Hotter summers for sprawling cities

Heat island effect

Jon Boyd, Jun 30, 10.

Summers in sprawling cities are getting warmer faster than compact cities, reports an article in USA Today.

The USA Today article reports the findings of article originally published in Environmental Health Perspectives:

A team of Atlanta-based scientists studied the number of very hot days in 53 sprawling metropolitan regions between 1956 and 2005, each of which had different climate zones, population sizes and rates of growth.

The scientists found that the annual number of very hot days in sprawling cities increased by 14.8 days, but cities with the least sprawl increased by only 5.6 days.

Two factors contribute to warming, greenhouse gases and the urban heat island effect. Sprawl development replaces vegetation with pavement at a greater rate than compact cities, therefore the heat island effect is more pronounced in sprawl cities.

USA Today reports on the methods for measuring sprawl and temperatures in cities:

The scientists used the sprawl index, which looks at population density, proximity of commercial and residential buildings and street network patterns, to categorize the regions. Those in the top 25% of the index had the most sprawl, while those in the bottom 25% had the least sprawl.

The team identified very hot days by using a city-specific heat stress index developed by the National Climatic Data Center (NCDC), which measures the average apparent temperatures, counting temperature and humidity.

(Photo credit: Mark Strozier)