Alan F. HamletPhilip W. MoteMartyn Clark

Dennis P. Lettenmaier

JISAO/SMA Climate Impacts Groupand Department of Civil and Environmental Engineering

University of Washington

March, 2004

Effects of Temperature and Precipitation Variability on Snowpack

Trends in the Mountain West

Current Climate 2020s 2040s

Snow Water Equivalent (mm)

VIC Simulations of April 1 Average Snow Water Equivalentfor Composite Scenarios (average of four GCM scenarios)

Climate Change in the WestThe main impact pathway : less snow

0

1000

2000

3000

4000

5000

6000

7000

8000

900010

/1

10/2

9

11/2

6

12/2

4

1/21

2/18

3/18

4/15

5/13

6/10 7/8

8/5

9/2

Date

Infl

ow

(ac

re-f

t) Simulated 20thCentury Climate

2020s ClimateChange Scenario

2040s ClimateChange Scenario

Effects to the Cedar River (Seattle Water Supply)for “Middle-of-the-Road” Scenarios

+1.7 C

+2.5 C

Linear Trends in Obs. April 1 SWE from 1950-1997From Snow Course Data

Source: Mote et al. (2004)

Snowmelt runoff timing trends, 1948-2000

Graphic provided by Dan Cayan, Scripps Institute of Oceanography and the USGS. To appear in Climatic Change, 2003

150000

200000

250000

300000

350000

400000

450000

190

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Ap

r-S

ept F

low

(cfs

)

Effects of the PDO and ENSO on Columbia River Summer Streamflows

Cool CoolWarm Warm

high highlow low

Ocean Productivity

PDO

Snow Model

Schematic of VIC Hydrologic Model and Energy Balance Snow Model

Preprocessing Regridding

Lapse Temperatures

Correction to RemoveTemporal

Inhomogeneities

HCN/HCCDMonthly Data

Topographic Correction forPrecipitation

Coop Daily Data

PRISM MonthlyPrecipitation

Maps

Schematic Diagram for Data Processing of VIC Meteorological Driving Data

Preprocessing Regridding

Lapse Temperatures

Correction to RemoveTemporal

Inhomogeneities

HCN/HCCDMonthly Data

Topographic Correction forPrecipitation

Coop Daily Data

PRISM MonthlyPrecipitation

Maps

Preprocessing Regridding

Lapse Temperatures

Correction to RemoveTemporal

Inhomogeneities

HCN/HCCDMonthly Data

Topographic Correction forPrecipitation

Coop Daily Data

PRISM MonthlyPrecipitation

Maps

Schematic Diagram for Data Processing of VIC Meteorological Driving Data

Result:Daily Precipitation, Tmax, Tmin

1915-1997

Met Data1915-1997

VIC SWELinear Trend

Analysis

Overview of Simulation and Analysis

•1916-1997 •1924-1946 (cool to warm PDO)•1947-1997 (warm to cool PDO)•1924-1946 with 1977-1995 (warm to warm PDO)

Linear Trends:

Experiments:•Base—combined effects of temp and precip trends•Static Precip—effects of temperature trends only•Static Temp—effects of precipitation trends only

Source: Mote et al. (2004)

Trends in April 1 SWE 1950-1997

Trend %/yr

djf

avg

T (

C)

Trend %/yr

Trend Results

Red = PNWBlue = CAGreen = COBlack = GBAS

Fig 31916-1997

A)

B)

C)

Trend %/yr

Trend %/yr

Trend %/yr

djf

avg

T (

C)

djf

avg

T (

C)

djf

avg

T (

C)

Trend %/yr

Trend %/yr

Trend %/yr

Both Temp and Precip

Precip Effects Only

Temp Effects Only

Fig 41924-1976

A)

B)

C)

Trend %/yr

Trend %/yr

Trend %/yr

djf

avg

T (

C)

djf

avg

T (

C)

djf

avg

T (

C)

Trend %/yr

Trend %/yr

Trend %/yr

Both Temp and Precip

Precip Effects Only

Temp Effects Only

Fig 51947-1997

A)

B)

C)

Trend %/yr

Trend %/yr

Trend %/yr

djf

avg

T (

C)

djf

avg

T (

C)

djf

avg

T (

C)

Trend %/yr

Trend %/yr

Trend %/yr

Both Temp and Precip

Precip Effects Only

Temp Effects Only

Fig 61924-1946with1977-1995

A)

B)

C)

Trend %/yr

Trend %/yr

Trend %/yr

djf

avg

T (

C)

djf

avg

T (

C)

djf

avg

T (

C)

Trend %/yr

Trend %/yr

Trend %/yr

Both Temp and Precip

Precip Effects Only

Temp Effects Only

Physical Characteristics of the Mountain West

Elevation (m) DJF Temp (C) NDJFM PCP (mm)

Figure 7

1

2

3

Region 1 (Coastal)Region 2 (Inland)Region 3 (Interior)

Region 1

Region 2

Region 3

Trend %/yr

Trend %/yr

Trend %/yr

Trend %/yr

djfa

vgT

(C

)

Trends from 1916-1997

Dworshak

y = 0.0001x + 0.7149

0.5

0.6

0.7

0.8

0.9

streamflow

Linear (streamflow)

Dworshak

y = -0.0006x + 0.506

0.3

0.4

0.5

0.6

0.7

0.8

streamflow

Linear (streamflow)

May-Sept

June-Sept

Fraction of Annual RunoffOccurring From:

BASE

Dworshak

y = -0.0004x + 0.7493

0.5

0.6

0.7

0.8

0.9

streamflow

Linear (streamflow)

Dworshak

y = -0.0008x + 0.5072

0.3

0.4

0.5

0.6

0.7

0.8

streamflow

Linear (streamflow)

May-Sept

June-Sept

STATIC PRECIP

Fraction of Annual RunoffOccurring From:

Conclusions

The Western US is experiencing losses of SWE in sensitive areas (such as coastal mountain ranges) due to observed regional warming.

Without precipitation trends, essentially the entire mountain west would be experiencing declines in April 1 SWE due to large-scale warming.

Precipitation trends are the major driver in areas with cold winter temperatures.

Precipitation trends seem to be most strongly associated with regionally-specific decadal scale climate variability. A consistent global warming signal for precipitation across the West is not apparent.

Decadal variability is apparently not a good explanation for losses of snowpack associated with temperature trends. (E.g. any period paired with 1977-1997 will show negative trends in SWE associated with temperature).

These results are consistent with the broad features of many global warming scenarios—i.e. rapid warming since the mid 1970s, modest increases in winter precipitation, streamflow timing shifts.