As rising global temperatures shift snow to rain, mountains across the Northern Hemisphere will be hotspots for extreme rainfall events that could trigger floods and landslides -- potentially impacting a quarter of the world's population

Date:
June 28, 2023
Source:
DOE/Lawrence Berkeley National Laboratory
Summary:
A new study finds that as rising global temperatures shift snow to
rain, mountains across the Northern Hemisphere will be hotspots for
extreme rainfall events that could trigger floods and landslides --
potentially impacting a quarter of the world's population.


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FULL STORY ==========================================================================
As the world warms, extreme weather events grow -- and they also change.

Researchers at the Department of Energy's Lawrence Berkeley National
Laboratory (Berkeley Lab) found that climate change is shifting snowfall
to rainfall on mountains across the Northern Hemisphere. Those surges
of liquid water bring a distinct set of dangers, including floods,
landslides, and soil erosion.

"One quarter of the global population lives in or downstream from
mountainous regions," said Mohammed Ombadi, first author of the paper
published today in Nature. "They are going to be directly affected by
this risk." Scientists already expect climate change to increase the
volume of water falling during extreme events (which typically take place
over a few hours to a day), but this study is the first time researchers
have looked at whether that extreme precipitation comes as rain or
snow. They found that the fraction of water falling as snow decreased
in mountainous regions, falling instead as rain -- making mountains particularly susceptible to extreme rain hazards. They even put a number
to it: For every 1 degree Celsius increase in the global temperature, researchers expect an average of 15% more rain at high elevations.

"This increase in rainfall extremes is not only something that is going
to happen from now until the end of the 21st century -- we're already
seeing it," Ombadi said. "That same rate was also evident in the data
from 1950 to 2019.

Rainfall extremes in mountains have already been increasing, and will
continue to change with that 15% rate." While all the mountain ranges
in the Northern Hemisphere are seeing the shift from snow to rain,
those at greatest risk of extreme rainfall events are the North American Pacific mountain ranges (the Cascades, Sierra Nevada, and coastal ranges
from Canada to Southern California), the Himalayas, and high- latitude
regions. Researchers are still working to understand why those areas are
at higher risk than other mountain ranges such as the Rockies or the Alps.

"We think that North American Pacific mountain ranges are more susceptible
to the risk of rainfall extremes than other mountain ranges because
a significant portion of snowfall in this region typically occurs at temperatures just below zero degrees Celsius," Ombadi said. "The slightest change in air temperature will shift this snowfall to rainfall. This
is unlike other mountain ranges where snowfall may occur at very low temperatures below zero degrees." Ombadi hopes that fellow climate
scientists will incorporate the distinction between snowfall and rainfall
to improve global climate models, and that civil engineers and planners
will use the data to better prepare for intense rain events.

"We need to factor these results into how we design and build the infrastructure in these mountainous regions, so that they can withstand
the negative consequences of increases in rainfall extremes," Ombadi said.

Meanwhile, countries continue efforts to meet targets established 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 rainfall: For instance, 1 degree of
warming causes 15% more rain, while 3 degrees leads to a 45% increase
in rainfall," Ombadi said.

"There are many technologies in progress that could help us reduce
greenhouse gas emissions and how much the planet warms. To me, this
study shows the need to invest in those clean solutions, and also start preparing for the consequences of warming now." This work was funded by
the DOE Office of Science Biological and Environmental Research program.

* RELATED_TOPICS
o Earth_&_Climate
# Global_Warming # Environmental_Issues # Climate
# Weather # Water # Environmental_Awareness #
Snow_and_Avalanches # Acid_Rain
* RELATED_TERMS
o Winter_storm o Effects_of_global_warming o Volcano o Avalanche
o Lake_effect_snow o Taiga o Coriolis_effect o Rain

========================================================================== Story Source: Materials provided by
DOE/Lawrence_Berkeley_National_Laboratory. Original written by Lauren
Biron. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mohammed Ombadi, Mark D. Risser, Alan M. Rhoades, Charuleka
Varadharajan.

A warming-induced reduction in snow fraction amplifies rainfall
extremes.

Nature, 2023; DOI: 10.1038/s41586-023-06092-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/06/230628130404.htm

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