APPLICATION

The Phoenix Arizona metropolitan area has experienced extreme rates of growth and development in recent years.  It is the fast rate of expansion in an area as large as Greater Phoenix that makes the Salt River Valley somewhat unique.  Over half of the land use conversion is from irrigated agriculture to urban land use (Salt River Project, 1992), thus converting one of the coolest categories of land cover to much hotter categories of land use.  In terms of human population expansion, Metro Phoenix grew from a 1970 population of 971,000 to a 1990 population of 2.1 million.  This 20 year growth rate of more than 110 percent places Phoenix as the fastest growing of the top 30 American urban areas.  Perhaps even more noteworthy is the Maricopa Association of Governments (MAG) predicts that Metro Phoenix will reach 4.0 million inhabitants by 2010 (Maricopa Association of Governments, 1985), and this is thought by many to be a significant under estimate.  While past growth has been sprawling, the Salt River Project (the utility company providing all of the water and most of the electricity to this region) predicts that future growth will continue to convert still more land to urban uses, squeezing another 2.0 million people into the Salt River Valley in the next 20 years. 

During the first half of the twentieth century much of the region surrounding Phoenix, Arizona was converted from natural desert to extensive irrigated agriculture.  In recent decades, increasing rates of land use conversion have resulted in extensive change to urban categories of land use.  According to Salt River Project projections, in the next 20 years residential uses will increase by about 30 percent while commercial and industrial uses will nearly double.  All of this growth in the urbanized area of Greater Phoenix must come at the expense of other land uses.  Not surprisingly, much of the irrigated agricultural acreage is being converted.  This has the effect of warming the earth's surface, and near surface air temperature, in the metropolitan area as a function of land use development.  This produces a daytime metropolitan temperature field much closer to that of the surrounding natural desert.

The relatively high resolution of Landsat remotely sensed thermal data have proven to be useful in assessing temperature patterns of urban environments at the neighborhood scale.  In addition, this image analysis has observed a strong correlation between patterns of environmental temperature and surface rates of evapotranspiration, where these rates of evapotranspiration are portrayed, in large, part by biomass as represented in the normalized difference vegetation index.  Spatial patterns of energy demand and human comfort associated with ambient temperatures did not correlate well with traditional categories of mapped land use (e.g., high, medium and low density residential).  The use of a multispectral classification of remotely sensed data did prove useful in identifying categories of environmental surfaces which exhibit relatively homogenous temperature patterns within the city.  These classified categories were found to be associated with identifiable biophysical surface conditions, and were associated with identifiable land use and land cover categories (e.g., irrigated residential,  xeriscaped residential, etc.).