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The West’s declining snowpack: is global warming to blame?

The West’s declining snowpack: is global warming to blame?. Philip Mote Climate Impacts Group University of Washington. 20th century decline in NH snow cover. R.D. Brown, J. Climate, 2000. Trends in snowpack. Use VIC and met data to evaluate trends, roles of temperature and precipitation.

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The West’s declining snowpack: is global warming to blame?

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  1. The West’s declining snowpack: is global warming to blame? Philip Mote Climate Impacts Group University of Washington

  2. 20th century decline in NH snow cover R.D. Brown, J. Climate, 2000

  3. Trends in snowpack Use VIC and met data to evaluate trends, roles of temperature and precipitation

  4. Snow course data Collected primarily ~April 1 beginning in 1915 (most in 1940s), added other months Purpose: streamflow forecasting Administered by USDA Natural Resource Conservation Service Mostly discontinued, some replaced by SNOTEL

  5. Snow course ???

  6. Data: NRCS CA DWR BC SRM Courtesy USDA NRCS

  7. Courtesy USDA NRCS

  8. decrease increase Trends in April 1 SWE, 1950-2000 824 snow courses 73% – trends Large – trends PNW Some + trends SW

  9. decrease increase Trends in April 1 SWE, 1950-2000 Relative to 1950 value

  10. Former snow course location

  11. Relating SWE to climate data • US Historical Climate Network (USHCN) • Use nearest 5 stations to form reference time series T(t) and P(t) • Regression: SWE(t)=aTT(t) + aPP(t)+(t)

  12. At almost every USHCN station, winters warmed + signs: warming but not statistically significant

  13. Winters wetter in much of the West Drier in some of Northwest (PDO)

  14. Correlations between Nov-Mar climate and Apr 1 SWE X-direction: precip Y-direction: temp Coldest locations insensitive to temperature Cascades very sensitive

  15. April 1 SWE trends, 1930-2002 aP<P> aT<T>

  16. April 1 SWE trends, 1950-2002 aT<T> aP<P>

  17. SNOTEL data: cold-season melt events vs Apr 1 SWE

  18. Relative trends 1950-1997

  19. Declining snowpack in the Cascades From a simulation with a hydrology model

  20. 1950-1997 relative trends vs DJF temperature Obs VIC

  21. Trends in April 1 SWE in VIC simulation with fixed precipitation

  22. As the West warms, winter flows rise and summer flows drop Figure by Iris Stewart, Scripps Inst. of Oceanog. (UC San Diego)

  23. Simulation of future snowpack with VIC hydrologic model Trend in total April 1 snowpack, 1950-97: -11% Courtesy Andrew W. Wood, University of Washington

  24. SNOTEL data: cold-season melt events vs Apr 1 SWE Figure by Martyn Clark, Univ. of Colorado

  25. Regional average April 1 SWE Obs o VIC x

  26. Changes in SWE vs changes in precip

  27. Trends/15yr in snow days in Switzerland From Scherrer et al., GRL 2004

  28. Trends in Swiss snow days attributed to temperature and precipitation days/42 yrs. days/42 yrs. Attribution of trends shown by pseudo vectors; altitude and latitude precip and temp attributions; contour lines indicate the sum. From Scherrer et al., GRL 2004

  29. Conclusions • Observations show substantial declines in western snowpack; corroboration with VIC suggests they are real and largely temperature-driven • Cascades, N. Calif most temp-sensitive • Large increases in precipitation have offset warming in some places • Is global warming causing the decline? Too soon to tell.

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