalizing the numbers?' he said. — AN
CLEAN IT UP: Congressional Democrats are putting more pressure on the EPA to clean up sewage flowing through the Tijuana River into San Diego.
Padilla, California Sen. Adam Schiff and New Jersey Sen. Cory Booker introduced a bill Thursday directing EPA to develop a new water management program for the San Diego-Mexico border. That would be similar to existing programs for the Chesapeake Bay, Great Lakes and other aquatic ecosystems to encourage restoration and local partnerships, Miranda Willson reports for POLITICO's E&E News.
Billions of gallons of raw sewage have flown through the Tijuana River Valley and into the ocean in recent years, while the slow pace of major infrastructure upgrades at the South Bay International Wastewater Treatment Plant — funded through the 2018 U.S.-Mexico trade agreement — has sparked bipartisan frustration.
EPA Administrator Lee Zeldin visited San Diego in April to negotiate with Mexican officials over steps for repairing and upgrading the international sewage treatment plant.
HEATING UP: California's budget crunch is cutting into the state's plan to reduce heat deaths in its prison system.
The state budget passed last month included a $6 million cut to an 'air cooling pilot program' the Department of Corrections and Rehabilitation plans to launch, a fourth of the $23.6 million the agency has requested in the wake of a death at a state women's prison, Mike Lee reports for POLITICO's E&E News.
California has the second-largest state prison system in the country, with about 94,000 people behind bars. About a fourth of its beds lack air conditioning, according to CDCR.
The cut comes as states around the country are scrambling to adapt as climate change warms the planet. In Texas, which has the country's largest prison population, a federal judge has called the conditions 'plainly unconstitutional.' Inmates in Florida have sued over hot conditions. — AN
— Cal Fire's new AI chatbot can't accurately describe wildfire containment or reliably provide information like evacuation supplies and evacuation orders.
— Tesla hasn't applied for permits to operate robotaxis in California, despite Elon Musk's claim that the company will expand to the Bay Area in two months.
— California isn't going to get a break from a brutal heatwave blanketing the West going into the weekend.