High and dry
New state climate report projects continued warming, declining streamflows

High and dry

The Crystal River in Carbondale, with a smoky view of Mount Sopris in the distance. According to the new Climate Change in Colorado Assessment report, Colorado will see an annual reduction of 5-30% in streamflow volume by 2050./Courtesy photo

Heather Sackett / Aspen Journalism - 01/11/2024

A new report by the Climate Change Center at Colorado State University predicts what many in Colorado, and around the globe, have already feared. Colorado’s future spring runoff will likely come earlier; soil moisture will be lower; heat waves, droughts and wildfires will be more frequent and intense; and a thirstier atmosphere will continue to rob rivers of their flows – all changes driven by the burning of fossil fuels. 

According to the Climate Change in Colorado Assessment report, released Mon., Jan. 8, and commissioned by the Colorado Water Conservation Board, by 2050, statewide annual temperatures are projected to warm by 2.5-5.5 degrees Fahrenheit compared to the late-20th-century and 1-4 degrees compared with today. Colorado temperatures have already risen by 2.3 degrees since 1980. By 2050, the average year is likely to be as warm as the hottest years on record through 2022.

The report’s findings have implications for the state’s water managers. Borrowing a phrase from climate scientist Brad Udall, climate change is water change – which has become a common maxim for water managers. As temperatures rise and streamflows decline, water supply is expected to decrease. 

According to the report, by 2050 there will be an annual reduction of 5-30% in streamflow volume; a 5-30% reduction of April 1 snow-water equivalent; and an 8-17% increase in evaporation. Peak snowpack, which usually occurs in April, is also predicted to shift earlier by a few days to several weeks. Consequently, a hotter, drier atmosphere can lead to an increase in wildfire risk. 

Scientists are less certain about whether precipitation will increase or decrease in the future. Dry conditions have persisted across the state for thepsast two decades. Most climate models project an increase in winter precipitation, but they suggest the potential for large decreases in summer precipitation. But even if precipitation stays the same, streamflows will dwindle because of increased temperatures.

“Streamflows are primarily driven by snowpack that melts in the spring,” Becky Bolinger, CSU researcher, assistant state climatologist and lead author of the report, said. “When you are warming your temperatures, you are first changing the timing of when that snowpack will melt. And because we’re losing more to the atmosphere, that means we have less to run off in our rivers and be available for us later.”

Planning for less water 

CWCB officials hope water managers across the state will use the report to help plan for a future with less water. Many entities have already shifted to developing programs that support climate adaptation and resilience.

“I think we can say with confidence that it is more likely that we will have water shortages in the future,” Emily Adid, CWCB senior climate adaptation specialist, said. “I think this report is evidence of that and can help local planners and people on the ground plan for those reductions in streamflow.” 

Denver Water, which is the oldest and largest in the state and provides water to 1.5 million people, helped to fund the report. Managers there have been preparing for a future of less-reliable water supply through conservation and efficiency, reservoir expansion and wildfire mitigation. 

“Projected future streamflows is a huge challenge,” Taylor Winchell, Denver Water’s senior planner, said. “The same amount of precipitation in the future means less steamflow because temperatures will continue to warm. … All this leads to this concept of uncertainty. We really need to plan for a variety of ways the future can happen, essentially.”

Another finding of the report is that temperatures have warmed more in the fall than other seasons, with a 3.1 degrees Fahrenheit increase statewide since 1980, a trend that is expected to continue. Although it’s hard to pinpoint the exact cause of fall warming, Bolinger said it may have to do with the summer monsoons, which have been weaker in recent years. That precipitation is critical, she said.

“First, you’re keeping the temperatures from getting too hot because you’re clouding over and getting storms,” Bolinger said. “And generally, with higher humidity, you’re going to have less evaporative loss from the soil. What we’ve been seeing in recent years is that we’re not getting that moisture in the late summer and into the fall.”

Less moisture and higher temperatures in the fall also lead to lower soil moisture, kicking off a vicious cycle heading into winter. The dry soil gets locked in under the snowpack, and when the spring melt begins, the water must first replenish the soil before feeding rivers and streams. This is what occurred in the Upper Colorado River Basin in 2021 when a near-normal snowpack translated to just 31% of normal runoff and the second-worst inflow ever into Lake Powell.

Some water users are already experience shortages, especially those with junior water rights. Initiatives to support the environment and recreation are also at risk. And shortages are likely to get worse in the future.

In addition to grant programs, one of the ways CWCB aims to help these water users is with a “future avoided cost explorer” (FACE) tool. This tool can help water managers figure out the costs of addressing – or failing to address – hazards such as wildfires, droughts and floods. 

“That gives you a little bit of perspective to ask, ‘Well, what if I invest to mitigate this now, how can I lessen the potential impact in the future?’” Russ Sands, chief of CWCB’s water supply planning section, said. “I’m not trying to scare people; what we’re trying to do is motivate change and help them invest early.

Despite the near-certainty of continued warming and resulting changes to the water system, Bolinger said there is a bright spot. Since the last time that a Climate Change in Colorado report was issued, in 2014, the world has begun to take action on reducing fossil fuel use and has shifted away from the worst-case scenario. Earlier projections were based on a “business as usual” assumption, with no climate mitigation.

“We do have things that have been put into place internationally like the Paris Accord,” Bolinger said. “We are more along the lines of a middle-case scenario. As long as we continue to take the actions that have been planned out, we are going to follow that middle scenario, which does show warming, but it’s not as bad.”

This story is provided by Aspen Journalism, an independent, nonprofit news organization. For more, visit aspenjournalism.org ?

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