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. To date there are few databases of modeled stream flows that are broad in coverage, fine in resolution, and available for both historical and future climate conditions. Here we present such a database.
The University of Washington Climate Impacts Group, Trout Unlimited, and the US Forest Service Rocky Mountain Research Station (RMRS) used the Variable Infiltration Capacity (VIC) macroscale hydrologic model to estimate stream flows at a daily timestep under historical and forecasted future climate conditions across major river basins of the western United States. Forecasts were for the A1B emissions scenario for the 2040s and 2080s, using (1) an ensemble of 10 global climate models (GCMs), (2) MIROC3.2, a model that predicts a large amount of warming in the region, and (3) PCM1 , a model that predicts a low amount of warming. The individual models (MIROC and PCM) were used to bracket the range of uncertainty in warming and precipitation, while the ensemble mean represented a best-guess model consensus. For the historical scenario and each of the six future scenarios, we estimated a hydrograph for every individual stream segment in the 1:100,000 scale National Hydrography Dataset (NHD), excluding large rivers. We then calculated a set of summary flow metrics to describe key attributes of the flow regime for each segment. These may be attached to the NHD stream segments for visualization, or used for various kinds of analyses.
