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Stream flow metrics for historical and future climate change scenarios

January, 2008

tech in a stream taking stream flow measurements
Western U.S. Stream Flow Metrics - A dataset of modeled flow metrics for streams in major river basins of the Western US for historical and future climate change scenarios.

Climate change is projected to alter the flow regimes of streams and rivers, with consequences for physical processes, aquatic organisms, and water resource management. To study these hydrologic changes, we have developed a database of flow metrics for streams across much of the United States (extent shown in Figure 1 of the User Guide) under historical conditions and future climate change scenarios. These are based on daily simulations of the Variable Infiltration Capacity (VIC) macroscale hydrologic model from the the Downscaled CMIP3 and CMIP5 Climate and Hydrology Projections archive.

The U.S. Forest Service Rocky Mountain Research Station and the Office of Sustainability of Climate used these model outputs to calculate a set of summary streamflow metrics to describe key attributes of the flow regime for each stream segment in the 1:100,000-scale National Hydrography Dataset (NHDPlus version 2) in the conterminous United States. Datasets are available for the historical period (1977-2006), mid-century (2030–2059) and end-of-century (2070–2099). Future projections are based on the average of five CMIP5 global climate models (GCMs) associated with the RCP 8.5 high emissions scenario. Please see the User Guide for more information and important caveats on appropriate use.

Note: This dataset updates the prior dataset, available for the western U.S., only. For information on the prior dataset, see the archived version of this page here.

Related datasets:

Key Findings

  • Climate change is projected to alter the flow regimes of streams and rivers, with consequences for physical processes and aquatic organisms.

  • The stream flow metric dataset makes it possible to study the effects of droughts, changes in snowpack, water resource impacts, and other hydrologic changes for historical and future climate change scenarios.

  • Datasets are available for historical conditions (1978-2006) and for future climate change scenarios associated with global climate models.



Wenger, Seth J. ; Luce, Charles H. ; Hamlet, Alan F. ; Isaak, Daniel J. ; Neville, Helen M. , 2010


Flow metrics for the western U.S. for the historical and future time periods, and for the changes between time periods, can be downloaded from the FSGeodata Clearinghouse. These data can also be explored on ArcGIS Online.

Note: This project is an update to a previously available version of streamflow data. The data from the FSGeodata Clearinghouse should be used, but information on the previous version, for the western U.S. is available on this page.


Western Flow Metrics Interactive Map includes:

  • Mean Annual Flow: calculated as the mean of the yearly cumulative discharge values. 
  • Mean Summer Flow: the average of daily flow between June 1 and September 30. 
  • Mean August Flow: the average of daily August flows, included as a generally dry month with high water demands.
  • Winter Flows Over the 95th Percentile: the number of daily flows between December 1 and March 31 that exceed the 95th percentile of daily flows across the entire year. 
  • 1.5-Year Flood: calculated by first finding the annual maximum series of flows (i.e. the largest flood for each year). The 33rd percentile of the annual maximum series defines the daily flow that occurs every 1.5 years, on average. 
  • 10-Year Flood: calculated as above, but for the flow that occurs every 10 years on average.
  • 25-Year Flood: calculated as above, but for the flow that occurs every 25 years on average.
  • Maximum Modeled Flood: calculated by finding the highest modeled daily flow occurring in any year.
  • Center of Flow Mass: calculated using a weighted mean, to find the day number of the water year (October 1–September 31) at which half of the year's flow occurs before, and half after.
  • Center of Flow Mass (Date): calculated by converting the Center of Flow Mass to a (non-leap year) date in month-date format for easier interpretation (e.g. a CFM value of 125.385 is converted to 02/03). 
  • Baseflow Index: The ratio of the lowest 7-day flow of summer (May 1–September 30) to the average annual flow.

Project Contact: 

Principal Investigators:
Nathan Walker - Forest Service Office of Sustainability and Climate