Important Paper “Remote New Paper “Sensing Of The Urban Heat Island Effect Across Biomes In The Continental USA” By Imhoff Et Al 2011

There is a paper on the urban effect on temperatures that relates to the BEST claim regarding the role of urban areas in determining the global average surface temperature trend [h/t to Marshall Shepherd].

This paper shows how spatially variable temperature effects are with respect to the details of urban areas.  Sampling of multi-decadal surface air temperature trends at specific fixed locations within this urban areas will be significantly affected as this landscape changes over time. 

Marc L. Imhoff , Ping Zhang, Robert E. Wolfe,and Lahouari Bounoua, 2011: Remote sensing of the urban heat island effect across biomes in the continental USA  Remote Sensing of Environment 114 (2010) 504–513

The abstract reads [highlight added]

Impervious surface area (ISA) from the Landsat TM-based NLCD 2001 dataset and land surface temperature (LST) from MODIS averaged over three annual cycles (2003–2005) are used in a spatial analysis to assess the urban heat island (UHI) skin temperature amplitude and its relationship to development intensity, size, and ecological setting for 38 of the most populous cities in the continental United States. Development intensity zones based on %ISA are defined for each urban area emanating outward from the urban core to the nonurban rural areas nearby and used to stratify sampling for land surface temperatures and NDVI. Sampling is further constrained by biome and elevation to insure objective intercomparisons between zones and between cities in different biomes permitting the definition of hierarchically ordered zones that are consistent across urban areas in different ecological setting and across scales.

We find that ecological context significantly influences the amplitude of summer daytime UHI (urban–rural temperature difference) the largest (8 °C average) observed for cities built in biomes dominated by temperate broadleaf and mixed forest. For all cities combined, ISA is the primary driver for increase in temperature explaining 70% of the total variance in LST. On a yearly average, urban areas are substantially warmer than the non-urban fringe by 2.9 °C, except for urban areas in biomes with arid and semiarid climates. The average amplitude of the UHI is remarkably asymmetric with a 4.3 °C temperature difference in summer and only 1.3 °C in winter. In desert environments, the LST’s response to ISA presents an uncharacteristic “U-shaped” horizontal gradient decreasing from the urban core to the outskirts of the city and then increasing again in the suburban to the rural zones. UHI’s calculated for these cities point to a possible heat sink effect. These observational results show that the urban heat island amplitude both increases with city size and is seasonally asymmetric for a large number of cities across most biomes. The implications are that for urban areas developed within forested ecosystems the summertime UHI can be quite high relative to the wintertime UHI suggesting that the residential energy consumption required for summer cooling is likely to increase with urban growth within those biomes.

The conclusion reads

“…. this research highlights a significant positive relationship between the urban heat island magnitude, the size of the urban area, and ecological setting estimated entirely from remotely sensed observations. The use of ISA as an estimator of the extent and intensity of urbanization is more objective than population density based methods and can be consistently applied across large areas for inter-comparison of impacts on biophysical processes. Overall, our results suggest that remotely-sensed land surface temperature provides an adequate characterization of both the magnitude and spatial extent of the urban heat island and allow objective comparisons of urban heat island effects around urban areas of different sizes at continental scales without the significant bias encountered in conventional ground observations.

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