KEY MESSAGES for CHAPTER 4
|Projected future change
|Confidence in change
|More and larger
|More and larger
|More large hail
|Greater dust levels
|Greater dust levels
- Warming temperatures have increased the severity of 21st century droughts in Colorado.
- Regardless of changes in precipitation, it is likely that warmer temperatures
will contribute to more frequent and severe droughts. Warmer temperatures will also
decrease the benefit of wetter years.
- Intense droughts have occurred multiple times in the 21st century, including in
2002, 2012, 2018, and 2020.
- Since 2000, Colorado has experienced a large increase in the number of large
wildfires and in the annual area burned by all wildfires; on average, fires have
burned at higher elevations and with higher intensity than in the late 20th century.
While several factors have contributed to these trends, rising temperatures are a major driver.
- Future warming is expected to lead to further increases in the occurrence of
large wildfires and in annual area burned by all fires, especially in forest
ecosystems, according to multiple studies. A greater percentage of fires will
occur in the fall, winter, and spring than at present.
Heavy and Extreme Rainfall
- There are some indications of recent increasing trends in heavy and extreme
rainfall in Colorado, but these are not consistent across all indicators and time
periods, unlike in other regions of the U.S.
- Atmospheric moisture has generally increased over Colorado, but not by as much
as one would predict from the warming atmosphere alone.
- Future warming, by increasing the moisture-holding capacity of the atmosphere,
will make heavy and extreme rainfall more likely unless counterbalanced by declining
trends in other storm “ingredients”. Climate-model projections for Colorado show
overall increases in the magnitudes of heavy and extreme rainfall events.
- Gaged streamflow records show no widespread, consistent trends in the magnitude
of flood events in Colorado of different frequencies (e.g., 1-year, 20-year, 50-year, 100-year).
- The expectation that heavy and extreme rainfall events will increase in Colorado
implies increases in future flood risk as well, but there are many factors influencing
how rainfall is translated into runoff. Increased exposure to flooding through
floodplain development may be more important than climate-driven changes in risk.
- Because of the relatively short data record for thunderstorm hazards and the
influences of changing observation systems, the sign and magnitude of any long-term
changes is unclear.
- Some studies have suggested increases in the average size of hail in a warmer
climate, with smaller hail becoming less frequent but larger hail more frequent.
Overall, however, there remain large uncertainties regarding future changes,
as data limitations and the infrequent and localized nature of these storms makes
them challenging to study in the context of a changing climate.
- Colorado is prone to intense winds in the mountains and from downslope windstorms
along the Front Range. These windstorms can cause considerable damage, and can
exacerbate wildfires, such as in the 2021 Marshall Fire. Long-term changes in extreme
winds have not been extensively studied, and potential future changes are highly uncertain.
- Despite warming temperatures in the winter, there are no detectable trends in
winter severity across the Colorado Front Range and Eastern Plains. There are also
minimal trends in large snowfall events.
- Several notable and high impact winter storm events have occurred over eastern
Colorado in the last decade, including extreme cold, high winds, strong cold fronts,
and large accumulations of snow.
- Future trends in winter storms remain highly uncertain, but the risk of
high-impact winter events is likely to remain.
- Dust-on-snow events have emerged as a concern since 2000 due to better
understanding of its hydrologic effects, as well as an overall increase in the
occurrence of dust-on-snow. Dust-on-snow causes earlier melt and runoff and may
reduce annual runoff.
- It is likely that in a future warmer climate, drier conditions in the
dust-source regions will allow for greater dust emission and thus deposition on
snowpacks. Dust-on-snow and warming will both drive earlier snowmelt and runoff.