Long-term Land-cover Mapping and Change Detection in the Phoenix Metropolitan Area

Background: Located in a semi-arid desert region, the Phoenix metropolitan area confronts a number of sustainability challenges, such as water scarcity and extreme heat in the context of population and economic growth and climate change. Land-cover change is an important cause and consequence of these challenges and understanding the long term changes in land cover is essential to addressing the water conservation and urban heat mitigation issues. This study is being conducted in conjunction with the Decision Center for a Desert City (DCDC) at Arizona State University (ASU), the mission of which is to understand decision making under uncertainty in the context of water sustainability and urban climate adaptation. Methods: Remote sensing data were used as primary sources for land-cover change detection in recent decades. Consistency among data sources and methods were critical for the accuracy of the change detection. To ensure this consistency, a series of the 30-meter Landsat images were obtained for the Phoenix metropolitan area from 1985 to 2010 with a time interval of five years. The images were classified using an object-oriented method in which pixels were grouped into image objects based on spectral similarity and spatial contiguity. Post-classification comparison among land-cover maps was used to analyze the rate, intensity, and spatial distribution of changes among land-cover classes, and to assess the accuracy of change detection results. Results and Conclusions: The long-term land-cover map series identified spatially and temporally complex changes in agriculture, desert and urban areas that result from natural and anthropogenic processes. Interpretations of the trajectories and spatial patterns of land-cover changes are fundamental in developing the holistic understanding of the trend in urban development and associated changes in water consumption and local climate conditions in metropolitan regions.