Colorado’s weather changes constantly, making it difficult to determine shifts or trends in climate. Still, there is evidence to suggest that temperatures are increasing.

• A 2008 study by the Western Water Assessment called “Climate Change in Colorado” shows a statewide temperature increase of 2 degrees in the last 30 years, but temperature trends vary greatly across the state. No consistent changes in precipitation patterns have been identified in Colorado.
• A study completed by the U.S. Geological Survey in 2007 showed that between the years 1978 and 2004, the date of peak spring runoff shifted about two weeks earlier. This was caused by warmer weather, but other factors, such as more dust deposited on mountain snow, also sped up the runoff.

A large range of possible changes are projected for Colorado’s climate. Most experts agree that warming will occur in Denver and in our mountain watersheds. But there is no agreement on how precipitation patterns could change. Some climate models project that precipitation will increase in the future and others project that it will decrease.

The statewide average temperature is projected to increase 2.5 degrees by 2025 and 4 degrees by 2050, according to the Western Water Assessment report.

• A warmer climate will cause the snowpack to melt earlier and will produce an earlier spring runoff.
• Because the snowpack will melt earlier, there will be less streamflow in the summer and fall months. 
• More frequent and severe droughts, as well as more frequent and severe floods, will occur under warmer conditions.
• A warmer climate will cause water to evaporate faster, increase the amount of water plants use, increase the number of wildfires and force more sediment to flow into rivers and streams.

Temperature increases alone, without any change in precipitation patterns, would dramatically decrease water supply and increase water use.

A simple assessment of a 2-degree Fahrenheit average temperature increase shows supply would decrease by 7 percent from our system's current yield, primarily because of an increase in evaporation. Water use could increase by 6 percent, mainly because customers would irrigate their landscapes more to keep them healthy.

A 5-degree Fahrenheit temperature increase could decrease supply 20 percent from current yield and increase water use by 7 percent.

Warmer weather is expected to increase the frequency and severity of wildfires in our mountain watersheds. Severe wildfires place watersheds at a high risk for flooding, which will cause more erosion and send more sediment into our water supplies. When dirt and sediment washes into reservoirs and rivers, it makes it harder for us to clean the water.

Most of the grasses, trees and other landscaping plants that require irrigation in our semi-arid environment will need more irrigation water to survive the stress of warmer summer temperatures. Even some Xeriscape and native plants may require irrigation or additional irrigation. Some plants, such as bluegrass, may survive by going dormant in hotter weather.

A simple assessment shows a 2 degree average temperature increase could increase water use by 6 percent, and a 5 degree temperature increase could increase water use 20 percent.

By studying the growth pattern of old trees, scientists have estimated streamflow patterns in Denver’s watersheds going back 400 years. Denver Water uses these estimates to analyze past droughts against water supply needs. Tree ring data indicate several droughts occurred in the past 400 years that were much worse than the modern droughts of the 1950s and the 2000s. Unfortunately, climate change could cause droughts to be worse than those of the last 400 years.

With the large amount of uncertainty about how much our climate could change and how those changes could affect the quantity, quality and use of our water supplies, Denver Water is addressing the uncertainties of climate change by following a four-step process:

1. Denver Water is staying informed about climate science and the range of projected changes and resulting impacts by employing a climate scientist, collaborating with water utilities regionally and nationally, and working with climate scientists and researchers to meet our information and assessment needs.

2. Denver Water is studying the vulnerability of Denver’s water system and how it could be impacted by climate change. This includes working with the Front Range Climate Change group to develop models that simulate the streamflow changes caused by climate model projections.

3. Denver Water is incorporating the possible impacts of climate change into our long-range water planning.

4. Denver Water also is making changes to deal with possible impacts, such as encouraging customers to use water wisely, diversifying our supply sources and preserving supply options for future use.

Pine beetles occur naturally in our mountain watersheds. Several factors have caused the unprecedented epidemic and death of trees. Among them are warmer summer temperatures that have stressed the trees and warmer winter temperatures that have kept the pine beetles from dying in the winter.