The role of heatwave characteristics in cardiovascular mortality in the Eastern Mediterranean region

Heatwaves constitute a major public health risk and climate change is projected to exacerbate this risk by increasing their intensity, duration, and frequency. This study focused on the Eastern Mediterranean and explored the impact of heatwave characteristics on cardiovascular (CVD) mortality in three typical sites (Athens, Thessaloniki and Cyprus). We demonstrated that the heatwave order and timing in the season, as well as the intensity and evolution, may determine the exposure-response relationship. Specifically, heatwave days occurring during the 1st heatwave were associated with a higher increase in CVD mortality risk compared to heatwave days of the 2nd and 3rd (or subsequent) event (e.g. for Athens: 28.3 %, 95%CI: 23.2 %, 33.6 % for 1st event; 17.0 %, 95% CI: 9.8 %, 24.7 % for 2nd event), while hotter heatwave days also amplified the health impact (increase in CVD risk per °C above the site-specific heatwave threshold for Athens: 11.79 %, 95%CI: 9.80 %, 13.79 %; for Thessaloniki: 18.44 %, 95 % 13.81 %, 23.13 %; for Cyprus: 36.14 %, 95% CI: 23.95 %, 49.14%). Heatwave days lagging from the onset of the event resulted in increased CVD mortality risk (e.g. for Athens: 7.96 %, 95%CI: 1.04 %, 15.02 % for the 1st heatwave day; 36.31 %, 95% CI; 27.59 %, 45.44 % for the 4th heatwave day and above) and the time-distance of heatwaves from the warm season onset was also found to be associated with increased CVD mortality. These findings suggest that tailored heatwave action plans and risk communication strategies could mitigate the higher risks associated with specific characteristics of more intense and prolonged heatwaves anticipated in the future.