National Forest Contributions to Streamflow
Forested and mountainous locations, such as national forests, tend to receive more precipitation than adjacent non-forested or low-lying areas. However the precise contributions of national forest lands to regional streamflow volumes is largely unknown. New modeling work illustrates the importance of water yield from National Forest System land to water quantity and quality through visual and textual presentations of each forest’s contributions to regional streamflow.
We extracted daily runoff and baseflow from each grid cell in the Variable Infiltration Capacity (VIC) hydrologic model dataset of Livneh et al. (2013). Similar to Wenger et al. (2010), area-weighted sums of runoff plus baseflow were calculated for each catchment in the NHDPlus V2 database. These values were routed downstream to create daily hydrographs for each 1:100,000 scale stream segment in the contiguous United States.
A second set of calculations was run in which the catchment values were area-weighted by the percent of the catchment on National Forest System land to create daily hydrographs for each stream segment representing the flow sourced from national forests. The areas of intersection between each catchment and individual national forests were also calculated and these were used to derive area-weighted hydrographs for each stream segment and each individual national forest. Mean annual flow volumes were calculated for each stream segment for total flow (all land) and for each national forest. For each stream segment, the flow volume from each forest was divided by the total mean annual flow to get the portion of flow in each stream segment contributed by each forest.
A comparison of this method with the method of Brown et al., [2016] as well as maps of water yield for the contiguous United States are available here.
These datasets can also be viewed in ArcGIS Online, and are available for download in geodatabase or shapefile format in the FSGeodata Clearinghouse, or as csv files in the Forest Service Research Data Archive.
Maps were created for each national forest, each USDA Forest Service region, and the contiguous United States showing the percent of streamflow contributed by national forests. Only streams above a minimum mean annual flow volume and with some contribution from the forest(s) were displayed. The line width of the stream segments is indicative of the total mean annual flow and the line color indicates the percent of flow contributed by the forest(s). Numbers on the maps identify the major rivers within the map scene. Text files accompanying each map indicate the percent of streamflow and percent of land the forest(s) contributes to each 8-digit and 4-digit HUC and to major streamflow points.
Maps and text files of national, regional, and individual national forest contributions to streamflow will be available on this page shortly.
Key Personnel
Principal Investigators
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Person
Charlie H. Luce, PhD
Research Hydrologisthttps://research.fs.usda.gov/about/people/charles.luce
Research Staff
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Person
Abby Lute
ORISE Research Fellow