The health of our waters is the principal measure of how we live on the land — Luna Leopold
What might planning for an 11 million acre foot or 10 million acre foot #ColoradoRiver look like? — @jfleck #COriver #aridification
Brad Udall: Here’s the latest version of my 4-Panel plot thru Water Year (Oct-Sep) of 2021 of the Colorado River big reservoirs, natural flows, precipitation, and temperature. Data (PRISM) goes back or 1906 (or 1935 for reservoirs.) This updates previous work with @GreatLakesPeck.
One of the central questions dimly visible in the early discussions around the upcoming renegotiation of the Colorado River’s water operations and allocations rules is the question of how bad a “worst case” scenario should be considered.
This is crucial, because it constrains what sort of questions must then be confronted. The lower the future flows considered, the more likely it is that the negotiators will have to stare down the third rail question of how much water the Upper Basin can delivery hydrologically, and must deliver legally, at Lee Ferry, the dividing point between the Upper and Lower Basins.
For the century since the Colorado River Compact was signed, we’ve avoided dealing with that central question – what happens if the river’s flows are so low that the Upper Basin cannot deliver the 7.5 million acre feet per year (or 8.25 million acre feet, we can’t even agree about which number to argue about) contemplated by the compact’s Article III.
This question is so untouchable that in work done for the 2012 Basin Study, the Bureau of Reclamation’s modelers famously added what came to be called “miracle water” at Lee Ferry every time one of their model runs dropped below the threshold that might have otherwise triggered this legal argument.
Under the low flows possible under climate change, we face a stark choice – either we reduce the Upper Basin’s Lee Ferry deliveries below 7.5/8.25 maf, or we will have to curtail existing Upper Basin uses. Advocates of modeling such low flows in the planning scenarios are essentially saying – Let’s have that conversation now.
At the tale end of yesterday’s (Friday 10/15/2021) House Natural Resources Sucommittee on Water, Oceans, and Wildlife, it was California Rep. Jim Costa, a congressman from outside the Colorado River Basin, who asked the question pointed at the heart of the matter – how do we redo water allocations that make no sense in a river much smaller than contemplated in our hallowed Law of the River?
“The Law of the River and the quantification of the Upper and Lower Basin states amounted to some 17 million acre feet of water that was determined at that time was the annual flow of the Colorado River, and we know that in the last two decades its been more like 12.4 million acre feet, and that doesn’t account for other Native American tribes that have reserved water right claims that have yet to be resolved. So there’s just a tremendous amount of demand. And with climate change, we know the yield is only going to decline.
“This is the question I’d like to submit to all of you, and if you want to provide written statement to your answer I think we would appreciate that.
“Let’s say the annual yield over the next 30 years is 10 million acre feet. I don’t know, with climate change, maybe it’s plus or minus. How do we take into account how we got to the original allocation, with the Upper and Lower Basin States and the Native tribes, the sovereign nations, and then reallocate that on a lot less water.”
At this point all we can see through the public windows into discussions about next-step Colorado River management guidelines is shadow boxing on this question.
But testimony yesterday from Southern Nevada’s John Entsminger suggests the public shadowboxing we’re seeing on this question is representative of disagreements in the private discussions. (I quote here from John’s written testimony.)
Climate change is causing the Southwest to aridify. (Left) Since the 1930s, increasing temperatures have caused the percentage of precipitation going to evapotranspiration (ET) to increase at the expense of precipitation going to Colorado River flow, resulting in an unprecedented and still ongoing megadrought (shading) starting in 1999 (8). (Right) Higher temperatures have already reduced Colorado River flow by 13%, and projected additional warming, assuming continued high emissions of greenhouse gases, will increase ET while reducing river flow even more through the 21st century. Data on Left are 20-y running means from ref. 5, and data on Right are calculated from Representative Concentration Pathways (RCP) 8.5 multimodel Coupled Model Intercomparison Project–Phase 5 (CMIP5) ensemble temperature increases projected for the Upper Colorado River Basin combined with temperature sensitivity of −9.3%/°C estimated by ref. 5, assuming no change in precipitation.
“Despite the fervent warnings from internationally renowned scientists like Jonathan Overpeck and Brad Udall that urge us to plan for a future with even less than 12.3 million acre-feet, the river community is far from consensus about how dry of a future to plan for. And, while this panel was asked to talk about drought, on-the-ground evidence suggests the Colorado River basin is not experiencing drought but aridification – a permanent transition to a drier future. If we are to build upon the river’s many successes over the last 25 years, we must confront the magnitude of the challenge in front of us and quickly reach agreement on what future scenario we’re willing to plan for. (emphasis added)”
Speaking two weeks ago at this year’s Getches-Wilkinson Center conference in Boulder, Entsminger put a number to Southern Nevada’s thinking. In the next iteration of its long range water resources plan, Entsminger’s Southern Nevada Water Authority will include a “what if” planning scenario for how the agency would deal with an 11 million acre foot per year Colorado River. This is not to say that Southern Nevada expects an 11 million acre foot river, but rather than it believes it needs to have a plan in place should that happen.
I could be wrong, but so far I’ve seen no public evidence that any of the states of the Upper Basin are willing to entertain flows that low in the planning scenarios to be considered in the modeling done to support the upcoming negotiations. I look forward to seeing the written answers the basin states’ representatives submit to Costa’s question.
