MSGID: 1:317/3 646c4172   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Earlier snowpack melt in Western US could bring summer water scarcity   
      
      
     Date:   
         May 22, 2023   
     Source:   
         University of Colorado at Boulder   
     Summary:   
         Mountain snowpack, typically seen as the water tower of the Western   
         United States and Canada, is in decline, according to a new study.   
      
         Researchers created the Snow Storage Index to assess snow water   
         storage from 1950-2013 and found that storage has significantly   
         declined in more than 25% of the Mountain West, in part because   
         more snow is melting during winter and spring.   
      
      
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   FULL STORY   
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   Snow is melting earlier, and more rain is falling instead of snow in   
   the mountain ranges of the Western U.S. and Canada, leading to a leaner   
   snowpack that could impact agriculture, wildfire risk and municipal water   
   supplies come summer, according to a new study from the University of   
   Colorado Boulder.   
      
   Published in Nature Communications Earth & Environment, the study   
   documents more than 60 years of change in snowpack water storage across   
   Western North America. It found that from 1950 to 2013, snowpack water   
   storage has significantly declined in more than 25% of the Mountain   
   West, in part because more snow is melting during winter and spring,   
   eroding this seasonal boundary.   
      
   "On average and in every mountainous region that we looked at, snow   
   melt is occurring closer in time to when it fell," said Kate Hale,   
   lead author of the study and a 2022 geography graduate. "The timing   
   of water availability is shifting toward earlier in the springtime,   
   with less snow melt and water availability later in the summertime,   
   suggesting that there will be water scarcity later in the year."   
   Timing is everything The Western U.S. and Canada depend on snow for most   
   of their water. The Rocky Mountains, Sierra Nevadas and other mountain   
   ranges have long served as, essentially, water towers for the region:   
   They store snow throughout the winter, which then melts and becomes   
   available as water in spring and summer, when demand is greatest.   
      
   Every year on April 1, state and regional water managers use a metric   
   known as snow water equivalent (SWE) -- how much water will be produced   
   when an amount of snow melts -- to predict and plan for water resources   
   that year, said Hale, now a postdoctoral researcher at University   
   of Vermont.   
      
   But that April 1 snapshot is exactly that: one moment in time. It doesn't   
   reveal if that snow slowly accumulated over the past six months, if it   
   all fell in one giant heap on March 31, or if it was already melting.   
      
   "From a hydrologic perspective, the only thing that's unique about   
   snow is that it delays the timing of water input to watersheds. And   
   just looking at a snapshot of snow water equivalent doesn't give you a   
   sense as to how long that snow water equivalent has been on the ground,"   
   said Noah Molotch, associate professor of geography and fellow at the   
   Institute of Arctic and Alpine Research (INSTAAR) at CU Boulder.   
      
   So Hale used two publicly available data sources to develop a new   
   measurement known as Snow Storage Index (SSI) that incorporates the   
   timingand amount of snowfall, as well as snowmelt, before and after   
   April 1. In contrast to the singular moment in time captured by SWE,   
   Hale's SSI shows a metaphorical video: incorporating into one number,   
   the time between when rain or snow falls on a landscape in the winter   
   season and when it becomes available to that area as surface water.   
      
   "The snow storage index allows us to look at snow water storage, not just   
   in the context of how much is there at any given time, but the duration   
   of that storage on the ground," said Molotch.   
      
   This allowed the researchers to analyze how well each mountainous region   
   of the West has acted as a water tower over the past 60 years and discover   
   that their performance has been declining across the board.   
      
   Managing water now and for the future A "high" SSI -- a number as close to   
   1.0 as possible -- was found in places where snowfall is very seasonal. In   
   the Cascades, for example, snow accumulates in the fall and winter season,   
   and is stored up to six months before melting somewhat continuously   
   in the spring and summer. Here in Colorado's Rocky Mountains, however,   
   the SSI is lower -- somewhere between 0 and 0.5 -- which means that snow   
   both accumulates and melts throughout the colder half of the year.   
      
   But because the Rockies and the Front Range are already used to this   
   alternating pattern of snowfall and snowmelt during winter and spring   
   seasons, as a region it may adjust easier to similar patterns of   
   decreased snowpack water storage associated with global warming. The   
   mountain regions near the West Coast that are highly reliant on snowpack   
   meltwater in the spring and summer, however, may be in for a painful   
   adjustment when that water melts earlier in the year -- and is simply   
   no longer available come late summer.   
      
   The researchers hope that this new measurement can serve as a tool for   
   scientists and water resource managers to make better predictions and,   
   when necessary, plan ahead for less.   
      
   Half a century ago, an era of dam building in the Western United States   
   allowed the region to flourish in terms of access to water for cities   
   and for agriculture, said Molotch. But as these "water towers" melt away,   
   so too may the reservoirs they filled.   
      
   "The snowpack is eroding and disappearing before our eyes. That's going   
   to present challenges in terms of managing the infrastructure that's   
   allowed the Western United States to flourish over the last 100 years,"   
   said Molotch.   
      
   Additional authors on this publication include: Keith Jennings,   
   Lynker, Boulder, Colorado; Keith Musselman, Department of Geography and   
   theInstitute of Arctic and Alpine Research (INSTAAR), CU Boulder; and   
   Ben Livneh, Cooperative Institute for Research in Environmental Sciences   
   (CIRES) and the Department of Civil, Environmental, and Architectural   
   Engineering, CU Boulder.   
      
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Snow_and_Avalanches # Water # Drought_Research #   
                   Environmental_Issues # Ecosystems # Pollution #   
                   Global_Warming # Sustainability   
       * RELATED_TERMS   
             o Lake_effect_snow o Snow o Mount_Rainier o Avalanche o   
             North_American_blizzard_of_2006 o Precipitation_(meteorology)   
             o Antarctic_ice_sheet o Iceberg   
      
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   Story Source: Materials provided by   
   University_of_Colorado_at_Boulder. Original written by Kelsey   
   Simpkins. Note: Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Katherine E. Hale, Keith S. Jennings, Keith N. Musselman,   
      Ben Livneh,   
         Noah P. Molotch. Recent decreases in snow water storage in western   
         North America. Communications Earth & Environment, 2023; 4 (1)   
         DOI: 10.1038/ s43247-023-00751-3   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/05/230522131337.htm   
      
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