Descrizione 1
Federica Aldighieri, Francesca de’ Donato (Dipartimento di Epidemiologia del Servizio Sanitario Regionale-Regione Lazio ASL Roma 1), Paola Michelozzi (Dipartimento di Epidemiologia del Servizio Sanitario Regionale-Regione Lazio ASL Roma 1), Pasqualino Rossi (Ministero della salute)
This indicator measures the health impact of heatwaves on the elderly population (aged 65 and over) across 27 Italian cities included in the National Heatwave Health Prevention and Warning Plan. The plan is implemented by the National Centre for Disease Prevention and Control (CCM) of the Ministry of Health and coordinated by the Epidemiology Department of the Lazio Regional Health Service (DEP Lazio). The cities are equipped with Heat Health Watch Warning (HHWW) systems to provide forecasts and alerts.
The summer of 2023 (15 May – 15 September) was characterized by temperatures above the seasonal reference average. Despite these elevated temperatures, observed mortality in the elderly population remained generally within expected levels. Monthly impact assessments highlighted increases in mortality rates associated with heatwave episodes during July and August in several monitored urban areas.
This indicator provides critical information for monitoring climate-related health risks and supports adaptation strategies aimed at reducing adverse health effects of heatwaves on vulnerable population groups.
Numerous epidemiological studies have demonstrated that elevated temperatures and heatwaves have short-term effects (from one to three days) on mortality, particularly affecting susceptible population subgroups such as the elderly and individuals with chronic diseases, especially cardiovascular and respiratory conditions.
The daily mortality impact indicator is developed by the Epidemiology Department of the Regional Health Service of Lazio (DEP Lazio) and calculated for 27 Italian cities (Figure 1) included in the National Heatwave Health Prevention and Warning Plan coordinated by the National Centre for Disease Prevention and Control (CCM) of the Ministry of Health. The National Plan has been operational for over 15 years, and the 27 cities are equipped with a Heat Health Watch Warning (HHWW) system and a rapid daily mortality monitoring system, enabling real-time assessment of heatwave impacts on public health.
This indicator quantifies increases in daily mortality among the exposed population by comparing expected versus observed mortality in the elderly population (aged 65 and over) during heatwave episodes, on a monthly basis and over the entire summer period (15 May – 15 September). A "heatwave" is defined as a sequence of three or more consecutive days with risk levels 2 or 3, as defined by city-specific HHWW systems. These systems are based on threshold values of maximum apparent temperature associated with significant mortality increases, combined with the consecutive number of risk days.
Maximum apparent temperature is an index of perceived temperature, accounting for air temperature and relative humidity. The HHWW system targets healthcare professionals and the general population. Within the National Plan, specific preventive measures are defined for vulnerable subgroups; these measures are adjusted according to the risk level predicted by the HHWW system and aim to reduce adverse health effects on the population.
Evaluate the health impact of exposure to high maximum apparent temperature values in terms of increases in daily mortality, taking into account the risk levels defined by the Heat Health Watch Warning (HHWW) system (heatwaves).
The indicator is not directly linked to any regulatory or legislative framework.
Descrizione 2
Michelozzi P, Bargagli AM, de’Donato F, De Sario M, D’ippoliti D, Leone M, Davoli M. Climate. Geographical heterogeneity of short-term effects of heat in Italian cities. Epidemiol Prev 2011; 35 (5-6) suppl 2: 1-160.
Michelozzi P, de’ Donato FK, Bargagli AM, D’Ippoliti D, De Sario M, Marino C, Schifano P, Cappai G, Leone M, Kirchmayer U, Ventura M, di Gennaro M, Leonardi M, Oleari F, De Martino A, Perucci CA. Surveillance of Summer Mortality and Preparedness to Reduce the Health Impact of Heat Waves in Italy. Int J Environ Res Public Health. 2010 May;7(5):2256-73. Epub 2010 May 6.
de'Donato F, Scortichini M, De Sario M, de Martino A, Michelozzi P. Temporal variation in the effect of heat and the role of the Italian heat prevention plan. Public Health. 2018;161:154-162. doi:10.1016/j.puhe.2018.03.030.
Ministry of Health, Results from the Heat Health Warning Systems (HHWWS), Daily Mortality Surveillance System (SiSMG), and Emergency Department Admissions – Summary of Findings Summer 2023
https://www.salute.gov.it/imgs/C_17_pubblicazioni_3376_allegato.pdf
The selection of cities was constrained by the objectives of the National Plan, the availability of historical data series (meteorological and mortality) used to develop the HHWWS models, and the availability of observed and forecast meteorological data used for the daily operation of the HHWW alert system.
Expand the mortality monitoring system for heatwave health effects to include other major urban areas, currently excluded due to data limitations. Assess the temporal trends of health-risk conditions and evaluate health impacts in terms of mortality. Additionally, evaluate other non-fatal health status indicators beyond mortality.
Qualificazione dati
For mortality data, information from the Ministry of Health’s National Daily Mortality Surveillance System (SiSMG) is utilized (http://www.salute.gov.it/portale/caldo/dettaglioContenutiCaldo.jsp?lingua=italiano&id=4547&area=emergenzaCaldo&menu=vuoto)
Municipal (27* / 7,903)
*The 27 cities are representative of all latitudes and various city types (altitude, population density, inland or coastal, small, medium, large, extensive, etc.)
2023
Qualificazione indicatore
For each city, the health impact is assessed in terms of daily mortality increases among the exposed population, by comparing observed and expected daily mortality during heat wave episodes (risk levels 2 and 3 as defined by the HHWW system, persisting for three or more consecutive days), on a monthly basis and over the entire summer period (May 15 – September 15). The reference maximum apparent temperature (red dashed line) is calculated as the daily average of maximum apparent temperatures recorded on the same days during the years 1995–2022.
Daily mortality for the elderly population is calculated as the sum of daily deaths, while the expected daily mortality (baseline) is defined as the average per day of the week and week number over a five-year reference period (2015–2019) in each city. The baseline is weighted according to the resident population to account for the recent increase in the elderly population.
Excess mortality is estimated as the difference between observed and expected mortality values. The statistical method applies a significance threshold of 0.05, to which the reported p-values refer. This approach characterizes short-term increases due to heat wave events and potential medium-term increases (monthly and seasonal), also accounting for possible mortality decreases in subsequent days caused by a harvesting effect—i.e., the advancement of deaths that would have occurred shortly thereafter.
Overall, the summer of 2023 was characterized by temperatures above the seasonal reference average. The total number of warning days (levels 2 and 3) issued by the HHWW alert system amounted to 458: 140 in the North, 204 in the Center, and 114 in the South (Figure 2). Between June and August 2023, Italy experienced two heat waves (levels 2 and 3); the first, occurring from July 10 to 25, mainly affected the Central-Southern regions, while the second, from mid-August until August 26, impacted most cities in the Central-Northern regions.
Overall, as indicated by the results from the daily mortality monitoring system (SiSMG) for the elderly population (65+ years), despite the elevated temperatures during summer 2023, no significant health impact was observed. Mortality rates remained generally in line with expected values (Table 1). Monthly health impact assessment (Table 2) highlighted a slight excess mortality (+4%) only in July, associated with the first intense heat wave event.
Dati
Figure 1: Cities equipped with the HHWWS Alarm System and Rapid Mortality Surveillance (included in the National Plan for the Prevention and Alert of Health Effects of Heatwaves) (2023)
Ministero della salute - CCM
Figure 2: Number of alert days (levels 2 and 3) recorded during the summer period in the 27 cities equipped with the Heat Health Watch Warning System (HHWWS).
Ministero della Salute – CCM
Figure 3a: Milan – Daily trend of maximum apparent temperature and number of observed and expected deaths in the 65+ age group (2023).
Ministero della Salute – CCM
Example of 4 out of the 27 graphical representations of the "Heatwaves and Mortality" indicator: Milan, Rome, Naples, Catania (period: 15 May – 15 September 2023)
Figure 3b: Rome – Daily trend of maximum apparent temperature and number of observed and expected deaths in the 65+ age group (2023).
Ministero della salute – CCM
Example of 4 out of the 27 graphical representations of the "Heatwaves and Mortality" indicator: Milan, Rome, Naples, Catania (period: 15 May – 15 September 2023)
Figure 3c: Naples – Daily trend of maximum apparent temperature and number of observed and expected deaths in the 65+ age group (2023).
Ministero della salute – CCM
Example of 4 out of the 27 graphical representations of the "Heatwaves and Mortality" indicator: Milan, Rome, Naples, Catania (period: 15 May – 15 September 2023)
Figure 3d: Catania – Daily trend of maximum apparent temperature and number of observed and expected deaths in the 65+ age group (2023).
Ministero della salute – CCM
Esempio di 4 delle 27 rappresentazioni grafiche dell’indicatore Ondate di calore e mortalità: Milano, Roma, Napoli, Catania (periodo 15 maggio - 15 settembre 2023)
Table 1: Observed daily deaths, expected deaths, percentage variation, and p-value in the 65+ age group for the entire summer period (2023)
Ministero della salute – CCM
Reference Period: 15 May – 15 September 2023
Table 2: Observed daily deaths, percentage variation between Observed and Expected deaths, and p-value in the 65+ age group, by month (2023)
Ministero della salute – CCM
Reference Period: 15 May – 15 September 2023
In 2023, the number of heat risk days was higher than the previous year in the Northern and Central regions of Italy (Figure 2). Tables 1 and 2 report observed and expected mortality values for the population aged 65 and over; specifically, Table 1 covers the entire summer period (15 May – 15 September), while Table 2 presents data for individual months within the same period, providing an assessment of mortality impact. Figures 3a–3d, selected as examples from the 27 monitored cities (Figure 1), illustrate exposure and impact measures: the graphs show the observed maximum apparent temperature (solid red line), the reference daily mean maximum apparent temperature based on the 1995–2022 period (red dashed line), observed daily mortality in 2023 (solid black line), and expected daily mortality (black dashed line) for the 65+ age group during the summer period. The vertical bands (orange or yellow) indicate heatwave periods.
To evaluate the health impact of heat, it is essential to consider Tables 1 and 2 together with Figures 2 and 3. Analyzing the individual months of summer 2023 (Table 2), no statistically significant excess mortality (p-value < 0.05) was detected except in July, which showed a slight overall increase (+4%). During heatwave periods (risk levels 2 and 3 according to the HHWW system) in July and August, several cities exhibited excess mortality. Overall, mortality in summer 2023 was aligned with expectations, although some southern cities most affected by heatwaves showed mortality rates exceeding the expected baseline (Table 1).