Heatwave characteristics and health impacts: a review of epidemiological evidence and implications for heatwave response plans

Abstract Heatwaves are widely recognized as one of the most serious threats to public health, with their specific characteristics largely shaping the relationship between heat exposure and health outcomes. There is evidence that heatwave intensity affects mortality and morbidity, but several studies have shown that duration, timing and sequence of heatwave events are also important. As the frequency and severity of heatwaves continue to rise due to climate change, these factors should be taken into account, to make early warning systems, public health recommendations, and protective interventions for vulnerable populations more sophisticated and responsive. This narrative literature review aims to summarize key insights from key studies to improve understanding of the relationship between heatwave characteristics and public health, and to inform the development and refinement of heatwave response plans. A total of 23 studies were included in the qualitative synthesis and the findings highlight that not all heatwaves have the same impact. There is evidence that both longer and more intense events, as well as those occurring earlier in the season, are frequently linked to higher risks of mortality and morbidity. It is suggested that refined early warning systems that incorporate multiple heatwave characteristics may more accurately reflect health risks and support increased preparedness and the development of more effective and locally tailored response plans. These plans should prioritize early activation of protective measures, targeted interventions and recommendations for those at risk and sustained public engagement throughout the warm season.