CNR: European capitals increasingly affected by heatwaves
Urban heatwaves are increasing in frequency, intensity and duration. It is revealed by a study published in the journal Atmosphere by four research institutions in Florence: the Institute of Biometeorology of the National Research Council (IBIMET-CNR), the Centre of Bioclimatology of the University of Florence, the Lamma Consortium, and Accademia dei Georgofili.
The study monitored the heatwave trends in the capitals of the 28 European Union member countries, using data collected in the May-September period from 1980 to 2015, classified according to the guidelines of the World Health Organization and the World Meteorological Organization.
A heatwave is a period of excessively hot weather, with unusually high daytime and nighttime temperatures compared to the average temperatures for that particular period and geographical area, with a duration of at least two-three days and a potential impact on humans and natural ecosystems in general.
“Most EU capitals showed positive trends of heatwave frequency, duration and intensity and a general increase in the earliness in the occurrence of the first heatwave of the season, with different impacts in the different geographical areas”, explained Marco Morabito of IBIMET-CNR, who led the study.
“Increases in the duration and intensity of heatwaves”, added Morabito, “were observed in the sub-period 1998-2015 compared with the sub-period 1980-1997, in more than 60% of the EU capitals, in particular in the central-eastern and south-eastern capitals: the duration of heatwave days went from 7-8% to 12-14% of summer days”.
The research team calculated a synthetic and informative indicator called Heatwave Hazard Index – HWHI which allows the effects of all heatwave characteristics to be analysed simultaneously: number of days, number of long and high-intensity heatwaves, and the timing of the first heatwave.
“The HWHI doubled in Vienna, Budapest, Ljubljana and Nicosia and tripled in Zagreb and Athens. In Rome, the index doubled between the period 1998-2015 and the previous period and, in particular, the frequency of heatwaves went up from 5 to 13%”, explained Marco Morabito.
“We noticed”, added Morabito, “that the differences in the impact of heatwaves in the periods studied are associated with two completely different climatic patterns. During the first 18-year sub-period, western and northern European areas showed the highest HWHI values, whereas southern and south-eastern European areas showed lower values and higher atmospheric instability. Conversely, an opposite situation was observed during the second sub-period, with a significant persistence of high-pressure systems, and consequently of extreme heat, in southern, and especially, southeastern Europe”.
Finally, Marco Morabito stressed the need for planning heat-related mitigation and adaptation strategies: “It would be useful to limit the use of air-conditioning and of electricity in general, reduce vehicle heat emissions, increase green spaces in urban areas while reducing soil sealing, resorting to the use of green-roofs (roofs covered with vegetation) and cool-roofs, the latter made of highly reflective and highly emissive materials which reduce temperatures. Finally, setting up cooling centres in cities, such as fountains, helps moderate temperature fluctuations and create favourable microclimates”.