Climate change fingerprint on the 2023 Emilia Romagna floods

The region of Emilia Romagna in northeastern Italy, with its capital in Bologna, experienced a sequence of flooding events on May 2nd, 10th, and 16th, 2023. These three events were linked to the passage of three extratropical cyclones, identified as Mediterranean cyclones, over the same region within a short period. We investigate the influence of climate change on each of these cyclones using an Extreme Event Attribution framework.

We use the analogues approach to identify similar cyclones in two periods characterized by weak and strong climate change. Cyclones are defined using a multivariate method based on sea level pressure, surface wind speed, and precipitation rate. We first normalize the fields via quantile normalization. We then calculate the spatially averaged Euclidean distance between the cyclones and other time steps within the phase space defined by the normalized sea level pressure, wind speed, and precipitation rate. Analogues are identified as those with the minimum Euclidean distance.

We assess detected changes using daily ERA5 reanalysis data, comparing the meteorological hazards of the analogues of the past period (1950–1985) with the present (1987–2022). To evaluate future changes, we conduct a multi-model study with high-resolution regional models within the EURO-CORDEX program, comparing historical (1970–2000) with future projections (2070–2100). We found an increase in precipitation associated with two of the cyclones during the present period compared to the past. Future projections also indicate an increase in precipitation compared to the present climate. Hence, our findings suggest a possible role of climate change in increasing the severity of such cyclones.