USFS Hydro Flow Metrics, Contiguous US: Historical and Future

This file represents modeled streamflow across the contiguous United States, for the historical time period (1977-2006), based on gridded simulations of daily total runoff. The flow regime is of fundamental importance in determining the physical and ecological characteristics of a river or stream, but actual flow measurements are only available for a small minority of stream segments, mostly on large rivers. Flows for all other streams must be extrapolated or modeled. Modeling is also necessary to estimate flow regimes under future climate conditions. We modeled streamflow across the contiguous United States, for the historical period (1977–2006), and two projected future time periods, mid-century (2030–2059), and end-of-century (2070–2099). These are based on gridded simulations of daily total runoff. These use RCP 8.5 projections of temperature and precipitation, downscaled to a 1/8 degree (~12 km) cell size, which are used as inputs to the Variable Infiltration Capacity (VIC) macroscale hydrologic model. This dataset updates the previous Western U.S. Stream Flow Metric Dataset (Wenger et al., 2010) (a link to the old datasets is available on the project website: https://www.fs.fed.us/rm/boise/AWAE/projects/modeled_stream_flow_metrics.shtml). It expands the spatial extent of this analysis, uses updated climate scenarios, and includes additional climate metrics. For each stream segment in the National Hydrography Dataset Plus Version 2 (NHDPlusV2) in the contiguous U.S. we calculated hydrographs for the three time periods. From these we calculated summary flow metrics to describe flow regimes for each stream segment and each time period and joined these to the NHD stream segments for visualization and analysis. These results allow scientists and managers to easily compare historical and projected flow patterns, including monthly, seasonal, and annual flow, flood and drought events, and timing of peak and low flows. Note: We recommend that line segments with an upstream area greater than 10,000 km2 be removed from the dataset for consideration of high flow metrics (using the field 'TotDASqKM'), since the downstream routing was simply an accumulation function. This is reasonable for larger watersheds at time scales of months and greater, but would be inaccurate for estimating floods at daily time scales on larger watersheds. Note also that the 10+ year flood models are not appropriate for use in engineering and design applications. Streams without flow metrics (null values) were removed from this dataset to improve display speed; to see all stream lines, use an NHD flowline dataset.