Mountain Snowpack,Variations and Influencing Factors in the

Western US: Two Decades of SnoTel Data

Mark Losleben1, Nick Pepin2, Kurt Chowanski11 Mountain Research Station, INSTAAR2 University of Portsmouth, UK

Significance and ImportanceSnowpack variability, both in amount and time, impacts planning for future water needs of human society, and sets boundary conditions for available water to ecosystems. (Mountains are the water towers of the west).

Variability and trend analyses may point to areas of greatest and least vulnerability to snowpack changes in the future.

QuestionsHow are Snow Water Equivalence (SWE), and Total Winter Precipitation (PPT) changing over time and by elevation?

Does SWE change only due to changes in precipitation?

Do SWE changes correlate with temperature changes?

Which areas are most variable and possibly most vulnerable to future change?

ApproachAnalyses for trends and variability through time and by elevation in the Western US as a whole, and in eight smaller regions roughly defined by mountain ranges.

We use: SnoTel Data:

Snowpack (SWE)

Cumulative Winter Precipitation (PPT) (Winter is October 1 through April 1)

Surface Temperature

Indices: Snowpack Index (SI)

FASTDIF (future work)

DefinitionsSnowpack Index (SI) = % Average SWE / % Average PPT (Controls for PPT variability) [Development beyond Serreze et al (2001) SWE/PPT ratio] SI Interpretation: Standardizes for precipitation

SI > 1 ; More water is sequestered in snowpack than normal for the winter precipitation received

SI = 1 ; Average SI < 1 ; Less water is sequestered in snowpack than

normal for winter precipitation received FASTDIF

Difference between the surface (screen level) and free air (above boundary layer) temperatures at the same elevation Interpretation: relates to changes in radiation regime

Coefficient of Variance (CV) used with SWE and PPT CV = Standard Deviation / Mean

Data

SWE, PPT, Surface Temperatures from NRCS SnoTelNetwork (via Mark Serreze)

FASTDIF uses both SnoTel and NCAR-NCEP reanalysis temperatures

Average SWE & PPT from NRCS

Study Period

1979 – 1999 (SnoTel Data began 1979)

April 1 conditions: Snowpack SWE

Cumulative values are from October 1 to April 1 (Water Year Basis): PPT & Temperature

-124 -122 -120 -118 -116 -114 -112 -110 -108 -106 -104

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Site Map

Latit

ude

Longitude

-124 -122 -120 -118 -116 -114 -112 -110 -108 -106 -104

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Results

April 1 SWE, & Oct 1-April 1 PPTWestern US

%SWE = -0.0075x + 1.0681

40%

80%

120%

160%

79 81 83 85 87 89 91 93 95 97 99

Year

Per

cent

%SWE %PPT Linear (%SWE)

Arizona

%SWE = -0.0262x + 1.1834

0%100%200%300%400%

79 81 83 85 87 89 91 93 95 97 99

Year

Per

cent

California

%SWE = -0.002x + 1.0317

0%100%200%300%400%

79 81 83 85 87 89 91 93 95 97 99

Year

Per

cent

Northern New Mexico & Southern Colorado

%SWE = -0.0285x + 1.373

0%50%

100%150%200%

79 81 83 85 87 89 91 93 95 97 99

Year

Per

cent

Colorado

%SWE = -0.0038x + 1.0349

60%80%

100%120%140%

79 81 83 85 87 89 91 93 95 97 99

Year

Per

cent

Idaho & Montana

%SWE = 0.0024x + 0.9262

40%

80%

120%

160%

79 81 83 85 87 89 91 93 95 97 99

Year

Per

cent

Oregon & Washington

%SWE = -0.0057x + 1.0516

0%50%

100%150%200%

79 81 83 85 87 89 91 93 95 97 99

Year

Per

cent

Utah

%SWE = -0.0178x + 1.2165

40%

80%

120%

160%

79 81 83 85 87 89 91 93 95 97 99Year

Per

cent

Wyoming

%SWE = 0.0058x + 0.9156

60%80%

100%120%140%

79 81 83 85 87 89 91 93 95 97 99

Year

Per

cent

April 1 Snowpack IndexWestern US

SI = -0.0066x + 1.0338

0.60.81.01.21.4

79 81 83 85 87 89 91 93 95 97 99

Year

SI

SI Linear (SI)

Arizona

SI = -0.0252x + 1.0269

0.0

1.0

2.0

3.0

79 81 83 85 87 89 91 93 95 97 99

Year

SI

California

SI = 0.001x + 0.9033

0.4

0.8

1.2

1.6

79 81 83 85 87 89 91 93 95 97 99

Year

SI

Northern New Mexico & Southern Colorado

SI = -0.0162x + 1.1567

0.4

0.8

1.2

1.6

79 81 83 85 87 89 91 93 95 97 99

Year

SI

Colorado

SI = -0.0022x + 1.0132

0.80.91.01.11.2

79 81 83 85 87 89 91 93 95 97 99

Year

SI

Idaho & Montana

SI = -0.0024x + 0.9997

0.80.91.01.11.2

79 81 83 85 87 89 91 93 95 97 99

Year

SI

Oregon & Washington

SI = -0.0064x + 1.0167

0.00.5

1.01.5

2.0

1 3 5 7 9 11 13 15 17 19 21

Year

SI

Utah

SI = -0.0111x + 1.0988

0.60.8

1.01.2

1.4

79 81 83 85 87 89 91 93 95 97 99

Year

SI

Wyoming

SI = 0.0021x + 0.9908

0.8

0.91.01.1

1.2

79 81 83 85 87 89 91 93 95 97 99

Year

SI

Western US

-10

-5

0

5

82 84 86 88 90 92 94 96 98

Year

Tem

pera

ture

(D

eg C

)

AvgMaxTmp AvgMinTmp

Arizona

-10-505

1015

82 84 86 88 90 92 94 96 98

Year

Tem

pera

ture

(Deg

C

)

California

-10

-5

0

5

10

82 84 86 88 90 92 94 96 98

Year

Tem

pera

ture

(D

eg

C)

Northern New Mexico & Southern Colorado

-15-10-505

10

82 84 86 88 90 92 94 96 98

Year

Tem

pera

ture

(Deg

C

)

Colorado

-15

-10

-5

0

5

82 84 86 88 90 92 94 96 98

Year

Tem

pera

ture

(Deg

C

)

Idaho & Montana

-15

-10

-5

0

5

82 84 86 88 90 92 94 96 98

Year

Tem

pera

ture

(Deg

C

)

Oregon & Washington

-15-10-505

10

82 84 86 88 90 92 94 96 98

Year

Tem

pera

ture

(D

eg

C)

Utah

-15-10-505

10

82 84 86 88 90 92 94 96 98

Year

Tem

pera

ture

(D

eg

C)

Wyoming

-15

-10

-5

0

5

82 84 86 88 90 92 94 96 98

YearT

empe

ratu

re (D

eg

C)

Oct1-Apr1 Avg Max & Min Temp

Trends April1: %SWE, %PPT, SIConfidence > 95%

-5%

0%

5%

West AZ CA NMCO CO IDMT ORWA UT WY

UT %SWE is at 93.5% Confidence

% C

hang

e P

er Y

ear

%SWE %PPT SI

Trends Oct1-April1: AvgTMax, AvgTMinConfidence > 95%

-0.4

-0.2

0

0.2

0.4

Wes

t

AZ

CA

NM

CO

CO

IDM

T

OR

WA UT

WY

CO AvgTMin is at 93.4% Confidence

Deg

rees

C P

er Y

ear

AvgTMax AvgTMin

Western US Means 1977-1999Confidence > 95%

96.85%

99.70%

94.97%

90%

95%

100%

%SWE %PPT SI

Per

cen

t

Western US Avgerage Max and Min Tempurature Oct1-April1

2.922

-8.068

-10

-8

-6

-4

-2

0

2

4

AvgTMax AvgTMin

Deg

ree

C

Trends

-124 -122 -120 -118 -116 -114 -112 -110 -108 -106 -104

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48

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

April 1 Snowpack Index

SI

Latit

ude

Longitude

-124 -122 -120 -118 -116 -114 -112 -110 -108 -106 -104

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0

4

8

12

16

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28

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48

52

56

60

April 1 SWE and Sites

Latit

ude

Longitude

SWE

-124 -122 -120 -118 -116 -114 -112 -110 -108 -106 -104

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48

Longitude

05101520253035404550556065707580859095100105110115120

April 1 cummulative Precipitation

cumPPT

Latit

ude