Characterization of 1-hr maximum rainfall values in Calabria, southern Italy, by means of the ERA-5 reanalysis

Heavy precipitation events are likely to become more frequent in most parts of Europe; yet, records of hourly precipitation are often insufficient to study trends and changes in heavy rainfall. Atmospheric reanalyses are an important source of long-term meteorological data, often considered as a solution to overcome the unavailability of direct measurements. Among the available reanalyses, the fifth generation of the ECMWF Atmospheric Reanalysis (ERA5) dataset, released by the European Centre for Medium-Range Weather Forecasts (ECMWF), can be considered one of the state-of-the-art products. In this paper, data from the ERA5-land reanalysis dataset were first used to detect possible trends in the 1-hr maximum rainfall values in a region of southern Italy and then the monthly distribution of these values has been analysed. To check the rainfall trend, the widely recognized non-parametric Mann–Kendall test and the Theil–Sen slope estimator have been employed at monthly, seasonal and annual scales considering a significant level equal to 95%. Then, the time frame 1961-2020 was divided into three intervals, and for each one, considering the entire study area, the frequency distribution of the months recording the annual maxima was calculated. Results showed a positive tendency of the maximum 1-hr rainfall on a yearly scale. This tendency is not uniform for all the seasons: positive in spring, summer and autumn, negative for winter but with a few number of cells involved. These not-uniform tendencies are also confirmed on a monthly scale. Finally, as regards the temporal distribution of the occurrence of the yearly maximum 1-hr rainfall, initially the maximum values mostly occurred in October while, in the more recent sub-period, September is the month with the highest number of occurrences of these values.