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Climate Warming Impacts on Snow and Water Resources

Mapping Temperature-Sensitive Snowpacks, Frequency of Warm Winters, and Winter Precipitation Variability in the Western U.S. Climate Warming Impacts on Snow and Water Resources. (From Barnett et al., 2005; Nature).

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Climate Warming Impacts on Snow and Water Resources

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  1. Mapping Temperature-Sensitive Snowpacks, Frequency of Warm Winters, and Winter Precipitation Variability in the Western U.S. CIG Seminar, 26 Oct 2006

  2. Climate Warming Impacts on Snow and Water Resources (From Barnett et al., 2005; Nature) CIG Seminar, 26 Oct 2006

  3. Fractional change in winter snowfall water equivalent (adjusted for changes in precipitation) for WY 1949 - 2004. Knowles et al., 2006 Trends in measured winter temperature Courtesy Phil Mote, UW/CIG CIG Seminar, 26 Oct 2006

  4. Research Goals • Map temperature sensitive snowcover in the Western US • Quantify the relative frequency of warm winters (recent and projected) for selected subregions • Consider impacts on • hydrology • ski industry • Explore variability of winter precipitation on a watershed scale CIG Seminar, 26 Oct 2006

  5. Model output is too coarse (10 x 12 km) for watershed-scale hydrology Data-driven approach can provide higher resolution Payne et al., 2004 CIG Seminar, 26 Oct 2006

  6. Mapping temperature sensitive snowcover Snow classification based on Sturm et al., 1995: • Used temperature, precipitation, and wind speed to define snow classes • Original scheme used 0.5 x 0.5 degree grid resolution (Data courtesy National Snow and Ice Data Center) CIG Seminar, 26 Oct 2006

  7. Focus Areas Background image: PRISM digital elevation CIG Seminar, 26 Oct 2006

  8. DATA • PRISM gridded temperature and precipitation (interpolated from station data) • Historical monthly averages for 1971-2000 • 4 km x 4 km • MODIS Vegetation Cover Fraction (VCF) product (proxy for wind speed) CIG Seminar, 26 Oct 2006

  9. Precipitation is classified based on a temperature threshold, Tsnow, above which all precipitation is considered to fall as rain 0oC 0oC (a) Colder than 0oC Colder than 0oC (b) Because this threshold temperature is somewhat arbitrary, we use a range of temperatures in the snow classification exercise CIG Seminar, 26 Oct 2006

  10. Now… • Let’s assume climate warming over the next 40-60 years • Using the IPCC Climate Model output for the Pacific Northwest, the models are in good general agreement that temperatures will continue to warm at the rate of 0.2-0.6oC per decade • Here, we modify the transition temperature for warm vs. cold snow by 0.5 degree increments for a total warming of 2oC CIG Seminar, 26 Oct 2006

  11. Decision tree thresholds • Snow vs. No Snow: DJF Tmean-2.0to +2.0oC, in 0.5oC increments • Warm snow vs. cold snow: DJF Tmean -2.0 to 0oC, in 0.5oC increments • High precip vs. low precip: DJF P  2mm/day • Low wind vs. high wind: Forest cover density  35% CIG Seminar, 26 Oct 2006

  12. CIG Seminar, 26 Oct 2006

  13. US Snowcover Classification CIG Seminar, 26 Oct 2006

  14. CIG Seminar, 26 Oct 2006

  15. CIG Seminar, 26 Oct 2006

  16. Sensitivity to Rain-Snow Temperature Threshold (6.5 km3 of water) CIG Seminar, 26 Oct 2006

  17. Percent of Snow-Covered Area That is “At-Risk” Pacific Northwest study area………<3% • Oregon Cascades…………………..22% • Washington Cascades……………..12% • Olympic Range.……………………..61% CIG Seminar, 26 Oct 2006

  18. California Sierra Nevada Total snow area = 24,128 km2 At-risk snow area = 7872 km2 At-risk snow percent = 32% 2300 - 2700 m elevation CIG Seminar, 26 Oct 2006

  19. White Mountains, Arizona Total snow area = 1600 km2 At-risk snow area = 640 km2 At-risk snow percent = 40% 2400 - 2600 m elevation CIG Seminar, 26 Oct 2006

  20. What is the relative frequency of warm winters? First, what is a “warm winter”? • Winter = DJF • Warm = When at least one winter month has a mean temperature above the 0oC • If Tmean LE 0oC in December and January and February then it is not a warm winter Relative Frequency: • The number of times (N’) an event occurs within a number of N trials • Thus, the relative frequency of an event is N’/N CIG Seminar, 26 Oct 2006

  21. We use monthly DJF Tmean from PRISM data (1971-2000) Evaluate relative frequency of DJF Tmean below a threshold temperature Shift threshold temperature upwards by increments of 0.5oC (going from -2oC to 0oC) CIG Seminar, 26 Oct 2006

  22. CIG Seminar, 26 Oct 2006

  23. Current In 40-60 yrs Nolin and Daly, 2006 CIG Seminar, 26 Oct 2006

  24. California Ski Areas CIG Seminar, 26 Oct 2006

  25. Hydrologic Implications • Temporal centroid of hydrograph will continue to shift to earlier date (Stewart et al., 2005) • Snowmelt is a significant contributor to mountainfront groundwater recharge • Snowmelt vs. rainfall runoff • Occurs during season of low evapotranspiration • How will landscape controls (geology, vegetation) interact with climate controls to change the spatial and temporal patterns of streamflow? CIG Seminar, 26 Oct 2006

  26. Monthly discharge for the Clear Lake, OR watershed in two historical periods (1948-1952, 2001-2005) and a predicted future discharge from Jefferson et al., submitted to Hydrological Proc. CIG Seminar, 26 Oct 2006

  27. Winter Precipitation Variability • For individual watersheds, how variable has winter precipitation been over the past 30 years? • 30-year PRISM precipitation data, computed DJF total DJF precipitation for each year • Preliminary analysis only (mean and variance by watershed) CIG Seminar, 26 Oct 2006

  28. Oregon: Mean of aggregate December-January-February Precipitation (1971-2000) mean DJF aggregate ppt [m] CIG Seminar, 26 Oct 2006

  29. Oregon: Mean of aggregate December-January-February Precipitation (1971-2000) per Watershed mean DJF aggregate ppt [m] per watershed CIG Seminar, 26 Oct 2006

  30. Oregon: Variance of aggregate December-January-February Precipitation (1971-2000) per Watershed variance of DJF aggregate ppt [m2] per watershed CIG Seminar, 26 Oct 2006

  31. To summarize: • Data-driven approach is useful for sensitivity studies • “At risk” snow represents a large proportion of the Oregon and southern Washington Cascades, Olympic range, CA Sierra Nevada, and AZ White Mountains • Relative frequency of warm winters will likely influence lower elevation ski areas across the Western US • Hydrologic impacts are already evident • Mapping efforts such as this can help identify sensitive areas that need to be integrated into climate measurement networks See: Nolin, A. and C. Daly, 2006. Mapping “at-risk snow in the Pacific Northwest, USA, J. Hydrometeorology, in press. CIG Seminar, 26 Oct 2006

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