Ozone pollution over Denver.

(Photo: Courtesy of CDPHE)
A new report on the future of Colorado's climate released Tuesday predicts rising temperatures will reduce the amount of water in many streams and rivers, melting mountain snowpack earlier in the spring and increasing the water needed by thirsty crops and cities.

The study, “Climate Change in Colorado: A Synthesis to Support Water Resources Management and Adaptation,”  by the Western Water Assessment and the Colorado Water Conservation Board, shows that statewide average annual temperatures are 2 degrees Fahrenheit higher than they were three decades ago and that temperatures will probably continue rising. Climate models predict a 2.5 to 6.5 degree rise by 2050.

A 2-degree F increase would make Denver’s temperatures in 2050 more like Pueblo’s today. A 4-degree increase would make Denver more like Lamar in southeastern Colorado. A 6-degree shift would push Denver’s temperatures into the range of those like Albuquerque, New Mexico, today.

One thing not clear, according to the study, is if precipitation will increase or decrease.  Climate models vary, showing a range of possible outcomes from a 5 percent decrease in precipitation to an 8 percent increase by the middle of the century. Even if Colorado's future is wetter, the report notes, skiers, farmers and cities may not benefit because a warmer atmosphere will pull more moisture out of the state’s snowpacks, soils, crops and other plants.

“Despite some uncertainties around precipitation, it’s clear that as temperatures rise in Colorado, there will be impacts on our water resources,” says Jeff Lukas, lead author of the new report and a researcher at the Western Water Assessment, a program of the University of Colorado Boulder. “Already, snowmelt and runoff are shifting earlier, our soils are becoming drier, and the growing season has lengthened. Wildfires and heat waves have become more common, too. Climate projections suggest those trendsall of which can affect water supply and demand -- will continue.”

The Western Water Assessment is part of the Cooperative Institute for Research in Environmental Sciences, a joint institute of CU-Boulder and the National Oceanic and Atmospheric Administration. The Colorado Water Conservation Board is a division of the Colorado Department of Natural Resources.