**7. Conclusion**

The main objective of this study was to create a common methodology to assess flood risk of extreme rainfall and large-scale flooding in the Netherlands. Based on the literature we were able to incorporate both types of flood risk within an integrated model that allowed us to compare the different types of flood risk in a plausible and consistent way.

We then applied the model to analyze flood risk in the 'Noord-Beveland' area. Results show that even though the highest total damages are found to result from inundations of largescale floods, the flood risk of extreme rainfall events are in general much higher when both are expressed in terms of annual expected damage. The reasons are that extreme rainfall events cause larger areas to inundate and occur with a higher probability, which combines to drive up flood risk. Further investigation should be done in other parts of the Netherlands to test if this is the case for more dike rings.

Our model does not quantify some types of indirect damage, such as human casualties and social disturbances. These should be taken into account to provide an even more consistent comparison. We expect that they would have increase the damage associated with largescale floods. Nonetheless, we question whether the difference large difference (64 times)

would be completely bridged by these additional effects. Aside from these unquantified factors, there are a number of data comparability issues, such as the differences in exposure and the distribution of the damage, which should also be kept in mind when comparing different types of flood risk.

Even though the model requires further refinements our initial results suggest it is possible to compare different forms of flood risk within an integrated model. Our finding that higher

Comparing Extreme Rainfall and Large-Scale Flooding

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#### **8. Acknowledgements**

As a start, Ylva Peddemors of the Province of Zeeland and Govert Verhoeven of Deltares are thanked for providing the inundation maps. Karin de Bruijn and Olivier Hoes are thanked for valuable discussion during the start-up phase of this project. Stuart Donovan is thanked for considerably improving the use of English. The Netherlands Environmental Assessment Agency (PBL) is thanked for providing the Land Use Scanner model and related data sets. This research was carried out as part of the Dutch National Research Programmes 'Climate changes Spatial Planning' and 'Knowledge for Climate'

(http://www.climateresearchnetherlands.nl/).

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**2** 

*Hungary* 

**Flash Flood Hazards** 

Dénes Lóczy, Szabolcs Czigány and Ervin Pirkhoffer

Climate change research has revealed that the frequency of extreme weather phenomena with increasing damage to human assets has been gradually growing worldwide (Intergovernmental Panel on Climate Change [IPCC], 2007). The likelihood of increasing frequency of heavy precipitation events is assessed as 'likely' for the last four decades of the 20th century and 'very likely' for the 21st century. This also means that over most regions of the Earth's land surface an ever growing proportion of total precipitation will fall in the form of heavy rainfalls (Burroughs, 2003). The intensification trend of tropical cyclone activity, observed in some regions since 1970, will probably also continue in the 21st century. As a consequence, rainfall events concentrated in time and space are expected to

Floods are remarkable hydrometeorological phenomena and forceful agents of geomorphic evolution in most physical geographical belts and, from the viewpoint of human society, among the most important environmental hazards. Except for extreme environments, floodplains and the immediate surroundings of streams are usually densely inhabited areas and, therefore, they are of high vulnerability to floods. According to the European Environment Agency (EEA, 2010), floods rank as number one on the list of natural disasters in Europe over the past decade. Authors of the report claim that "the events resulting in the largest overall losses were the floods in Central Europe (2002, over EUR 20 billion), in Italy, France and the Swiss Alps (2000, about EUR 12 billion) and in the United Kingdom (2007, over EUR 4 billion)" (p. 8.). With accumulating knowledge on the water regime of major rivers, the inundation hazard from riverine floods can be defined with some precision. To estimate the magnitude of this hazard in small catchments, however, poses more problems.

Flash floods (synonym: storm-driven floods) can be defined from various aspects: as hydrometeorological phenomena, natural hazards or geomorphic agents. Inundations can be referred to four basic classes: riverine floods, excess water (from rising groundwater table), coastal floods and flash floods (Lóczy, 2010). Although riverine floods along major rivers remain to be the most severe natural hazard which threaten to inflict serious damage to human life and property, recently the latter classes have also attracted more attention in

lead to serious local flooding in many parts of the world.

**1. Introduction** 

**2. Flash flood research** 

scientific circles.

**2.1 Definitions and approaches** 

 *Institute of Environmental Sciences, University of Pécs* 

*vegetatie, aquatische ecosystemen en historische bouwkunde.* Wageningen, Alterra, Research Instituut voor de Groene Ruimte. Alterra-rapport 709 (Dutch).

