Heat mortality monitoring report: 2023
Updated 29 February 2024
© Crown copyright 2024
This publication is licensed under the terms of the Open Government Licence v3.0 except where otherwise stated. To view this licence, visit nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: psi@nationalarchives.gov.uk.
Where we have identified any third party copyright information you will need to obtain permission from the copyright holders concerned.
This publication is available at https://www.gov.uk/government/publications/heat-mortality-monitoring-reports/heat-mortality-monitoring-report-2023
1. Summary
During summer 2023, there were an estimated 2,295 (95% confidence interval (CI): 1,681 to 2,910) deaths associated with the 5 heat periods of heat across the summer. UKHSA has published annual statistics on the impact of adverse heat episodes since 2016. Previous reports are available at Heat mortality monitoring reports. This UKHSA report is an interim report aiming to summarise the observed heat associated deaths during heat episodes in summer 2023, with a final report published in 2024 with more detailed analysis.
The summer of 2023 was the eighth warmest on record. June saw the majority of the hot weather with July particularly wet and unsettled. A late season surge in temperatures was also observed with high temperatures occurring in September. The year 2023 was also the first season in which the new impact-based Heat-Health Alerts (HHA) system was in operation. A full seasonal summary of the weather conditions for summer 2023 is available from the [Met Office].(https://www.metoffice.gov.uk/binaries/content/assets/metofficegovuk/pdf/weather/learn-about/uk-past-events/summaries/uk_monthly_climate_summary_summer_2023.pdf)
2. Methods
In June 2023, UKHSA launched the new impact-based HHA system, which moved away from a simple threshold-based approach to an impact-based approach. Details of the new alerting approach can be found on the Weather-Health Alert system user guide.
For the purposes of this interim report, a heat episode for analysis of heat-associated mortality was defined as an amber HHA in at least one region or the mean Central England Temperature (CET) being at least 20°C. One day either side was also included. There were 5 heat periods that met this definition as outlined below.
2.1 Episode 1 (E1)
The first heat episode lasted 7 days (8 June to 14 June), during which an amber HHA was issued in the West Midlands and East Midlands, East of England, Southeast and Southwest regions. The mean CET also reached 20°C during this period.
2.2 Episode 2 (E2)
The second heat episode lasted 4 days (23 June to 26 June), during which no amber HHAs were issued. However, a yellow HHA was issued for Yorkshire and Humber, East Midlands, West Midlands, East of England, London, Southeast and Southwest, with mean CET reaching 20°C.
2.3 Episode 3 (E3)
The third heat episode lasted 3 days (7 July to 9 July), during which no amber HHAs were issued. However, a yellow HHA was issued for Yorkshire and the Humber, East Midlands, West Midlands, East of England, London and the Southeast with mean CET reaching 20°C.
2.4 Episode 4 (E4)
The fourth heat episode lasted 3 days (10 August to 12 August), during which no amber HHAs were issued. However, a yellow HHA was issued for Yorkshire and the Humber, East Midlands, West Midlands, East of England, London, Southeast and Southwest England. Mean CET also reached 20°C during this period.
2.5 Episode 5 (E5)
The fifth heat episode lasted 11 days (3 September to 13 September), during which a yellow HHA was issued for the Northwest, Yorkshire and Humber, West Midlands and East Midlands, East of England, Southeast, Southwest and London, with the East of England, Southeast and London all upgraded to an amber warning on the 9 September. The mean CET in this period also reached 20°C.
As in previous years, the estimate of all-cause heat-associated mortality was calculated by taking the difference between the observed number of all-cause deaths obtained from General Registry Office (GRO) (corrected for delays in registration) on the episode days with the average from the combination of the 14 non-episode days preceding and subsequent to the heat episode (forming a baseline level), having subtracted the estimated number of deaths attributed to COVID-19 on those days (defined as deaths with COVID-19 recorded on the death certificate).
3. Observed mortality
During summer 2023, there were an estimated 2,295 (1,681 to 2,910) deaths associated with the 5 heat periods that occurred during the heat-health alerting season. Total heat-associated deaths observed during summer 2023 were significant in all regions, apart from the North East of England, in the age groups under 65. Across genders, heat associated deaths were relatively equal. See tables 1, 2 and 3 for full breakdown of estimates across the whole season and by episode.
Across each period, spikes in daily mortality values can be observed in Figure 1. There are additional spikes within the daily series that are not associated with heat episodes and an increasing trend in daily mortality towards the end of the season. E1 observed the second highest heat-associated mortality, 635 (317 to 953) of which were significant in the 85-and-over and 65-and-over age groups and in males and females. Over the 7 days there were on average 91 heat-associated deaths per day. The lowest total mortality was observed in E2, with 119 (-105 to 343) where on average there were 30 heat-associated deaths per day. A total of 221 (29 to 412) heat-associated deaths occurred during E3, with an average of 74 heat-associated deaths occurring per day over the 3-day period, where no significant deaths were observed in any age group or region. E4 observed a total of 387 (189 to 585) heat-associated deaths, with an average of 129 heat-associated deaths per day over the 3-day period. Significant heat-associated deaths were observed in the 65-and-over age groups and in males and females. E5 was the longest heat period with 11 days of temperatures steadily rising, peaking on the 7 September, with total of 934 (522 to 1,346) heat-associated deaths over the period, with an average of 85 heat-associated deaths per day over the period. Significant heat-associated deaths were observed in the West Midlands, Southeast, London and Southwest regions, for the 65-and-over age groups and for males and females.
Table 1. Total estimated heat associated mortality by heat episode and by region
| Heat period | 1 | 2 | 3 | 4 | 5 | All |
|---|---|---|---|---|---|---|
| Date | 8-14 June | 23-26 June | 7-9 July | 10-12 August | 3-13 September | All |
| Whole population |
635 (317-953) (note 2) |
119 (-105-343) | 221 (29-412) (note 2) |
387 (189-585) (note 2) | 934 (522-1,346) (note 2) |
2,295 (1,681-2,910) (note 2) |
| Average number of heat associated deaths per heat episode day | 91 | 30 | 74 | 129 | 85 | 82 |
| North East | 53 (-24-130) | 32 (-23-88) | 9 (-37-54) | 49 (0-98) | -21 (-117-75) | 122 (-28-272) |
| North West | 107 (-13-227) | 36 (-50-122) | 11 (-61-83) | 49 (-26-125) | 87 (-69-243) | 291 (57-524) (note 2) |
| Yorkshire and Humber | 67 (-36-170) | 16 (-57-89) | 22 (-40-83) | 61 (-4-127) | 96 (-38-230) | 262 (62-462) (note 2) |
| West Midland | 62 (-45-169) | -20 (-95-55) | 27 (-39-93) | 37 (-30-103) | 147 (7-287) (note 2) | 252 (45-459) (note 2) |
| East Midlands | 66 (-28-160) | -4 (-69-61) | 47 (-11-105) | 24 (-35-82) | 77 (-43-198) | 209 (28-391) (note 2) |
| East | 29 (-64-121) | 4 (-61-70) | 48 (-10-105) | 9 (-47-65) | 53 (-66-171) | 143 (-35-322) (note 2) |
| South East | 126 (-14-266) | 50 (-48-149) | 48 (-36-132) | 63 (-23-148) | 186 (4-367) (note 2) | 473 (204-742) (note 2) |
| London | 65 (-37-166) | 7 (-64-79) | 15 (-44-75) | 47 (-16-110) | 173 (40-305) (note 2) |
307 (111-502) (note 2) |
| South West | 63 (-44-169) | -6 (-81-69) | -7 (-70-56) | 47 (-21-115) | 144 (2-286) (note 2) | 240 (32-448) (note 2) |
Note 1: Estimated all-cause heat-associated mortality by region for each individual heat period and total cumulative excess mortality across all heat periods.
Note 2: Statistically significant values.
Note 3: 95% confidence intervals are in brackets.
Table 2. Total estimated heat-associated mortality by heat episode and age groups
| Heat period | 1 | 2 | 3 | 4 | 5 | All |
|---|---|---|---|---|---|---|
| Date | 8-14 June | 23-26 June | 7-9 July | 10-12 August | 3-13 September | All |
| 0 to 24 | 19 (-14-53) | 9 (-15-32) | -1 (-19-18) | 7 (-13-27) | -3 (-43-37) | 31 (-31-94) |
| 25 to 44 | -25 (-71-22) | -19 (-52-14) | 1 (-28-31) | -2 (-30-27) | 11 (-50-73) | -33 (-124-58) |
| 45 to 64 | 43 (-69-154) | -57 (-133-20) | 64 (-6-135) | 5 (-63-72) | 125 (-19-269) | 180 (-34-394) |
| 65 to 74 | 120 (-6-247) | 34 (-56-124) | 10 (-65-85) | 93 (12-174)* | 60 (-103-223) | 317 (70-564) (note 5) |
| 75 to 84 | 162 (-12-336) | 48 (-74-171) | 57 (-48-161) | 139 (30-247) (note 5) |
402 (176-628) (note 5) | 808 (472-1,144) (note 5) |
| 85+ | 315 (118-513) (note 5) |
104 (-36-244) | 89 (-29-207) | 145 (22-268) (note 5) |
339 (82-596) (note 5) | 992 (611-1,374) (note 5) |
| 65+ | 598 (306-890) (note 5) |
186 (-20-393) | 156 (-19-330) | 377 (194-559) (note 5) |
801 (422-1,180) (note 5) |
2,117 (1,552-2,683) (note 5) |
Note 4: Estimated all-cause heat-associated mortality by age group for each individual heat period and total cumulative excess mortality across all heat periods.
Note 5: Statistically significant values.
Note 6: 95% confidence intervals are in brackets.
Table 3. Total estimated heat associated mortality by heat episode and gender
| Heat period | 1 | 2 | 3 | 4 | 5 | All |
|---|---|---|---|---|---|---|
| Date | 8-14 June | 23-26 June | 7-9 July | 10-12 August | 3-13 September | All |
| Male | 323 (96-549) (note 8) | -18 (-175-140) | 132 (-4-269) | 192 (52-332) (note 8) |
488 (197-779) (note 8) | 1,117 (682-1,552) (note 8) |
| Female | 312 (89-535) (note 8) | 137 (-22-296) | 88 (-46-223) | 195 (55-335) (note 8) |
446 (154-738) (note 8) | 1,178 (744-1,613) (note 8) |
Note 7: Estimated all-cause heat-associated mortality by gender for each individual heat period and total cumulative excess mortality across all heat periods.
Note 8: Statistically significant values.
Note 9: 95% confidence intervals are in brackets.
Please note, the overall column and row totals in tables 1 to 3 may not align due to rounding of mortality estimates.
Figure 1. Heat impact on mortality: aged 65 and over
Shaded areas on Figure 1 highlight periods that meet UKHSA criteria for estimating heat-associated mortality and were analysed by age, gender and region. All other aspects of Figure 1 are:
- daily all-cause deaths adjusted for registration delay (solid black line)
- daily all-cause deaths adjusted for registration delay and with COVID-19 deaths removed (dashed black line)
- pre-pandemic 5-year mean daily deaths baseline (grey dotted line)
- plus or minus 2-week baseline (solid green line)
- COVID-19 deaths (dotted black line)
- mean central England temperature (solid red line)
4. Discussion
Meteorologically, summer 2023 was the eighth warmest on record. Only 2 of the heat episodes were associated with an amber HHA in at least one region of England, however 3 other periods of heat resulted in yellow HHAs being issued. Despite the relatively mild and cool summer, 2023 observed the third highest heat-associated mortality since the heat-mortality reports were first published in 2016. While E5 was the longest and had the highest total heat-associated mortality, the most impactful episode of heat appears to have been E4, in which an average of 129 heat-associated deaths per day occurred.
The recent trend of increasing numbers of HHAs being issued and increasing numbers of heat-associated deaths has continued in 2023, as have other trends observed since the start of the COVID-19 pandemic, such as the shifting mortality baselines and underlying patterns in mortality (for example increasing trend in COVID-19 deaths in summer months, general increased trend in cardiovascular disease deaths and more deaths occurring at home). This means that this analysis and the interpretation of heat-associated mortality estimates are more complex than pre-pandemic reports. Therefore, it’s important that caution is taken when interpreting these results.
Further analysis will be undertaken by UKHSA once more detailed data is available. This additional analysis will include comparing the observed heat-associated mortality reported here with a modelled estimate based on the historical relationship between temperature and mortality over the last 5 years and the observed temperatures in summer 2023. Further improvements in the analysis methods will also be undertaken to enhance the granularity and detail of this analysis. This will help further understanding of observed impacts during summer 2023 and help in assessing the decision-making aid thresholds used in the first year of implementation of the new impact-based HHA system. The final UKHSA heat mortality report for summer 2023 will be published before the core heat-health alerting season 2024.