Operational Simulation Modeling at the NRCS National Water and Climate Center

The Water and Climate Services (WCS) division of the Natural Resources Conservation Service National Water and Climate Center produces seasonal water supply outlooks monthly, January through June, in partnership with the National Weather Service (NWS) and local cooperating agencies, such as the Salt River Project in central Arizona. Although forecasts have historically been regression based, simulation modeling is an emerging forecasting technology and an experimental prototype system for 16 basins was established in 2004. This system requires a high level of automation and objectivity because of the limited resources available to WCS and the time-critical demands of realtime forecasting. This paper describes the current status of the prototype and anticipated near-term future directions of WCS with respect to the use of simulation models. It begins with a description of the water supply forecasting operations, and continues with a review of past attempts to adopt operational simulation models. Next, the modeling environment is described, with emphasis on one model, the Precipitation Runoff Modeling System (PRMS) and its environment, the Modular Modeling System (MMS). Automatic calibration is used to derive parameter values and spatially-based quality control is applied to the historical data. Case studies of two basins are provided, the role of soil moisture on the Santa Clara Basin, Utah and quick hydrograph response and flooding on the Little Wood Basin, Idaho.