Potential Drivers of Urban Heat Island in Northeast USA Cities

Impervious surface area (ISA) from National Land Cover Database 2001 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) signature on LST amplitude and its relationship to settlement size and shape, population, development intensity distribution, and land cover component over the surrounding rural area for 40 urban settlements embedded in forests biomes over Northeast USA. Development intensity zones based on %ISA were defined for each urban area emanating outward from the urban core to the non-urban rural areas nearby and used to stratify sampling for land surface temperatures. Sampling was further constrained by biome and elevation to insure objective intercomparisons between zones and between settlements. Stratification based in ISA permits the definition of hierarchically ordered zones that are consistent across urban areas and scales. We find that the besides ecological context, settlement size and shape as well as development intensity distribution significantly influence the amplitude of summer daytime UHI. Within the North-eastern temperate broadleaf mixed forest biome, UHI magnitude has been found positively related (correlation R>0.84) with logarithm of the urban area, population, and the area to perimeter ratio. Our case studies indicate that when the area sizes are similar, the development intensity distribution is one of the major drivers that cause the significant UHI difference. For instance, Providence with a high density skewed ISA profile tends to have more significant UHI (12.2C) than Buffalo (7.2C) which has a low density skewed ISA distribution. In addition to urban area and development intensity distribution, the difference in shape (represented by area to perimeter ratio) also causes the significant UHI difference in Syracuse (10.6C) and Harrisburg (7.6C). At last, the land cover component of the surrounding rural area will also affect the UHI magnitude among different urban settlements. Overall, our results indicate a possible way to examine and compare the amplitude as well as the drivers of the UHI between different cities.