In Brief

Climate Change and Water

Perspectives from the Forest Service

Freshwater availability is an increasing concern across the globe and it may be the most important natural resource issue 

of the century. Climate change and its effects on water are expected to intensify freshwater scarcity and conflict. A 

forthcoming Forest Service, U.S. Department of Agriculture report will highlight the importance of managing forests to 

provide clean, abundant water. The report will explore likely impacts of climate change on the Nation’s forested watersheds and 

describe how natural resource managers can incorporate a climate change perspective into watershed stewardship.

The cleanest water flows from healthy, forested 

watersheds.

Of the many ecosystem services provided by forests, watershed services are among the most valuable. Healthy forests 

capture and store water, naturally regulate streamflows and 

water quality, reduce flood and storm damage, control 

erosion, and replenish ground water. Highelevation forests protect and enhance our 

water supplies downstream. 

Forests provide nearly two-thirds of 

the freshwater in the 48 conterminous 

States—water that fills our 

rivers, lakes, and streams; 

sustains fish, plants, and 

wildlife; supports food, 

energy, and industrial 

production; enables 

navigation; and pours 

 from the faucets of our 

homes and businesses.

Climate change will impact the ability of the Nation’s 

forests to provide water and other critical watershed 

services. Warming over the past several decades has fundamentally altered the hydrologic cycle, and these changes are 

percolating through our watersheds (see illustration below). 

Snowpacks are shrinking and stream temperatures will likely 

increase. Precipitation patterns may change, and floods, 

droughts, and severe weather disturbances may become 

more common. 

Climate change is hydrologic change.

Water supplies stored as snow cover in high-elevation forests 

are particularly vulnerable to climate change and are projected to decline over the course of the century. Earlier spring 

runoff and reductions in low flows will reduce water availability downstream during the summer and fall months. Higher 

water temperatures, flooding, and droughts will affect water 

quality and exacerbate water pollution. 

The Forest Service is a steward of the Nation’s 

forested watersheds, ensuring a continued supply 

of high-quality water and watershed services as 

we adjust to a changing climate. 

Forests in the 

United States provide 

drinking water to more 

than 180 million 

people. Sixty-six million 

people rely on a 

national forest as their 

water source.

Sustaining Healthy Watersheds

More evapotranspiration. 

Drier vegetation and 

soils. More frequent and 

severe droughts. Increased 

wildfires and area burned.

More intense storms with 

more flooding and extreme 

winds.

Sea level rises. More coastal 

erosion. Saltwater intrusion 

into coastal freshwater 

aquifers.

Water in streams and lakes 

becomes warmer.

Earlier spring runoff. 

Larger flood peaks. 

Less summer stream 

flow. Smaller headwater 

stream networks.

More rain and less snow. 

Snow melts sooner in 

Spring.

Less precipitation in 

some areas, more in other 

areas. Greater interannual 

variability.

Projected climatic changes 

 to the hydrologic cycle

Glaciers are reduced or 

eliminated. Increased 

high elevation erosion.

Forest Service
Climatic Changes Location Ecosystem Effects Consequences for 

Watershed Services

Warmer air temperatures Widespread

Greatest change in mountains and 

northern latitudes

 Precipitation as snow; faster and earlier 

snowmelt

 Evapotranspiration and primary productivity

 Water temperatures

 Sea level; coastal erosion and saltwater 

intrusion into freshwater supplies

 Amount, type, quality, and distribution of 

aquatic habitat and biota

 Water availability and recreational and 

cultural experiences

 Water quality and timing

 Function and operation of existing water 

infrastructure in coastal areas

Changes in precipitation patterns

(projected changes vary by location and 

have substantial uncertainty)

Less winter precipitation at lower 

latitudes (Southwest, Intermountain 

West) 

 Snow; changes in streamflow timing

 Risk of disturbance, e.g., drought, wildfires, 

insects, disease

 Vegetation growth; changes in composition

 Water supplies for people, agriculture, 

energy, and other uses

 Water demand, ground water withdrawals, 

and consumptive use of surface waters 

 Fisheries and water-based tourism

More precipitation at higher latitudes 

(Pacific Northwest, New England)

 Streamflow 

 Vegetation growth and composition

 Soil erosion and landslides

 Freshwater supplies

 Improvements in warm water fisheries

Greater variability in precipitation 

from year to year

More extreme floods and droughts

Everywhere  Variability in stream, lake, and riparian habitats 

 Risk of aquatic and riparian species extirpation

 Soil erosion, stream and lake sedimentation, 

and landslides

 Uncertainty in water supply

 Uncertainty for reservoir operations

 Risk to aquatic habitat and water supply 

infrastructure

Climate change will affect water availability—quantity, quality, 

timing, and distribution—and other watershed services. It 

will affect the people who rely on water for 

everyday use (see table below). 

Availability of clean drinking 

water is a critical issue for most 

people in the world. Seventy 

percent of the Earth’s surface is 

covered by water, but less than 1 

percent of this amount is freshwater, 

present on the land surface, in the 

atmosphere, or in the ground. 

A small fraction of the world’s 

freshwater is renewable and 

available for human use, and 

this water supply is unequally 

distributed across the 

continents. Seasonal 

differences in precipitation, 

waterflows, and demand mean 

that freshwater is not always 

available when and where it’s needed. 

Forty percent of 

the world’s population 

will be living in water-scarce 

regions by 2025.

World Resources Institute, United Nations 

Environment Programme, and World Business 

Council for Sustainable Development, 

2002

At least 36 

States anticipate 

water shortages within 

the next 10 years.

U.S. Government Accountability 

Office, 2003

As populations, incomes, and consumption levels increase, 

people put more pressure on our forested watersheds to deliver the services they want and need. Declining water quantity and quality are becoming common issues, especially where 

our demands exceed supply. Growing water demands, in turn, 

put aquatic resources and other services at risk because less 

water is available to sustain them. Many municipalities, businesses, farmers, and citizens already face difficult decisions 

about how—and where—to get their water. Future changes 

in the timing, magnitude, and quality of waterflows resulting 

from climate change will compound these water challenges.

Caring for the Nation’s forests will help protect 

watershed services into the future.

We may not be able to precisely predict the extent, location, 

or timing of climate change impacts, but we can recognize 

ecosystem changes and respond with flexible and adaptive 

watershed management strategies. The following 

actions will help resource professionals and landowners 

incorporate a climate change perspective into their work. 

Prepare for change

Preparing now to face future challenges is essential.

 Managers, planners, and conservation groups can use 

existing information to identify watersheds and services 

that are most vulnerable to adverse changes. Planning for 

change and priority-setting will need to begin with the most 

vulnerable and highest value watersheds. 

Three examples of current and projected climatic changes, their effects on ecosystems, and potential consequences to the supply and 

delivery of watershed services. Climatic changes are based on current trends and projections from the Intergovernmental Panel on Climate 

Change Fourth Assessment Report (2007). For all changes, uncertainty is substantial and the geographic variability is expected to be high. 

 = probable increase,  = probable decrease,  = change

Adaptive management is an approach that promotes learning 

through doing. This approach involves actively making 

decisions and monitoring results to improve our understanding 

about the complex systems we manage. 

In Brief: Climate Change and Water
 

 Broad-scale inventories, assessments, and early-warning 

monitoring can help managers identify trends, anticipate 

effects, and act quickly to limit loss or reduction in critical 

watershed services.

 Ensuring that land managers, landowners, and 

decisionmakers can access people with skills and training in 

water resources will be important as climate change further 

complicates issues. 

Advance and share knowledge about 

water and climate change

Together, scientists and managers can provide new 

information and tools for the management toolbox.

 New information will be needed to track and evaluate 

changing watershed conditions, understand the effects of 

management practices, and forecast quality, quantity, and 

timing of water supplies. New technologies will be needed 

to improve data collection. Dynamic, process-based models 

will be needed to improve climate change projections and 

evaluate management options. 

 National forests and experimental research sites will continue to serve as learning laboratories to help land managers 

understand interactions between climate and ecosystems, 

evaluate management options, and test solutions. 

 Intensive cooperation between scientists and land 

managers in both natural and social sciences will promote 

adaptive management and learning.

Manage for watershed resilience and enhance 

ecosystem adaptability

Healthy, resilient watersheds are the best insurance policy for a

changing climate.

 Managing wildland and urban forests for a set of watershed 

services—like high water quality, flood control, and fish 

habitat—ensures that management and land use decisions 

are designed to maintain and protect healthy watersheds.

 Public forests will continue to serve as natural reservoirs for 

high-quality water and as refuges for biodiversity.

 Current management practices applied broadly, more 

strategically, and in new ways can help watersheds adapt to 

change. Best management practices protect watersheds that 

are actively managed, and restoration activities reestablish 

processes or services that have been lost or are at risk. 

Active management will need to...

Restore meadows, wetlands, and floodplains to 

improve natural storage, reduce flood hazards, and 

prolong seasonal flows

Protect and restore riparian forests to moderate 

changes in stream temperature

Remove migration barriers and reestablish habitat 

connectivity to help species adapt to changing 

conditions

Reduce flood and wildfire risks in vulnerable watersheds to prevent erosion and maintain clean 

water supplies

Improve or decommission roads to reduce adverse 

impacts during large storms

Support entrepreneurial projects and leaders

New approaches to watershed management will help us meet 

future challenges.

 Management approaches will need to be flexible and 

forward-thinking, with a focus on desired processes and 

benefits rather than individual species and specific, 

static conditions.

 Demonstration projects that integrate science and 

management will foster innovation and provide new 

information for land managers and the public.

 Emerging ecosystem markets can align economic interests 

with conservation objectives, and new market opportunities 

can provide incentives for private landowners to maintain 

and improve watershed services.

 Capture and store rainfall

 Recharge ground water reservoirs

 Minimize erosion losses and protect soil quality

 Sustain and regulate streamflows

 Store and recycle nutrients

 Support natural riparian and floodplain functions

 Provide habitat for native aquatic species

 Resist and recover quickly from floods, fire, insect

outbreaks, and other extreme events

Vital signs of a healthy, resilient watershed

Adapted from: Sprague et al. [eds]. 2006. The State of Chesapeake Forests. The 

Conservation Fund and the Forest Service. 

Resilient ecosystems are those that rebound after disturbance and continue to provide ecosystem services. 

A healthy, resilient watershed has the capacity to:
Connect with partners and the public

We will need to step across boundaries to expand our reach.

 Creating and cultivating effective partnerships will promote 

collaborative action across larger landscapes. Reaching out 

to new partners, such as developers, health and environmental organizations, private businesses, municipal water 

managers, and city planners, will increase awareness about 

the critical role of healthy forested watersheds.

 Conserving water will keep water in streams and help to 

sustain healthy watersheds. We can all lead by example and 

reduce our water footprint, encouraging others to make 

similar commitments. 

 Connecting people to their water source will have a lasting 

effect on watershed stewardship.

 

Climate change is a formidable challenge and there is much 

we can do to respond. Actions taken now can minimize potential negative impacts and unlock new opportunities—

they must include a focus on water.

The mission of the Forest 

Service is to sustain the health, 

diversity, and productivity of 

the Nation’s forests and 

grasslands to meet the needs 

of present and future 

generations. This mission 

rests on a tradition of 

managing forests to protect 

the Nation’s clean water 

supplies. Today, our commitment to watershed stewardship 

is even more critical as we 

respond to new challenges like 

climate change. Through research, 

partnerships, and mindful, meaningful 

management, we will enhance the ability of the 

Nation’s watersheds to adapt to change and 

continue to support the health and well-being of 

people and ecosystems.

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Independence Avenue, S.W., Washington, D.C. 20250-9410, or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer.

June 2008

FS-908

The Forest Service

The National Forest System was established with the purpose 

of “securing favorable conditions of waterflows” in the Nation’s 

headwaters. For over a century, the Forest Service has 

protected water and managed public forests to provide the 

goods and services that people want and need. 

State and Private Forestry extends the Forest Service mission 

to urban and community forests and to more than 400 million 

acres of private land. Nearly 60 percent of the Nation’s forests 

are privately owned—the people who own and manage these 

lands serve as stewards of the Nation’s water supply and other 

ecosystem services that benefit society. 

In 1910, Forest Service Research established its first 

experimental watershed to conduct research that informed 

management and policy on public and private lands. This 

tradition continues today with a wide array of partners.

International Programs works with agencies, countries, and 

nonprofit partners to assist others around the world in 

protecting and managing natural areas.

http://www.fs.fed.us