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A recent study of extreme temperatures in over 40 years has found that world cities are experiencing more heatwaves and fewer cold spells. The study, published in Environmental Research Letters, also found that many cities are seeing fewer extremely windy days than in the 1970s.
Prolonged periods of extreme hot days have significantly increased in over 200 urban areas (with populations greater than 250,000) across the globe between 1973 and 2012. Four of the five years with the most heatwaves – defined as periods of at least six days where the daily maximum temperature was hotter than 99% of the days since 1973 - were found to have occurred since 2009 and were experienced mostly in Africa, East Asia, Europe and North America.
The study also showed a significant decline in six-day or longer cold spells. Furthermore, 17% of urban areas were found to have experienced a significant increase in daily rainfall and 10% experienced a significant increase in annual maximum precipitation.
Urban areas make up a relatively small part of the global land area, yet they are now home to more than half the world’s population. Therefore it is particularly important to understand how the climate and climate extremes, in particular, are changing in these areas since it has profound implications for urban infrastructure and human society.