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Future Climate Extremes in Larimer County

A report by the Rocky Mountain Climate Organization (RMCO) projects large increases in the frequency and extent of extremely hot days in Larimer County, with the extent depending on whether global heat-trapping emissions continue on a high trajectory or are reduced.

“On our current path of steadily increasing heat-trapping emissions, Fort Collins by the middle of the century is projected to average 24 days a year 95° or hotter. By late in the century, an average of 58 95°-plus days are projected. This would be fundamentally different from the climate we know in Colorado,” said Stephen Saunders, president of RMCO and lead author of the report.

The projections also address future precipitation extremes. Although projections for precipitation are more uncertain than for temperature, the models suggest that heavy storms may become more frequent.

“This shows why we need preparedness actions to address the impacts we could face, from more wildfires and possibly more floods to more heat waves that can threaten people’s health and even 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.”

The following projections show the medians of the projections from multiple climate models, based on two possible levels of future heat-trapping emissions—continued high increases as in recent years, reflecting a business-as-usual approach, and very low increases, reflecting rapid and sustained global reductions in emissions. The projections are shown for mid-century (2040–2059) and late in the century (2080–2099). The full report, however, analyzes two other medium-level emissions scenarios, and two other time periods, 2020–2039 and 2060 – 2079.

  Days per year with high temperatures of 95° or hotter:

  • In 1970 – 1999, averaged two occurrences per year.
  • With high continued growth in global heat-trapping emissions, in mid-century (2040 – 2059) are projected to average 24 times per year and by late in the century (2080 – 2099) to average 58 times per year.
  • With very low emissions instead, are projected to average 10 times in both time periods.

Days with high temperatures of 100° or hotter:

  • In 1970 – 1999, averaged less than one occurrence per year.
  • With high emissions, in mid-century are projected to average 4 times per year and by late in the century 23 times per year.
  • With very low emissions instead, are projected instead to average once a year in both time periods.

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

  • In 1970 – 1999, averaged 91°.
  • With high emissions, in mid-century is projected to average 98°, and late in the century 103°.
  • With very low emissions, is projected instead to average 95° in both time periods.

For precipitation in Larimer County mountains, 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 high emissions, are projected by mid-century to become 12 percent more frequent, and by late in the century 33 percent more frequent.
  • With very low emissions instead, are projected to average 21 percent more frequent by mid-century and 15 percent more by late in the century.

For this and a companion report addressing Boulder County, RMCO analyzed 44 million individual projections for daily temperature and precipitation values for four locations: Boulder and vicinity, Boulder County mountains, Fort Collins and vicinity, and Larimer County mountains. The projections are from the latest generation of downscaled global climate models. A projection for an individual day does not have any particular value, but enough of them over a sufficient period of time enables analysis of how often particular conditions are projected to occur in that period.

The reports were funded by the Colorado Department of Local Affairs, using Community Development Block Grant—Disaster Recovery funding through the Resilience Planning Program. Boulder and Larimer counties were heavily affected by the High Park wildfire in 2012 and the September 2013 flooding that led to federal disaster designations. The purpose of the reports is to help local governments in these two counties better understand and prepare for the increased risks of wildfire and flooding expected to come with further climate change.

 

Links

The full report, Future Climate Extremes in Larimer County.

The news release announcing the report.

A spreadsheet with the full results of 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.