The aim of this research is to identify and characterize, in terms of length, intensity, and spatial propagation, the main drought events which took place in the Po Valley (Italy) from 1965 to 2017. Two drought indices were applied, the Standardized Precipitation Evapotranspiration Index (SPEI) and Standardized Precipitation Index (SPI). Daily precipitation and temperature series belonging to the National System for the Collection, Processing, and Dissemination of Climatic Data of Environmental Interest (SCIA) database were collected. Subsequent to an accurate quality control, the converted weekly climatic values were spatialized on a 20 × 20 km cell grid, and for each index, weekly severe and extreme drought episodes at a 12-, 24-, and 36-month time scale were calculated. Results showed that the application of two indices is fundamental in the study of drought episodes, and that different triggering factors act over time. Especially, since the 2001 drought, episodes have become stronger in terms of frequency and length, and they seem to be mostly related to changes in the intra-annual precipitation distribution. An analysis of the spatial propagation also indicates that two spatial gradients follow each other during the analysed period.

The aim of this study was to investigate the spatial and temporal distribution of rainfall in Piedmont, a region in northwestern Italy, in order to evaluate the high intensity precipitation events that occurred in the 2004−2016 period. A daily precipitation series of 211 ground stations, belonging to 2 different meteorological monitoring networks, were analysed. As at first step, a quality control was performed on the daily precipitation series to evaluate the homogeneity of the series. The annual rainfall events were spatialised, using the ordinary kriging method, considering the whole set of weather stations. Moreover, 5 climatic areas were identified through a cluster analysis method. In order to better understand the extreme rainfall events, the main climatic precipitation indices were calculated, using ClimPACT2 software, and the thresholds by percentile were calculated for each cluster on a daily scale to identify the different precipitation types (weak, medium, heavy, very heavy [R95p]). Non-parametric (Kolmogorov-Smirnov and Wilcoxon) and parametric (Student's t-test) tests were applied to the annual and seasonal number of events observed for each rainfall class in order to study the statistical relationship between the clusters. The results lead to the conclusion that the investigated area is characterised by an increase in precipitation. Considering the extreme events, this methodology shows that even though the north sector is the wettest, central Piedmont is the area in which the highest number of extreme events was recorded.

We analyse the expected characteristics of drought events in northern Italy for baseline (1971–2000), near (2021–2050), and far (2071–2100) future conditions, estimating the drought spatial extent and duration, the percentage of affected area, and the frequency of drought episodes. To this end, daily ensembles of precipitation and temperature records from Global Climate Models (GCMs) and Regional Climate Models (RCMs) pairs, extracted from EURO-CORDEX and MED-CORDEX for the RCP 4.5 and 8.5 scenarios, are collected at spatial resolution of 0.11 degrees. Before the analysis, model outputs are validated on daily weather station time series, and scaling factors for possible use in bias correction are identified. Annual temperature and precipitation anomalies for near and far future conditions are investigated; drought events are identified by the standardized precipitation evapotranspiration index and standardized precipitation index at the 12-, 24-, and 36-month timescales. This study highlights the importance of using multiple drought indicators in the detection of drought events, since the comparison reveals that evapotranspiration anomaly is the main triggering factor. For both scenarios, the results indicate an intensification of droughts in northern Italy for the period 2071–2100, with the Alpine chain being especially affected by an increase of drought severity. A North-to-South spatial gradient of drought duration is also observed.