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Floods are one of the most threatening natural hazards for human societies (e.g. WBGU 1999). This is evident from the increase in damages in the last 50 years due to a series of extreme floods (Munich Re Group 2003). Recently, the tsunami in South East Asia caused 220,000 deaths which makes it probably one of the most disastrous floods. During the International Decade of Natural Disaster Reduction (IDNDR) from 1990 to 1999 it was appreciated that the previous paradigm of “flood protection” was inappropriate (UNDRO 1991, Plate 1999). Absolute protection is both unachievable and unsustainable, because of high costs and inherent uncertainties. Instead, risk management has been recommended as being more suitable and this paradigm is now receiving growing attention within flood research (e.g. Plate 1999, Schanze 2002, Hall et al. 2003, Hooijer et al 2004). Also currently environmental and regional policies in many countries are starting to shift from flood protection to flood risk management (e.g. Budapest Initiative 2002, EU 2004).

Flooding poses a threat to many millions of the citizens of Europe. In the Netherlands more than half of the population live below mean sea level. In the UK about 10% of the population lives in areas of flood risk; and in Hungary about a quarter of the population live on the floodplain of the Danube and its tributaries. Although the greatest loss of life in Europe in recent decades occurred from the 1953 North Sea floods, which caused about 2500 deaths across the UK, Netherlands, Belgium and Germany, flooding remains the most widely distributed natural hazard in Europe leading to significant economic and social impacts. Concentrations of fatalities in river floods are associated with flash flooding events, such as Vaison-la-Romaine (1992), and the mudflows at Sarno (1997). Recent internationally and nationally significant floods have occurred, for example, in Slovak Republic (1993 and 1997), the Czech Republic (1997, 1998 and 2002), Poland and Germany (1997, 2002), Britain (1998, 2000), Austria (1991, 1997, 1999, 2002), Eastern Slovakia and Hungary (1998 and 2001) and France (2002 and 2003).

For the Czech Republic, floods represents the highest direct risk stemming from natural disasters and they can be a casual factor of serious crises, which can be associated with high material property damages, ecological and cultural damages and also losses of human lives in the areas affected by floods. The flood events have their genesis almost exclusively inside the borders of the country and are provoked by snowmelt in the period from December to April, and by precipitation in the period from May to August.

The very varied flow regime of River Tisza is characterized by repeated floods with gradually increasing and sometimes very high peak water levels and by frequent, long-lasting low flows. The main causes of these characteristics are: the shape of drainage basin; the discharge of tributary streams related to the one of the main channel; the high sediment transport; the low slope of the low-land reach and the trained low-flow and high-flow river channel. The present length of R. Tisza is 945.8 km and its drainage basin is 157 200 km. According to discharge measurements of the recent decades, the maximum discharge of Tisza River at section Tivadar (705.7 rkm) exceeds 4 000 m/s, in the middle reach between Szolnok and Kisköre: 2 600-2 900 m/s and in the lower reach, at section Szeged (173.6 rkm) above 4 000 m/s.

The Slovnaft refinery complex is one of the key elements in the Slovak economy. It is situated in Bratislava, the capital of Slovakia, close to the Danube river. Catastrophic floods, which occurred in the central Europe in the summer of 2002, emphasized urgent need for revision of flood management plan in this important factory. The peak discharge of Danube in Bratislava was close to Q. The flood consequences in Bratislava were not so dramatic as in the Czech Republic, however the weak elements of flood control in the city were discovered. The refinery, area of which is about 5.2 km, is situated in a very flat territory. A lot of refinery objects and technological equipment are vulnerable in the case of flooding, which could occur as a consequence of various crisis scenarios. Overtopping of flood protection dykes or flood protection lines in the city or in the refinery surrounding area, as well as dyke breaks represent the most probable flooding scenarios. The flood management plan of the refinery was out of date, not taking into account dynamic character of possible flooding. Therefore, the refinery representatives turned to Water Research Institute (WRI) experts in the end of 2002 with a request to elaborate study of possible flooding. The cooperating organizations were - DHI Hydro-inform, Prague, DHI Slovakia, Bratislava and Slovak Water Management Enterprise, Danube River Basin Authority in Bratislava. It was decided to apply hydroinformatics software tools of the DHI Water & Environment, Denmark in the frame of study, in order to represent properly dynamic effects of the flooding phenomenon.

“Flooding of urban land is a frequent, natural or manmade disaster in large or small scale” (Yen, 1995). Flood inundation constitutes a complex problem due to the interaction between flow and infrastructures present in the plain. In this study, by means of a two-dimensional unsteady flow model that implements the complete De Saint Venant equations, different conditions of inundated plain are analysed. Floodplain analysis is needed in many practical situations, mainly because is in lowlands that human activities are concentrated. The study of the inundated plain requires at the same time quite of effort in terms of modelling, computational resources and data acquisition. The need for a two-dimensional model and the presence of a great number of different structures in the inundated zone make the problem complex. The effect of the plain topography, the presence of irrigation and/or natural channels, of roads, highways, railways, low dikes and culverts affect the pattern of the flooding flow and can change it considerably.

Spatially distributed measurements of precipitation have gained renewed interest in connection with the spread of distributed hydrological modeling and the increased use of remotely sensed data for a number of tasks such as land use and climate-change impact studies, determination of water budgets at different temporal and spatial scales, etc. Point precipitation measurements are usually only available from a limited number of meteorological stations and spatial estimates of precipitation fields for the described tasks are obtained by interpolation or geo-statistical techniques. Mountainous environments represent a special challenge to spatial data analysis and interpolation because the measured data are sparse, often restricted to lower elevations while the temporal and spatial variability in precipitation can be substantial.

Floods and other seemingly weather related natural disasters have been increasing not only by reported damage but also by frequency and intensity (www.munichre.com). As global climate models predict a clear increase in temperature and weather extremes (IPCC 2001) due to increase in the atmospheric concentration of green house gases (GHG) it is obvious to relate the reported increase in flood risk to climate change. However, extreme precipitation is neither correctly modelled in existing global models nor correctly covered in existing statistical analysis of the past due to its inherent variability in space and time. This is specially true for the data base of future risk analysis as along with the spatial extend of typical flood prone catchments the need for regional and local estimates of extreme precipitation is increasingly important. New methods as well as new combinations of existing methods are required to address climate change related flood risk on the regional level.

The risk of flooding due to runoff is a major concern in many areas around the globe and especially in Romania. In the latest years river flooding and accompanying landslides, occurred quit frequently in Romania, some of which isolated, others-affecting wide areas of the country's territory.

For the transboundary area between Romania and Hungary many destructive floods have occurred provoking severe inundation events and even ruptures of embankments. A close cooperation between these countries in searching the best and adequate methods and technology to impede these undesirable events is therefore a prerequisite for needed actions.