The May 2023 flood in Emilia-Romagna and 50-year trends in extreme precipitation based on ERA5-Land

Study region Emilia-Romagna, northern Italy. Study focus This study analyses the extreme precipitation events of May 2023 in Emilia-Romagna, which caused fatalities and widespread damage, including flooding and landslides, with economic losses exceeding €8 billion. These events are characterised using rain gauge observations together with ERA5 and ERA5-Land reanalyses, and long-term (1974–2023) precipitation trends are derived from ERA5-Land to provide a multi-decadal context. New hydrological insights for the region At the scale of individual ERA5-Land grid points, over the 50-year reference period, statistical evidence indicates mean increases of 5 % for accumulations lasting up to 2 h and of 10 % for 1-h extreme accumulations, the latter consistent with the thermodynamic Clausius–Clapeyron rate given a concurrent 2-m air-temperature increase of 1.3 °C. In terms of frequency, statistical evidence indicates a 12 % reduction for 1-h accumulations and an average increase of 26 % for extreme accumulations with durations up to 3 h. The analysis also reveals a reduction in wet hours and a more fragmented distribution of precipitation in time and space. For events defined as extreme in terms of regional spatiotemporal extent, duration, persistence and accumulated precipitation, the mean values of these characteristics decrease by 16 % without significant changes in frequency, whereas events defined as extreme only in terms of mean precipitation increase by 9 % in magnitude and 61 % in frequency.