Influence of humidity and temperature on mortality in the Mediterranean, a case study for Cyprus

Over the past two decades, the Mediterranean region has experienced a rapid increase in the frequency, intensity and duration of temperature-related extremes. These conditions have led to a rise in heat stress, posing serious threats to human health, especially when combined with high levels of humidity in the atmosphere. These impacts are particularly concerning for vulnerable population groups, such as seniors, who are more susceptible to the adverse effects of extreme moist heat. Investigating the effects of moist heat on mortality is essential for comprehending the broader impacts of climate change. Such research is critical for identifying how rising temperatures in conjunction with humidity extremes affect human health, enabling thus better preparation and response strategies to mitigate these adverse effects.

In this direction, several studies employ humidity metrics, such as relative humidity and wet bulb temperature, to explore their relationship with epidemiological data. However, the results often remain inconclusive. The inverse relationship between temperature and relative humidity can obscure the impact of temperature on health outcomes, leading to ambiguous results in assessing heat-health exposure. To overcome these limitations, in this study, we concentrate on Cyprus, a Mediterranean island, and explore the relationship between temperatures and vapour pressure in conjunction with mortality data.

The meteorological data were initially derived from a high spatial resolution (5.5km x 5.5km) reanalysis, namely the Copernicus European Regional Reanalysis (CERRA), at hourly temporal resolution. Subsequently, they were aggregated across the five districts of Cyprus. Daily mortality counts, including deaths attributed to cardiovascular and respiratory diseases (ICD10 codes: I00-I99 and J00-J99), were analyzed over a nearly two-decade period (2004-2019). Distributed Lag non-Linear models (DLNMs) within the general framework of Generalized Additive Models (GAMs) were applied to the five districts of Cyprus. This modelling framework produces estimates of the temporally distributed combined effect of temperature and vapour pressure on mortality rate.

We demonstrate how the health risks vary across the elderly population in Cyprus, specifically focusing on individuals aged over 65 years, aggregated without gender distinction. Our findings suggest that there is a significant link between environmental conditions and the mortality rate of individuals aged 65 and above, a group that has been repeatedly identified as highly vulnerable. The combined effect of high temperatures and vapour pressure levels significantly increases the health risk attributed to elderly groups, in agreement with thermo-physiological evidence.