Researchers at the Lawrence Berkeley National Laboratory (Berkeley Lab), under the US Department of Energy, have discovered that climate change is transforming snowfall into precipitation in the mountains of the northern hemisphere. These waves of liquid water entail a series of dangers, such as floods, landslides and soil erosion, as published in the journal Nature.
“A quarter of the world’s population lives in mountainous regions or downstream from them,” says Mohammed Ombadi, first author of the study. They are going to be directly affected by this risk,” he adds.
Scientists already anticipate that climate change will increase the amount of water that falls during extreme events (which typically take place within a few hours to a day), but this study marks the first time that researchers have looked at whether such extreme precipitation occurs. in the form of rain or snow.
The researchers found that the fraction of water falling as snow decreased in mountainous regions and fell as rain, making mountains especially vulnerable to extreme rainfall hazards. They even put a figure on it: for every degree Celsius increase in global temperature, an average of 15% more rain is expected in the highlands.
“This increase in extreme precipitation is not just something that is going to happen between now and the end of the 21st century: we are already seeing it,” says Ombadi. “That same rate was also evident in the data from 1950 to 2019. extremes in the mountains have already been increasing, and will continue to change at that 15% rate.”
While all mountain ranges in the Northern Hemisphere are seeing the change from snow to rain, those most at risk from extreme precipitation events are the Pacific mountain ranges of North America (the Cascades, Sierra Nevada, and the coastal ranges from Canada to the southern California), the Himalayas, and high latitude regions. Researchers are still working to understand why these areas are more at risk than other mountain ranges like the Rockies or the Alps.
“We believe that the North American Pacific ridges are more susceptible to extreme precipitation risk than other ridges because a significant portion of the snowfall in this region typically occurs at temperatures just below zero degrees Celsius,” Ombadi explains. “The slightest change in the air temperature it will transform these snowfalls into precipitations, unlike other mountain ranges, where snowfalls can occur at very low temperatures, below zero degrees.”
Ombadi hopes that his climatologist colleagues will incorporate the distinction between snowfall and precipitation to improve global climate models, and that civil engineers and planners will use the data to better prepare for heavy rain events.
“We have to take these results into account when designing and building the infrastructures of these mountainous regions, so that they can withstand the negative consequences of increased extreme rainfall,” says Ombadi.
Meanwhile, countries continue to strive to meet the goals set by the Paris Agreement that would limit global warming to less than 2 degrees Celsius above pre-industrial levels.
“Our findings revealed a linear relationship between the level of warming and the increase in extreme precipitation: For example, 1 degree of warming causes 15% more rainfall, while 3 degrees leads to a 45% increase in precipitation.” , highlights Ombadi.
“There are many technologies underway that could help us reduce greenhouse gas emissions and global warming,” he adds. “To me, this study demonstrates the need to invest in these clean solutions, and also to start preparing now for the consequences of warming”, he concludes.
