Cities such as New York, Philadelphia, and Boston are prominent centers of political
power. Less known: Their size, background ecology, and development patterns also
combine to make them unusually warm, according to NASA scientists who presented new
research recently at an American Geophysical Union (AGU) meeting in San Francisco,
Summer land surface temperature of cities in the Northeast were an average of 7 °C
to 9 °C (13°F to 16 °F) warmer than surrounding rural areas over a three year period,
the new research shows. The complex phenomenon that drives up temperatures is called
the urban heat island effect.
By comparing 42 cities in the Northeast, they found that densely-developed cities
with compact urban cores are more apt to produce strong urban heat islands than more
sprawling, less intensely-developed cities.
The compact city of Providence, R.I., for example, has surface temperatures that
are about 12.2 °C (21.9 °F) warmer than the surrounding countryside, while similarly-sized
but spread-out Buffalo, N.Y., produces a heat island of only about 7.2 °C (12.9 °F),
according to satellite data. Since the background ecosystems and sizes of both cities
are about the same, Zhang's analysis suggests development patterns are the critical
She found that land cover maps show that about 83 percent of Providence is very or
moderately densely-developed. Buffalo, in contrast, has dense development patterns
across just 46 percent of the city. Providence also has dense forested areas ringing
the city, while Buffalo has a higher percentage of farmland. "This exacerbates the
effect around Providence because forests tend to cool areas more than crops do,"
Cities in desert regions, such as Las Vegas, in contrast, often have weak heat islands
or are actually cooler than the surrounding rural area. Providence, R.I.; Washington,
D.C.; Philadelphia, Pa.; Baltimore, Md.; Boston, Ma.; and Pittsburgh, Pa.; had some
of the strongest heat islands of the 42 northeastern cities analyzed.
This graph shows the result of a model that calculated the likely magnitude of the
effect during the 2003 heat wave in Paris