Recent tendencies of extreme heat events in Italy: from 1991 to present days

Recent records about extreme events linked to high temperatures have enhanced the attention over the heat wave phenomenon. 2022 summer has seen a worrisome heat-related excess mortality in Europe and 2023 is the hottest year of record at the global scale, according to the Copernicus Climate Change Services.

Heat waves are a major natural hazard for the most fragile parts of the population. In order to understand their impact, how communities can adapt, and to provide reliable scenarios over the close future, the key point lies in the quantitative addressing of all the aspects that compose heat waves. These include the monitoring of their change in frequency and intensity over time.

This study is focused on the analysis of several temperature-extremes indices, including those specifically related to heat waves. Each of them regards a specific aspect, such as number, frequency, duration and severity. The dataset is based upon a set of quality-controlled and homogenized daily maximum and minimum temperature data from more than 250 ground-based weather stations in Italy. To catch the tendencies of the recent Italian climate, the period analysed covers the latest 33 year time span: 1991 – 2023. Data have been extracted for the most part from SCIA, the Italian national system for climate data collection, processing, and dissemination (www.scia.isprambiente.it) and have therefore undergone a series of automatic procedures which ensure the data quality.

Two analyses have been used in this study: the first one is based on single stations time series and reports an extrapolated trend of the indices over the Italian territory; the second analysis is targeted to look for a global signal about temperature extremes behaviour and therefore considers stations’ data in an aggregated form. The latter analysis splits the 33 year time frame into three decades plus the last 3 years, to get a statistically robust assessment of climate tendencies over time.

The two analyses are found in agreement in depicting a heat wave presence in Italy which is increasing. In particular, half of the stations report an increase of 4 days or more of heat waves per decade, with a national average value of almost 2.5 days per decade. Such behaviour is observed in terms of persistency and intensity too, composing an alarming picture for both the close and the far future. The quantitative findings of the present work can support the development of adaptation measures in the country.

This work is supported by the Italian PNC - Investimento E.1- SALUTE AMBIENTE - BIODIVERSITA' - CLIMA, Missione 6 - Linea di Investimento 1.4, progetto: "Cobenefici di salute ed equità a supporto dei piani di risposta ai cambiamenti climatici". Area A-6. Codice PREV-A-2022-12376994 - Financed by the European Union - NextGenerationEU