Estimating compounding heat waves and rainfall extremes under projected climate change over the island of Sicily, Italy

According to the IPCC AR6 report, the frequency and intensity of high temperatures and precipitation extremes, such as heat waves, and extreme rainfall events that can lead to flash floods have increased in recent decades and are projected to keep increasing. These extreme events, which can occur in separate or as compound events can lead to droughts and flooding, causing severe economic and health impacts including loss of lives. Especially when such events occur shortly or directly in sequence, they can cause more severe impacts than in isolation. Understanding their compound behavior and timing in current and future climates can help to better estimate associated risks and require protection and adaptation planning.

In this study, the frequency and intensity of the compound events of heat waves and extreme precipitation over Sicily, Italy were analyzed and characterized for the present (1980-2010) and near future (2030-2050) periods. We used high resolution gridded datasets from observations (E-OBS) and from the EURO-CORDEX ensemble of regional climate change simulations. Heat waves were defined using a daily maximum temperature threshold persistent for at least three consecutive days while the extreme precipitation events were defined using the 95th percentile threshold of daily data. Results showed that the highest frequency of heat waves occured near the coastal regions of Sicily, while the extreme rainfalls were located in the west of Sicily.  We identified the areas where heat waves and extreme rainfall events have occurred in the past and we demonstrate how they are expected to change in the future, separately and as compound events. The results of this study will be used to develop a workflow for estimating climate risks in the region, which is part of the “risk workflow for CAScading and COmpounding hazards in COastal urban areas” (CASCO) project, and can be combined with other workflows on geophysical risks (earthquakes and tsunamis) to characterize overall natural hazard risks for the island of Sicily.