Nearly two weeks ago, heavy rains caused a mudslide between Glenwood Springs and Carbondale, closing Highway 82 for several days. The area got more than an inch of rain overnight.
As forecasters consider severe weather events like this one, and the potential for rockslides and mudslides, there are a few different factors they consider.
Erin Walter is a service hydrologist at the National Weather Service Grand Junction Office.
She said there had been moisture in the days leading up to August 10th, when the mudslide occurred.
“If we've had a lot of moisture prior to a thunderstorm or heavy rain event, you will have pretty saturated soils,” she said. “And that can also enhance or support runoff and rockslides.”
She said even though this specific event was surprising, because of how destructive it was, there’s lots of areas in western Colorado and eastern Utah where highways and roads run through steep terrain, like Highway 82 and are prone to slides.
One of those areas is the Crystal River Valley near Redstone, which Walter says is notorious for mud and rock slides, and which has a lower threshold for the agency to issue a warning to residents.
“Those are areas that we keep our eye on and we have lower thresholds,” she said. “So they may not need as much rainfall in a shorter period of time than, say, kind of a gentle slope area or a flat area.”
Walter also said it’s been a really wet August.
“Just within the first half of August, so month to-date, we've seen over 200% of normal precipitation across the Roaring Fork: kind of that, like, eastern Garfield, Eagle, and Pitkin County corridor,” she said.
Peter Goble is a climatologist at the Colorado Climate Center. He said it’s not clear that human-caused climate change is responsible for a more intense monsoon season.
“So we know that a warmer atmosphere has the potential to hold more water vapor, so that that tends to lead to more potential for flooding in a lot of areas,” he said. “But because Colorado is so landlocked and the moisture has to come from so far away, the trends in heavy precipitation and flooding have not materialized here yet, in the same way they have throughout much of the eastern U.S. and other parts of the globe.”
And climate models can be difficult to read. In fact, climate models say different things about the future of Colorado’s summer precipitation. Goble said some models have the state getting 40% drier in July on average, and others have Colorado getting 40% wetter in July on average.
“It's a likely outcome that the year-to-year summer precipitation will become even more variable,” he said. “I guess, the messaging to the public, and to people who are trying to plan, is just to be ready for anything and try to plan for an even wider scope of variability.”
But extreme heat caused by climate change does impact water resources in Western Colorado, Goble said.
“Even if we don't know exactly what's going on with precipitation, we know the warming temperatures alone are impacting our water cycle in every phase,” he said. “Because we're seeing more events during the shoulder seasons that are rain where they might have been snow before. We're seeing that snow is melting earlier and that, our average spring runoff along with that is, again, that's very highly variable from year-to-year and highly dependent on precipitation.”
