Are events that occur suddenly with little warning taking the lives of people and destroying the means of production?

 
Frequency of Natural Disasters

Again, it is important to understand that natural disasters result from natural processes that affect humans adversely.

First - Size Matters

For example:
  

• Humans coexist with rivers all the time and benefit from them as a source of water and transportation. Only when the volume of water in the river becomes greater than the capacity of the stream channel is there a resulting disaster.
• Small earthquakes occur all of the time with no adverse effects. Only large earthquakes cause disasters.
  

Second – Location, location, location

For example:
 

• A volcanic on an isolated uninhabited island will not result in a natural disaster.
• A large earthquake in an unpopulated area will not result in a disaster.
• A hurricane that makes landfall on a coast where few people live, will not result in a disaster.

So, what we have to worry about is large events that strike areas where humans live.

Thus, in natural hazards studies, it is important to understand the relationship between frequency of an event and the size of the event. Size is often referred to a magnitude.

For just about any event, statistical analysis will reveal that larger events occur less frequently than small events.

Statistical analysis of some types of events for specific locations allow one to determine the return period or recurrence interval.

Examples:

Earthquakes -

As we have just noted, large earthquakes occur much less frequently than smaller earthquakes.

Those with magnitudes greater than 8.5 only occur once every 3 years on the average (see Table 3.3 in your text or https://www.iris.edu/gallery3/general/posters/exploring_earth/EarthquakeFrequency)

Is the Frequency of Natural Disasters Increasing?

Are natural disasters becoming more frequent as it seems from news reports of recent activity?  The short answer appears to be that yes, natural disasters are increasing in frequency (see https://commons.wikimedia.org/wiki/File:Trends_in_natural_disasters.jpg. But, this suggests some other important questions before we start making conclusions about the end of the world:

1. Is the frequency of hazardous events increasing?
2. Why is the frequency of natural disasters increasing (what could explain the trend)?

First, Is the frequency of hazardous events increasing? This is much more difficult to answer since natural events responsible for natural disasters have been occurring throughout the 4.5 billion year history of the Earth. Nevertheless, there is no evidence to suggest that hazardous events are occurring more frequently.

What about global warming? There is evidence to suggest that weather related disasters are becoming more frequent, compared to other disasters like earthquakes. For example, the frequency of disasters from tropical cyclones and floods has been increasing, the frequency of earthquakes has changed little.   Although this is what we expect from global warming, there is not yet enough statistical data to prove this right now.

Second, is there another explanation for the the frequency of natural disasters increasing? First consider the following facts: 

Human population has been increasing at an exponential rate.  With more people, vulnerability increases because there are more people to be affected by otherwise natural events.

Human population is moving toward coastal areas (see http://www.livescience.com/4167-flocking-coast-world-population-migrating-danger.html).  These are areas most vulnerable to natural hazards such as tropical cyclones, tsunami, and, to some extent, earthquakes.

Our ability to communicate news of natural disasters has been increasing, especially since the invention of the internet.  Earlier in human history there may have been just as many disasters, but there were few ways the news of such disasters could be communicated throughout the world.

Meanwhile: Deaths from natural disasters has decreased in developed countries and increased in developing countries. What could explain this? Politics? Economics? Cultural Differences? Education?

The cost of natural disasters has been increasing in developed countries. What could explain this? Economics?

This Course

This course is not about the political, cultural, or economic aspects of natural disasters.

It is about the science of natural disasters and how can use our knowledge of the scientific aspects of disasters to reduce the death and destruction caused by otherwise natural events.

Textbook Theme

The textbook selected for this course uses 5 fundamental concepts in the study of natural hazards and disasters:

1. Science helps us predict hazards
2. Knowing hazard risk can help people make decisions
3. Linkages exist between natural hazards
4. Humans can turn disastrous events into catastrophes
5. Consequences of hazards can be minimized

We will discuss each of these concepts for each of the hazards we study.