Alan F. Hamlet, Philip W. Mote, Dennis P. Lettenmaier

•JISAO/CSES Climate Impacts Group•Dept. of Civil and Environmental Engineering

University of Washington

Hydrologic Implications of Climate Change for the Western U.S.

Example of a flawed water planning study:The Colorado River Compact of 1922

The Colorado River Compact of 1922 divided the use of waters of the Colorado River System between the Upper and Lower Colorado River Basin. It apportioned **in perpetuity** to the Upper and Lower Basin, respectively, the beneficial consumptive use of 7.5 million acre feet (maf) of water per annum. It also provided that the Upper Basin will not cause the flow of the river at Lee Ferry to be depleted below an aggregate of 7.5 maf for any period of ten consecutive years. The Mexican Treaty of 1944 allotted to Mexico a guaranteed annual quantity of 1.5 maf. **These amounts, when combined, exceed the river's long-term average annual flow**.

      

Despite a general awareness of these issues in the water planning community, there is growing evidence that future climate variability will not look like the past and that current planning activities, which frequently use a limited observed streamflow record to represent climate variability, are in danger of repeating the same kind of mistakes made more than 80 years ago in forging the Colorado River Compact.

Long-term planning and specific agreements influenced by this planning (such as long-term transboundary agreements) should be informed by the best and most complete climate information available, but frequently they are not.

What’s the Problem?

Image Credit: National Snow and Ice Data Center, W. O. Field, B. F. Molniahttp://nsidc.org/data/glacier_photo/special_high_res.html

Aug, 13, 1941 Aug, 31, 2004

Recession of the Muir Glacier

DJF Temp (°C) NDJFM Precip (mm)

PNW

CA CRB

GB

Cool Season Climate of the Western U.S.

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Ap

r-S

ept F

low

(cfs

)Natural Flow Columbia River at The Dalles

Patterns of ENSO Related Variability About a Shifting Long-Term Mean Seem to be Robust in the 20th Century

Red = Warm ENSO, Green = ENSO Neutral, Blue = Cool ENSO

Global Climate Change Scenarios and Hydrologic Impacts for the PNW

Consensus Forecasts of Temperature and Precipitation Changes from IPCC AR4 GCMs

Pacific Northwest

°C

0.4-1.0°C0.9-2.4°C 1.2-5.5°C

Obse

rved 2

0th

centu

ry v

ari

abili

ty

+1.7°C+0.7°C

+3.2°C

Pacific Northwest

% -1 to +3%

-1 to +9% -2 to +21%

Obse

rved 2

0th

centu

ry v

ari

abili

ty

+1% +2%

+6%

Will Global Warming be “Warm and Wet” or “Warm and Dry”?

Answer: Probably BOTH!

150000

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45000019

00

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Ap

r-S

ept F

low

(cfs

)

Natural Flow Columbia River at The Dalles

-3

-2

-1

0

1

2

3

419

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Std

An

om

alie

s R

elat

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to 1

961-

1990

PNW

CA

CRB

GB

Regionally Averaged Cool Season Precipitation Anomalies

PRECIP

Snow Model

Schematic of VIC Hydrologic Model and Energy Balance Snow Model

The warmer locations are most sensitive to warming

+2.3C,+6.8% winter precip

2060s

April 1 SWE (mm)

20th Century Climate “2040s” (+1.7 C) “2060s” (+ 2.25 C)

-3.6% -11.5%

Changes in Simulated April 1 Snowpack for the Canadian and U.S. portions of the Columbia River basin(% change relative to current climate)

-21.4% -34.8%

Mote P.W.,Hamlet A.F., Clark M.P., Lettenmaier D.P., 2005, Declining mountain snowpack in western North America, BAMS, 86 (1): 39-49

Trends in April 1 SWE 1950-1997

Trend %/yr

DJF

avg

T (

C)

Trend %/yr

Overall Trends in April 1 SWE from 1947-2003

Trend %/yr

DJF

avg

T (

C)

Trend %/yr

Temperature Related Trends in April 1 SWE from 1947-2003

Trend %/yr

DJF

avg

T (

C)

Trend %/yr

Precipitation Related Trends in April 1 SWE from 1947-2003

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oct nov dec jan feb mar apr may jun jul aug sep

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ted

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in A

vg R

un

off

(m

m)

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plus2c

Simulated Changes in Natural Runoff Timing in the Naches River Basin Associated with 2 C Warming

Impacts:•Increased winter flow•Earlier and reduced peak flows•Reduced summer flow volume•Reduced late summer low flow

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oct nov dec jan feb mar apr may jun jul aug sep

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plus2c

Chehalis River

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oct nov dec jan feb mar apr may jun jul aug sep

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m)

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plus2c

Hoh River

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m)

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plus2c

NooksackRiver

Mapping of Sensitive Areas in the PNW by Fraction of Precipitation Stored as Peak Snowpack

HUC 4 Scale Watersheds in the PNW

Changes in Flood Risk in the Western U.S.

-1.00

-0.50

0.00

0.50

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2.00

2.50

3.00

oct nov dec jan feb mar apr may jun jul aug sepL

inea

r T

ren

d (

Deg

. C p

er c

entu

ry)

CA

CRB

GBAS

PNW

0.00

0.50

1.00

1.50

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2.50

3.00

3.50

4.00

oct nov dec jan feb mar apr may jun jul aug sep

Lin

ear

Tre

nd

(D

eg. C

per

cen

tury

)

CA

CRB

GBAS

PNWTmin

Tmax

PNW

CA CRB

GB

Regionally Averaged Temperature Trends Over the Western U.S. 1916-2003

X20 2003 / X20 1915

DJF

Avg

Tem

p (

C)

DJF

Avg

Tem

p (

C)

Simulated Changes in the 20-year Flood Associated with 20th Century Warming

X20 2003 / X20 1915 X20 2003 / X20 1915

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-2

-1

0

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419

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Std

An

om

alie

s R

elat

ive

to 1

961-

1990

PNW

CA

CRB

GB

Regionally Averaged Cool Season Precipitation Anomalies

PRECIP

DJF

Avg

Tem

p (

C)

20-year Flood for “1973-2003” Compared to “1916-2003” for a Constant Late 20th Century Temperature Regime

X20 ’73-’03 / X20 ’16-’03

X20 ’73-’03 / X20 ’16-’03

150000

200000

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300000

350000

400000

450000

1900

1910

1920

1930

1940

1950

1960

1970

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1990

2000

Ap

r-S

ept F

low

(cfs

)Natural Flow Columbia River at The Dalles, OR

Effects of ENSO on Cool Season Climate in the PNW

Red = warm ENSO, Green = ENSO neutral, Blue = cool ENSO

DJF

Avg

Tem

p (

C)

DJF

Avg

Tem

p (

C)

DJF

Avg

Tem

p (

C)

X100 nENSO / X100 2003 X100 cENSO / X100 2003X100 wENSO / X100 2003

X100 nENSO / X100 2003 X100 cENSO / X100 2003X100 wENSO / X100 2003

Summary of Flooding Impacts

Rain Dominant Basins:Possible increases in flooding due to increased precipitation variability, but no significant change from warming alone.

Mixed Rain and Snow Basins Along the Coast:Strong increases due to warming and increased precipitation variability (both effects increase flood risk)

Inland Snowmelt Dominant Basins:Relatively small overall changes because effects of warming (decreased risks) and increased precipitation variability (increased risks) are in the opposite directions.

Landscape Scale Ecosystem Impacts

19101910 19301930 19501950 19701970 19901990 2010201000

1.01.0

2.02.0

3.03.0

4.04.0

5.05.0

6.06.0

YearYear

8.08.0

7.07.0

19991999

20012001

20002000

20032003

20022002

Ann

ual a

rea

(ha

× 1

06 ) a

ffect

ed b

y M

PB

in B

CA

nnua

l are

a (h

a ×

106 )

affe

cted

by

MP

B in

BC

200520059.09.0

20042004

Bark Beetle Outbreak in British Columbia

(Figure courtesy Allen Carroll)

Temperature thresholds for coldwater fish in freshwater

+1.7 °C+1.7 °C +2.3 °C+2.3 °C

• Warming temperatures will increasingly stress coldwater fish in the warmest parts of our region– A monthly average temperature of 68ºF (20ºC) has been used as an upper

limit for resident cold water fish habitat, and is known to stress Pacific salmon during periods of freshwater migration, spawning, and rearing

•Changes in water quantity and timingReductions in summer flow and water supplyIncreases in drought frequency and severityChanges in hydrologic extremes

Changing flood risk (up or down) Summer low flows

Changes in groundwater supplies•Changes in water quality

Increasing water temperatureChanges in sediment loading (up or down)Changes in nutrient loadings (up or down)

•Changes in land cover via disturbanceForest fireInsectsDiseaseInvasive species

Impact Pathways Associated with Climate

•Changes in energy resources and designHydropower Energy demand“Green” building design

•Changes in outdoor recreationTourismSkiingCampingBoating

•Changes in engineering design standardsRoad constructionStorm water systemsFlood plain definitionsBuilding designLand slide risks

Impact Pathways Associated with Climate

•Changes in transportation corridorsChanging risk of flooding, avalanche or debris

flows•Sea level rise

Coastal engineeringLand use planning

•Human health risksTemperature and water-related health risks

Impact Pathways Associated with Climate

•Anticipate changes. Accept that the future climate will be substantially different than the past.

•Use scenario based planning to evaluate options rather than the historic record.

•Expect surprises and plan for flexibility and robustness in the face of uncertain changes rather than counting on one approach.

•Plan for the long haul. Where possible, make adaptive responses and agreements “self tending” to avoid repetitive costs of intervention as impacts increase over time.

Approaches to Adaptation and Planning

Some Thoughts Regarding Civil Engineering Practice:

•The fundamental concept of fixed design standards related to water is unlikely to produce satisfactory outcomes in a rapidly evolving climate system.

•New design approaches that emphasize robustness in the face of uncertainty and/or adaptability in the face of rapid change will be needed.

•Academic research is playing a significant role in shaping future engineering practice associated with climate change adaptation, but academic training programs are adjusting themselves much more slowly.

•How can we best prepare our students to address the storm we know is coming?