64

he West has a variable climate,diverse topography and ecosystems,an

increasing human population,and a rapidly growing and changing economy. Western landscapes range from the coastal areas of California to the deserts

of the Southwest to the alpine meadows of the Rocky and Sierra Nevada

Mountains. Since 1950,the region's population has quadrupled,with most people now living in urban areas. Thus,once predominantly rural states are now

among the most urban in the country. The economy of the West has been transformed from one dominated by agriculture and resource extraction to one

dominated by government,manufacturing,and services. National parks attract

tourists from around the world. The region has a slightly greater share of its

economy in sectors that are sensitive to climate than the nation as a whole;

these include agriculture,mining,construction,and tourism,which currently

represent one-eighth of the region’s economy.

As a result of population growth and development,the region faces multiple

stresses. Among these are air quality problems,urbanization,and wildfires.

Perhaps the greatest challenge,however, is water, which is typically consumed

far from where it originates. Competition for water among agricultural,urban,

power consumption, recreational,environmental,and other uses is intense,with

water supplies already oversubscribed in many areas.

Observed Climate Trends

he climate of the West varies strongly across the region and over time.

Historically, the region has experienced exceptionally wet and dry periods. During the 20th century,temperatures in the West have risen 2-5oF (1-3oC).

The region has generally had increases in precipitation,with increases in some

areas greater than 50%. However, a few areas,such as Arizona,have become

drier and experienced more droughts. The length of the snow season

decreased by 16 days from 1951 to 1996 in California and Nevada. Extreme

precipitation events have increased.

The Hadley and Canadian

models suggest increased

precipitation during winter,

especially over California,

where runoff is projected to

double by the 2090s.

The Oakland Fire 

and Response

Climate change is likely to increase fire frequency in the West. However, as shown by

the response to the Oakland fire, there is

substantial potential to reduce the risk of

urban fires. On October 20, 1991, a small

brush fire started in the hills above

Oakland, California. Fire-conducive conditions, including high winds, unseasonably

high temperatures, large stores of fuel in

the form of dead plant parts, housing developments with dense and flamable vegetation, and low humidity, enabled the fire to

spread rapidly. Before the fire was brought

under control, it covered 1,600 acres, killed

25 people, consumed 3,229 structures and

damaged another 2,992, and caused an

estimated $2 billion in damage. 

In response to this and other recent severe

wildfires, the State developed the California

Fire Plan to address pre-fire management

prescriptions and improved response capabilities. Fire-prevention methods include

fire-resistant construction standards for

roofing and other materials, changes in

zoning, and hazard reduction near structures such as vegetation clearing and management. Improved response capabilities

T

WEST

T

KEY ISSUES

• Changes in Water

Resources

• Changes in Natural

Ecosystems

• Effects on Agriculture

and Ranching

• Shifts in Tourism and

Recreation
65

include better neighborhood access for firefighting equipment and adequate nearby

water supplies. In addition, very high fire

hazard severity zones were identified. The

State requires construction ordinances for

structures in these zones, including roof

specifications and a minimum vegetation

clearance around structures. Much of the

area burned in the Oakland Hills fire has

since been rebuilt according to these standards. 

Scenarios of Future Climate 

he two models used in this

Assessment project annual average temperature increases from 3 to

over 4oF (2oC) by the 2030s and 8-

11oF (4.5-6oC) by the 2090s. The

models project increased precipitation during winter, especially over

California,where runoff is projected

to double by the 2090s. In these climate scenarios,some areas of the

Rocky Mountains are projected to get

drier. Both models project more

extreme wet and dry years. Due to

uncertainties about regional precipitation, the possibility of a drier climate was also considered.

Studies have found that fire protection programs that included prevention elements

reduced the losses from wildfires by anywhere from 50 to 80%. Results indicate

that prevention strategies can aid in fuels

management, control fire behavior, reduce

the physical impact of fire on natural

resources, improve forest health, and

reduce the cost and losses due to wildfires.

Temperature Change - 20th & 21st Centuries

Precipitation Change - 20th & 21st Centuries

Observed 20th Canadian Model 21st

Both models project substantially increased rainfall,

especially in California,

Nevada, and Arizona. 

Much of the

west has had

increases of

precipitation,

but with some

decreases in

Arizona and

the Central

Rockies. 

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

Temperatures in the West

are projected to rise substantially in both models.

The Canadian scenario projects increases of 8-11oF for

Colorado, New Mexico, and

Utah, while California is projected to warm by about 5oF

by both models.

The west has

warmed by

about 2-5oF

over the 20th

century.

Hadley Model 21st

+15oF

+10oF

+5oF

0o

-5oF

+15oF

+10oF

+5oF

0o

-5oF

Western State Populations

(millions)

A defining feature of the West is

rapid population growth. Much

of this growth has occurred in

cities, and once predominantly

rural states are now urbanized.

Growth in urban areas is

expected to continue for at

least several decades. In the

middle growth scenario the

total population of the West is

projected to grow from 48 million in 1999 to between 60 and

74 million in 2025.

Nevada

New Mexico

Utah

Colorado

Arizona

California

T
Changes in Water Resources

he West's water resources are

sensitive to climate change. The

semiarid West is dependent upon a

vast system of engineered water storage and transport,such as along the

Colorado River, and is governed by

complex water rights laws. Much of

the water supply comes from

snowmelt,and higher temperatures

will very likely reduce the snowpack

and alter the amount and timing of

peak flows. In some places,it is likely that current reservoir systems will

be inadequate to control earlier

spring runoff and maintain supplies

for the summer, but more research is

necessary to identify which systems

are most vulnerable.It is also possible

that demand will increase.

In a wetter climate,the potential for

flooding will increase when precipitation comes in more intense events

or where total precipitation increases

substantially. It is possible that more

precipitation would also create additional water supplies, reduce demand,

and ease competition among competing uses.Greater runoff would likely

increase hydropower production and

ease some water quality problems,

although it is also possible that there

would be more non-point source pollution.

In contrast,a drier climate is likely to

decrease supplies and increase

demand for such uses as agriculture,

urban needs,and power production,

thus making water supplies much

tighter. Native Americans,among others,are exercising their rights to

water, and may do so to a greater

extent,further tightening supplies.

Adaptations: Improved technology,

planting of less water-demanding

crops,pricing water at replacement

cost,and other conservation efforts

can help reduce demand. Flexibility

to transfer water across basins and

water users,and to integrate the use

of surface and groundwater, can also

serve as adaptation strategies for

water managers under conditions of

scarcity. Environmental and cost constraints will be an important consideration in building additional flood

control or storage facilities.

Changes in Natural Ecosystems

nder the Hadley and Canadian

scenarios, vegetation models

suggest an increase in plant growth, a

reduction in desert areas,and a shift

toward more woodlands and forests

in many parts of the West. However,

a less positive CO2fertilization effect

than assumed in the models,increase

in fires,and persistence of other

stresses such as air pollution,are

important sources of uncertainty. It

is possible that continued increases

in temperature and leveling off of the

CO2fertilization effect would result

in an eventual decline in forest productivity. A drier climate would also

likely reduce forest productivity.

The diverse topography coupled with

landscape fragmentation and other

development pressures in the West

will likely make it difficult for many

species to adapt to climate change by

migrating. It is likely that some

ecosystems,such as alpine ecosystems,will disappear entirely from

some places in the region.On the

other hand it is possible that mountains may enable some species to

adapt by permitting their migration

to higher elevations.

66

WEST KEY ISSUES

T

U

Domestic 0.04%

Irrigation

86.58%

Commercial 0.85%

Public Supply 10.21%

Livestock 0.92%

Thermo-electric 1.00% Mining

0.24%

Industrial 0.15%

in millions of gallons/day

In 1995, 87% of the water used in the West was for irrigation. However, water use for irrigation has declined slightly since 1980, while municipal uses have grown. 

Climate change is projected to

cause major changes in vegetation distribution during the

21st century. Overall, the

model scenarios project

increases in grasslands, woodlands, and forests in the West,

and a loss of desert vegetation.

The far left map shows potential vegetation types in the

West (the vegetation that

would naturally flourish in the

absence of human activity

given today’s climate), while

the two maps on the right

show model-projected scenarios for future vegetation shifts

in the face of climate change. 

Current Ecosystems

Ecosystem Models

Relative Consumptive Water Use 

in the West
Non-native invasive species have

already stressed many Western

ecosystems and are likely to make

adaptation to climate change much

more difficult for native species.

Climate change is also likely to

increase fire frequency. As long as 

year-to-year variation in precipitation

remains high, fire risk is likely to

increase whether the region gets wetter or drier. This is because fuel loads

tend to increase in wet years as a

result of increased plant productivity

and are consumed by fire in dry

years. In addition, rising sea levels

will threaten many coastal wetlands,

such as those in the San Francisco

Bay area,and the diversity of species

they support.

Adaptations: Devising strategies to

reduce negative climate change

impacts on natural ecosystems and

biodiversity is particularly challenging. Improved management of urban

development can help reduce habitat

fragmentation. The creation of migration corridors to help some species

migrate to more suitable locations

has been suggested,but its effectiveness is not known. Controlled burns

and restricting building in fire prone

areas are among the strategies for

reducing fire risks.

Effects on Agriculture 

and Ranching 

igher CO2concentrations and

increased precipitation are likely to increase crop yields and

decrease water demands,while

milder winter temperatures are likely

to lengthen the growing season and

result in a northward shift in cropping areas.

There is the possibility that higher

temperatures will also negatively

affect crops by increasing heat stress,

weeds,pests,and pathogens. There is

a possibility that increased flooding

will reduce crop production.

Fruit and nut crops,which come

from perennial plants,are 32% of the

value of the West’s crop production,

with a third of that from grapes.Since

fruit and nut plants can take decades

to get established,relocating such

crops as an adaptive response to climate change is very likely to be more

difficult than relocating annual crops.

In the ranching industry, there is a

possibility that higher temperatures

and increased precipitation will

increase forage production and

lengthen the growing and grazing

season.There is also a possibility that

flooding and increased incidence of

animal disease will adversely affect

ranching.

Adaptations: Increasing crop diversity can improve the likelihood that

some crops will fare well under variable conditions,while switching to

less water-demanding crops and

improving irrigation efficiency would

conserve water. Improved weather

forecasting could aid farmers in

selecting crops,timing planting and

harvesting,and increasing irrigation

efficiency, and aid ranchers in timing

cattle sales and breeding,and in

improving range management.

Shifts in Tourism 

and Recreation

ourism,a growing component of

the Western economy, is strongly

oriented to the outdoors and sensitive to climate. Higher temperatures

are likely to mean a longer season for

summer activities such as backpacking,but a shorter season for winter

activities,such as skiing. Ski areas at

low elevations will be at risk from a

shortening of the snow season and

rising snowlines. There is a possibility that increases in precipitation will

provide more water for sports,but

some chance that there will be less

water available for summer recreation

and that recreation days will be limited by heat. Changes in the distribution and abundance of vegetation,

fish,and wildlife will also affect recreation.

Adaptations: Strategies for tourism

and recreation involve diversification

of income sources. The larger, bettercapitalized resorts have adapted their

facilities to support winter and summer activities. These options,however, might not be available to smaller,

less well-capitalized resorts.

67

H

T

Canadian Model Hadley Model 

Tundra

Taiga / Tundra

Conifer Forest

Northeast Mixed Forest

Temperate Deciduous Forest

Southeast Mixed Forest

Tropical Broadleaf Forest

Savanna / Woodland

Shrub / Woodland

Grassland

Arid Lands

The maps are projected by the

Canadian and Hadley climate models

with the vegetation simulations done

using a computer model called MAPPS,

for the years 2070-2099.