MEDEX: a general overview

Abstract. The metropolitan area and the city of Genoa has become a national and international case study for geohydrological risk, mainly due to the frequency of floods. In 2014, there were landslides again, as well as flash floods that have particularly caused casualties and economic damage. The weather features of the Gulf of Genoa and the geomorphological-environmental setting of the Ligurian coastal land are the predisposing factors that determine heavy rains and their resulting effects on the ground.This study analysed the characteristics of the main meteorological disasters that have hit Genoa since the start of the 20th century; changes in the rainfall regime are evaluated and the main stages of urbanization of the area are detailed, with the resulting changes to the drainage network, in order to identify the main causes of this high geohydrological risk. To this end, scientists have used climate data recorded at the station of Genoa University, in operation since 1833, and at Ponte Carrega station, located in the middle reach of the Bisagno stream, a well-known watercourse because of its frequent floods. Urban sprawl was evaluated through a multi-temporal mapping comparison, using maps available from the beginning of the 19th century up to the current regional technical maps.The average air temperature in Genoa shows a statistically significant increase, while the number of rainy days displays an equally clear decrease over time. The total annual rain value does not seem to indicate rather noticeable changes. The intensity of rain in Genoa expressed as rainfall rate, i.e. the ratio of annual rainfall and number of rainy days, shows statistically significant growth.The geohydrological vulnerability in Genoa has increased over time due to urban development which has established modifications in land use, from agricultural to urban, especially in the valley floor. Waterways have been confined and reduced to artificial channels, often covered in their final stretch; in some cases they have even been totally removed. These actions should be at least partially reversed in order to reduce the presently high hydrological risk.

Section: Geographical Features Of Genoamentioning

confidence: 99%

Geohydrological hazards and urban development in the Mediterranean area: an example from Genoa (Liguria, Italy)

Faccini

Luino

Sacchini

et al. 2015

“…6 shows that autumn was the season with the highest frequency of flash flood events, as well as with the highest number of fire service operations, followed by winter. Autumn in Greece is actually the season with the highest frequency of rainfall and the highest accumulated rainfall, particularly in what concerns the mainland (Jansa et al, 2014;Lagouvardos and Kotroni, 2007;Kotroni et al, 1999; 1996). This is in accordance with previous analysis of historical floods in Greece, which concluded that autumn was the season with the richest flood record for the period 1880-2010 .…”

Section: Relation Between Hazard and Impact Indicatorsmentioning

confidence: 99%

Flash flood occurrence and relation to the rainfall hazard in a highly urbanized area

Papagiannaki

Lagouvardos

Kotroni

et al. 2015

Self Cite

Abstract. The paper examines the flash flood events that occurred over a decade in the Attica prefecture, the most urbanized region of Greece, with the aim of identifying triggering rainfall thresholds, as well as assessing the effect of rainfall upon the magnitude of the induced damages. The analysis incorporates rainfall records from a network of 28 surface meteorological stations and information on the spatial distribution of the flash flood events that is derived from the active database of damaging weather events maintained by the atmospheric modelling group of the National Observatory of Athens. The main findings concern firstly the relation between the flash flood impact, as measured by the fire service operations in flooded properties, and precipitation in various time intervals. In the period 2005-2014, 48 damaging flash flood events occurred in the target area and caused more than 3500 fire service operations in flooded properties. Most of the events are associated with maximum accumulated rainfall of more than 20 mm in 24 h and 3 mm in 10 min. However, the flash flood impact intensity, as measured by the number of the fire service operations per event, increases significantly above the levels of 60 mm in 24 h and 10 mm in 10 min. Secondly, graphs of rainfall intensity versus duration are developed for 15 sub-areas of Attica in order to define rainfall intensity thresholds for flood triggering at a more local level. It is shown that conclusions regarding the reliability of the estimated thresholds should take into account the representativity of the rain gauges, which is determined by the local network's density, the gauges' location and record length.

“…For this reason, gaining insights into the synoptic climatology of cyclones for the whole MB (i.e., seasonal frequency, spatial distribution and regions favoring cyclogenesis) is important. A significant contribution to this task is the comprehensive paper (Campins et al, 2011) and the MEDEX database as part of the MEDEX program (Jansa et al, 2014).…”

Section: Synoptic Circulation Patterns That Induce Heavy Rainmentioning

confidence: 99%

Review Article: Atmospheric conditions inducing extreme precipitation over the eastern and western Mediterranean

Dayan

Nissen

Ulbrich

2015

Abstract. This review discusses published studies of heavy rainfall events over the Mediterranean Basin, combining them in a more general picture of the dynamic and thermodynamic factors and processes that produce heavy rain storms. It distinguishes the western and eastern Mediterranean in order to point out specific regional peculiarities. The crucial moisture for developing intensive convection over these regions can be originated not only from the adjacent Mediterranean Sea but also from distant upwind sources. Transport from remote sources is usually in the mid-tropospheric layers and associated with specific features and patterns of the larger-scale circulations. The synoptic systems (tropical and extratropical) that account for most of the major extreme precipitation events and the coupling of circulation and extreme rainfall patterns are presented. Heavy rainfall over the Mediterranean Basin is caused at times in concert by several atmospheric processes working at different atmospheric scales, such as local convection, upper synoptic-scale-level troughs, and mesoscale convective systems. Under tropical air-mass intrusions, convection generated by static instability seems to play a more important role than synoptic-scale vertical motions. Locally, the occurrence of torrential rains and their intensity is dependent on factors such as temperature profiles and implied instability, atmospheric moisture, and lower-level convergence.