1.5 How natural are natural hazards?
A physical event that does not affect human beings is a natural phenomenon but not a natural hazard. A natural phenomenon that occurs in a populated area may be a potential hazardous event. A hazardous event that causes unacceptably large numbers of fatalities and/or overwhelming property damage is a natural disaster.
A natural hazard has an element of human involvement.
Human intervention can increase the frequency and severity of natural hazards (e.g, removing the toe of a landslide to make room for a housing development).
Human intervention may also cause natural hazards where none existed before (e.g, subsidence related to withdrawal of groundwater).
Human intervention reduces the mitigating effects of natural ecosystems (e.g. destruction of coral reefs, which removes the shore's first line of defense against storm surges, or desertification).

1.5 Terminology for hazards and risks:
Figure 2 defines the terminology on hazards and risks that has found a universal acceptance.
Land-use planning often struggles with defining the risk of occurrence of some natural or technological hazard.
There are several different aspects of defining risk.
First, the land-use decision usually is focused on the elements, which would be at risk ( see page 1-13 in OAS/DRDE, 1991).
These are the people, properties, and economic activities that would be impacted such as the homes which would be damaged by landslide movement;
the water wells which could be contaminated by leakage from a waste disposal site;
the people who might be killed or injured during the earthquake;
or the crops destroyed by flood waters.

The second aspect of defining risk is the nature of the hazard.
For geological processes, it is necessary to define the probability of occurrence within a specified period of time and within a given area. Land-use decisions need to be based on the likelihood of the hazard event occurring (probabilistic approach). A familiar example is flood hazard zonation. For insurance and land-use planning purposes, the area to be affected by a 100-year flood recurrence is treated as the area of concern for this natural hazard.
The 100-year flood is a way of saying the likelihood of a flood is a 1-year in every 100 years or a probability of 1 percent.
See flood hazard map of theYallahs River prepared by ODPEM.