Descrizione 1
Piero Fraschetti, Francesca Lena, Walter Perconti, Emanuela Piervitali, Giulio Settanta
The indicator describes the trend in extreme heat events in Italy, specifically representing the number of days with a maximum daily air temperature exceeding 25 °C. In 2023, an increase of approximately 19 summer days was observed compared to the climatological average for the 1991–2020 reference period.
The occurrence of extreme temperature events and the presence of significant trends are assessed through the analysis of absolute minimum and maximum daily air temperature values. Specifically, the indicator “summer days”, as defined by the CCL/CLIVAR Working Group on Climate Change Detection, refers to the number of days when the daily maximum air temperature exceeds 25 °C.
The annual time series of the average number of summer days, expressed as the deviation from a climatological baseline, allows for the estimation of the frequency of extreme heat events and the assessment of any significant trends over time.
The indicator is not directly linked to any regulatory or legislative framework.
Descrizione 2
https://scia.isprambiente.it;
APAT-OMS, 2007, Cambiamenti climatici ed eventi estremi: rischi per la salute in Italia;
ISPRA, 2022, I normali climatici 1991-2020 di temperatura e precipitazione in Italia;
ISPRA, 2018, Variazioni della temperatura in Italia: estensione della base dati e aggiornamento della metodologia di calcolo;
ISPRA, 2016, Controlli di qualità delle serie di temperatura e precipitazione; ISPRA, 2015, Valori climatici normali di temperatura e precipitazione in Italia;
ISPRA, 2014, Focus on "Le città e la sfida ai cambiamenti climatici";
ISPRA, 2013, Variazioni e tendenze degli estremi di temperatura e precipitazione in Italia;
ISPRA, 2012, Elaborazione delle serie temporali per la stima delle tendenze climatiche;
Peterson T.C ., Folland C , Gruza G, Hogg W, Mokssit A e Plummer N., 2001, Report on the activities of the Working Group on Climate Change Detection and Related Rapporteurs 1998-2001. World Meteorological Organization, Rep. WC DMP-47, WMO -TD 1071, Geneva, Switzerland, 143 pp.;
SNPA, 2024, Il clima in Italia nel 2023;
Toreti A. e Desiato F., 2007, Changes in temperature extremes over Italy in the last 44 years, Int. J. Climatology, DO I 10.1002/joc.1576.
Improvements in the estimation of summer days in Italy could result from extending the indicator calculation system to include additional sources of raw temperature data, with the objective of increasing the availability of historical temperature series that meet the requirements of temporal length, continuity, and completeness.
Qualificazione dati
SCIA – Sistema nazionale per l’elaborazione e diffusione di dati climatici (https://scia.isprambiente.it)
Italy
1961-2023
Qualificazione indicatore
To determine whether a given calendar day can be classified as a summer day, the maximum daily air temperature is compared against a threshold value of 25 °C. Therefore, validated daily maximum temperature data must be available. The SCIA system (National System for the Processing and Dissemination of Climate Data) processes raw temperature data and provides a daily maximum temperature value, which is accepted as valid only if it passes predefined quality control procedures. If the data meet the validation criteria, it is compared to the 25 °C threshold to assess whether the day qualifies as a summer day.
The annual indicator value is calculated by summing the number of summer days observed in a given year. This annual value is considered valid only if at least 75% of daily values for the year are available and have passed quality checks.
The climatological reference period used to calculate anomalies has been updated to the most recent 30-year baseline, 1991–2020, in accordance with recent World Meteorological Organization (WMO) guidance recommending the regular decadal update of climate normals for operational climatology purposes.
In 2023, an increase of approximately 19 summer days was observed compared to the average value calculated over the 1991–2020 reference period.
Over the past 10 years, the number of summer days has consistently exceeded the 1991–2020 reference period average, with the exception of 2014 and 2016. Since the main international climate change strategies and policy programmes aim to mitigate ongoing warming in the climate system, the assessment of an unfavourable trend and the assignment of the corresponding icon can be interpreted as an indication of deviation from that objective.
The time series of annual mean anomalies in the number of summer days in Italy indicates that 2023, with an increase of approximately 19 days compared to the 1991–2020 climatological baseline, ranks as the second highest value in the entire historical dataset (Figure 1)