In Brief Climate Change and Water

In Brief Climate Change and Water S u s d s e Perspectives from the Forest Service ta h i s ni r ng ate Freshwater availability is an increasing concern across the globe and it may be the most important natural resource issue Healthy W of the century. Climate change and its effects on water are expected to intensify freshwater scarcity and conflict. A Forest Service 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 Climate change will impact the ability of the Nation’s watersheds. forests to provide water and other critical watershed services. Warming over the past several decades has funda- Of the many ecosystem services provided by forests, water- mentally altered the hydrologic cycle, and these changes are shed services are among the most valuable. Healthy forests percolating through our watersheds (see illustration below). capture and store water, naturally regulate streamflows and Snowpacks are shrinking and stream temperatures will likely water quality, reduce flood and storm damage, control increase. Precipitation patterns may change, and floods, erosion, and replenish ground water. High- droughts, and severe weather disturbances may become elevation forests protect and enhance our more common. water supplies downstream. Forests in the Climate change is hydrologic change. United States provide Forests provide nearly two-thirds of drinking water to more the freshwater in the 48 conterminous Water supplies stored as snow cover in high-elevation forests are particularly vulnerable to climate change and are pro- than 180 million States—water that fills our rivers, lakes, and streams; jected to decline over the course of the century. Earlier spring people. runoff and reductions in low flows will reduce water availabil- Sixty-six million sustains fish, plants, and wildlife; supports food, ity downstream during the summer and fall months. Higher people rely on a energy, and industrial water temperatures, flooding, and droughts will affect water national forest as their production; enables quality and exacerbate water pollution. water source. navigation; and pours from the faucets of our The Forest Service is a steward of the Nation’s homes and businesses. forested watersheds, ensuring a continued supply of high-quality water and watershed services as Projected climatic changes we adjust to a changing climate. to the hydrologic cycle Glaciers are reduced or Less precipitation in More intense storms with eliminated. Increased some areas, more in other high elevation erosion. more flooding and extreme areas. Greater interannual winds. variability. More evapotranspiration. More rain and less snow. Drier vegetation and Snow melts sooner in soils. More frequent and Spring. severe droughts. Increased wildfires and area burned. Earlier spring runoff. Larger flood peaks. Less summer stream flow. Smaller headwater stream networks. Sea level rises. More coastal erosion. Saltwater intrusion into coastal freshwater Water in streams and lakes aquifers. becomes warmer. In Brief: Climate Change and Water Climate change will affect water availability—quantity, quality, As populations, incomes, and consumption levels increase, timing, and distribution—and other watershed services. It people put more pressure on our forested watersheds to de- will affect the people who rely on water for liver the services they want and need. Declining water quanti- everyday use (see table below). ty and quality are becoming common issues, especially where At least 36 our demands exceed supply. Growing water demands, in turn, States anticipate Availability of clean drinking put aquatic resources and other services at risk because less water is a critical issue for most water is available to sustain them. Many municipalities, busi- water shortages within people in the world. Seventy nesses, farmers, and citizens already face difficult decisions the next 10 years. percent of the Earth’s surface is about how—and where—to get their water. Future changes U.S. Government Accountability covered by water, but less than 1 in the timing, magnitude, and quality of waterflows resulting Office, 2003 percent of this amount is freshwater, from climate change will compound these water challenges. present on the land surface, in the atmosphere, or in the ground. Caring for the Nation’s forests will help protect Forty percent of A small fraction of the world’s watershed services into the future. the world’s population freshwater is renewable and available for human use, and We may not be able to precisely predict the extent, location, will be living in water-scarce this water supply is unequally or timing of climate change impacts, but we can recognize regions by 2025. distributed across the ecosystem changes and respond with flexible and adaptive World Resources Institute, United Nations continents. Seasonal watershed management strategies. The following Environment Programme, and World Business differences in precipitation, actions will help resource professionals and landowners Council for Sustainable Development, 2002 waterflows, and demand mean incorporate a climate change perspective into their work. that freshwater is not always available when and where it’s needed. Prepare for change Preparing now to face future challenges is essential. Adaptive management is an approach that promotes learning through doing. This approach involves actively making Managers, planners, and conservation groups can use existing information to identify watersheds and services decisions and monitoring results to improve our understanding that are most vulnerable to adverse changes. Planning for about the complex systems we manage. 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 Consequences for Climatic Changes Location Ecosystem Effects Watershed Services Warmer air temperatures Widespread Precipitation as snow; faster and earlier Amount, type, quality, and distribution of Greatest change in mountains and snowmelt aquatic habitat and biota northern latitudes Evapotranspiration and primary productivity Water availability and recreational and Water temperatures cultural experiences Sea level; coastal erosion and saltwater Water quality and timing intrusion into freshwater supplies Function and operation of existing water infrastructure in coastal areas Less winter precipitation at lower Snow; changes in streamflow timing Water supplies for people, agriculture, latitudes (Southwest, Intermountain Risk of disturbance, e.g., drought, wildfires, energy, and other uses Changes in precipitation patterns West) insects, disease Water demand, ground water withdrawals, (projected changes vary by location and Vegetation growth; changes in composition and consumptive use of surface waters have substantial uncertainty) Fisheries and water-based tourism More precipitation at higher latitudes Streamflow Freshwater supplies (Pacific Northwest, New England) Vegetation growth and composition Improvements in warm water fisheries Soil erosion and landslides Greater variability in precipitation Everywhere Variability in stream, lake, and riparian habitats Uncertainty in water supply from year to year Risk of aquatic and riparian species extirpation Uncertainty for reservoir operations Soil erosion, stream and lake sedimentation, Risk to aquatic habitat and water supply More extreme floods and droughts and landslides infrastructure Broad-scale inventories, assessments, and early-warning Active management will need to... monitoring can help managers identify trends, anticipate .Restore meadows, wetlands, and floodplains to effects, and act quickly to limit loss or reduction in critical improve natural storage, reduce flood hazards, and watershed services. prolong seasonal flows .Protect and restore riparian forests to moderate Ensuring that land managers, landowners, and changes in stream temperature decisionmakers can access people with skills and training in .Remove migration barriers and reestablish habitat water resources will be important as climate change further connectivity to help species adapt to changing complicates issues. conditions .Reduce flood and wildfire risks in vulnerable water- Advance and share knowledge about sheds to prevent erosion and maintain clean water and climate change water supplies Together, scientists and managers can provide new .Improve or decommission roads to reduce adverse information and tools for the management toolbox. impacts during large storms New information will be needed to track and evaluate Support entrepreneurial projects and leaders changing watershed conditions, understand the effects of New approaches to watershed management will help us meet management practices, and forecast

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