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   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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   
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   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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