Large scale drivers and historical analogs of the 15 September 2022 Marche heavy precipitation event

On 15th September 2022, the Marche region in central Italy was affected by a heavy precipitation event that caused extensive flooding, 13 deaths and 2 billion in damage. The event was associated with a mesoscale convective system that stationed over the Marche region from early afternoon until the late evening of 15 September. In this thesis work, we focus on the large scale atmospheric circulation that determined the event. We identify as the key drivers a low pressure over the Iberian Peninsula and a high pressure over the Ionian Sea that forced a southwesterly humid flow which triggered and sustained the precipitation event. Very high values of precipitable water (PW) (up to 50 Kg/m2) and convective available potential energy (CAPE) (up to 5500 J/Kg) in the Mediterranean area ensured a thermodynamic environment favourable to very intense convection over central Italy. We then focus on determining whether and to what extent anthropogenic climate change (ACC) played a role in the occurrence of the event. By using the analogs method for extreme events attribution, we identify past circulation states during fall (September-November) similar to that of the event in a reanalysis dataset spanning the time period 1940-2022. We evaluate changes in variables associated with flow-analogs in the more recent period (1992-2022) relative to the early period (1944-1970). Our results suggest no significant trend in the frequency of occurrence of the large scale drivers of the event. The most significant changes are instead found in the thermodynamic environment over Italy during these circulations analogs: PW increases up to 6 Kg/m2 and CAPE up to 1500 J/Kg in the central Mediterranean. These results highlight the impact on atmospheric thermodynamic of anthropogenic global warming in increasing the potential for stronger convective events during similar synoptic conditions.