Urbanization Trends (2001-2006) In The Conterminous United States And Regional Climate Impacts
Abstract
More than 50% of the world population now lives in urban and suburban areas. The rate of urbanization in the world is expected to continue to accelerate in the near future. As urban areas expand by transforming the surrounding landscape into impervious surface, the changes of urban land cover (ULC) have significant implications for wide range consequences. Monitoring changes in large urban areas becomes increasingly important. The U.S. Geological Survey (USGS) recently published the National Land Cover Database (NLCD) 2006 products including land cover and percent impervious surface area (ISA) for the conterminous United States (CONUS). The percent ISA, which represents the fraction of impervious area in a 30 m grid, was estimated using regression tree algorithms with both Landsat and nighttime lights imagery. Generally, the approach comprises four major procedures: creating a training dataset, modeling a synthetic impervious surface, comparing model outputs for optimal selection and final product clean up. The ISA product was used to define four different ULC types by categorizing percent ISA and quantitatively determining the extent of ULC. We analyzed 2001 and 2006 imperviousness variations to summarize two areal increments: ISA, which calculates the area of imperviousness proportion in every 30 m pixels, and urban area, which totals the number of 30 m pixels that contain any impervious surface. The new ISA in 2006 increases 4.1% (4095 km2) from the 2001 base amount across the CONUS. The growth of ISA reached approximately 819 km2 per year during the period. The total ISA in 2006 reached 103,615 km2, which is slightly smaller than the state of Kentucky. The new urban area in 2006 was 12,365 km2 and the total urban area reached 500,153 km2, which is close to the size of California and Indiana combined. To analyze the interactions between ULC change and climate systems, we used both the gridded climate data from the Parameter-elevation Regressions on Independent Slopes Model (PRISM) dataset and NLCD ISA product. Mean annual precipitation, mean annual minimum temperature (Tmin), and mean annual maximum temperature (Tmax) from 1980 to 2010 were converted to a raster format. A standardized anomaly method was used to calculate climatic anomalies by A(t)=(X(t)-Xmean)/σ , where A(t) is the standardized anomaly of a given quantity X (e.g., mean annual Tmin) in a specific year t, Xmean is the long time mean, and σ is the standard deviation. The means of annual Tmin in the periods of 1995-2000 and 2001-2006 were averaged in the newly urbanized areas that emerged after 2001. The average in the urbanized time period (2001-2006) is about 0.3 °C higher than the average in the pre-urbanized time (1995-2000). Similarly, in the new urban areas, the six year averages of standardized anomaly of Tmin were 0.12 and 0.52 in the periods of 1995-2000 and 2001-2006, respectively, indicating a larger anomaly due to ULC change. The land cover change characterized by urbanization apparently affects surrounding ecological system conditions and imposes a significant forcing function on the climate system.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMGC33B1083X
- Keywords:
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- 0426 BIOGEOSCIENCES / Biosphere/atmosphere interactions;
- 1631 GLOBAL CHANGE / Land/atmosphere interactions