Natural Hazards and Risk Assessment
 

The following quote illustrates the practice of risk assessment which is a rapidly developing science.

    "  In the Tigris-Euphrates valley about 3200 B.C. there lived a group called the Asipu.  One of their primary functions was to serve as consultants for risky, uncertain, or difficult decisions.  If a decision needed to be made concerning a forthcoming risky venture, a proposed marriage arrangement, or a suitable building site, one could consult with a member of the Asipu.  The Asipu would identify the important dimensions of the problem, identify alternative actions, and collect data on the likely outcomes (e.g., profit or loss, success or failure) of each alternative.  The best available data from their perspective were signs from the gods, which the priest-like Asipu were especially qualified to interpret.  The Asipu would then create a ledger with a space for each alternative.  If the signs were favorable, they would enter a plus in the space; if not, they would enter a minus.  After the analysis was completed, the Asipu would recommend the most favorable alternative.  The last step was to issue a final report to the client, etched upon a clay tablet."
[L.Oppenheimer, Ancient Mesopotamia, University of Chicago press, Chicago, IL   1997]
    Risk assessment is the identification, measurement and characterization of threats to human welfare by observation of  natural processes from a historical viewpoint and drawing conclusions. The process of risk assessment is a sociopolitical process that involves bringing together available information about risks and hazards from experts and lay sources for the purpose of making a policy decision about appropriate response. 9  What complicates this process is that not only are the scientific assessments used to estimate risk, but laws, customs, ethics, values, attitudes, and preferences are factors that must be woven into the total risk estimate.  This is a theoretical approach which in reality is not the usual approach.  Many of the factors are measured separately and with varying degrees of thoroughness.
    The occurrence of the event is going to happen and it is the outcome of that event that is important.  Therefore, the probability of the occurrence needs to be estimated is best done by modeling such as STELLA.  The list below gives a format for constructing and gathering the data to make and estimate of risk.
 
Factors Needed to Estimate Risk
  1. A summary of recent disasters and extreme events.
  2. A comparison of the past loss of life and economic loss during the previous natural disasters with the prediction of previous risk assessments.
  3. Assessment of risk in future years, over time frames ranging from the next year to the next quarter century (1, 5, 10, 20 30 years).
  4. Identification of special risks by theme (e.g.. hazard type or engineering vulnerability, or ecological and environmental concerns) and/or by urban area or geographical region.
  5. Highlight of advances in risk assessment methodology and/or national capabilities for risk assessment.
    When estimating the risk involved the natural and physical vulnerability needs to be recognized.  The best strategy for establishing a risk estimate is a 'bottom-up' perspective.  It emphasizes the diversity of places in which changes occurs and the great range of natural and human factors that create diversity: it focuses on direct human experience and favors fieldwork; it encourages the use of dynamic interactive models of human ecological adjustment and adaptation; and it places a premium on the skills of interdisciplinary collaboration, synthesis, and integration.  The assessment when it is completed is based on the probability of an event occurring in a given time period, such as a flood of a specific depth occurring once every twenty years.

    The task of establishing a commonality of risk is not easy, considering the following points:

  1. A single common method of predication of shoreline change, valid for all situations, does not appear to be possible, owing to the extreme variations in coastal morphology and oceanographic demography.
  2. Risk is based on a combination of time-dependent effects from both long-term trend averages, which can be established from past observations of shoreline locations, and large fluctuations of stochastic process, caused by the random nature of storms.
    On an eroding beach of established evolution, the average risk increases with time.  Seasonal fluctuations (winter-sumer profiles in some regions) can be added (based on previous field data) to long-term profile change.  However, damage often occurs during an unpredictable short-time episodic event or perturbation that takes place in addition to (and contributes to ) general shore erosion.  Because of the rise of the level of the sea, the submergence of the land may be greater than the erosion due to wave action.   For example, Cape Cod has a rapidly eroding outer shoreline due to wave action which results in about 9 acres a year loss, while the annul loss as a result of passive submergence is about 24 acres per year6.

    The National Safety Council in 1967 published the 'calculated' risk associated with natural hazards based on the data and models that were available at the time.
 
 

Floods 2.5 x 10-10 fatality/person-hour of exposure
Tornados in Midwest 2.46 x 10-10 fatality/person-hour of exposure
Major Storms 0.8 x 10-10 fatality/person-hour of exposure
Cal. Earthquakes 1.9 x 10-10 fatality/person-hour of exposure
 
from "Accident Facts" , National Safety Council Publications 1967
 
 
These numbers were based on a completely different paradigm of risk assessment and understanding of the nature of natural hazards and human influence.  perceptions of risk will interact with perceptions of entitlements in environments - real or imagined - to produce unique behaviors on the part of public decision makers in matters of environmental policy.
 
TOTAL RISK = COMPOSITE OF INDIVIDUAL RISKS

    There are a number of changes in the perception of risk that have changed. The following is a list of seven of the most important changes.

    1.    shift in the nature of risk from infectious disease to chronic degenerative disease
    2.    increase in the average life expectancy
    3.    increase in the number of new risks (physical and biological)
    4.    increase in the ability of scientists to identify and measure risk
    5.    increase in the Federal government in assessing and managing risk (FEMA)
    6.    increase in the participation of special interest groups in societal risk management
    7.    increase in the public interest, concern and demands for protection.8
 
 
Human Intrusion

    Paul Ehrlich (Ehrlich, 1991) has suggested a simple mathematical model the can be applied to the estimation of the impact (I) of human intrusion within a given ecosystem.  The three variables of the equation are interconnected and not independent so the model is limited, but the impact can be estimated and used as part of the an inquiry of risk assessment of erosion.  Population (P) is a known quantity that will be multiplied by the other two variables.  Per-capita affluence (A) is a reported value that is a measurement of consumption.  The last variable is damage done by technology (T) that is employed in supplying the members of the population, this is not a known quantity.
 

I  =  P x A x T

    If one looks at the change in population with the other variables held constant you can see that the impact will double with doubling of population.   For example; As population increases, the damage done per person by the technological systems that support consumption tend to increase as well.  Consider the natural tendency for people to use easily accessible resources first. Resources to be used by each additional person must on average be mined deeper or further from shore, transported from more distant sources, grown on land requiring more mechanical cultivation, irrigation, more synthetic fertilizers or pesticides and so on.  Each person added to the original population has a disproportionately heavy impact on the environment compared to that of those who came earlier.  Since T is not known a modification to the equation has to be that  A x T   is approximately A .  When making estimates you will have to make approximations.

    There is no question as to whether or not we effect our environment - the questions all center on the scale and consequence of our influence.  Faced with a plethora of environmental problems, societies must make all manner of decisions about which poses the greatest risks, which are most important to deal with first, and how much effort (if any) to allocate to each.  All of the decisions will involve trade-offs.  For example; the money spent on scrubbers smoke stacks will not be available to improve the quality of the factory's waste-water effluent.
 

Comparison of natural disaster fatalities in the United States.
 

    Cumulative size-frequency distributions for annual earthquake, flood, hurricane, and tornado fatalities. In addition to demonstrating linear behavior over 2 to 3 orders of magnitude in loss, these data group into two families. Earthquakes and tornadoes are associated with relatively flat slopes (D=0.4 - 0.6); while floods and tornadoes have steeper slopes (D=1.3 - 1.4). Open symbols were not used to calculate slope of lines.
 

Inquiry Directions for Risk Assessment

The following is a list of areas that need to be considered to make an accurate estimate of risk.  Not all of the categories will be applicable to a given situation.  Following the list will be an example of  how to apply these parameters to an assessment, specifically on Coastal Erosion.

  1. weather patterns - temperature, wind velocity, pressure, storm patterns
  2. geologic patterns- rock sources, glacial influence, coastal construction
  3. tectonic patterns - action/inaction of existing faults PEPP
  4. wave energy patterns - increases/decrease and influence on sand loss
  5. wave direction and current - changes and patterns
  6. water quality and pollution - changes
  7. human intrusion - attempts at reversing trends IMCS-Rutgers
  8. decision tree
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