Urban areas turn up the heat

Heatwaves are becoming more prominent in cities, new research has revealed. The last four decades have seen significant increases in prolonged periods of extreme heat in more than 200 urban areas.

Prolonged periods of extreme heat significantly increased in more than 200 urban areas across the world between 1973 and 2012, according to results published in Environmental Research Letters.

Over the same period, more than half of the studied areas showed a significant increase in the number of individual extreme hot days. Almost two thirds measured significant increases in the number of individual extreme hot nights.

The study, which was conducted by researchers at the Indian Institute of Technology (IIT) Gandhinagar, Northeastern University, the University of California, Los Angeles and the University of Washington, is one of the first to focus on the extent of extreme weather on a global scale and disparities between urban and non-urban areas.

The researchers used daily observations of rain, air temperature and wind speed from the ‘Global Summary of the Day’ data produced by the National Climatic Data Center. They then identified extremes of temperature, precipitation, wind, calculated heatwaves, cold waves and individual extreme hot days and nights.

Heatwaves were defined as periods in which the daily maximum temperature was hotter than on 99 per cent of the days between 1973 and 2012, for a consecutive duration of six days or more.

Of the five years with the largest number of heatwaves, four were the most recent years on record.

Lead author Professor Vimal Mishra of IIT Gandhinagar said in a press release: “Over half of the world’s population now live in urban areas; hence, it is particularly important to understand how the climate and climate extremes, in particular, are changing in these areas.

“Urban areas make up a relatively small part of the global land area; however, they are the centre of wealth, so damage to urban infrastructure could result in potentially large economic losses.”

The team are now examining the impacts of climate and weather extremes in urban regions on critical lifeline infrastructures, as well as on urban and coastal ecosystems and marine life.

Photo credit: Vasilios Sfinarolakis/ CC BY-ND 2.0

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