As the climate warms, mountain regions will receive more extreme rainfall than previously thought, and more of the dangers associated with it, according to a study published Wednesday in the journal Nature.
While scientists have been studying how climate change may increase extreme precipitation in general, until now they hadn’t teased apart how much of the most extreme precipitation will fall as snow and how much as rain. The distinction is important because rain poses more hazards to humans than snow, including flooding, landslides and soil erosion.
As the planet warms, snow begins to turn to rain, even in the mountains. The study found that for every degree Celsius, or 1.8 degrees Fahrenheit, that the planet warms, higher elevations can expect 15 percent more extreme rainfall.
“This is the first time it’s ever been quantified,” said the study’s lead author, Mohammed Ombadi, an environmental data scientist at Lawrence Berkeley National Laboratory. This increase in extreme rainfall is “almost double” the increase in total extreme precipitation, including both rain and snow, that climate scientists had previously expected. The precipitation finding only applies to the world’s highest regions, above about 2,000 meters or 6,500 feet in elevation.
But about a quarter of the human population lives in mountain areas or immediately downstream from them, said Dr. Ombadi. While landslides don’t get very far, floods tend to affect people more downstream, he explained, adding that rainfall is one of the most important factors in predicting the risks of both hazards. Soil erosion can undermine farms and natural ecosystems and further increase the risk of flooding and landslides. These threats are in addition to those from melting glaciers in the same mountain ranges and river valleys.
Frances Davenport, a professor of civil and environmental engineering at Colorado State University who was not involved in the study, confirmed that while researchers had separately examined how extreme precipitation increased and how snowfall transitioned to rainfall, not much research had been done to examine these factors. to combine. two questions to this new study.
“It’s a nice way to bring those changes together and highlight the regions where we should be especially wary of major changes in flood risk and extreme rainfall,” said Dr. Davenport.
In their study, Dr. Ombadi and his colleagues produced historical data from 1950 to 2019, as well as projections of climate change through the end of the 21st century. They focused on the temperate and arctic regions of the Northern Hemisphere, as data from the tropics and the Southern Hemisphere is lacking.
While modeling different global warming scenarios, the researchers found that extreme rainfall continued to increase steadily, at the same rate, for each degree of warming. “If you have one degree of warming, that is an increase of 15 percent. If it’s three degrees, that means a 45 percent increase in rainfall,” explains Dr. Ombadi out.
This came as a surprise, as the team expected the increase in rainfall to slow and stabilize as temperatures continued to rise. They used different climate models, all with relatively consistent results. “The big message is that every degree matters,” said Dr. Ombadi. However, he warned that climate models are still somewhat uncertain at more extreme temperatures.
The researchers also found that the higher the elevation, the greater the increase in extreme rainfall. Unlike the shift associated with rising temperatures, this change was not linear: the higher they looked, the more rain they saw increasing. Different mountain ranges around the Northern Hemisphere also had slightly different risks of extreme rainfall. Researchers are still trying to figure out why.
According to a separate 2019 study, the number of deadly landslides around the world has risen in recent decades. Most of these landslides occurred in places exposed to extreme rainfall.
The areas of highest risk in this older landslide study match the areas of highest risk in the new rainfall study, said Ubydul Haque, a geospatial epidemiologist at Rutgers University and the lead author of the 2019 paper. Haque was impressed with the volume of data Lawrence Berkeley’s team used. Their approach was “extremely new,” he said. Dr. Haque thought the new study’s findings and the underlying data could be useful for future research into the health and safety implications of extreme rainfall.
Dr. Ombadi, who has a background in civil engineering, hopes his team’s findings will help improve landslide and flood risk assessment models and lead to better planning and infrastructure in places vulnerable to these hazards. The research could also be useful for improving the climate models that researchers rely on to predict long-term changes in rainfall.
