Classification of Extreme Rainfall for a Mediterranean Region by Means of Atmospheric Circulation Patterns and Reanalysis Data

Abstract

The atmospheric circulation can be recognized as one of the causes of severe rainfall events occurrence. Such events, especially when are characterized by short durations and high intensities, result in flood events in the Mediterranean area. It is very important to understand how these heavy rainfall events, which can be usually identified with convective rainfall, are related to the different types of atmospheric circulation. In order to do this, some weather circulation patterns (WPs), which have been derived for the Europe, have been first connected with the rainfall annual maxima (AMAX) recorded over the Sicily. The analyses allowed to identify those WPs that are more likely to result into the occurrence of the AMAX. Secondly, two ERA-Interim reanalysis indexes have been used to define a criterion to distinguish those AMAX mainly due to a convective component from those more related to a stratiform precipitation, also detecting a transient zone between these two types of events. Finally, the main results have been connected together with the aim to define a set of triggering factors of extreme rainfall events.

A PCA-based clustering algorithm for the identification of stratiform and convective precipitation at the event scale: an application to the sub-hourly precipitation of Sicily, Italy

“…Despite advances made in recent years, the distinction between convective and stratiform precipitation based on ground observations is not trivial and still today a challenge (Cipolla et al 2020). Although many authors in the last years have faced this issue, they always developed methodologies based on the use of an arbitrary threshold to separate the two components (Feloni et al 2019;Llasat 2001;Ruiz-Leo et al 2013;Tremblay 2005).…”

“…Despite advances made in recent years, the distinction between convective and stratiform precipitation is not trivial and still today a challenge (Cipolla et al 2020). The first attempts to deal with such a separation began during the 80's and were mostly concerned with the spatial aspect of the problem, i.e., to distinguish between convective and stratiform regions.…”

“…The same author identified a threshold equal to 20 mm/6 h for partitioning precipitation into convective and stratiform components. In general, after the work of Tremblay (2005), the practice of a critical intensity threshold to discriminate between the two components has been widely adopted (Cipolla et al 2020;Feloni et al 2019;Ruiz-Leo et al 2013), since its simplicity and since it requires only time series of precipitation.…”

“…With this respect, Rulfová and Kyselỳ (2013) introduced a class of mixed/unresolved events to take into account all those events that, according to their algorithm, could be classified as both convective and stratiform events or do not have a sufficiently clear distinction between those two classes. In order to overcome the potential drawbacks due to the application of a fixed critical intensity threshold, based on the use of a couple of reanalysis indexes, Cipolla et al (2020) developed a fuzzy framework to distinguish between annual maxima precipitation mainly related to convective and stratiform components. This framework involved the use of a third class (mixed/unresolved) to include all those annual maxima precipitation not belonging to the convective or stratiform classes.…”

Seasonal predictability of Mediterranean weather regimes in the Copernicus C3S systems

“…The weather regimes approach provides an effective framework for exploring the relationship of the WRs with temperature and precipitation patterns e.g. Cipolla et al (2020), Zhang and Villarini (2019) in the Mediterranean. For their societal and economic relevance particular focus should be given to extreme events like extreme dry spells (Raymond et al 2016) and meteorological droughts (Richardson et al 2020), assessing the ability of seasonal forecasting ensembles to forecast them (Bloomfield et al 2020).…”