This interview by Allen Best with scientists Eric Kuhn, Anne Castle and John Fleck appeared on BigPivots.com on September 28, 2025. We are sharing it in three parts.
The significant reductions you’ve seen in the lower basin are clearly not enough. The reservoirs are still dropping. But it shows what is possible.
Castle: The action that I found most surprising and hopeful or constructive was the lower basin’s willingness to own the structural deficit. The lower basin stepped up and said, “we’re not negotiating this. This is what we’re going to do.” I think that was huge and I think it shows that there can be movement that kind of goes against the political expediency.
Kuhn: Another example is that California basically accepted a portion of the shortages. This happened a while ago. This happened back in 2018 or 2019. Under the 1968 law (that authorized the Central Arizona Project), Arizona was to absorb the shortages and not California. They basically realized that that agreement that was made in the ’60s was tying up the lower basin from being able to move forward. California compromised on that, at least for the moment. And I think that this willingness of California to go along with what else has happened in the lower basin shows progress. Where we haven’t made any progress is what I would call the crossing of the Lee Ferry divide. That’s going to take more effort.
Editor’s note: The Colorado River Compact distinguished between the upper basin and the lower basin, creating an artificial dividing line at “Lee Ferry,” a point just below Glen Canyon Dam. George Sibley, a water writer from Gunnison, along with others. have maintained that this artifice creates unnecessary problems. See: “Why not create the Colorado River Compact they wanted in 1922?”
Fleck: We’ve just contradicted ourselves here, or at least I’ve contradicted myself. We talked about the political incentives that make it difficult to accept the reality of what the numbers are showing us, but we have just described a situation where, in fact, the political leadership, especially in Arizona, but also in California, and for a long time in Nevada, has been willing to accept this reality.
Partly, it’s just through a lot of long, hard learning, the realization by these communities that we took these steps to use less water. And we’re still okay, you know, we still have water in the fountain at the Bellagio (hotel in Las Vegas). We still have hundreds of thousands of acre-feet of irrigated ag land in the Imperial Valley. There’s less than there used to be, but there’s still a lot. There’s still a robust agricultural economy there. So, in fact, this runs counter to the notion that political incentives always lead you to ignoring convenient science, because there’s clearly evidence to the contrary.
In your papers, you have consistently said that the water rights of the tribal nations must be honored. Can their claims on the river actually be resolved at this juncture? Or is there an irreconcilable conflict?
Castle: There are several reasons we’ve called attention to the Tribal rights. One is historically, Tribal rights and interests haven’t been front and center. The tribes have historically been left out of these kinds of high-level negotiations. But the fundamental reason, in my mind is the tribal water rights are part of the bargain that our federal government made with individual tribes in exchange for the relinquishment of some of their ancestral lands. They were promised a livable homeland. Part of a livable homeland is the amount of water necessary to fulfill the purposes of that land, and that’s a promise of the federal government.
Many tribes have quantified their water rights, so we know exactly how much that promise meant in terms of the amount of water that goes along with their reservation land. And it’s a different animal than all the other kinds of Western water rights. It’s important that we keep that in mind, that it is a different kind of promise. It’s a different kind of property right. And we can’t solve this supply and demand imbalance on the backs of the tribes.
Fleck: Anne talked about a promise made by the federal government. But that’s us. This is our promise. We are the people of this country, the people of the federal government, right? The federal government is a creature of us. This is our promise to those people. It’s not something that we as individuals in this particular state should get in a fight with the federal government over. We made this promise to those people and that’s important. I describe it as a legal and a moral obligation. Respecting the legal obligation is critical to making the books balance. It’s also this moral obligation.
Eric, I have a question for you. I know you have followed climate science very closely over the years. We’ve talked about it from time to time, the current state of the science. How would you describe that? I mean, there’s a lot of uncertainty. What we really don’t know, we can’t know until it happens. Nonetheless, if you were to summarize, what should that tell us about the Colorado River going forward?
Kuhn: There is a lot of uncertainty, but with time, we’re seeing a narrowing of that uncertainty. We’re in some would say the 25 years of a drought, others would say it started in the late 80s. We’re seeing a very distinct stepwise reduction in flows, natural flows at Lee Ferry, and we’re seeing temperatures increase. We have documented both.
I still think there’s going to be a lot of uncertainty when it comes to what happens in those rare, odd years where we have a real wet winter and you have atmospheric rivers that run into the San Juans or the central Rockies. We could end up with a big year, and that’s all a part of climate science.
But I think the message is pretty clear that it’s unlikely that river flows will return to what we thought there was historically, which was around 14 to 14.5 million acre-feet per year. That’s unlikely. And I know no one in the basin, including the current administration, based on comments from Mr. Cameron (Scott Cameron, acting assistant secretary for water and science, Department of the Interior), who thinks that it’s likely. We’re dealing with the river that we have today, and that means that the uncertainty around the climate science has narrowed, and we sort of understand the future of this river. As long as temperatures keep going up, we’re going to see aridification of the basin.
A final question, if you will abide it, and it’s kind of a big, sweeping question. It strikes me that it’s a really interesting journey that all three of you have been on during this shift in attitudes in the Colorado River Basin. I remember going to the Colorado River Water Users Association conference in Las Vegas maybe 15 years ago, and there were people from Los Angeles or wherever who were kind of dubious. This was drought. This wasn’t climate change. We don’t have to have fundamental change. That (attitude) has clearly dissipated. My question has to do with what has not changed. How have attitudes NOT changed?
Kuhn: People are still going to be very reluctant to give up what they believe was their entitlement. They’ll compromise; they’ll reach agreements. But Colorado, which is among the leaders when it comes to the public’s acknowledgement of the issues related with climate change, has yet to say we’re going to sacrifice any portion of our theoretical entitlement. But we all have to give up some of those theoretical claims. So the culture is still “protect our entitlement,” even though that entitlement was based on data and science that are no longer valid. Just the word entitlement is indicative of the problem.
Castle: A component of that problem is the failure to recognize that while I have a perfectly good legal argument about why I have this entitlement, there are other perfectly good legal arguments about why I don’t, and we haven’t made huge steps toward acknowledging that. There are lots of legal arguments and lots of good ones, but they can’t all carry the day. Like John says, there’s not enough water for all the lawyers to be right.
Allen Best publishes the e-journal Big Pivots, which chronicles the energy transition in Colorado and beyond.