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DENVER - 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.
Over the past 30 years, average temperatures in Colorado have increased by 2 degrees Fahrenheit, the report finds. That is the same amount by which North America has warmed over the same period.
"These global changes have been attributed mainly to anthropogenic (human-caused) influences, primarily the increase in greenhouse gases in the atmosphere to the highest levels in at least 800,000 years," the report's executive summary says.
While it says that warming in Colorado is "plausibly linked to anthropogenic influences," it says recent variability in annual precipitation here "has not exhibited trends that might be attributed" to humans. The next paragraph, however, states human influences may have increased the severity of the drought in the western United States.
"Drought is not just a matter of precipitation, the amount of evaporation is just as important. Even if the total annual precipitation were to remain the same, a warmer Colorado will experience more drought due to the increase in evaporation," 7NEWS Chief Meteorologist Nelson said.
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.
"Climate model projections show less agreement regarding future precipitation change for Colorado," the report states. Most predict additional precipitation by 2050 during the winters, but there is weaker consensus in the projections for the other seasons.
Hydropower facilities or power plants that need water for cooling could also be impacted, it says.
"Water truly is liquid gold in Colorado, the long term trend toward a warmer and drier climate is something we will need to plan for in the future," Nelson said.