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Climate: How hot will it get in Colorado?

State releases draft climate change report, comments wanted

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How warm will it get in Colorado?

By Summit Voice

FRISCO — Climate experts say it’s about to get warmer —probably much warmer — in Colorado. A draft state climate report released this week for public comment shows that Colorado has warmed by 2.5 degrees Fahrenheit in the past 50 years. By the middle of this century, summer temperatures will be higher than in all but the hottest years, with another 2.5 to 5.5 degrees of warming expected.

The report, aimed at helping resource managers prepare for changing conditions, found no long-term trends in annual precipitation, even with the relatively dry period in the early 2000s. Annual observed precipitation changes the past few decades are within the range of natural variability, according to the report.

The draft report has been posted to the CWCB website.  A comment form is also available on the website to download. Both documents can be found at http://cwcb.state.co.us/environment/climate-change/Pages/Draft2014ClimateChangeReport.aspx. Comments are due by April 14.

One big question mark with implications for water management is the effect of global warming in the mountains. Some recent research suggests greater warming at high elevations as global temperatures increase, but there’s a lack of data from sites above 10,000 feet in Colorado. Data gaps point to the need for better climate monitoring, some experts say, warning that federal budget cuts could threaten existing monitoring programs.

Cold snaps in Colorado have become less frequent.

Cold snaps in Colorado have become less frequent.

Other observed climate trends in Colorado include:

  • Snowpack, as measured by April 1 snow‐water equivalent (SWE), has been mainly below‐average since 2000 in all eight major Colorado river basins, though a long‐term trend has only been detected in one basin.
  • The timing of snowmelt and peak runoff has shifted earlier in the spring by 1‐4 weeks across Colorado’s river basins over the past 30 years, due to the combination of lower SWE since 2000, the warming trend in spring temperatures, and enhanced solar absorption from dust‐on‐snow.
  • The Palmer Drought Severity Index (PDSI) shows a trend towards more frequent soil‐ moisture drought conditions in Colorado over the past 30 years, reflecting the combination of the warming trend and below‐average precipitation since 2000.
  • Tree‐ring records and other paleoclimate indicators for Colorado show multiple droughts prior to 1900 that were more severe and sustained than any in the observed record.

The report describes linkages between global climate and changes in Colorado:

  • The global climate system has warmed in the past century, particularly the past 30 years, as evidenced by increased surface, atmospheric, and ocean temperatures; melting glaciers and ice sheets; rising sea levels; and increased atmospheric water vapor.
  • These global changes have been attributed to anthropogenic (human‐caused) factors, mainly the increase in greenhouse gases to the highest levels in at least 800,000 years.
  • In North America, temperatures have increased by about 2 degrees Fahrenheit in the last 30 years, and most of this increase has been attributed to greenhouse gases and other human factors.
  • In Colorado, temperatures have also warmed by 2 degrees Fahrenheit in the past 30 years. The amount of warming is broadly consistent with climate model runs in which anthropogenic greenhouse gas emissions are the main driver of recent warming.
  • Recent variability in annual precipitation is consistent with past natural variability of Colorado’s climate and is not attributable to anthropogenic changes.
  • The observed warming trend may have increased the severity of recent drought conditions in Colorado due to the influence of temperature on snowpack, streamflow, and soil moisture.

In the next few decades, summers will probably warm more than winter, and nearly all climate models project more winter precipitation for the state. Despite more winter precipitation, most projections show declines in the snowpack due to the effect of the large projected warming. In some simulations, however, winter precipitation increases sufficiently to overcome the impact of warming, and snowpack increases.

Most projections also show decreased annual naturalized runoff for Colorado’s major rivers, due mainly to the large warming increasing the loss of moisture from snowpacks, soils, and vegetation.

In a minority of the hydrologic projections, the projected increases in precipitation are large enough to overcome the effect of warming, and there is an increase in annual runoff.

There is higher confidence in future changes in the timing of runoff than changes in the amount of runoff. The timing of spring runoff is projected to shift 1–3 weeks earlier by the mid‐21st century due to warming. Late‐summer flows are projected to decrease as the peak shifts to earlier in the season.

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