Geospatial data resampling and resolution effects on watershed modeling: A case study using the agricultural non-point source pollution model

Researchers have been coupling geographic information systems (GIS) data handling and processing capability to watershed and waterquality models for many years. This capability is suited for the development of databases appropriate for water modeling. However, it is rare for GIS to provide direct inputs to the models. To demonstrate the logical procedure of coupling GIS for model parameter extraction, we selected the Agricultural Non-Point Source (AGNPS) pollution model. Investigators can generate data layers at various resolutions and resample to pixel sizes to support models at particular scales. We developed databases of elevation, land cover, and soils at various resolutions in four watersheds. The ability to use multiresolution databases for the generation of model parameters is problematic for grid-based models. We used database development procedures and observed the effects of resolution and resampling on GIS input datasets and parameters generated from those inputs for AGNPS. Results indicate that elevation values at specific points compare favorably between 3and 30-m raster datasets. Categorical data analysis indicates that land cover classes vary significantly. Derived parameters parallel the results of the base GIS datasets. Analysis of data resampled from 30-m to 60-, 120-, 210-, 240-, 480-, 960-, and 1920-m pixels indicates a general degradation of both elevation and land cover correlations as resolution decreases. Initial evaluation of model output values for soluble nitrogen and phosphorous indicates similar degradation with resolution. Now with SBC Communications, Inc., St. Louis, MO, USA Now with USGS, Mapping Partnership Office, Lafayette, LA, USA Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. We are grateful to Dr. David D. Bosch, ARS, Southeast Watershed Research Laboratory (SEWRL), Tifton, GA, for his assistance in installing and initializing the AGNPS model and, in particular, for supplying the specific land cover categorization developed by SEWRL for Little River and Piscola Creek. J Geograph Syst (2004) 6:289–306 DOI: 10.1007/s10109-004-0138-z Geospatial data resampling and resolution effects on watershed modeling: A case study using the agricultural non-point source pollution model E. Lynn Usery, Michael P. Finn, Douglas J. Scheidt, Sheila Ruhl, Thomas Beard, and Morgan Bearden U.S. Geological Survey, Mid-Continent Mapping Center, 1400 Independence Road, Rolla, Missouri 65401, USA (e-mail: [email protected]) Received: 10 March 2003/Accepted: 21 May 2004