THE IMPORTANCE OF PRECISE RAINFALL INPUTS IN NONPOINT-SOURCE POLLUTION MODELING

Rainfall data provide a prime input in nonpoint source pollution (nps) modeling. The sensitivity of model outputs to variations in the time step selected for rainfall data has been explored for two nps models, a field-scale continuous model, and an event-based watershed-scale mod el, for the temperate climatic conditions of Southern Ontario, Canada. This study has revealed that model outputs regarding runoff, soil los s and sediment yield, and calibrated parameters representing soil hydr aulic properties and erosion characteristics are extremely sensitive t o small variations in the rainfall time step. Model users must use cau tion therefore to take these variations into account during the calibr ation and application of such models.