The Mediterranean countries are experiencing important challenges related to the water cycle, including water shortages and floods, extreme winds, and ice/snow storms, that impact critically the socioeconomic vitality in the area (causing damage to property, threatening lives, affecting the energy and transportation sectors, etc.). There are gaps in our understanding of the Mediterranean water cycle and its dynamics that include the variability of the Mediterranean Sea water budget and its feedback on the variability of the continental precipitation through air–sea interactions, the impact of precipitation variability on aquifer recharge, river discharge, and soil water content and vegetation characteristics specific to the Mediterranean basin and the mechanisms that control the location and intensity of heavy precipitating systems that often produce floods. The Hydrological Cycle in Mediterranean Experiment (HyMeX) program is a 10-yr concerted experimental effort at the international level that aims to a... The Mediterranean countries are experiencing important challenges related to the water cycle, including water shortages and floods, extreme winds, and ice/snow storms, that impact critically the socioeconomic vitality in the area (causing damage to property, threatening lives, affecting the energy and transportation sectors, etc.). There are gaps in our understanding of the Mediterranean water cycle and its dynamics that include the variability of the Mediterranean Sea water budget and its feedback on the variability of the continental precipitation through air–sea interactions, the impact of precipitation variability on aquifer recharge, river discharge, and soil water content and vegetation characteristics specific to the Mediterranean basin and the mechanisms that control the location and intensity of heavy precipitating systems that often produce floods. The Hydrological Cycle in Mediterranean Experiment (HyMeX) program is a 10-yr concerted experimental effort at the international level that aims to a...

International audienceThe Mediterranean region is frequently affected by heavy precipitation events associated with flash floods, landslides, and mudslides that cause hundreds of millions of euros in damages per year and often, casualties. A major field campaign was devoted to heavy precipitation and flash floods from 5 September to 6 November 2012 within the framework of the 10-year international HyMeX (Hydrological cycle in the Mediterranean Experiment) dedicated to the hydrological cycle and related high-impact events. The 2- month field campaign took place over the Northwestern Mediterranean Sea and its surrounding coastal regions in France, Italy, and Spain. The observation strategy of the field experiment was devised to improve our knowledge on the following key components leading to heavy precipitation and flash flooding in the region: i) the marine atmospheric flows that transport moist and conditionally unstable air towards the coasts; ii) the Mediterranean Sea acting as a moisture and energy source; iii) the dynamics and microphysics of the convective systems producing heavy precipitation; iv) the hydrological processes during flash floods. This article provides the rationale for developing this first HyMeX field experiment and an overview of its design and execution. Highlights of some Intense Observation Periods illustrate the potential of the unique datasets collected for process understanding, model improvement and data assimilation

A large number of intense cyclones occur every year in the Mediterranean basin, one of the climate change hotspots. Producing a broad range of severe socio-economic and environmental impacts in such a densely populated region, Mediterranean cyclones call for coordinated and interdisciplinary research efforts. This article aims at supporting these efforts by reviewing the status of knowledge in the broad field of Mediterranean cyclones. First, we focus on the climatology of Mediterranean cyclone tracks, their relationship to large-scale atmospheric circulation and their future trends. Second, we discuss the dynamics and atmospheric processes that govern the genesis and development of Mediterranean cyclones. Then, we present the different subtypes of Mediterranean cyclones, devoting special attention to medicanes, i.e. cyclones with tropical characteristics and subjects of numerous recent studies. In a subsequent section, we review the state of the art in forecasting cyclones and relevant high-impact weather, and we discuss in detail the challenges and recent efforts to increase their forecast skill. Finally, we discuss the main impacts produced by cyclones, namely heavy precipitation, windstorms, dust transport, storm surges and sea wave extremes. In the last section of this review article, we thoroughly outline the future directions of research that would advance the broader field of Mediterranean cyclones.

The Liguria coastal region in Italy was affected by two heavy rainfall episodes and subsequent severe flooding that occurred at the end of October and the beginning of November 2011. In both cases, the very large accumulated precipitation maxima were associated with intense and quasi-stationary convective systems that developed near the coast, both related to orographic lift and similar low-level mesoscale flow patterns over the Ligurian Sea, giving rise to pronounced convergence lines. This study aims at analysing the main dynamical processes responsible for the onset, lifecycle, intensity and localisation/propagation of the precipitating systems, using the ISAC convection-permitting model MOLOCH applied at different spatial resolutions and comparing model output fields with available observations. The ability of the model in quantitative precipitation forecasting (QPF) is tested with respect to initial conditions and model horizontal resolution. Although precipitation maxima remain underestimated in the model experiments, it is shown that errors in QPF in both amount and position tend to decrease with increasing grid resolution. It is shown that model accuracy in forecasting rainfall amounts and localisation of the precipitating systems critically depends on the ability to represent the cold air outflow from the Po Valley to the Ligurian Sea, which determines the position and intensity of the mesoscale convergence lines over the sea. Such convergence lines controls, together with the lifting produced by the Apennines chain surrounding the coast, the onset of the severe convection.

The Mediterranean storm “Vaia” developed within a typical autumn synoptic circulation, generally associated with heavy rain conditions over the western Mediterranean Sea basin. Intense precipitation was responsible for floods over Italy between 27 and 30 October 2018, and the storm was accompanied by explosive cyclogenesis, storm surge, and extremely intense wind gusts that caused casualties and extensive damage, especially to the Alpine forests. This study investigates the contribution of different moisture sources to the extreme precipitation by means of numerical model simulations using the Bologna Limited Area Model (BOLAM). In particular, the attention is focused on the significant amount of water vapor transported into the Mediterranean basin from the Atlantic Ocean tropical area and organized along a narrow corridor across the African continent. First, a newly developed detection algorithm is applied to identify this transport as an atmospheric river (AR). Then, the implementation of an atmospheric water budget diagnostic, supported by sensitivity experiments, allows us to assess the role of the AR in terms of water supply to the precipitation systems. Although the transport of moisture from remote regions is known to be an important ingredient for the onset of heavy precipitation in the Mediterranean, the role of ARs, already identified in correspondence with some of these events, has not been deeply investigated and quantified yet in this specific area. The results demonstrate that the AR was critical for determining the magnitude of this heavy precipitation episode over Italy, whereas evaporation from the sea played a secondary role, especially for precipitation over the Alps.

Demonstration of probabilistic hydrological and atmospheric simulation of flood events in the Alpine region (D-PHASE) is made by the Forecast Demonstration Project in connection with the Mesoscale Alpine Programme (MAP). Its focus lies in the end-to-end flood forecasting in a mountainous region such as the Alps and surrounding lower ranges. Its scope ranges from radar observations and atmospheric and hydrological modeling to the decision making by the civil protection agents. More than 30 atmospheric high-resolution deterministic and probabilistic models coupled to some seven hydrological models in various combinations provided real-time online information. This information was available for many different catchments across the Alps over a demonstration period of 6 months in summer/ fall 2007. The Web-based exchange platform additionally contained nowcasting information from various operational services and feedback channels for the forecasters and end users. D-PHASE applications include objectiv... Abstract Demonstration of probabilistic hydrological and atmospheric simulation of flood events in the Alpine region (D-PHASE) is made by the Forecast Demonstration Project in connection with the Mesoscale Alpine Programme (MAP). Its focus lies in the end-to-end flood forecasting in a mountainous region such as the Alps and surrounding lower ranges. Its scope ranges from radar observations and atmospheric and hydrological modeling to the decision making by the civil protection agents. More than 30 atmospheric high-resolution deterministic and probabilistic models coupled to some seven hydrological models in various combinations provided real-time online information. This information was available for many different catchments across the Alps over a demonstration period of 6 months in summer/ fall 2007. The Web-based exchange platform additionally contained nowcasting information from various operational services and feedback channels for the forecasters and end users. D-PHASE applications include objectiv...