Extreme heat in the summertime can amplify the urban heat island effect, putting cities and buildings at risk of uncomfortable temperatures and high air conditioning costs. New research published in Environmental Research Letters used data collected from 150 temperature sensors in and around Madison, WI, during the 2012 heat wave and the 2013-14 polar vortex to give scientists a rare look at how the varying weather extremes would affect cities. During the heat wave, researchers from the University of Wisconsin-Madison found that urban areas experienced up to twice as many hours over 90 degrees F. than did rural areas.
The data also showed that the most densely populated areas of the city spent over four consecutive nights with temperatures staying about 80 degrees F., the National Weather Service’s heat advisory threshold for nighttime. The researchers note that prolonged exposure to high temperatures can cause heat stress and other threats to public health – meaning the boosted heat island effect could not only prove expensive due to higher air conditioning costs but dangerous as well.
With summer temperatures such as those in 2012 expected to become more common in the future, the scientists note that current climate projections could be underestimating the threat posed to urban areas in particular. While summers are predicted to become hotter, the researchers also found a small bright side to the data, which showed that the effect was also a factor in the wintertime, with areas in the city seeing 40% fewer hours of exposure to below-zero temperatures.