EENS 3050 | Natural Disasters |
Tulane University | Prof. Stephen A. Nelson |
Natural Disasters & Assessing Hazards and Risk |
Natural Hazards and Natural Disasters A natural hazard is a threat of a naturally occurring event will have a negative effect on humans. This negative effect is what we call a natural disaster. In other words when the hazardous threat actually happens and harms humans, we call the event a natural disaster. Natural Hazards (and the resulting disasters) are the result of naturally occurring processes that have operated throughout Earth's history.
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As discussed before, natural disasters are produced by processes that have been operating since the Earth formed. Such processes are beneficial to us as humans because they are responsible for things that make the Earth a habitable planet for life. For example:
Such processes are only considered hazardous when they adversely affect humans and their activities. Classification of Natural Hazards and Disasters Natural Hazards and the natural disasters that result can be divided into several different categories:
Natural Hazards can also be divided into catastrophic hazards, which have devastating consequences to huge numbers of people, or have a worldwide effect, such as impacts with large space objects, huge volcanic eruptions, world-wide disease epidemics, and world-wide droughts. Such catastrophic hazards only have a small chance of occurring, but can have devastating results if they do occur. Natural Hazards can also be divided into rapid onset hazards, such as Volcanic Eruptions, Earthquakes, Flash floods, Landslides, Severe Thunderstorms, Lightening, and wildfires, which develop with little warning and strike rapidly. Slow onset hazards, like drought, insect infestations, and disease epidemics take years to develop.
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Anthropogenic Hazards These are hazards that occur as a result of human interaction with the environment. They include Technological Hazards, which occur due to exposure to hazardous substances, such as radon, mercury, asbestos fibers, and coal dust. They also include other hazards that have formed only through human interaction, such as acid rain, and contamination of the atmosphere or surface waters with harmful substances, as well as the potential for human destruction of the ozone layer and potential global warming.
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Effects of Hazards Hazardous process of all types can have primary, secondary, and tertiary effects.
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Vulnerability to Hazards and Disasters Vulnerability refers the way a hazard or disaster will affect human life and property Vulnerability to a given hazard depends on:
In general, less developed countries are more vulnerable to natural hazards than are industrialized countries because of lack of understanding, education, infrastructure, building codes, etc. Poverty also plays a role - since poverty leads to poor building structure, increased population density, and lack of communication and infrastructure. Human intervention in natural processes can also increase vulnerability by |
Affluence can also play a role, since affluence often controls where habitation takes place, for example along coastlines, or on volcanic slopes. Affluence also likely contributes to global warming, since it is the affluent societies that burn the most fossil fuels adding CO2 to the atmosphere. Assessing Hazards and Risk Hazard Assessment and Risk Assessment are2 different concepts! Hazard Assessment consists of determining the following
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Risk Assessment involves not only the assessment of hazards from a scientific point of view, but also the socio-economic impacts of a hazardous event. Risk is a statement of probability that an event will cause x amount of damage, or a statement of the economic impact in monetary terms that an event will cause. Risk assessment involves
Risk assessment aids decision makers and scientists to compare and evaluate potential hazards, set priorities on what kinds of mitigation are possible, and set priorities on where to focus resources and further study. |
Prediction and Warning Risk and vulnerability can sometimes be reduced if there is an adequate means of predicting a hazardous event. Prediction Prediction involves:
Forecasting Sometimes the word "forecast" is used synonymously with prediction and other times it is not.
Early Warning A warning is a statement that a high probability of a hazardous event will occur, based on a prediction or forecast. If a warning is issued, it should be taken as a statement that "normal routines of life should be altered to deal with the danger imposed by the imminent event". The effectiveness of a warning depends on:
If warnings are issued too late, or if there is no means of disseminating the information, then there will not be time enough or responsiveness to the warning. If warnings are issued irresponsibly without credible data or sources, then they will likely be ignored. Thus, the people responsible for taking action in the event of a potential disaster will not respond.
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Again, it is important to understand that natural disasters result from natural processes that affect humans adversely. First - Size Matters For example:
Second – Location, location, location For example:
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:
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Flood Frequency - For any river, high discharge events are rare. Large discharge events occur much less frequently than small discharge events. |
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Meteorite Impacts - Although we as humans have not had the opportunity (fortunately) of observing large asteroid or meteorite impacts, the data suggest that impacts of large asteroids (1 km or larger) occurs only once every 10 million years.
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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:
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:
We will discuss each of these concepts for each of the hazards we study. |
Examples of questions on this material that could be asked on an exam
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