Click here to read the executive summary. Here’s an excerpt:
In the past 30 years, Colorado’s climate has become substantially warmer. The recent warming trend in Colorado is in step with regional and global warming that has been linked to increasing atmospheric concentrations of greenhouse gases. Annual precipitation, which has high natural variability, has not seen a statewide trend over that period. However, some drought indicators have worsened due to the warmer temperatures.
As greenhouse gases and other human effects on the climate continue to increase, Colorado is expected to warm even more by the mid-21st century, pushing temperatures outside of the range of the past century. The outlook for future precipitation in Colorado is less clear; overall increases or decreases are possible. The risk of decreasing precipitation appears to be higher for the southern parts of the state.
The future warming is projected to generally reduce Colorado’s spring snowpack, cause earlier snowmelt and runoff, and increase the water use by crops, landscaping, and natural vegetation. While future increases in annual natural streamflow are possible, the body of published research indicates a greater risk of decreasing streamflow, particularly in the southern half of the state.
From TheDenverChannel.com (Phil Tenser, Mike Nelson):
Colorado’s warming climate is projected to cause significant changes for state’s water supply, according to a new study.
Released by the Western Water Assessment and the Colorado Water Conservation Board, the study echoes many of the predictions included in a national assessment issued by the federal government in May. Both forecast that ongoing warming of the local climate will reduce Colorado snowpack, cause earlier snowmelt and increase water use for agriculture and landscaping.
“Climate Change in Colorado,” the report issued Tuesday and led by a University of Colorado researcher, is based on compiled climate science. It focuses on current observed trends and forecasts for the mid-21st century…
The authors also stated that Colorado snowpack has been mainly below-average since 2000 and snowmelt timing has shifted earlier in the spring over the past 30 years. Projections call for the peak runoff time to continue shifting earlier, but the report says that changes in the timing are more certain than predictions for the amount of runoff.
The report says, “The uncertainty in projections of precipitation and streamflow for Colorado should not be construed as a ‘no change’ scenario, but instead as a broadening of the range of possible futures, some of which would present serious challenges to the state’s water systems.”
According to the report, these observations and predictions could influence reservoir operations including flood control and water storage. Changes in the timing and volume of runoff may also “complicate” future water rights issues and interstate water compacts. Lower streamflows could also lead to higher concentrations of pollutants.
Earlier peak flows could have impacts on aquatic ecosystems and rafting or fishing industries, while reduced snowpack may also impact Colorado mountain tourism.
Every climate model assessed in the report indicates future warming will increase average annual temperatures by 2.5 to 5 degrees Fahrenheit by 2050 if greenhouse gas emissions are in the lower range of estimates. If emissions are in a higher range, the increase could be 3.5 to 6.5 degrees.
“We will still have cold winters and cool summers, but as the global climate warms, these cooler trends will become less frequent in the coming decades,” Nelson said.
Here’s a release from the University of Colorado at Boulder:
As Colorado’s climate continues to warm, those who manage or use water in the state will likely face significant changes in water supply and demand, according to a new report on state climate change released today by the Western Water Assessment and the Colorado Water Conservation Board.
Rising temperatures will tend to reduce the amount of water in many of Colorado’s streams and rivers, melt mountain snowpack earlier in the spring, and increase the water needed by thirsty crops and cities, according to the new report, “Climate Change in Colorado: A Synthesis to Support Water Resources Management and Adaptation,” which updates and expands upon an initial report released in 2008.
The Colorado report comes on the heels of international and national assessments that discuss likely impacts of climate change in broad regions, and it leverages those assessments to provide state-specific information. Because Colorado is located between an area likely to dry further (the U.S. Southwest) and one likely to get wetter (Northern Great Plains), our precipitation future is less certain.
“Despite some uncertainties around precipitation, it’s clear that as temperatures rise in Colorado, there will be impacts on our water resources,” said Jeff Lukas, lead author of the new report and a researcher at the Western Water Assessment, a program of the University of Colorado Boulder funded by the National Oceanic and Atmospheric Administration.
“Already, snowmelt and runoff are shifting earlier, our soils are becoming drier, and the growing season has lengthened,” Lukas said. “Wildfires and heat waves have become more common, too. Climate projections suggest those trends—all of which can affect water supply and demand—will continue.”
The newest climate models are split on whether the future will see increasing, decreasing or similar amounts of annual precipitation in Colorado. Even if the future brings more precipitation, the report notes, skiers, farmers and cities may not benefit because a warmer atmosphere will pull more moisture out of the state’s snowpack, soils, crops and other plants.
In producing “Climate Change in Colorado,” the authors sought to provide information that would be useful to people involved in making long-term decisions about Colorado’s water in the face of climate change.
“This report will help to inform critical products like the Statewide Water Supply Initiative (SWSI) and Colorado’s Water Plan,” said James Eklund, Colorado Water Conservation Board director. “This report will add value, just as the 2008 report was widely used by the state and other entities to inform their long-term planning processes such as the Colorado Drought Mitigation and Response Plan and the city of Denver’s Climate Adaptation Plan.”
Among the findings presented in the new report:
Colorado has warmed: Statewide average annual temperatures are 2 degrees Fahrenheit higher than they were three decades ago.
Climate models indicate that the state’s average annual temperature will continue to increase, by 2.5 to 6.5 degrees by 2050.
A 2-degree 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, and a 6-degree shift would push Denver’s temperatures beyond any found in Colorado today, to more like those in Albuquerque, New Mexico, today.
Future warming in the state is likely to lead to more heat waves, wildfires and droughts. Observations show there have already been increasing trends in these three extremes over the past 30 years.
Warmer temperatures and other changes (dust on snow) mean that snowpack is melting earlier, on average, by one to four weeks compared with 30 years ago. This creates a strain for farmers and other users who draw water directly from rivers.
Colorado has seen no long-term increase or decrease in total precipitation or heavy rainfall events. Climate models are split about Colorado’s future precipitation, showing a range of possible outcomes from a 5 percent decrease in precipitation to an 8 percent increase by midcentury.
Climate models tend to show a shift toward higher midwinter precipitation across the state.
Hydrology models show a wide range of outcomes for annual streamflow in Colorado’s river basins, but an overall tendency towards lower streamflow by 2050, especially in the southwestern part of the state.
The Western Water Assessment (WWA) is part of the Cooperative Institute for Research in Environmental Sciences (CIRES), a joint institute of CU-Boulder and the National Oceanic and Atmospheric Administration (NOAA). The Colorado Water Conservation Board (CWCB) is a division of the Colorado Department of Natural Resources and spearheads the state’s climate change adaptation efforts.
Co-authors of the report are Joseph Barsugli of CIRES and NOAA’s Earth System Research Laboratory (ESRL), Nolan Doesken of Colorado State University and the Colorado Climate Center, Imtiaz Rangwala of WWA, and Klaus Wolter of CIRES and ESRL.
Read a summary of the report at http://cires.colorado.edu/news/press/2014/Climate_Change_CO_Report_Exec_Summ.pdf, and see the full report at http://wwa.colorado.edu/climate/co2014report/.