The reasons for the increased flood hazard are several and correlated. Potential climate changes are expected to cause a rise in the frequency as well as the intensity of rainfall, which may lead to more widespread and severe natural disaster.
On the other hand, built-up areas are spreading across Europe and increasing much faster than population. Social changes in Europe are being driven by EU enlargement, demographic processes and globalization. Demographic and socio-economic trends are playing a role in increasing society's exposure to weather- and climate-related damage, through factors such as housing developments in areas vulnerable to flooding and other risks (EEA Signals, 2004).
This twofold expansion increases the exposure and vulnerability of urban areas to flooding, and also, as a consequence, the social and economic damage in case of a catastrophic flood event (AquaDeltaForum, 2004).
In response to the growing number of natural disasters, the European Commission (EC) and the Member States of the European Union (EU) have recognized the significance of natural hazards regarding protection of the environment and citizens. The flooding throughout central Europe in August 2002 is a dramatic example of the damage caused by unforeseen natural hazards. It is estimated that in Europe around three-quarters of economic losses caused by catastrophic events are weather- or climate-related (EEA Signals, 2004).