Know your enemy: hazards and their effects

The most critical part of implementing mitigation is the full understanding of the nature of the threat. In each country and in each region, the types of hazards faced are different. Some countries are prone to floods, others have histories of tropical storm damage, and others are known to be in earthquake regions. Most countries are prone to some combination of the various hazards and all face the possibility of technological disasters as industrial development progresses. The effects these hazards are likely to have and the damage they are likely to cause depends on what is present in the region: the people, their houses, sources of livelihood and infrastructure. Each country is different. For any particular location or country it is critical to know the types of hazards likely to be encountered.

The understanding of natural hazards and the processes that cause them is the province of seismologists, volcanologists, climatologists, hydrologists and other scientists. The effects of natural hazards on structures and the man-made environment is the subject of studies by engineers and risk specialists. Death and injury caused by disasters and the consequences of damage in terms of the disruption to society and its impact on the economy is a research area for medical practitioners, economists and social scientists. The science is still relatively young - most of the recordings of damaging earthquakes by strong motion instruments were obtained in the past twenty years, for example, and only since satellite photography has it been possible to routinely track tropical storms. The understanding of the consequences of failure of social organizations and regional economies is even more recent. However there are now many books and case studies that document the incidence of disasters and a growing body of knowledge about hazards and their effects.

Understanding hazards involves comprehension of:

how hazards arise

probability of occurrence and magnitude

physical mechanisms of destruction

the elements and activities that are most vulnerable to their effects

consequences of damage

Brief summaries of some of the major hazards and their effects are given in hazard-specific disaster mitigation summaries in the following pages.

These demonstrate that hazards have different effects on different parts of the community, sectors of the economy and types of infrastructure: floods tend to destroy agricultural produce but cause less damage to the structure of buildings; earthquakes tend to destroy structures but have little impact on crops growing in fields. The vulnerability of people, buildings, roads, bridges, pipelines, communications systems and other elements is different for each hazard.