World’s cities experiencing more heatwaves: Number of extremely hot days has increased since 1970s

Londoners experience the unexpected intensity of localised solar rays, reflected off the concave plate glass windows of one of the capital's newest skyscrapers known as the Walkie Talkie. The hotspot has surprised developers and passers-by below and which has already melted a parked car and left soft street fittings smouldering in Eastcheap Street, City of London, the capital's financial district. Thermometers placed in the street reached 144F (62 celcius) and city workers poured out of their of

Figure 2  (a) Changes in frequency (number) of extreme hot days per year (exceeding 99th percentile for the reference period 1973–2002), (b) percentage of sites showing positive (hollow red), significantly positive (solid red), negative (hollow blue), and significantly negative (solid blue) changes in extreme hot days per year, (c) median changes in frequency of extreme hot days per year (increasing non-significant open red; significantly increasing solid red; decreasing non-significant open blue; significantly decreasing solid blue), (d) median changes in extreme hot days by region; solid bars in (d) represent field significant trends; open bars are not field significant. In (a) positive (negative) and significantly positive (negative) changes are shown with red (blue) and filled red (blue) circles, respectively. Changes and their statistical significance (at 5% level) were estimated using the Mann–Kendall trend test.

Figure 3. (a) Changes in frequency (number) of extreme windy days per year (exceeding 99th percentile of the reference period (1973–2012). (b) Percentage of sites with positive (hollow red), significantly positive (solid red), negative (hollow blue), and significantly negative (solid blue) changes, (c) median changes in frequency (number) of extreme hot days per year for sites with positive, significantly positive, negative, and significantly negative changes. (d) Median changes in extreme hot days by region. Solid bars in (d) represent field significant trends; hollow bars indicate lack of field significance. In (a) positive (negative) and significantly positive (negative) changes are shown with red (blue) and filled red (blue) circles, respectively. Changes and their statistical significance (at 5% level) were estimated using the Mann–Kendall trend test.

Figure 4. (a), (b) Change in frequency (number) of hot days (above 95th percentile) for urban and paired non-urban areas for the period of 1973–2012, (c), (d) same as (a), (b) but for frequency of extreme windy days (above 95th percentile), (e) box plots showing changes in frequency of hot days in all urban and non-urban areas, and (f) same as (e) but for changes in extreme windy days. In (e), (f) numbers in red (blue) show urban/non-urban areas with positive (negative) changes while numbers in parenthesis show number of urban/non-urban areas with significant changes

Further information:

Open access journal article : Changes in observed climate extremes in global urban areas

http://iopscience.iop.org/1748-9326/10/2/024005/article

Guardian news article: World’s cities experiencing more heatwaves, study shows

http://www.theguardian.com/environment/2015/jan/30/worlds-cities-experiencing-more-heatwaves-study-shows

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