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Flood risk maps

by Nicola Lugeri, Stefan Hochrainer, Zbigniew Kundzewicz

Aim of the work

Floods have been the most reported natural disaster events in many regions, affecting more than 100 million people, worldwide, in average year.

Even if largest flood disasters occur overseas, Europe is not immune to flood hazard. Indeed, large parts of the continent have been hit by major floods in recent decades.

Floodplains have often been sought as sites for urban development because of the facilities they offer, including access to a source of water for a variety of uses. Cities have been permanently developing their water-related infrastructure and discharging their urban waters into the nearest water body (Andjelkovic, UNESCO, 2001). The development of urbanization and activities has continued, although this expansion represents a hazard if the vulnerability of those activities exceeds an acceptable level (Colombo and Vetere Arellano, 2002).

The possible interaction between human use of the floodplain and the onset of a flood event potentially creates a natural risk. In fact a disaster only exists once a flood occurs, depending on the amount of property damage, disruption and loss of lives. As urban areas grow, both geographically and demographically, the flood hazard and risk increase in part because there is more exposure, but also because the process of urbanization itself alters local hydrological characteristics (Montz, 2000).

In undeveloped areas such as forests and grasslands, rainfall and snowmelt collect and are stored on vegetation, in the soil column, or in surface depressions. When this storage capacity is filled, runoff flows slowly through soil as subsurface flow.

In contrast, urban areas, where roads and buildings cover much of the land surface, have less capacity to store rainfall and snowmelt (Konrad, 2003). Construction of roads and buildings often involves removing vegetation, soil, and depressions from the land surface. The permeable soil is replaced by impermeable surfaces such as roads, roofs, parking lots, and sidewalks that store little water, reduce infiltration of water into the ground and accelerate runoff to ditches and streams. Development along stream channels and floodplains can alter the capacity of a channel to convey water and can increase the height of the water surface (Konrad, 2003). Bridges, in particular, reduce the natural carrying capacity of the river and provide barriers upon which debris can accumulate. In addition, development along the river can intrude on the river and restrict flow as a result.

Keywords: Risk Mapping; Hazard map; Hydrologic modelling, DTM; CORINE Land Cover; upscaling; aggregation; NUTS; GDP; Annual Average Damage.


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