This unit looks at definitions, terminologies, and types of potential hazards (including natural and non-natural disasters); understanding disasters, their causes and implications; and the contents of an effective disaster management plan.
Upon completion of this unit you will be able to:
Define and describe disaster management, hazard, emergency, disaster, vulnerability, and risk.
Distinguish between an emergency and a disaster situation.
Identify and describe the types of natural and non-natural disasters.
List and describe the main hazards to which your region is, or may be, vulnerable.
Identify and briefly discuss implications of disasters on your region and environment.
Is more than just response and relief (i.e., it assumes a more proactive approach)
Is a systematic process (i.e., is based on the key management principles of planning,organising, and leading which includes coordinating and controlling)
Aims to reduce the negative impact or consequences of adverse events (i.e., disasters cannot always be prevented, but the adverse effects can be minimised)
Is a system with many components (these components will be discussed in the other units)
“Is the potential for a natural or human-caused event to occur with negative consequences” (key words)
A hazard can become an emergency; when the emergency moves beyond the control of the population, it becomes a disaster.
“Is a situation generated by the real or imminent occurrence of an event that requires immediate attention” (key words)
Paying immediate attention to an event or situation as described above is important as the event/situation can generate negative consequences and escalate into an emergency. The purpose of planning is to minimize those consequences.
“Is a natural or human-caused event which causes intensive negative impacts on people, goods, services and/or the environment, exceeding the affected community’s capability to respond” (key words)
“Is the probability that loss will occur as the result of an adverse event, given the hazard and the vulnerability” (key words)
Risk (R) can be determined as a product of hazard (H) and vulnerability (V). i.e. R = H x V
“Is the extent to which a community’s structure, services or environment is likely to be damaged or disrupted by the impact of a hazard” (key words)
Types of Vulnerability
(easy to see; value easily determined)
People – lives, health, security, living conditions
Property – services, physical property loss, loss of use
An emergency and a disaster are two different situations:
An emergency is a situation in which the community is capable of coping. It is a situation generated by the real or imminent occurrence of an event that requires immediate attention and that requires immediate attention of emergency resources.
A disaster is a situation in which the community is incapable of coping. It is a natural or human-caused event which causes intense negative impacts on people, goods, services and/or the environment, exceeding the affected community’s capability to respond; therefore the community seeks the assistance of government and international agencies.
Types of natural and non-natural disasters
Disasters are often classified according to their:
causes – natural vs. human
speed of onset – sudden vs. slow
An excellent summary of frequently asked questions can be found at the Global Development Research Centre’s website (Srinivas, 2005).
These types of disaster naturally occur in proximity to, and pose a threat to, people, structures or economic assets. They are caused by biological, geological, seismic, hydrologic, or meteorological conditions or processes in the natural environment (e.g., cyclones, earthquakes, tsunami, floods, landslides, and volcanic eruptions).
Cyclones, Hurricanes or Typhoons
Cyclones develop when a warm ocean gives rise to hot air, which in turn creates convectional air currents. Cyclones occur when these conventional air currents are being displaced. The term hurricane/typhoon is a regionally specific name for a “tropical cyclone”. In Asia they are called ‘typhoons’; in the Indian and Pacific Oceans they are called ‘cyclones’; and over the North Atlantic and Caribbean Basin, they are called ‘hurricanes’.
Tropical warning procedures:
Small crafts and fishing boats: approx 25-35mph winds.
Wind advisory for the public: approx. 25-35mph winds.
Gale watch: when a mature tropical cyclone has a significant probability to threaten a part of the country within 48 hours.
Gale force warning: issued when wind speeds are expected to reach gale force intensity of (34-47knots) within the next 24 hours.
Storm watch: if a post tropical cyclone disturbance is a notable to threat to an area or the entire country within a 24 to 48 hour timeframe, a storm watch statement would be included with the gale warning.
Storm warning: issued every three (3) hours when the average wind speeds are expected to reach storm force intensity of 48-63 knots within the next 12 to 24 hours.
Cyclone watch: issued when tropical cyclone winds is expected to reach cyclone force winds of above 63 knots (or 70 mph) in 24 to 48 hours.
Cyclone warning: issued every three (3) hours, when wind speeds are expected to exceed 63 knots within the next 12 to 24 hours.
An earthquake is a trembling or shaking movement of the earth’s surface, resulting from plate movements along a fault-plane or as a result of volcanic activity. Earthquakes can strike suddenly, violently, and without warning at any time of the day or night. The following terminologies are associated with earthquakes: epicentre, fault, magnitude and seismic waves.
For practical purposes, earthquakes are usually defined by their magnitude (or quantitative energy released) which is measured using a logarithm scale of 1 – 10. This logarithm scale is referred to as the Richter scale. The magnitude is determined by analysing seismic data obtained from seismometers.
The intensity of an earthquake is measured using the Modified Mercalli Intensity (MMI) Scale, which is determined qualitatively by physical observations of the earthquake’s impact.
A tsunami is an ocean wave generated by a submarine earthquake, volcano or landslide. It is also known as a seismic sea wave, and incorrectly as a tidal wave. Storm surges (or Galu Lolo) are waves caused by strong winds1.
The largest earthquake event recorded in Samoa was on 26 June 1917, measuring 8.3 on the Richter scale. The event originated in Tonga (approximately 200km south of Apia) and it triggered a tsunami of four to eight (4-8) metre run-ups in Satupaitea, Savaii. The tsunami arrived less than ten (10) minutes from its point of origin, meaning it travelled at a speed of more than 1,000km/hr. Hence, when an earthquake occurs, you must heed the tsunami warning, for example, people living in low-lying coastal areas must relocate to higher and safer grounds immediately.
This phenomenon occurs when water covers previously dry areas, i.e., when large amounts of water flow from a source such as a river or a broken pipe onto a previously dry area, or when water overflows banks or barriers.
Floods can be environmentally important to local ecosystems. For example, some river floods bring nutrients to soil such as in Egypt where the annual flooding of the Nile River carries nutrients to otherwise dry land. Floods can also have an economic and emotional impact on people, particularly if their property is directly affected. Having a better understanding of what causes flooding can help people to be better prepared and to perhaps minimize or prevent flood damage.
The term landslide refers to the downward movement of masses of rock and soil. Landslides are caused by one or a combination of the following factors: change in slope gradient, increasing the load the land must bear, shocks and vibrations, change in water content, ground water movement, frost action, weathering of shocks, removal or, or changing the type of vegetation covering slopes.
Landslide hazard areas occur where the land has certain characteristics which contribute to the risk of the downhill movement of material. These characteristics include:
A slope greater than 15 percent.
Landslide activity or movement occurred during the last 10,000 years.
Stream or wave activity which has caused erosion, undercut a bank or cut into a bank to cause the surrounding land to be unstable.
The presence or potential for snow avalanches.
The presence of an alluvial fan which indicates vulnerability to the flow of debris or sediments.
The presence of impermeable soils, such as silt or clay, which are mixed with granular soils such as sand and gravel.
Landslides can also be triggered by other natural hazards such as rains, floods, earthquakes, as well as human-made causes, such as grading, terrain cutting and filling, excessive development, etc. Because the factors affecting landslides can be geophysical or human-made, they can occur in developed areas, undeveloped areas, or any area where the terrain has been altered for roads, houses, utilities, buildings, etc.
These are disasters or emergency situations of which the principal, direct causes are identifiable human actions, deliberate or otherwise. Apart from “technological disasters” this mainly involves situations in which civilian populations suffer casualties, losses of property, basic services and means of livelihood as a result of war, civil strife or other conflicts, or policy implementation. In many cases, people are forced to leave their homes, giving rise to congregations of refugees or externally and/or internally displaced persons as a result of civil strife, an airplane crash, a major fire, oil spill, epidemic, terrorism, etc.
B. Speed of onset
Sudden onset: little or no warning, minimal time to prepare. For example, an earthquake, tsunami, cyclone, volcano, etc.
Slow onset: adverse event slow to develop; first the situation develops; the second level is an emergency; the third level is a disaster. For example, drought, civil strife, epidemic, etc.
The main hazards a region is, or may be vulnerable to, will depend on the geographic location of the country. In Samoa, for example, the main hazards which may turn into disasters are:
Implications of disasters on your region and environment
Cyclones have been a frequently occurring disaster in Samoa for the past decade; the impact of each occurrence has been devastating. The following list identifies a few of the unpleasant impacts: