The grip of the African anticyclone that is gripping Italy this summer of 2024 is making us talk about it again tropical nightswhich in Europe are defined as the nights in which the temperature measured on the ground always remains above 20 °C. Especially on hot, sultry days, one of the consolations is knowing that temperatures will drop at night and you will have a bit of a break, but on tropical nights this becomes more difficult, especially if the humidity makes us perceive a higher temperature. Tropical nights are on the rise almost all over Italy: in 2022 Milan in The problem of tropical nights does not only concern well-being: increasingly higher minimum temperatures in fact have a direct impact on health (deterioration of sleep quality, risk of dehydration and heat stroke etc.) and also on energy consumption (air conditioners, dehumidifiers and fans remain on for longer).
Tropical Nights, the Italian Cities and Regions where they are most widespread
According to the European Environment Agency, Italy is at the third place of the ranking of European countries with the most tropical nights during a year. In the thirty-year period 1981-2010, Italy recorded an average of 41.6 tropical nights per year; in second place we find the Greece with 77.5 nights per year and Cyprus with 138.1 nights per year in the same reference period. According to the latest ISTAT data, in 2022 the Italian cities that recorded the most tropical nights (with more than 100 per year) were Messina (122), Agrigento and Reggio Calabria (121), Palermo (119), Catania (117), Genoa (112), Bari (111), Croton (110), Taranto (107), Milan And Cagliari (101). In the same year Rome recorded 73 tropical nights.
The Italian regions most affected by the phenomenon are Sicily (87.4 tropical nights per year), Apulia (72.5 nights per year), Calabria (65.2 nights per year), Sardinia (50.2 nights per year), Campania (37.5 nights per year). The ranking closes with Province of Bolzano (0.0 nights per year), the Province of Trento and the Aosta Valley (0.3 nights per year), theUmbria (7.9 nights per year) and the Piedmont (8.9 nights per year).
In Italy the tropical nights are more frequent in the South because at low latitudes temperatures are on average higher, so it is easier to exceed the fateful threshold of 20 °C for daily minimum temperatures. Furthermore, tropical nights occur especially in the citiesdue to the so-called “heat island”.
Tropical nights in Italy are increasing
The most recent data made available by ISPRA are updated to 2022 and show a sharp increase in the number of tropical nights in Italy. The graph below shows the anomaly in the number of tropical nights from 1961 to 2022 compared to the average value for the period 1991-2020. 2022 saw well 22 more tropical nights than averagethe highest value in the last 50 years together with the historic summer of 2003.
This clear trend is also confirmed by ISTAT data, also updated to 2022, relating to Italian provincial capitals. They have been 58 Tropical Nights in the Cities20 more than the average for the period 2006-2015. An increase was recorded in 96 out of 109 provincial capitals considered. The cities that have seen the greatest increase are Oristano (+65 nights), Bologna (+47 nights), Genoa (+45) and Massa Carrara (+44).
Why Tropical Nights Are More and More
It will not be surprising to learn that the worrying increase in tropical nights is due to global warming, which brings a trend of rising temperatures in Italy as in many other areas of the world. However, there are interesting details and nuances from a climatic point of view. In fact, Italy is not only affected by the increase in average temperatures, but also by the warming of the Mediterranean Sea. And the two effects add up. A study published this year on tropical nights in the Mediterranean, for example, showed that the phenomenon is occurring throughout the Mediterranean area. especially in coastal regionsdue to the warming of the waters of the Mediterranean Sea (a phenomenon which also leads to the tropicalization of the Italian climate and the tropicalization of the Mediterranean).
The Mediterranean is warming 3.7 times faster than the global average of seas and oceans, and this leads to the accumulation of large quantities of heat that raise maximum temperatures but especially minimum temperatures. One of the reasons is that the increasingly high humidity (due to the evaporation of an increasingly warm sea) prevents the water from condensing and therefore absorbing heat from the air. This leads to the fact that at the mid-latitudes of the northern hemisphere minimum ground temperatures increase more rapidly compared to the maximums (a phenomenon known as asymmetrical daytime warming).
The Effects of Tropical Nights on Health and the Environment
Having entire consecutive days without temperatures dropping can create problems especially for people with more fragile health. The main impact is having a short-term and low-quality restwhich has both physical and psychological repercussions on daily life. Others symptoms linked to excessive temperatures include dehydration, drops in blood pressure, weakness, headaches and in some cases even nausea or vomiting. A 2017 study found a correlation between nights above 23 °C and increased mortality from natural causes in Barcelona, Spain.
Rising temperatures also have consequences on ecosystems, with the proliferation of species that can carry diseases (for example, some species of mosquitoes) or a reduction in agricultural productivity. Indirectly, increased energy consumption related to air conditioners, dehumidifiers or fans contributes to greenhouse gas emissions, thus exacerbating global warming.
