Using the IDRISI Geographical Information System to Determine Watershed Model Inputs

As part of a research project on the potential effects of climate change on aquatic ecosystems, a basin scale hydrologic model has been chosen to simulate the effect of climate change on the non~point source inputs from rural watersheds to lakes and impoundments. The goal of this study is to develop methods for conducting a regional analysis of watershed response to climate change. In this report, the methods required to compile the input data for SWAT (Standard Watershed Assessment Tool, Arnold et al., 1994) using the IDRISI geographical information system (GIS) software (Eastman, 1993) are described. There were three major steps in the process. The first step, map acquisition, required downloading three different types of maps from the USGS Eros Data Center via the Internet. Two methods for the second step, determining the boundaries of the entire watershed and its subbasins, were used and compared. The third step was the determination of the input parameters using the maps and watershed boundaries derived in steps one and two, SWAT requires three files of input data for the entire basin and ten input files for each subbasin. Whenever it was possible (and appropriate), GIS methods were used to calculate these data.National Agricultural Water Quality Laboratory, US Department of Agricultur