A multistep automatic calibration scheme for river forecasting models

Operational flood forecasting models vary in complexity. but nearly all hav e parameters for which values must be estimated. The traditional and widesp read manual calibration approach requires considerable training and experie nce and is typically laborious and time consuming. Under the Advanced Hydro logic Prediction System modernization program. National Weather Service (NW S) hydrologists must produce rapid calibrations for roughly 4000 forecast p oints throughout the United States. The classical single-objective automati c calibration approach, although fast and objective, has not received wides pread acceptance among operational hydrologists. In the work reported here. University of Arizona researchers and NWS personnel have collaborated to c ombine the strengths of the manual and automatic calibration strategies. Th e result is a multistep automatic calibration scheme (MACS) that emulates t he progression of steps followed by NWS hydrologists during manual calibrat ion and rapidly provides acceptable parameter estimates. The MACS approach was tested on six operational basins (drainage areas from 671 to 1302 km(2) ) in the North Central River Forecast Center (NCRFC) area. The results were found to compare favorably with the NCRFC manual calibrations in terms of both visual inspection and statistical measures, such as daily root-mean-sq uare error and percent bias by flow group. Further, implementation of the M ACS procedure requires only about 3-4 person hours per basin, in contrast t o the 15-20 person hours typically required using the manual approach. Base d on this study, the NCRFC has opted to perform further testing of the MACS procedure at a large number of forecast points that constitute the Grand R iver (Michigan) forecast group. MACS is a time-saving, reliable approach th at can provide calibrations that are of comparable quality to the NCRFC`s c urrent methods.