Exploring Atmospheric Rivers in the Mediterranean and their connection with extreme hydrometeorological events over Italy: observation, modelling and impacts (ARMEX)

Atmospheric rivers (ARs) have emerged as a global relevant driver for extreme hydrometeorological events and water budget modulator in many areas of the globe. Defined as narrow corridors of enhanced horizontal transport of moisture, ARs transfer huge amounts of water vapour from the tropics to the mid-latitudes. Low-latitude moisture export can be important for extreme events at higher latitudes because it may cause critical precipitation thresholds for flooding to be exceeded. ARs have been studied in the last 20 years along the Pacific US Coast, being responsible for heavy precipitation originated by the interaction -up lift- with the coastal orography. In the last decade, emerging regions such as Europe have been explored, where ARs have been connected to extreme events, especially those areas facing the Atlantic coast. The detection and investigation of ARs in the Mediterranean basin have started only in the very last years, so that the knowledge on this phenomenon is scarse. Only few studies showed the relevant role of an AR in severe hydrometeorological events affecting the Mediterranean coast of Spain or the Italian peninsula. The main purpose of the project is to explore systematically the presence of ARs in the Mediterranean basin in terms of frequency of occurrence, intensity and characteristics and to understand their possible connection with extreme hydrometeorological events that frequently impact different areas of Italy. This will be achieved by developing and applying detection algorithms based on different datasets and approaches, exploiting available catalogues of floods and heavy rainfall and attributing precipitation and flood to ARs. Besides filling the knowledge gap through a general and long-term analysis of the phenomenon, it is also of paramount importance to investigate the characteristics of ARs in the area and to gain a better understanding of the role they play in extreme hydrometeorological events or in modulating water budget and resources in the area. In fact, the peculiar location in the middle of the basin makes the Italian peninsula particularly exposed to moisture-laden flows, even originating from remote sources and the complex and steep orography in proximity of the seaboard, as well as the Alpine barrier, provide the necessary lift to produce intense precipitation. This requires on the one hand to identify the large scale precursors and conditions, and the mesoscale processes favourable for triggering heavy rainfall as well as the main properties of ARs; on the other hand to investigate the differential hydrological response as a result of catchment characteristics. To increase knowledge, a case study approach will be pursued, based on meteorological and hydrological modelling, complemented by satellite monitoring.