Climate change and Boulder’s shrinking water supply

I’m not a professional water supply engineer. But I’ve learned enough over my decades of involvement in our city government to be very concerned about our future ability to keep providing adequate water for existing residents and businesses, much less the significant amounts of additional development being approved.

Boulder’s water comes from three sources:

The city-owned watershed is on the east side of the Continental Divide, from South Arapahoe Peak to Niwot Ridge. It feeds many small reservoirs, and then comes via pipeline from above the Peak-to-Peak Highway to the Betasso treatment plant on Sugarloaf Road.

We also own water coming down Middle Boulder Creek, stored in Barker Reservoir near Nederland, and delivered via the Boulder Canyon gravity pipeline past the Boulder Canyon hydroelectric plant to Betasso.

About a third comes from our shares of the Colorado-big Thompson Project (managed by the Northern Colorado Water Conservancy District), piped from the Colorado River through the Continental Divide, down to Carter Lake near Loveland, and then to Boulder Reservoir, where it is treated.

According to city staff, we use more Colorado River water in dry years than wet.

A few data points I’ve seen regarding climate change: We are in a 1,200year drought. Over half the contiguous U.S. was in drought at the beginning of May, per government climate officials. This year’s Colorado snowpack is way below average; some reports have it at twothirds of historic norms. Reservoirs upstream on the Colorado River are being drained to keep enough water in Lake Powell and Lake Mead to run the hydro generators. The final NOAA forecast for the season predicts the amount of water to reach Lake Powell this year at about 60% of average.

Our warmer and drier climate affects not just the amount of water, but the timing of its arrival at Boulder’s reservoirs.

Early runoff means water is not stored in the snowpack as long, so our reservoirs must absorb water earlier and so hold it lon

We are in a 1,200year drought. Over half the contiguous U.S. was in drought at the beginning of May, per government climate officials. This year’s Colorado snowpack is way below average; some reports have it at two-thirds of historic norms.

ger, creating concerns about capacity as well as issues with exchanges we do with other water rights holders.

And of course, with less water overall, our ability to manage it becomes even more difficult.

A potentially bigger concern is our Colorado River water. The legal structure for owning this water is based on the 1922 Colorado River Compact. This agreement, formulated during a period of above-average flows, gives the Lower Basin states (California, Arizona and Nevada) first rights on 7.5 million acre feet per year (maf/yr) on a 10-year running average.

The Upper Basin states (Colorado, Wyoming, Utah and New Mexico) get whatever remains, except for a share owed to Mexico (initially 1.5 maf/yr, but reduced now to something less, per my understanding.) An acre-foot of water covers one acre with water one foot deep.

This may seem like a bad deal for the Upper Basin, and it is. But as Patricia Rettig noted in her excellent May 5 Camera commentary, some say that “renegotiation is politically impossible.” Data on the usage by the Upper Basin states is hard to get, but one paper I read has that total at slightly below 5 maf/yr in 2020.

The problem is that the guaranteed 7.5 maf/yr for the Lower Basin plus Mexico’s share plus current Upper Basin consumption is more water than the Colorado River has.

That means the Upper Basin must cut its usage, plain and simple. Per a

1948 agreement, Colorado gets 51.75% of the Upper Basin’s share.

Things gets worse for Boulder because of “precompact rights.” These are water rights that preexisted the Colorado River Compact. Another paper I read indicated that users in the Upper Basin states own at least 2.2 maf/yr of these rights; Colorado users own about half of that.

Plus, there are conditional rights that predate the compact, but were not being used when the compact was created. And then there are claims by Indigenous people for additional rights, reducing available yield even more.

So more than half of what, in theory, is left for the Upper Basin states’ water users could go to these precompact water rights.

So, there won’t be much left for our shares of Northern District water (which serves multiple municipal and agricultural users, and is already down to about 70% of original yield), because the district was created in 1937, well after the compact. Thus, it’s “junior” to all these other entities.

So, when all this hits the proverbial fan, the only question is — what’s left, if any, and who gets cut off?