Heat waves hit cities the hardest

City dwellers will have to bear the maximum brunt of heat waves as extreme summers like that of 2012 - which saw record temperatures in various cities across the world - become increasingly common, predicts a study.

The study found heat waves hit urban areas hardest, shedding light on what a future with more extreme summers might mean for the world's growing population of urbanites.

As the chances of a heat wave rise, many city-dwellers could face more uncomfortable summers, increased health risks and potentially higher energy bills from air conditioning, the study noted.

"Not only do heat waves intensify the urban heat island, but the heat island also intensifies the heat wave, which is pretty much the opposite of what you would want," said the study's lead author Jason Schatz from University of Wisconsin-Madison in the US.

Using data from the 150 sensors Schatz installed in and around Madison, the researchers found that urban areas experienced up to twice as many hours over 90 degrees Fahrenheit (32 degrees Celsius) than rural areas during the 2012 heat wave.

The researchers noted that in densely built areas, the heat-retaining asphalt, brick and concrete make things hotter than their non-urban surroundings.

Since prolonged heat exposure, rather than isolated hot days, is what can cause heat stress, long stretches with no night time reprieve in densely populated areas pose a greater risk to public health.

This risk is bound to grow if cities do not plan accordingly, co-author Chris Kucharik, professor at University of Wisconsin-Madison warned.

"2012 is pretty representative of summers we are likely to experience 50 years from now," he said.

The study was published in the journal Environmental Research Letters.