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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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Mapping Temperature-Sensitive Snowpacks, Frequency of Warm Winters, and Winter Precipitation Variability in the Western U.S.

CIG Seminar, 26 Oct 2006


Climate warming impacts on snow and water resources
Climate Warming Impacts on Snow and Water Resources Winters, and Winter Precipitation Variability in the Western U.S.

(From Barnett et al., 2005; Nature)

CIG Seminar, 26 Oct 2006


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


Research goals
Research Goals (adjusted for changes in precipitation) for WY 1949 - 2004.

  • 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


Model output is too coarse (adjusted for changes in precipitation) for WY 1949 - 2004.

(10 x 12 km) for watershed-scale hydrology

Data-driven approach can provide higher resolution

Payne et al., 2004

CIG Seminar, 26 Oct 2006


Mapping temperature sensitive snowcover
Mapping temperature sensitive snowcover (adjusted for changes in precipitation) for WY 1949 - 2004.

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


Focus Areas (adjusted for changes in precipitation) for WY 1949 - 2004.

Background image: PRISM digital elevation

CIG Seminar, 26 Oct 2006


DATA (adjusted for changes in precipitation) for WY 1949 - 2004.

  • 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


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


  • Now… threshold, T

  • 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


Decision tree thresholds
Decision tree thresholds threshold, T

  • 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



Us snowcover classification
US Snowcover Classification threshold, T

CIG Seminar, 26 Oct 2006




Sensitivity to rain snow temperature threshold
Sensitivity to Rain-Snow Temperature Threshold threshold, T

(6.5 km3 of water)

CIG Seminar, 26 Oct 2006


Percent of snow covered area that is at risk
Percent of Snow-Covered Area That is “At-Risk” threshold, T

Pacific Northwest study area………<3%

  • Oregon Cascades…………………..22%

  • Washington Cascades……………..12%

  • Olympic Range.……………………..61%

CIG Seminar, 26 Oct 2006


California Sierra Nevada threshold, T

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


White Mountains, Arizona threshold, T

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


What is the relative frequency of warm winters
What is the relative frequency of warm winters? threshold, T

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


We use monthly DJF T threshold, 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



Current threshold, T

In 40-60 yrs

Nolin and Daly, 2006

CIG Seminar, 26 Oct 2006


California ski areas
California Ski Areas threshold, T

CIG Seminar, 26 Oct 2006


Hydrologic implications
Hydrologic Implications threshold, T

  • 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


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


Winter precipitation variability
Winter Precipitation Variability historical periods (1948-1952, 2001-2005) and a predicted future discharge

  • 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


Oregon: Mean of aggregate December-January-February Precipitation (1971-2000)

mean DJF aggregate ppt [m]

CIG Seminar, 26 Oct 2006


Oregon: Mean of aggregate December-January-February Precipitation (1971-2000) per Watershed

mean DJF aggregate ppt [m] per watershed

CIG Seminar, 26 Oct 2006


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


To summarize
To summarize: Precipitation

  • 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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