Impact of compound events (heatwaves and ozone episodes) on mortality over the Mediterranean basin under climate change scenarios

The Mediterranean Basin is nowadays considered as one of the most vulnerable areas worldwide to extreme climate/weather events, especially those related to photochemical pollution (tropospheric ozone) and extreme temperatures (e.g. heatwaves). Heatwaves and air pollution have a high impact on society, both from a health and an economical perspective, leading to increases on heat stroke hospital admissions and mortality. For this reason, heatwaves and their associated ozone pollution have to be taken into account for dwellers welfare.

In addition, in recent years, it has become increasingly clear that climatic or meteorological impacts often result from the compounding nature of several variables and/or events, even if they are not extreme when analysed independently. Such compound events can lead to socio-economic damage exceeding that expected if the individual hazards were to occur separately. For instance, compound events of heat wave and stagnation display higher temperature than stagnation events or heat wave events alone, so the formation of secondary pollutants like tropospheric ozone is enhanced relative to individual events.

Under this umbrella, this study assesses compound climate events using high-resolution regional chemistry/climate simulations, with the aim of characterizing and quantifying the influence of temperature/pollution compound events on mortality over Europe, with a special focus on the Mediterranean Basin. Model data from the REPAIR and ACEX projects (obtained from simulations with the on-line chemistry/coupled WRF-Chem model) is used in order to check the changes in mortality under both present-observed and future-forced conditions. The results presented in this contribution quantify the important increase in mortality causes associated to cerebrovascular diseases (CEV) and other pathologies during those compound events (especially under future climate change scenarios) with respect to episodes led by single drivers. This increase in mortality is more evident in northern countries in relative terms; and in southern European countries in absolute mortality incidence, since the concurrent presence of heatwaves and high levels of tropospheric ozone will have a higher frequency in future scenarios over the Mediterranean basin.