Study reveals cities are experiencing more heatwaves

Monday 02nd Feb 2015 by theWeather Club

A recent study has revealed that urban heatwaves have become more frequent over the past 40 years. The findings, published in Environmental Research Letters, found that data from 2017 urban areas across the globe showed that there have been a significant increase in the number of heatwave during 1973-2012, whilst the frequency of cold waves declined.

Heatwaves were defined as periods lasting six days consecutively or more with a daily maximum temperature greater than 99 per cent of the temperatures recorded at that time of the year, as measured over the whole 40 years. The researchers found that four of the five years with the most heatwaves had occurred since 2009 and were experienced mostly in Africa, East Asia, Europe and North America. Almost half of the urban areas experienced significant increases in the number of extreme hot days, while almost two-thirds showed significant increases in the frequency of extreme hot nights.

Local climate variability and microclimates, artificial surfaces and anthropogenic heat from buildings and vehicles, city design, architecture and morphology, land cover and reduced vegetation all play a part in creating elevated air temperatures in cities, known as the ‘urban heat island’ effect, which have a compounding effect during heatwave events.

More than half the world’s population now live in urban areas; climate extremes have significant implications for urban infrastructure and society, yet there are few studies of observed changes in climate extremes over the global urban area.

Lead author Vimal Mishra, a professor at the Indian Institute of Technology Gandhinagar, said. “Urban areas make up a relatively small part of the global land area; but they are the centre of wealth, so damage to urban infrastructure could result in potentially large economic losses.

It is particularly important to understand how the climate and climate extremes, in particular, are changing in these areas."