DESERTIFICATION EVALUATED USING AN INTEGRATED ENVIRONMENTAL ASSESSMENT MODEL DAVID MOUAT 1 , JUDITH LANCASTER 2 , TIMOTHY WADE 2 , JAMES WICKHAM 3 , CARL FOX 4 , WILLIAM KEPNER 5 and TIMOTHY BALL 2 1 Biological Sciences Center, Desert Research Institute, 7010 Dandini Boulevard, Reno, NV 89512, U.S.A. Current address: U.S. Environmental Protection Agency, 200 SW 35th Street, Corvallis, OR 97333, U.S.A.; 2 Biological Sciences Center, Desert Research Institute, 7010 Dandini Boulevard, Reno, NV 89512, U.S.A.; 3 Environmental Research Center, Tennessee Valley Authority, 17 Ridgeway Road, Norris, TN 37828, U.S.A.; 4 Office of Research and Development, University of North Dakota, Box 7134, Grand Forks, ND 58202, U.S.A.; 5 U.S. Environmental Protection Agency, 944 E. Harmon Avenue, Las Vegas, NV 89119, U.S.A. (Received 15 March 1996; in final form 18 September 1996) Abstract. Desertification has been defined as land degradation in arid, semi-arid and dry sub-humid areas resulting from various factors, including climatic variations and human activities (United Nations, 1992). A technique for identifying and assessing areas at risk for desertification in the arid, semi-arid, and subhumid regions of the United States was developed by the Desert Research Institute and the U.S. Environmental Protection Agency (EPA), using selected environmental indicators inte- grated into a Geographic Information System (GIS). Five indicators were selected: potential erosion, grazing pressure, climatic stress (expressed as a function of changes in the Palmer Drought Severity Index [PDSI]), change in vegetation greenness (derived from the Normalized Difference Vegetation Index [NDVI]), and weedy invasives as a percent of total plant cover. The data were integrated over a regional geographic setting using a GIS, which facilitated data display, development and exploration of data relationships, including manipulation and simulation testing. By combining all five data layers, landscapes having a varying risk for land degradation were identified, providing a tool which could be used to improve land management efficiency. Key words: desertification assessment, GIS, integrated models, land degradation, remote sensing 1. Introduction Desertification is a process which operates principally in arid, semi-arid and sub- humid environments, and involves excessive pressure of human use, changes in land use or changes in natural processes. Desertification is associated with long-term change in ecosystem function (Dregne, 1977), involves both spatial and tempo- ral components, and results in reduced productivity, biodiversity and diminished economic viability. The purpose of this study was to develop a methodology for creating a plausible and workable model to identify areas at risk from desertification. The Colorado Plateau was selected as a study region because desertification has been identified The information in this document has been funded wholly (or in part) by the U.S. Environmental Protection Agency. It has been subjected to the Agency’s peer and administrative review, and it has been approved for publication as an EPA document. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. Environmental Monitoring and Assessment 48: 139–156, 1997. c 1997 Kluwer Academic Publishers. Printed in the Netherlands.