Expert Report

Each report is produced by a committee of experts selected by the Academy to address a particular statement of task and is subject to a rigorous, independent peer review; while the reports represent views of the committee, they also are endorsed by the Academy. Learn more on our expert consensus reports.

Of all the resources that forests produce, water may be the most important-streamflow from forests provides two-thirds of the nation's clean water supply. Forest managers face increasing pressure to cut trees to increase water supply for human uses, especially in western states where population is rising. However, cutting trees for short term water gains does not guarantee that water will be available in dry seasons, and it can ultimately degrade water quality and increase flooding vulnerability. At the request of the U.S. Bureau of Reclamation and the U.S. Forest Service, the National Research Council convened a committee to examine the present understanding of forest hydrology (the study of how water moves through forests), connections between forest management and attendant hydrologic effects, and directions for future research and management needs to sustain water resources from forests. The report concludes that forest hydrology must advance if it is to deal with today's complexities, and it identifies actions that scientists, forest and water managers, and citizens can take to help sustain water resources from forests.

Key Messages

  • To meet the needs of the managers and users of forests and water, forest hydrology research has to move from principles to prediction. Predictions are needed to understand the indirect and interacting hydrologic responses to changes in forested landscapes associated with climate change, forest disturbances, forest species composition and structure, and land development and ownership, and how these changes will affect water quantity and quality downstream and over long time scales.
  • Compared to the extensive literature on hydrologic responses to forest management, relatively few studies have examined hydrologic responses to fire, insects, and disease in forests, especially at long time scales or in large watersheds.
  • Cumulative Watershed Effects research strives to establish cause-effect relationships among forests, water, and watersheds over large spatial and temporal scales.
  • More research is needed to better predict indirect effects of climate change, including evaluations of how changes in forests and forest management influence hydrologic response.
  • The hydrologic effects of many of the new management practices and BMPs have not been studied, and dynamic forest conditions make it important to understand how contemporary practices influence water resources.