Fires, Then Floods: Risk of Deadly Climate Combination Increases


With global warming drastically increasing the risk of heavy rains following extreme wildfires in the western United States, a new study highlights the need for better preparations for hazards such as mudslides and flash floods that can wreak havoc long after the flames. fierce flames broke out.

Fires destroy forests, devastate homes and kill people and animals, but they also destroy vegetation and make soil less permeable. This makes it easy for even short bursts of heavy rain to cause flooding and runaway mud and debris flows. There may be rains after forest fires pollute drinking water by suffocating rivers and basins with sediment from eroded slopes.

Scientists believe that human-caused climate change is bringing more of the hot, dry conditions that lead to catastrophic fires. Warmer air can hold more moisture, which means precipitation becomes more intense.

So far, climate researchers who have studied the western United States have not attempted to determine how often these two opposite extremes might occur in the same place over a short period of time, said Danielle Touma, a postdoctoral researcher at the National Atmospheric Center. Research at Boulder, Colo, and lead author of the new study.

Dr. Three months to six months after a fire, before the soil and vegetation have had time to recover, “the times when these events can be really risky,” Touma said. Study It was published Friday in the journal Science Advances.

Residents of western states have seen a lot of these one-two-hit air disasters and their sad consequences in recent years.

The new study uses computer models to predict how the frequency of such combined events might change across the West under a high global warming scenario for the coming decades.

Climate scientists believe that greenhouse gas emissions from human activities are less likely on their own to cause such high levels of warming than they once were. The study’s authors said they expect smaller but still significant increases in precipitation following wildfires under less pessimistic pathways for global warming.

The study reveals that by the end of the century, more than half of the days with an extremely high risk of wildfires in the Pacific Northwest, parts of Idaho, Nevada and Utah could follow heavy showers within a year. The study found that for California and Colorado, this ratio was smaller, but still significantly higher than the average between 1980 and 2005. And the increase is significant both in six months of fierce fire days and in a year.

Western Colorado and much of the Pacific Northwest are expected to see a jump in the probability of heavy rain within three months of dangerous fire conditions. In California, wildfire season and rainy season tend to be more separate throughout the year.

“Even by the middle of the century, the risk appears to have doubled or tripled in some places,” said Daniel L. Swain, a climate scientist at the University of California, Los Angeles and another author of the study. “The future isn’t that far off, and that’s not much more additional warming than we’ve seen so far.”

Dr. Swain said he and his colleagues were impressed that computer models showed such a consistent increase in risk across the West, even though the region’s climate is so diverse. While California has dry summers and wet winters, both floods and wildfires peak during the hot season in Colorado.

It didn’t take much rain to trigger a debris flow on a recently burned slope, said hydrologist Jason W. Kean of the United States Geological Survey in Golden, Colo., who was not involved in the study. In some areas, a drop as little as an inch in 15 minutes may be sufficient, he said.

But as more wildfires occur in places that weren’t a big problem before, scientists are trying to understand how thresholds might differ in these wetter climates, said Dr. kean “It’s a struggle for us to be ahead of the game,” he said.

Dr. Touma conducted most of the analysis of the new study as a postdoctoral researcher at the University of California, Santa Barbara, not far from Montecito, which was devastated by post-fire mudslides in 2018. certain areas to be evacuated, but most chose not to.

Dr. “There was a lot of evacuation fatigue from the fire just a month ago,” Touma said.

Samantha Stevenson, an environmental scientist at the University of California at Santa Barbara who also worked on the study, said Western residents are often very aware of the risks of flooding and mudflow in burnt areas. But “the degree to which it is increasing as a result of climate change, and the pace of that increase, is perhaps something we should try to be more aware of,” she said.



Source link

Leave a Reply

Your email address will not be published. Required fields are marked *