Tracking urban growth and composition along the western portion of the U.S. - Mexico border: 1985 -2010
Rapid urban growth has been a key characteristic of global land cover change over the last century. A microcosm of global urbanization can be seen in the US-Mexico border region. This dissertation follows the growth and composition of urban areas along the western portion of the border from 1985 - 2010 through three chapters. First, the remote sensing technique Multiple Endmember Spectral Mixture Analysis (MESMA) was used with spatial metrics to compare relative quantities of vegetation, impervious surface and soil, between eight cities along the western portion of the international boundary. Three separate study areas enabled comparison of MESMA modeling techniques along a varying climatic gradient. For each study area a spectral library was constructed and applied to Landsat TM imagery. The most complex mix of urban materials required the most complex combination of MESMA models but spectral library complexity was related to the presence of abundant desert soils and lack of vegetation in the eastern border cities. Metrics of vegetation dominance and impervious surface orientation are well suited for differentiation of sociopolitical processes that result in variations in urban form on either side of the boundary. In the second chapter, the products of MESMA were used to represent urban areas in three ways: urban extent, dominant land cover, and continuous representations of vegetation, impervious surface, and soil. The urban representations were used to calculate landscape metrics and the metrics were subsequently analyzed over time from 1985 - 2010. Urban areas in the U.S. and Mexico follow a pattern of diffusion and coalescence however the scale of development in each country differs. Despite the differing scale and patterns of growth, the landscape metrics used in this study do not readily differentiate them. Also, in Mexico and the U.S., overall urban vegetation cover declined in terms of density and patch size while distance between patches of dominant vegetation cover increased. The use of differing representation of urban area, especially of dominant vegetation cover has implications for investigations in urban ecology, planning, and socioeconomics. Finally, the third chapter demonstrates that the coupling of satellite imagery and socioeconomic data can highlight the interaction of macroeconomic processes and urban land development in developed and less developed countries. Urban growth rate information derived in the second chapter was combined with socioeconomic and policy data to estimate econometric equations. The results indicate that the primary correlate with urban growth in the U.S. counties was housing while in Mexico, housing and the concurrent rapid growth of manufacturing were the major influences on urban growth rate. No role in the increase or decrease of growth in either country could be detected with the instigation of the North American Free Trade Agreement. Several events in 2001, including a U.S. recession and China's entry in to the World Trade Organization, occur at the same time as a downturn in Mexico's growth rate. A better understanding of the interaction between internal and external factors that influence urban growth should help inform decisions taken during the long-range planning process. The chapter also demonstrates that remote sensing data may provide a proxy for socioeconomic data in locations where socioeconomic data are unavailable. This research contributes to the understanding of urban form on the U.S. Mexico border and demonstrates the utility of remotely sensed data in exploring the broad-scale geographic outcomes of socioeconomic influences on urban growth across political boundaries.
Remote Sensing, Urban landscape metrics, U.S. - Mexico border
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