68

KEY ISSUES

he Pacific Northwest encompasses extensive forests,topography that creates abrupt changes in climate and ecosystems over short distances,and

mountain and marine environments in close proximity. The Cascade Mountains

divide the region climatically, ecologically, economically, and culturally. Three

quarters of the region's population live west of the Cascades,concentrated in

the metropolitan areas of Seattle and Portland,where the aerospace and computer industries have largely supplanted the traditional resource sectors of

forestry, fishing,and agriculture. The Northwest provides a quarter of the nation's

softwood lumber and plywood. The fertile lowlands of eastern Washington produce

60% of the nation's apples and large fractions of its other tree fruit.

The region has seen several decades of population and economic growth nearly

twice the national rate,with population nearly doubling since 1970. The region’s

moderate climate,quality of life,and outdoor recreational opportunities contribute

to its continuing attraction to newcomers. The same environmental attractions that

draw people to the region are increasingly stressed by rapid development. Stresses

arise from dam operation, forestry, and land-use conversion from natural ecosystems

to metropolitan areas,intensively managed forests, agriculture,and grazing. The consequences include loss of old-growth forests, wetlands,and native grasslands;urban

air pollution; extreme reduction of salmon runs;and increasing numbers of threatened and endangered species.

Observed Climate Trends

ver the 20th century, the region has grown warmer and wetter. Annual-average temperature has increased 1 to 3°F (0.5-1.5°C) over most of the region,

with nearly equal warming in summer and winter. Annual precipitation has also

increased across the region, by 10% on average,with increases reaching 30 to 40%

in eastern Washington and Northern Idaho. The region's climate also shows significant recurrent patterns of year-to-year variability. Warm years tend to be relatively

dry with low streamflow and light snowpack,while cool ones tend to be relatively

wet with high streamflow and heavy snowpack. Though the differences in temperature and precipitation are small,they have clearly discernible effects on important

regional resources. Warmer drier years tend to have summer water shortages,less

abundant salmon,and increased probability of forest fires. These variations in the

region’s climate show clear correlations with two large-scale patterns of climate

variation over the Pacific:the El Niño/Southern Oscillation (ENSO) on scales of a

few years;and the more recently discovered Pacific Decadal Oscillation (PDO) on

• Changes in Timing of

Freshwater Resources

• Added Stresses on

Salmon

• CO2and Summer Drought

Effects on Forests 

• Sea-level Rise Impacts on

Coastal Erosion

Learning from Water

Shortages

Seattle Public Utilities (SPU) experienced

summer droughts and potential shortages in

1987, 1992, and 1998. Their responses to

the three events illustrate institutional flexibility and learning. Summer 1987 began

with full reservoirs, but a hot dry summer

and a late return of autumn rains created a

serious shortage in which water quality

declined, inadequate flows were maintained

for fish, and the main reservoir fell so low

that an emergency pumping station had to

be installed. In response, the City developed a plan with four levels of response to

anticipated shortage: advising the public of

potential shortages and monitoring use;

requesting voluntary use reductions;

mandatory prohibitions of certain uses

(such as watering lawns and washing cars);

and rationing. Another drought came in

1992, following a winter with low snowpack

but in which SPU had followed standard

flood-control rules by spilling water from

their reservoirs. With a small snowmelt,

reservoirs were low by the spring, and SPU

invoked mandatory restrictions during the

hot dry summer that followed. Water quality declined sharply, prompting a decision to

begin building a costly ozone-purification

plant.

The ill-advised spilling of early 1992 alerted

SPU to the danger of following rigid reservoir rule curves, and they have since taken

O

PACIFIC NORTHWEST

T
Temperature Change - 20th & 21st Centuries

69

By the 2090s, average

summer temperatures are

projected to rise by 7-8°F

(4-4.5°C), while winter temperatures rise by 8-11°F

(4.5-6°C). Projected annual average precipitation

increases range from a few

percent to 20% in the

Hadley model, and from 20

to 50% in the Canadian

model.

a more flexible approach, projecting annual

supply and demand using a model including

probabilistic predictions based on ENSO

and PDO. During the strong El Niño of

1997-1998, SPU took early conservation

education measures and allowed higher

than normal reservoir fill. When 1998

brought a small snowmelt and a hot dry

summer, these measures allowed the

drought to pass with the public experiencing

no shortage. In integrating seasonal forecasts into its operations, SPU is an uncommonly adaptable resource-management

agency. But it still has a long way to go in

adapting to longer-term climate variability

and change. SPU presently projects that

new conservation measures will keep

demand at or below present levels until at

least 2010, while conservation measures

and planned system expansion (including a

connection with a neighboring system) will

maintain adequate supply until at least

2030. Over this period, climate change is

likely to have significant effects on both

Precipitation Change - 20th & 21st Centuries

Observed 20th Canadian Model 21st

Both climate models project

continued precipitation

increases, with the largest

increases in the southern

part of the region.

Precipitation

has increased

over most of

the Pacific

Northwest

since 1900. 

100%

75%

50%

25%

0

-25%

-50%

-75%

-100%

100%

80%

60%

40%

20%

0

-20%

-40%

-60%

-80%

-100%

Hadley Model 21st

Observed 20th Canadian Model 21st

By 2100, both models project warming near 5oF west

of the Cascades, with much

larger warming further east

in the Canadian model. 

Warming

since 1900 in

the Pacific

Northwest

ranges from

0 to 4oF. 

Hadley Model 21st

scales of a few decades.The obser ved effects of these patterns provide powerful

illustrations of regional sensitivities to climate,but how they might interact with

future climate change is not yet understood.

Scenarios of Future Climate

odel scenarios project regional warming in the 21st century to be much

greater than observed during the 20th century, with average warming

over the region of about 3°F (1.5°C) by the 2030s and 5°F (3°C) by the 2050s.

By the 2090s, average summer temperatures are projected to rise by 7-8°F (4-

4.5°C),while winter temperatures rise by 8-11°F (4.5-6°C). Through 2050, average precipitation is projected to increase,although some locations have small

decreases. Precipitation increases would be concentrated in winter, with little

change or a decrease in summer. Because of this seasonal pattern of wetter winters and drier summers, even the projections that show annual precipitation

increasing,show water availability decreasing,especially in the Hadley model. By

the 2090s,projected annual average precipitation increases range from a few percent to 20% in the Hadley model,and from 20 to 50% in the Canadian model.

M

+15oF

+10oF

+5oF

0o

-5oF

+15oF

+10oF

+5oF

0o

-5oF

supply and demand, but is not yet included

in planning. The warmer drier summers projected under climate change are likely to

stress both supply and demand, requiring

earlier capacity expansion, and triggering

the more restrictive conservation measures

more often. Moreover, the recent shift to

cool PDO phase that has been suggested

could well mask this effect for a couple of

decades, risking sudden appearence of

shortages when PDO next shifts back to its

warm phase.
70

PACIFIC NORTHWEST KEY ISSUES

Columbia Streamflow Changes Observed Effects of Climate Variability on Salmon

Relative to present flows (dashed), the wetter winters and drier summers simulated by climate models are very likely to shift peak streamflow earlier

in the year, increasing the risk of late-summer

shortages. Though the Columbia system is only

moderately sensitive to climate change, allocation

conflicts and a cumbersome network of interlocking authorities restrict its ability to adapt, producing substantial vulnerability to these shortages.

Abundances of many salmon

stocks closely track interdecadal climate variation

since 1940. Upper Columbia

bright spring Chinook are

abundant when the Pacific

Northwest Index (one measure of decadal climate variation) is negative. Both are 5-

year moving averages.

Changes in Timing of Freshwater Resources

espite its reputation as a wet place,most of the Northwest receives less

than 20 inches (0.5 meter) of precipitation a year, and dry summers make

freshwater a limiting resource for many ecosystems and human activities. Water

resources are already stressed by multiple growing demands. The projected

warmer wetter winters will likely increase flooding in rainfed rivers,because

there is more precipitation,and because more of it falls as rain. Projected yearround warming and drier summers will likely increase summer water shortages

in both rainfed and snowfed rivers,including the Columbia,because there

would be less snowpack and because it would melt earlier. In the Columbia,

allocation conflicts are already acute,and the system is vulnerable to shortages.

Adaptations: Adapting to projected increases in summer shortages will likely

require a combination of reducing demand,increasing supply, and reforming

institutions to increase flexibility and regional problem-solving capacity. In the

Colombia Basin,current infrastructure and institutions are inflexible and inadequate to deal with the projected scarcity.

Added Stresses on Salmon 

hile non-climatic stresses on Northwest salmon presently overwhelm climatic ones,salmon abundances have shown a clear correlation with

20th century variations in climate from decade to decade. Climate models cannot yet project the most important oceanic conditions for salmon,but the likely

effects on their freshwater habitat all appear unfavorable. Increased winter

flooding,reduced summer and fall flows,and rising stream and estuary temperatures are all harmful for salmon. In addition,it is possible that earlier

snowmelt and peak spring streamflow will deliver juveniles to the ocean before

D

W

Increased winter flooding,

reduced summer and fall

flows, and rising stream

and estuary temperatures

are all harmful for salmon.

In addition, it is possible

that earlier snowmelt and

peak spring streamflow

will deliver juveniles to the

ocean before there is

adequate food for them.
71

Regional Impacts:

Climate Change projected for 2050 vs observed 20th century variability

This chart compares possible Northwest

impacts from climate change by the

2050s with the effects of natural climate

variations during the 20th century. The

orange bars show the effects of the

warm phase of the Pacific Decadal

Oscillation (PDO), relative to average

20th century values. During warm-PDO

years, the Northwest is warmer, there is

less rain and snow, stream flow and

salmon catch are reduced, and forest

fires increase. The blue bars show the

corresponding effects of cool-phase

years of the PDO, during which opposite

tendencies occurred. 

The pink bars show projected impacts

expected by the 2050s, based on the

Hadley and Canadian scenarios.

Projected regional warming by this time

is much larger than variations experienced in the 20th century. This warming

is projected to be associated with a

small increase in precipitation, a sharp

reduction in snowpack, a reduction in

streamflow, and an increase in area

burned by forest fires. Although quite

uncertain, large reductions in salmon

abundance ranging from 25 to 50%, are

judged to be possible based on projected changes in temperature and streamflow.

there is adequate food for them. Climate change is consequently very likely to

hamper efforts to restore already depleted salmon stocks,and to stress presently healthy stocks.

Adaptations: It is possible that operational changes on managed rivers would

reduce current stream warming and slow future warming,although such measures will very likely be overwhelmed by continued climate warming. Measures

to reduce general stress on fish,such as changing dam operations to provide

adequate late-summer streamflows,might possibly increase salmon's resilience

to other stresses,including climate. It is very likely that maintaining such flows

will become increasingly difficult,however, under the projected regional warming that will very likely shift peak streamflows to earlier in the year. Other

options include maintaining the diversity of salmon by increasing preservation

of their habitat,or removing existing dams and accepting reduced ability to

manage summer shortages.

Water resources are

already stressed by

multiple growing

demands. The projected year-round warming

and drier summers will

likely increase summer

water shortages,

because there is less

snowpack and because

it melts earlier.

Temperature Change in annual average regional temperature (oF)

Precipitation Change in annual average regional precipitation (%)

Snow depth Change in average winter snow depth at Snoqualmie Pass, WA (%)

Streamflow Change in annual streamflow at The Dalles on the Columbia River 

(corrected for changing effects of dams) (%)

Salmon Change in annual catch of Washington Coho salmon (%)

Forest fires Change in annual area burned by forest fires in WA and OR (%)

Temperature

Precipitation

Snow Depth

Streamflow

Washington

Coho Forest Fires

-6

-4

-2

0

2

4

6

8

-60

-40

-20

0

20

40

60

80

 ̊F %

Warm Phase Cool Phase Regional impacts of climate change in 2050

Salmon

Warm PDOYears Cool PDOYears Regional impacts of climate change in 2050

(1900-1924, 1946-1975) (1925-1949, 1977-95)
72

PACIFIC NORTHWEST KEY ISSUES

CO2and Summer Drought Effects on Forests 

vergreen coniferous forests dominate the landscape of much of the

Northwest. West of the Cascades,coniferous forests cover about 80% of

the land,and include about half the world’s temperate rainforest. Northwest

forests have been profoundly altered by timber management and land-use conversion. These forests are quite sensitive to climate variation because warm dry

summers stress them directly, by limiting seedling establishment and summer

photosynthesis,as well as indirectly, by creating conditions favorable to pests

and fire. The extent,species mix,and productivity of Northwest forests are likely to change under projected 21st century climate change,but the specifics of

these changes are not known with confidence at present. They are very likely

to depend on interactions between the timing and amount of precipitation,the

seasonal water-storage capacity of forest soils,and changes in trees’ water-use

efficiency under elevated CO2. It is very likely that these factors will jointly

determine the consequences of the likely increase in summer moisture stress,

which will also depend on interactions with forest management practices,landuse conversion,and other pressures from development.

Adaptations: Options include planting species adapted to projected climate

rather than present climate;managing forest density to reduce susceptibility to

drought stress and fire risk;and using prescribed burning to reduce the risk of

large,high-intensity fires. Increased capacity for long-term monitoring and planning would likely help with management. Reduced tree cutting, reduced road

construction,and establishment of large buffers around streams are some of the

ways to promote diversity of plant and animal species and the services provided by forest ecosystems (such as purifying air and water). Improved seasonal

forecasts,and knowledge of the typical effects of ENSO and PDO, could possibly assist in decision making on timing and species of planting,and use and timing of prescribed burning.

E

Canadian Model Hadley Model

Summer Soil Moisture

Change - 21st Century

>100%

+75

+50

+25

0

-25

-50

-75

-100

>100%

+75

+50

+25

0

-25

-50

-75

-100

The Hadley model projects drier soils over

important forest areas. For example, soil

moisture decreases reach 25% in the

Puget Sound area. 

The Canadian model also projects drier

soils over important forest areas, but to a

lesser degree. Soil moisture is projected

to decrease by 10 to 15% in the Puget

Sound area. 

Northwest forests are quite

sensitive to climate variation

because warm dry summers

stress them directly, by limiting seedling establishment

and summer photosynthesis,

as well as indirectly, by creating conditions favorable to

pests and fire. The extent,

species mix, and productivity

of Northwest forests are likely to change under projected

21st century climate

change...
Winter Snow Depth Change - 21st Century

Canadian Model 

73

Sea-level Rise Impacts on Coastal Erosion

ea-level rise is likely to require substantial investments in order to avoid

coastal inundation,especially in the low-lying communities of southern

Puget Sound where coastal subsidence is occurring. Other likely effects include

increases in winter landslides,and increased erosion on sandy stretches of the

Pacific Coast. Severe storm surges and erosion are presently associated with El

Niño events,which raise sea level for several months and change the direction of

prevailing winds. Climate change is projected to bring similar shifts. Projected

heavier winter rainfall is likely to increase soil saturation,landsliding,and winter

flooding. All these changes would likely increase the danger to property and

infrastructure on bluffs and beachfronts,and beside rivers.

Adaptations: The current coastal management system is not particularly adaptable, even to current climate variability and risks,and there is little inclination to

restrict development in vulnerable locations. Adaptation strategies would involve

conserving remaining natural coastal areas,placing less property at risk in lowlying or flood- or slide-prone areas,assigning more of the associated risk to property owners through insurance rates,and more effective transfer of climatechange information to local governments,where most planning authority lies.

S

Severe storm surges

and erosion are presently associated with El

Niño events, which raise

sea level for several

months and change the

direction of prevailing

winds. Climate change

is projected to bring

similar shifts.

Projected Northwest Daily Precipitation Change - 21st Century

-20

-10

0

10

20

30

40

50

60

Percentiles

Light Moderate Heavy

Northwest Daily Precipitation/CGCMI

-15

-10

-5

0

5

10

15

20

25

30

35

40

Moderate

Light

Heavy

Canadian Model Hadley Model

Over the 21st century, both

models project increases in

annual average precipitation

and in extreme precipitation

events. As the graphs for both

models show, the largest precipitation increases are projected to occur on days already

receiving the most. 

These maps show projected changes in annual snow depth, averaged over December,

January, and February. The Hadley and Canadian models project 30 to 50-inch reductions in average snow depth in the mountains of the Pacific Northwest and West during the 21st century. (Due to limitations in model resolution, the highest mountains

appear to be farther east than they actually are).

Hadley Model 

>0”

-10

-20

-30

-40

-50

-60

-70

-80

lightest 5%

Moderate

Heaviest 5%

lightest 5%

Heaviest 5%

Days receiving precipitation, sorted by percentile.

Moderate