Reflecting on the Summer, and What's Ahead for Spring 2026?

[Ryan]

There's also a less than 10% chance that I'll ever eat a doughnut for breakfast without regretting it.

1 = 0%
2 = 10%
3 or more = 50%

 

[Colorado Expat]

One of the narratives (which probably proves to have some truth to it) is that there have been factors other than the snowpack that are now different than in the past affecting the runoff. Said factors were always present in reality (e.g. how dry the soil and vegetation are, how much dry wind blows in the winter, how much dust ends up on the snowpack) but in the past some were only indirectly included in the modeling. That is to say some specific factors just ended up encoded in a mapping from X snowpack leads to Y runoff without the model actually using a measurement of that factor as an input. As long as those factors didn't vary too much, and didn't vary well outside historical climatology, then all is good and your model perhaps has a bit more variance than it would if you had included those factors directly, but won't necessarily have a bias.

Now if one of those factors starts deviating significantly from history (e.g. snowpack often gets lots more dust than in the past) now you are in trouble.

It would seem that the major variable that the runoff prediction models have not been incorporating accurately is the steady increase in air temperature over the past 30 years, and the associated changes in vapor pressure deficit, evapotranspiration, and soil moisture deficit. In the historical record on which the models are based we have had wide fluctuations in the amount and timing of precipitation and thus snow pack, and this was factored in. But air temperature has showed a marked and historically non-analog deviation upward starting in the early 1990s, and has never reverted to anything close to the previous pre-1990s mean. As such, we now need more and more snow each winter to generate what we would have been considered a normal runoff year just three decades ago.

Within the context of these climate dynamics, what is also starting to become clear is what a thin reserve of water the BOR now has to operate with in Lake Powell and Lake Mead over the remainder of this water year and into the next. At the moment there is about 6.8 maf of storage in Lake Powell, but only 2.4 maf is above the 3500 foot level at which BOR prefers to retain the reservoir in order to preserve hydropower capacity and prevent undue use of the questionably durable river outlet works. Similarly, although there is about 8.2 maf in Lake Mead, only 3.6 maf lie above the 1000 foot elevation that BOR has indicated is its minimum acceptable lake level, after which significant water delivery reductions would be implemented. So although the combined current storage of the two reservoirs is 15 maf, in fact only 6.0 maf of this is realistically available, and if the Compact guidelines for Lower Basin deliveries are followed, about half this could be utilized in excess of inflows by mid-2026. The other 9.0 maf remaining in the system is just stuck behind the dams, given that neither has any river level outlet works. This is a very narrow cushion on which to operate, but there are not any easy solutions. And it is not a good situation to be in when projected future climatology indicates that there is likely to be progressively less runoff available with each passing year. At this point we are basically at the mercy of the weather, and the coming winter will be a very critical one for the Colorado River basin.