USDA Forest Service

Pacific Southwest Research Station

Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Research Topics Water and Watersheds


Kings River Experimental Watersheds (KREW)

Why Study Watersheds?

Stream headcut There are many reasons why the study of watersheds is important. Understanding the impacts of fire on the forest ecosystem and climate change are two of the most important reasons why the KREW project was established.


Wildfire burning near house
Before the European settlement of the American West, fire played an important role in the shaping of many ecosystems. For centuries, lightning strikes and Native Americans were the main sources of fire in the Sierra Nevada. Because fire was consistently present, the forests adapted to fire and became dependent upon it. After several large, devastating wildfires in the early 20th century, land managers, with strong support from Americans nationwide, began suppressing all fires. This century-long policy has resulted in forests that are much more crowded with trees and plants than they were historically when fire was present. These crowded conditions have become dangerous as more plants grow in and none are thinned out by fire. These hazardous conditions put humans, including firefighters and homeowners, trees, plants, and animals all at risk for severe wildfires.

Prescribed fires are being studied as a means of safely reintroducing fire into the Sierra Nevada. These prescribed fires are carefully planned and applied by well-trained, experienced fire managers. There are many things taken into consideration before a prescribed fire is lighted, including the season of the burn, fuel moisture, air temperature, relative humidity, and wind speed. The scientists working on KREW are studying the effects of prescribed fire in order to understand the best way to restore the forest to its historic condition.

The effects of fire are being studies for: stream water quality, soil condition, vegetation, shallow soil water, stream invertebrates and algae, carbon storage, and nutrient cycling.

Climate Change
Satellite image of California
Global Climate Change: Enhancing the Greenhouse Effect

Today’s atmosphere is very different than it was at the time of the industrial revolution, and that change is mostly due to human activities.  The facts are inescapable.  Concentrations of carbon dioxide, methane, and nitrous oxide have increased in the atmosphere since the mid 19th century. Carbon dioxide in particular has risen by over 30% since the mid 19th century and continues to increase more than 1% each year. We single out these gases for three reasons:

  • They trap heat in the atmosphere and therefore warm the air and the Earth’s surface, i.e., they are greenhouse gases.
  • The increases of carbon dioxide, methane, and nitrous oxide in the atmosphere are clearly due to human activities.
  • These gases have long lifetimes in the atmosphere. A molecule of methane stays in the atmosphere for about 12 years, carbon dioxide stays in the atmosphere for several decades up to a century, and nitrous oxide has a lifetime of over a hundred years.
What is the Greenhouse Effect?

The greenhouse effect is the rise in temperature that the Earth experiences because certain gases in the atmosphere (i.e., water vapor, carbon dioxide, nitrous oxide, and methane) trap energy from the sun. Without these gases, heat would escape back into space and Earth's average temperature would be about 60°F colder. Because of how they warm our world, these gases are referred to as greenhouse gases.

The issues: What does it mean for forests and their watersheds?

Forests cover nearly one-third of the U.S., providing wildlife habitat, clean air and water, cultural and aesthetic values, carbon storage, recreational opportunities such as hiking, camping, fishing, and autumn leaf tours, and products that can be harvested such as timber, pulpwood, fuelwood, wild game, ferns, mushrooms, and berries. Across the U.S., forests are routinely altered by harvesting, fire management practices, conversion to agriculture, and by the expansion of urban areas and roads. Now, climate change is also exerting its influence. Leading scientists have attempted to predict how future climate change may affect forests in the U.S. Potential impact areas include:

  • Forest hydrology and productivity
  • Disturbances
  • Biodiversity
  • Socioeconomic
Prescribed fire
Forest Hydrology

Forest processes are critical to providing clean air and water, moderating stream flows, and maintaining aquatic habitats. These processes control responses of forests to environmental factors. Several environmental factors are changing rapidly and simultaneously. The global increase in atmospheric CO2 concentrations are the best documented factor. However, in some areas, other important atmospheric constituents are also increasing, including nitrogen oxides (a direct product of fossil fuel combustion that causes acid rain) and ground-level ozone (“smog”, a product of chemical reactions between hydrocarbons and nitrogen oxides in the presence of sunlight). Understanding how climate change will impact forests is needed to assure that supplies of water and wood are adequate during the next century.

Natural Disturbances Such as Fire and Drought

Natural disturbances having the greatest effects on forests include insects, disease, introduced species, fires, droughts, hurricanes, landslides, wind storms, and ice storms. Tree species have developed adaptations to some of these disturbances. For example, some tree species have developed very thick bark to protect them from repeated ground fires. Over millennia local, regional, and global changes in temperature and precipitation have influenced the occurrence, frequency, and intensity of these natural disturbances. These changes in disturbance regimes are a natural part of all ecosystems. However, forests may soon be facing rapid alterations in the nature of these disturbances as a consequence of global climate change.


Changes in the distribution and abundance of plant and animal species reflect the birth, growth, death, and dispersal rates of individuals in a population. While climate and soils exert strong controls on the establishment and growth of plant species, the response of plant and animal species to climate change will be the result of many interacting and interrelated processes operating over several scales of time and space. Migration rates, changes in disturbance regimes, and interactions within and between species will affect the distribution of plants and animals. In addition, human activities influence the occurrence and abundance of species on the landscape.


North America is the world’s leading producer and consumer of wood products. The U.S. has substantial exports of hardwood lumber, wood chips, logs, and some types of paper. However, the U.S. also imports forest products, including 35% of its softwood lumber and more than half of its newsprint from Canada. The market for wood products in the U.S. is highly dependent on the future area in forests, species composition of forests, future supplies of wood, technological change in production and use, availability of substitutes such as steel and vinyl, demands for wood products, and competitiveness among major trading partners.

Potential impacts: What are the consequences for the environment and people?
Water Resources

The potential for flooding is likely to increase because of earlier and more rapid melting of the snowpack and more intense precipitation. Even if total precipitation increases substantially, snowpacks are likely to be reduced. However, it is possible that more precipitation would also create additional water supplies, reduce demand, and ease some of the competition among users. In contrast, a drier climate is very likely to decrease water supplies and increase demand for such uses as agriculture, recreation, aquatic habitat, and power, thus increasing competition for scarcer supplies. Improved technology, planting of  less water-demanding crops, pricing water at replacement cost, and other conservation efforts can help reduce demand and vulnerability to drought. Advanced planning for potentially larger floods is needed to reduce flood risks.

Natural Disturbances

The interactions between climate change and natural disturbances are difficult to predict; however, as climate changes, alteration in these disturbances and in their effects on forests are possible. For example, the seasonal severity of fire hazard is projected to increase about 10% in the next century over much of the U.S. The interactions between climate change and hurricanes, landslides, ice storms, wind storms, insects, disease, and introduced species are difficult to predict. But as climate changes, alterations in these disturbances and in their effects on forests are likely.

Natural Ecosystems

Vegetation models estimate that under wetter conditions there is likely to be an increase in bio-mass, a reduction in desert areas, and a shift toward more woodlands and forests in many parts of the West. However, should the climate become drier, forest productivity would likely be reduced and arid areas would expand. It is possible that fire frequency could increase whether the region gets wetter or drier. Human development of the West has resulted in habitat fragmentation, creation of migration barriers such as dams, and introduction of invasive species. The combination of development, presence of invasive species, complex topography, and climate change is likely to lead to a loss of biodiversity in the region. However, it is probable that the mountains will enable some species to migrate to higher altitudes. It is also possible that some ecosystems, such as alpine ecosystems, would virtually disappear from the region. Human interventions to aid adaptation by species will be challenging, but reducing the pressures of development on ecosystems and removing barriers to migration could be the most effective strategies.

Tourism and Recreation

Higher temperatures are very likely to result in a longer season for summer activities such as back-packing, but a shorter season for winter activities such as skiing. Ski areas at low elevations and in more southern parts of the region are very likely to be at particular risk from a shortening of the snow season and rising snowlines. Effects on fishing will likely vary; warmer water will increase fish production and opportunities for some warm water species, but decrease habitat and opportunities for cold water species. Adaptation strategies for tourism and recreation involve diversification of income sources.

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Last Modified: Apr 14, 2016 12:23:01 PM