Extreme precipitation events and their relationships with circulation types in Italy

Abstract

Extreme precipitation (EP) events are life‐threatening phenomena that are expected to continue to increase because of ongoing climate change. In the past decade, these events have been caused by important and well‐documented variations in large‐scale atmospheric circulation. Identifying the trends, dynamics, and related causes of EP could help in recognizing geographical areas that are at great risk and reducing their adverse impacts, particularly on a relatively small area such as the Italian peninsula. The relationships between large‐scale circulation types (CTs) and EP were investigated using a long time‐series (1979–2015) of meteorological data recorded by 46 weather stations in Italy. EP was defined as the number of days with accumulated precipitation above the 90th percentile (R90p). The seasonal trends of R90p were not homogeneous and showed significant increases primarily in winter and spring. Only a few CTs were significantly related to R90p, and this relationship was strongly dependent on latitude, orographic exposure, and season. Heterogeneous seasonal trends for daily CT occurrences were also observed. ‘Cyclonic’ CTs grouped together showed significant increasing trends in all seasons, whereas ‘Anticyclonic’ ones showed a generalized decreasing trend, explaining, only partially, the increase of R90p observed in some stations. Meanwhile, the R90p trends seem to be more influenced by the variations in the internal characteristics of CTs (i.e., the variation of some meteorological parameters that characterize them) observed over the past few decades than by changes in CT frequencies but still with high heterogeneity in Italy. The results of this and other similar studies can provide useful support for the implementation of mitigation and adaptation strategies to minimize the impacts of severe weather, particularly in complex areas such as the Mediterranean basin.

Links between precipitation, circulation weather types and orography in central Italy

“…(2018) and Iannuccilli et al . (2021), but on the input data. In this study we use ERA5 reanalysis data (Hersbach et al ., 2020) from 1951 to 2019, instead of the NCEP reanalysis two datasets from 1979 to 2015 used in previous studies.…”

Evolution of Frequency and Intensity of Concurrent Heavy Precipitation and Storm Surge at the Global Scale: Implications for Compound Floods

“…Even though using a lower threshold (i.e., 90th percentile) implies that the concurrent extreme precipitation and extreme storm surge may not lead actual compound floods, but it can ensure that enough compound flood days could be sampled to conduct a more robust analysis. The 90th percentile was widely used as a threshold to define flood events in previous studies (Gemmer et al, 2011;Iannuccilli et al, 2021;Li et al, 2015;Muis et al, 2018;Zhang et al, 2013). Besides, whether an actual flood occurs or not highly depends on localized characteristics such as topography, land use, regional climate, and their interactions (Bevacqua et al, 2020a;Hendry et al, 2019).…”

Past evolution of western Europe large-scale circulation and link to precipitation trend in the northern French Alps

“…More recently, the flood-rich period in central Europe in the 19th century appears to be associated with a more zonal and southward-shifted circulation (Brönnimann et al, 2019). Using LSC classification, Iannuccilli et al (2021) show that part of the increase in extreme precipitation over central Italy in winter and spring can be explained by changes in the occurrence of the circulation types. In southern France, the decreasing autumn and winter precipitation from 1951 to 2000 appears to be explained by a decrease in the occurrence of weather types driving precipitation over the region (Boé and Terray, 2008).…”