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More Extreme Heat Projected in Denver Metro Area

Climate change is projected to lead to much more extreme heat in the Denver metropolitation area, according to the first phase of a climate extremes analysis released on September 22, 2016, by the Rocky Mountain Climate Organization and the City and County of Denver's Department of Environmental Health.

According to the analysis, with continued high heat-trapping emissions, the Denver metro area is projected to experience an average seven days a year at 100° or hotter by 2050, and a full month’s worth—34 days a year—late in this century.

“This would be fundamentally different from the climate we know here, which only rarely hits 100 degrees,” said Stephen Saunders, the president of RMCO.

Commissioned by the Department of Environmental Health, the analysis was one of three completed and released by RMCO today. Similar analyses of Boulder and Larimer Counties were funded by the Colorado Department of Local Affairs, Community Development Block Grant—Disaster Recovery funding through the Resilience Planning Grant Program.

The results released today are for projected single-day occurrences. An analysis of multi-day heat waves in Denver will be completed later this year.

In the following key projections for the metro area, the medians of the projections from multiple climate models based on two possible levels of future heat-trapping emissions: The first reflects a business-as-usual trajectory with continued high increases as in recent years; the second scenario reflects very low emissions from rapid and sustained global reductions in emissions. Projections are shown for mid-century (2040 – 2059) and late in the century (2080 – 2099).

Days 95° or hotter per year:

  • In 1970 – 1999, averaged five occurrences per year.
  • With continued high growth in global heat-trapping emissions, the median projection for mid-century is an average of 35 days per year and by late in the century 77 days per year.
  • With very low emissions instead, the median projection for mid-century is an average of 20 days and for late in the century 19 days.

Days 100° or hotter:

  • In 1970 – 1999, averaged 0.3 such day per year.
  • With continued high emissions, the median projection for mid-century is an average of seven days per year and by late century 34 such days.
  • With very low emissions instead, the median projections are two such days both in mid-century and late in the century.

The average temperature of the 30 hottest days in a year:

  • From 1970 – 1999, averaged 93 degrees.
  • With continued high emissions, the median projection for mid-century is 99 degrees, and for late century 104 degrees.
  • With very low emissions instead, the median projection is 97 degrees in both time periods.

The projections also suggest that heavy storms may become more frequent. Storms with less than a quarter-inch of precipitation in a day are projected to have little change in their frequency, regardless of emissions levels. Storms of a half-inch of precipitation or more in a day:

  • With continued high emissions, the median projection is that by mid-century would become 15 percent more frequent, and by late in the century 31 percent more frequent.
  • With very low emissions instead, the median projections are for increases by mid-century of 25 percent and by late in the century 17 percent.

“This shows why we need preparedness actions to address the impacts we could face, including heat waves that can threaten people's health and even their lives,” Saunders said. “It also powerfully illustrates how important it is to reduce future emissions to keep the extent of climate change within manageable limits.”

 

Figure Caption

The figure above shows how the number of days 95° or hotter in the Denver metro area could go from an average of 5 per year late in the last century to 77 per year late in this century. For future periods, the figure shows the range of the middle 80 percent of projections from multiple climate models (the checkered portions of the columns) and the medians (the numerals), for four possible levels of future heat-trapping emissions.

Links

The joint news release by RMCO and Denver Environmental Health on the first phase results of the climate extremes analysis

A table of key projected changes in extreme temperature and precipitation

Full results from the first phase analysis, showing the analysis of scores of temperature and precipitation projections for four different assumptions (scenarios) for future levels of heat-trapping emissions, and for each scenario for four 20-year periods: 2020-2039, 2040-2059, 2060-2079, and 2080-2099. For an explanation of the analysis methodology and to better understand this spreadsheet, see the full report for a completed, comparable analysis either of Boulder County or of Larimer County.