ESP natural forecasts simulate the unregulated, naturally occurring streamflow at a point. All known reservoir operations and river diversions are accounted for and returned to the streamflow simulation. Natural runoff volume estimates (historical and current) are estimated using the same techniques.
ESP natural forecasts differ from ESP water supply forecasts, which are typically adjusted only for major upstream reservoir storage, or in some cases, left unadjusted (for instance in the lower Snake and Yakima systems).
Another important difference between the two forecast methods is that ESP natural forecasts are computed from streamflow simulations that are routed from headwater basins downstream through the system. ESP water supply forecasts do not have a routing component. The natural forecast methodology accounts for travel time between points whereas the water supply methodology does not.
