Climate change turns snow to rain in mountains – 7/1/2023 – Environment

As the global climate warms, mountainous regions will experience more heavy rainfall than previously thought, and more of the dangers that come with it, according to a study published Wednesday in the journal Nature.

While scientists have studied how climate change could increase extreme rainfall in general, until now they have not distinguished between how much of the heaviest precipitation will fall as snow and how much as rain. The distinction is important because rain tends to produce more hazards for humans than snow, including flooding, landslides and soil erosion.

As the planet warms, snow starts to turn to rain, even in the mountains. The study found that for every 1°C the planet warms, higher areas can expect 15% more heavy rainfall.

“This is the first time this has been quantified,” said the study’s lead author, Mohammed Ombadi, an environmental data scientist at Lawrence Berkeley National Laboratory in the United States.

This increase in extreme precipitation is “nearly double” the increase in total extreme precipitation, including rain and snow, that climate scientists previously expected. The rainfall finding only applies to the highest regions of the world, above approximately 2,000 meters in altitude.

But about a quarter of the human population lives in mountainous regions or directly downstream (below) them, Ombadi said. While landslides don’t go very far, floods tend to affect downstream populations more, he explained, adding that rainfall is one of the most important factors in predicting the risks of both hazards.

Soil erosion can harm farms and natural ecosystems and further increase the risks of floods and landslides. These threats add to those posed by 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 have separately examined how extreme precipitation is increasing and how snowfall is turning into rain, little research combined these factors until this new study.

“It’s a good way to piece these changes together and highlight regions where we should be particularly vigilant for big changes in flood risk and extreme rainfall,” Davenport said.

In their study, Ombadi and his colleagues analyzed 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 because data on the tropics and the southern hemisphere are lacking. .

By 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 1°C of warming, that represents a 15% increase. If it’s 3°C, there will be a 45% increase in precipitation,” explained Ombadi.

This came as a surprise, as the team expected the increase in rainfall to slow and stabilize as temperatures rise higher and higher. They used several different climate models, with relatively consistent results across them.

“The big message is that all grades matter,” said Ombadi. He cautioned, however, that climate models are still somewhat inaccurate at more extreme temperatures.

The researchers also found that the higher the elevation, the greater the increase in extreme rainfall. Unlike the change that accompanied rising temperatures, this change was not linear: the higher they looked, the more they noticed the increase in rainfall.

Different mountain ranges across the Northern Hemisphere also had slightly different risks of heavy rainfall. Researchers are still trying to figure out why.

The number of deadly landslides around the world has increased in recent decades, according to another study from 2019. Most of these landslides happened in places exposed to extreme rainfall.

The highest-risk areas in this older landslide study match the highest-risk areas in the new precipitation study, said Ubydul Haque, a geospatial public health researcher at Rutgers University and lead author of the 2019 paper.

Haque was impressed by the scale of data used by the Lawrence Berkeley team. Their approach is “extremely new,” he said. For Haque, the new study’s findings and the underlying data could be useful in future research into the health and safety implications of extreme rainfall.

Ombadi, who has a background in civil engineering, hopes his team’s findings will help improve risk assessment models for landslides and floods 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.

_{Translated by Luiz Roberto M. Gonçalves}