1587 Flood Risk Management: Research and Practice – Samuels et al. (eds) © 2009 Taylor & Francis Group, London, ISBN 978-0-415-48507-4 Representative flash flood events in Romania Case studies G. Stancalie, B. Antonescu, C. Oprea, A. Irimescu, S. Catana & A. Dumitrescu National Meteorological Administration, Bucharest, Romania M. Barbuc & S. Matreata National Institute of Hydrology and Water Management, Bucharest, Romania ABSTRACT: The paper presents a diagnostic evaluation of the Romanian representative flash floods events, included in HYDRATE project, which main objective is to improve the scientific basis of flash flood forecast- ing, through analysis of past flash flood events at the European scale. The ten severe flash flood cases analyzed in this paper can be divided in three categories: 1) those resulting from intense rainfall in superior part of the natural watershed in the mountain regions, 2) those resulting from intense rainfall in catchments altered by humans conductive of dam or levee failure and 3) those resulting from excessive rainfall in natural watershed in the plain regions. The analysis is supported by the detailed presentation of three case studies for which the most important meteorological, climatological and hydrographical factors that lead to flash floods are highlighted. A synthesis of the main characteristics of the analyzed flash floods is also presented. 1 INTRODUCTION Flash flooding is responsible for more fatalities in the Romanian territory than any other convective storm- related phenomenon. This flooding occurs when a large amount of rain falls at a certain location in a short period of time. The synoptic and mesoscale atmospheric condi- tions most often responsible for bringing these ingre- dients together have been well documented in the literature (Doswell el al., 1996, Maddox et al., 1979). Heavy precipitation events in the Romanian region typically occur downstream of a significant cyclone aloft, often exhibiting “cut-off ” cyclone characteris- tics. Mediterranean and Black Sea proximity provide a source of moisture for Romanian territory and the “S” shape of the Carpathian Mountains provide local circulations that help the forcing. For extreme rainfall to occur in the Carpathian environment of Romania, certain atmospheric ingre- dients must be in place. The precipitation rate depends on the available moisture in the air, vertical motion, and precipitation efficiency, while the rainfall dura- tion is related to the size and speed of the system as well as within-storm variations in rainfall intensity. Large local rainfall totals often occurs when deep convective cells are organized such that they move repeatedly over a given area, a process commonly called “echo training”. Radar depiction of flash-flood producing mesoscale convective system has shown a linear organization in many cases. Size, organization and motion char- acteristics of the mesoscale convective systems are the principal factors that determine heavy rainfall. In addition to mesoscale convective systems, high precipitation super cells have significant flash flood potential. Torrential rain is key to the onset of flash flood- ing but the drainage and topography of the surround- ing area determines the scale and impact of the event (e.g. steep-sided valleys in the Carpathian Moun- tains, accentuated flooding by acting as funnels for the runoff). More than 150 flash flood events have been observed in the last 30 years in Romania. The paper presents an analysis of the representa- tive flash flood events which took place in Romania. This work has been carried out for the HYDRATE project, which is a currently ongoing STREP-EC funded project that is aiming to improve techniques for flash flood forecasting. 2 GENETIC CONDITIONS RENDERING EXTREME PRECIPITATION IN ROMANIA 2.1 Climate characteristics of Romania Romania has a climate continental pattern with a non- uniform distribution of precipitation during the year, in both time and space. An important characteristic of the Romanian climate is the wide variability of the