Recommendation 1

HM Government Accepted

2004. The new Weather-Health Alert (WHA) system was launched on 1 June 2023. This system was developed as part of collaboration between the UKHSA and the Met Office. The WHA system represented a move from the previous system which was based on the probability of reaching specific threshold temperatures, to an impact-based alerting system. Impact based alerting provides users with information beyond just the hazard and gives an indication of the impacts likely to be observed as a result of the weather. Moreover, the new WHA system complements other established Met Office National Severe Weather Warning systems already in operation. The WHA system is based on: (i) weather forecasts provided by the Met Office Environment Monitoring and Response Centre (EMARC) forecasts and data to UKHSA; and (ii) a joint dynamic risk assessment (JDRA) conducted by the UKHSA Extreme Events and Health Protection team, the Met Office, and, if of relevance, other governmental departments, as part of the common responsibilities under the Civil Contingencies Act (CCA) 2004. The decision-making process underpinning the issuing of an alert incorporates a range of factors as outlined in the user guide.1 Temperature thresholds are considered when determining whether to issue an alert only as an aid to the decision-making process and not the sole factor. Additional criteria are also considered which might influence the impact that a high temperature might have on health or the health service, such as the geographical extent of the adverse weather or other weather indicators of relevance – including humidity. For example, Met Office weather forecasts provided through the Public Weather Service and which contribute to the JDRA process, routinely include forecasts of temperature, “feels like” temperature, and humidity. The current WHAs are a good example of government cooperation and use of collaborative dynamic risk assessments (not only considering risks such as temperature or humidity, but also a plethora of other risks described in the user guide). International evidence on the impact of humidity on heat-related health outcomes is variable.2 Although international lessons are important and inform our action and our advice on behaviours, further work is required to evaluate those recommendations in the UK’s climate and cultural context and adapt them as required. As was noted in testimony provided to the EAC and contributing to their report, UKHSA has previously reviewed the evidence on health impacts of humidity in relation to effects on mortality in England. At this time, humidity does not appear to be a strong predictor 1 https://assets.publishing.service.gov.uk/media/65450c2b59b9f5001385a240/User-guide-impact-based-weather- and-health-alerting-system.pdf 2 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10231239/ of mortality. However, if we were to see periods of high temperatures and significantly high humidity, this would be considered when making the decision to issue an alert, as noted above. UKHSA will continue to engage with academic partners to build a greater understanding of the role that humidity has on health when combined with significant heat events, as well as the improvement of its adverse heat messaging in accordance to best-available evidence.