Synoptic and regional meteorological ingredients which induced severe flash floods in Romania

1. Synoptic and regional meteorological ingredients which induced severe flash floods in Romania G. Stancalie, B. Antonescu, , S. Cheval, A. Irimescu and A. Dumitrescu National Meteorological Administration Bucharest, Romania International Disaster and Risk Conference IDRC Davos 2010

7. The Romanian weather and rain gauge stations network

13. Examples of selected flash flood cases Casimncea 28 August 2004 Distribution of pp (mm) 28/08/2004 - 22:30 UTC 29/08/2004 - 17:30 UTC Dofteana 28 July 2004 Distribution of pp (mm) in 5 hours on 28 July 2004 Distribution of pp amounts (mm) 03:30 - 12:30 UTC 7 May 2005 07 May 2005 – Nehoiu basin Distribution of pp (mm) for 11 hours between 2 and 3 July 2005 03 July 2005 - Cartalu and Topol og basins

14. Examples of selected flash flood cases 23 August 2005 - Sarat and Feernic basins Distribution of pp (mm) for 5 hours on 23 August 2005 20 August 2006 – Ilisua Basin D istribution of pp (mm) for 2 hours on 20 June 2006 Distribution of pp (mm) in 6 hours in 4 August 2007 Distribution of pp 05/09/2007 05:30 – 06/09/2007 05:30 05.09.2007 Tecucel basin

18. Flash flood in Tecucel basin - 05.09.2007 Synoptic conditions Sea level pressure and 10 m wind at 06 UTC from the analysis of ALADIN model (a) and from the corresponding analysis of DWD (b). The blue arrow show the location of the flash-flood event. The frontal analysis shows at 06 UTC a warm front over the central and western part of Romania, and a cold front advancing rapidly from the south-west . The analysis from ALADIN model the 850 hPa shows the existence of an area with high values of relative humidity in the south-east Romania. The low level jet from the south brings the humidity necessary for maintaining the convection. a b Relative humidity and wind direction at 850 hPa at 09 UTC from the analysis of ALADIN model

20. Flash flood in Tecucel basin - 05.09.2007 Storm scale conditions 200 mm in 6h - estimated from radar data 235 mm in 6h - measured by rain gauges. 3 hours accumulated precipitation estimation (08:02-11:02 UTC) Radar loops Reflectivity and radial velocity at 0.5° elevation angle from the WSR-98D radar at 5 September 2007, 06:59 UTC (upper part) and 10:30 UTC (down)

24. Large scale atmospheric patterns associated with the flash flood events in Romania Composite map with wind at 700 hPa (m s-1) and vertical velocity at 700 hPa (.10-2 Pa s-1) for the flash-flood event in class 1 and class 2, according to HYDRATE classification. Class 1 and 2 . In the western part of Romania, due to the opening to the west of the Carpathian Mountains and also to the high altitudes, the precipitation accumulations increase over the western and northern slopes. Class 1 composite maps - characterized by a westerly flow at 700 hPa , Class 2 – a north-westerly flow at 700 hPa.

25. Large scale atmospheric patterns associated with the flash flood events in Romania (cont.) Class 1 and 2 . The wind at 925 hPa and relative humidity at the same level, indicate that for class 1 and 2 , moist air is advected toward eastern part of Carpathian Mountains. Thus, the flash-flood cases from these two classes are manly generated by orography . Composite map with wind at 925 hPa (m s-1) and relative humidity at 925 hPa (•10-2 Pa s-1) for the flash-flood event in class 2 according to HYDRATE classification.

26. Large scale atmospheric patterns associated with the flash flood events in Romania (cont.) Class 5 is characterized by instability over entire Romania , with a low pressure system located over Black Sea , and a high pressure system over Baltic Sea . Also, in the Western region of Romania there is a influence region of the easterly flow at 700 hPa , with a relative humidly between 70-80%. The precipitations in this case are observed over the northern-part of Romania . Composite map with wind at 700 hPa (m s-1) and vertical velocity at 700 hPa (•10-2 Pa s-1) for the flash-flood event in class 5 according to HYDRATE classification.

27. Large scale atmospheric patterns associated with the flash flood events in Romania (cont.) Class 6 is characterized by a high pressure system over Mediterranean Sea and low pressure over the western and central Europe , with a south-westerly flow at 700 hPa over the north-western Romania , and positive values for the vertical velocity at 700 hPa over the extern north-western Romania. The area of precipitation is concentrated over north-western Romania , where the relative humidy is between 60-70% (right). Composite map with wind at 925 hPa (m s-1) and relative humidity at 925 hPa (•10-2 Pa s-1) for the flash-flood event in class 6 according to HYDRATE classification.

32. This work has been carried out in the framework of the HYDRATE project which is a currently ongoing EC funded project (FP6-2006-STREP-037024) ACKNOWLEDGEMENT

33. Thank you for your kind attention !