earthquakes, storms and floods. Less has been done to carry the analysis one step further, i.e. to increase the basic understanding of how these natural phenomena by their severity, including the occurrence of natural disasters, can affect lives and property. For a number of purposes (such as disaster preparedness, regional and settlement planning and insurance activities), it is necessary to estimate the casualty and damage potential of geo- physical events on existing or future populations and properties at risk, using whatever pertinent information is currently available. Operational decisions must be made on a day-to-day basis whether or not appropriate background knowledge is available. One method that has been found to be useful particularly for insurance purposes is based upon the utilization of computer simulation techniques for approximating the overlapping and interaction of storm, flood and earthquake severity patterns with the spatial arrays of population and properties at risk, The interaction of four factors determines the magnitude of natural hazard impact : - The first factor is the geographical pattern of the severity of the phenomenon. For a tropical cyclone, it is the pattern of highest wind which occurred during the storm’s passage and the geographical extent and depth of coastal inundation caused by the storm surge. For an earthquake, corresponding examples are the geographic pattern of strong motion, the potential for fire following and earthquake, and flooding caused by the possible occurrence of an accompanying tsunami. - The second factor is the number, spatial distribution and density of population which is exposed to the effects of the various natural hazards. - The third factor is the vulnerability of the elements at risk when they are subjected to a given wind speed, flood depth or strong ground motion intensity. - The final factor is the effect of local conditions in modifying the severity of the event 
**Analysis**
The text appears to be focused on the impact of natural disasters on human populations and properties, discussing the factors that determine the magnitude of natural hazard impact. It also mentions the importance of estimating the casualty and damage potential of these events for purposes such as disaster preparedness, insurance activities, and regional planning. This suggests that the text is more concerned with the consequences of natural disasters rather than the causes or mitigation measures.

**Category**
Natural resources and environment, Humanitarian aid and relief