1. Introduction
1.1 Natural hazards and the need for mitigation
Human society has always been threatened by natural disasters. Since the earliest times, people
have feared the incredible forces of nature. In the last decades, the number of disasters seems to
be infinite. One after the other flood, earthquake, hurricane or blizzard shakes up the world.
Between 1950 and 1990, costs for disaster relief in the US in have increased fourteen-fold and
are now estimated at $54 billion per year worldwide and it is likely that these numbers will
increase dramatically over the next 50 years (Benson & Clay 2003, Freeman 2003, Burby
1998). Many mega cities are situated in a disaster-prone area. Rio de Janeiro has to deal with
landslides, Bangkok with floods, Mexico City with subsidence, Shanghai with tropical storms,
Sydney with wildfires, Los Angeles with earthquakes, Miami with hurricanes and New York
with blizzards (Mitchell 1999). It seems as though every mega city in the world is challenged
by one or more natural hazards.
Of old, natural disasters were perceived as acts of God or as mystical forces. In more recent
times, the notion that they where merely part of nature flourished. During the last decades,
scholars realized that these disasters where caused by incorrect human decisions on where to
live, where to built en how to interact with the environment (Weichselgartner 2001, Mitchell
1999, Davis 1998, Beatley & Berke 1992, McEntire 2004, Palm & Carroll 1998). This change
in perceptions meant that from now on natural disasters where the field of study not only of
geophysicists, but also of social scientists, including planners. Land use planning has the power
to divert spatial development away from the most hazardous areas and/or to regulate the use of
such areas, and can thus contribute to a less hazardous environment.
In the near future, increasing numbers of people and cities will be threatened by natural
disasters. Historically, the most hazardous areas were usually avoided when founding and
expanding our cities. Nowadays, the earth’s population is growing at an ever increasing rate,
thereby forcing people to settle previously un-used hazardous land. At the same time, climate
change will increase the number of climate related events such as floods and hurricanes
(Mitchell 1999). Finally, through ongoing urbanization large concentrations of people live in
relatively small areas. This means that if a disaster strikes a mega city, the consequences are
extreme because so many people are involved (Albala-Bertrand 2003). Although it is
impossible to prevent earthquakes, floods, storms and other natural hazard events from