Mean and extreme precipitation regime in North and Central Italy – between stability and change

The work was carried out on the gridded precipitation dataset of the ARCIS consortium
(hereafter ARCIS) that was produced spatializing a daily dataset of 1762 stations coming from
7 regions of Northern Italy and three regions of Central Italy for the period 1961-2023, with a
pixel of 4.7 x 4.7 km. The mean yearly precipitation value from 1961 to 2023 shows a large
interannual variability. On the other hand, the trend in frequency and intensity of extreme
events (daily events above 50 mm) exhibit high space and time variability. Highlighting areas
with significant or not significant trends is crucial for designing hydraulic infrastructures and
managing the impacts of natural risks such as floods and landslides. Overall, results reveal that
83% and 86% of the areas do not show significant increases respectively in frequency and
intensity while 11% and 15% show significant increases and 2% and 3% show significant
decreases. Moreover, the spatial pattern of the areas aWected by increasing frequency and
intensity, highlights the presence of some regions characterized by increasing trend in North
Italy at the beta mesoscale (20-200 km) which is the theatre of phenomena like mesocyclones
or low-level jets. Finally, it should be noted that the 1991-2023 analysis of seasonal variations
highlights a frequency increase of extreme phenomena in autumn (from October to December
with a more marked increase in November), a weak decrease from January to April and a
marked decrease in August. These variations can be interpreted as the result of the interaction
of the synoptic circulation with mesoscale eWects triggered by orography and sea surface
temperature.