A major goal of the HYDRATE initiative is to improve the understanding of the relative role of both meteorological and hydrological processes in causing flash floods. To achieve this task,
a radar-based nowcasting system has been used within the project. The objective consists in identifying the characteristics of heavy storms which lead to flash flood-generating storms. A network of Doppler radars was used in this flood preventing approach.
Flash floods are usually the result of high intensity rainfall over a small area. Both the very localized and the short duration feature of such flash flood induced storms make their observation a huge challenge. It is particularly the case when terrain layout is complex, which complicates in-situ measurements. Nevertheless, recent developments in weather radar systems have allowed researchers to overcome several observational barriers. In the framework of the project, radar observations were carried out in order to investigate (i) the life duration (i.e. initiation, maturity and dissipation period) of flash flood events, (ii) rainfall characteristics and (iii) connections between the lightning activity and the stage of the flooding and the rainfall production.
The Romania National Meteorological Administration (RNMA) installed a network of Doppler radars in 2002. The study focused on four regions of Romania where flash flood events occurred. These regions are:
- the Simonesti basin, which is located in the central part of the country and has a drainage area of 168 km2,
- the Casimcea basin, located in the southern part of Romania with an area of about 500 km2,
- the Tecuci basin which is situated in the east of Romania and which covers 111 km2, and
- the Grinties basin, located in the northern part of the country and which covers 51 km2.
A number of convective cells have been analysed in terms of life cycle duration, rainfall production and lightning activity. These convective cells are responsible for the high intensity rainfall and for the flooding over the area. As a result, the tracking of extreme rainfall events, the analysis of their characteristics and the investigation of the relationships between them have allowed the researchers to increase the knowledge of such events and improve their forecasting as well. The major conclusions are listed below:
- there is no apparent correlation between rainfall volume and lightning activity;
- both rainfall production and lightning activity vary from one convective cell to another;
- a more intense lightning activity has been observed during most of the mature stages of storm events;
- flash flood-induced storms have been characterised by short duration, high rainfall intensity and the persistence of the convective cell over the area.
HYDRATE WP 6 report