The Colorado Climate Center’s report on the 2023 climate year and its outlook on the future of our climate and our snowpack, is full of data that shows a trend we all saw coming: the seasons are getting warmer, the melt-off is happening sooner, and most of all, the snowpack is decreasing year after year.
Colorado’s average temperature, season after season, since 1980 has increased by an average of 2.3 degrees. The winter has seen a 1.0 degree increase; spring has increased by 1.7 degrees; summer at 2.5 degrees; and autumn has seen an increase in temperature by 3.1 degrees.
“Annually,” the report says, “the greatest warming has been observed over the Southwest and San Luis Valley climate regions.”
The seven of the 10 hottest years on record have occurred since 2010. The rise in temperature means a reduced snowpack. Nothing is more of a key indicator for the health and wellness of Colorado than its snowpack.
Snowpack serves as a seasonal reservoir that stores upwards of 15 million acre-feet, on average, across the state. Colorado is a “headwaters state,” which means that four major rivers have their headwaters right here: the Colorado River, the Rio Grande, the Arkansas River and the Platte River.
Precipitation from snow is more likely to end up as runoff than precipitation from rain.
The 21st century record, which ranges from 2001 to 2022, showed an average of three percent to 23 percent lower snow water equivalent on April 1 than the 1951 to 2000 average.
Snow water equivalent (SWE) is the amount of water you get if you melted the snow down and were able to measure what was left. These measurements are more accurate than snowfall or snow depth, because those measurements don’t always account for a wide array of snow densities.
“The largest decreases occurred in the southwestern portion of the state, specifically in the San Juan and Rio Grande basins.”
Projections show a negative five percent to negative thirty percent measure of snow water equivalent by the year 2050. April 1 to May 15 is historically when true mountain runoff starts to occur with a change in temperature, but projections show that by 2050 that date will shift earlier by a few days then to a few weeks.
The 114 SNOTEL sites that give us this information are mostly situated between 8,500 feet and 11,000 feet elevation, and report data every hour. They are all monitored by the National Resource Conservation Service.
Studies showed that snowpack has decreased in many of Colorado’s major river basins; however the percentage of decline when compared to other Mountain West regions was “generally smaller” due to Colorado’s higher elevations and colder winters.
“These studies also found that warming temperatures were an important cause of the observed SWE declines, while below-normal fall and spring precipitation in the past few decades has also played a role.”
Although larger snowpacks have become less common, big snowfall years like 2019 can and will occur.
Severe droughts are projected to increase, as well. “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.”
“Southwestern and South-central Colorado have experienced the largest magnitude
of warming. The observed warming trend in Colorado is strongly linked to the overall human influence on climate and recent global warming.”
Over the next several decades, the report suggests, further and significant warming is expected in all parts of Colorado, in all seasons.
KEY REPORT FINDINGS
Temperature
- Statewide annual average temperatures warmed by 2.3°F from 1980 to 2022.
- Only one year in the 21st century has been cooler than the 1971-2000 average. 2012 remains the state’s warmest year in the 128-year record, at 48.3°F (3.2°F warmer than the 1971-2000 average).
- The greatest amount of warming has occurred in the fall, with statewide temperatures increasing by 3.1°F from 1980-2022.
- Southwestern and South-central Colorado have experienced the largest magnitude of warming.
- The observed warming trend in Colorado is strongly linked to the overall human influence on climate and recent global warming. The observed warming over the last 20 years is comparable to what was projected by earlier climate models run in the 2000s.
- Further and significant warming is expected in all parts of Colorado, in all seasons, over the next several decades.
- By 2050 (the 2035-2064 period average), Colorado statewide annual temperatures are projected to warm by +2.5°F to +5.5°F compared to a 1971-2000 baseline, and +1.0°F to +4.0°F compared to today, under a medium-low emissions scenario (RCP4.5).
- By 2070 (the 2055-2084 period average), Colorado statewide annual temperatures are projected to warm by +3.0°F to +6.5°F compared to the late 20th century, and +1.5°F to +5.0°F compared to today, under RCP4.5.
- By 2050, the average year is likely to be as warm as the very warmest years on record through 2022. By 2070, the average year is likely to be warmer than the very warmest years through 2022.
- Summer and fall are projected to warm slightly more than winter and spring.
Precipitation
- Colorado has observed persistent dry conditions in the 21st century. According to water year precipitation accumulations, October 1 – September 30, four of the five driest years in the 128-year record have occurred since 2000.
- Drying trends have been observed across the majority of the state during the spring, summer, and fall seasons.
- Northwest Colorado summer precipitation has decreased 20% since the 1951-2000 period.
- Southwest Colorado spring precipitation has decreased 22% since the 1951-2000 period.
- Precipitation is slightly more favorable over the northern mountains during a La Niña winter. For most regions and the remaining seasons, wetter conditions are slightly enhanced during an El Niño.
- The direction of future change in annual statewide precipitation for Colorado is much less clear than for temperature. The climate model projections for 2050 range from -7% to +7% compared to the late 20th century average, under a medium-low (RCP4.5) emissions scenario.
- The model projections for precipitation change by 2070 are very similar to those for 2050.
- Most climate models project an increase in winter (Dec-Feb) statewide precipitation; the model consensus is weaker for the other seasons. The models do suggest enhanced potential for large decreases (-10% to -25%) in summer precipitation.