Evaluation of the NWS (National Weather Service) Soil Moisture Accounting Model for Automated Flash Flood Forecasting in Small Arid and Semi-Arid Watersheds

摘要

An analysis of the NWS model and the hydrological characteristics of small arid watersheds indicated that modifications to the model would be necessary for arid zone applications. One modification, based on the absence or insignificance of base-flow in the typical small, arid watershed, involves removal of the lower zone reservoirs and replacement of the complex percolation function by a proportional loss rate. In light of the extreme rainfall intensities and rapid runoff rates associated with desert floods, the infiltration representation was revised so that overland flow may begin before the upper zone is saturated and so that maximum infiltration capacity is a parameter. Other modifications include the use of watershed subcells and routing which simulates percolation of flows into the channel bed. The amount of data required for model calibration can be reduced by the use of the modified model in conjunction with recommended calibration procedures.