Tropical Cyclones
(Working document of the Service national du RÉCIT de l’univers social)
www.recitus.qc.ca
Introduction
Causal Phenomena
Mixture of heat and moisture forms a low pressure center over oceans in tropical
latitudes where water temperatures are over 26 degrees C.
Wind currents spin and organize around deepening low pressure […].
Depression becomes a tropical cyclone when winds reach gale force or 117 km per
hour.
General Characteristics
When the cyclone strikes land, high winds, exceptional rainfall and storm surges cause
damage with secondary flooding and landslides.
Predictability
Tropical cyclones can be tracked from their development but accurate landfall forecasts
are usually possible only a few hours before as unpredictable changes in course can
occur.
(An Overview of Disaster Management, http://www.undmtp.org/modules_e.htm, page 38)
Image 1
Downtown
Image 2
Manila shantytowns
Team 1: Identify the most vulnerable areas on the image
General observations: Identify geographical areas (economic centre and outlying area,
flood-risk areas, etc.) and types of buildings (skyscrapers, institutions, shantytowns,
industries, etc.).
Using the image, the two texts below and the table, identify elements in Manila that are
vulnerable to natural hazards.
Text 1
Factors contributing to vulnerability (in cases of tropical cyclones)
Settlements located in low lying coastal areas (direct impact).
Settlements in adjacent areas (heavy rains, floods).
Poor communications or warning systems.
Lightweight structures, older construction, poor quality masonry.
Infrastructural elements, fishing boats and maritime industries.
(An Overview of Disaster Management, http://www.undmtp.org/modules_e.htm, page 38)
Elements most at risk (in cases of tropical cyclones)
Lightweight structures and timber housing. Informal housing sectors and shanty
settlements. Roofs and cladding. Loose or poorly attached building elements,
sheets and boards. Trees, fences, signs, etc. Telegraph poles, pylons and highlevel cables. Fishing boats or other maritime industries.
(Disaster Mitigation, http://www.undmtp.org/modules_e.htm, page 23)
Vulnerable Areas
Vulnerability Factors (Text 1)
Observations about Photo
Team 2: Identify the various types of buildings and the risk
elements and solutions they may represent
Note your results in the table below.
Text 2
Mitigation also entails the protection of the economy from disasters. Economic
activity in the more industrialized societies is complex and interdependent, with
service industries dependent on manufacturing, which in turn relies on supplies of
raw materials, labor, power and communications. This complex interdependency
is extremely vulnerable to disruption by hazards affecting any one link in the
chain. Newly industrializing societies are most vulnerable of all.
(Disaster Mitigation, http://www.undmtp.org/modules_e.htm, page 17)
Main mitigation strategies
Engineering of structures to withstand wind forces. Wind load requirements in
building codes. Wind safety requirements for non-structural elements. Good
construction practices. Micro-climatic siting of key facilities, e.g., in lee of hillsides.
Planting of windbreaks, planning of forestry areas upwind of towns. Provision of
windsafety buildings (e.g., strong village halls) for community shelter in vulnerable
settlements.
(Disaster Mitigation, http://www.undmtp.org/modules_e.htm, page 23)
Urban Development and Natural Hazards
Types of Buildings (Text 2)
Observations about Photo
Team 3: Identify the various settlements of Manila: major
urban centre vs. shantytown
Rural Exodus and Economic Draw
What explains the inhabitants’ decision to live along the coast in a country that
experiences torrential downpours and typhoons? Why is the economic draw of the city
stronger than fear of natural disasters?
Text 3
The prohibition of building houses on hazardous slopes may seem sensible but is
unenforceable in cities where economic pressures to locate on such locations
outstrip concerns of illegality.
(Disaster Mitigation, http://www.undmtp.org/modules_e.htm, page 29)
In many rapidly developing cities, the control of private sector land use through
urban masterplanning and development permissions is almost impossible. It is
often private sector land use, the informal sectors and shanty towns that pose the
highest risks of disaster. Flood plains and steep slopes are often the marginal
lands that are available to the lower-income communities and the most vulnerable
social groups. The economic pressures that drive these groups, first to the city for
jobs and opportunity, and second to the marginal lands to live, need to be fully
understood as the context for reducing their risk.
(Disaster Mitigation, http://www.undmtp.org/modules_e.htm, page 33)
Economic Draw of Major Urban Centres
Elements of Economic Draw (Text 3)
Observations about Photo
Sharing of Observations Using a Sketch
Synthesis of observations to create the sketch:
-
Illustrate the economic draw of major urban centres (team 1).
Illustrate the elements of the city that are most at risk (team 2).
Illustrate a solution to protect the population (team 3).
Text sources:
Training modules from the United Nations Disaster Management Training Programme (DMTP)
http://www.undmtp.org/modules_e.htm
Presentation of Synthesis Sketch by Teacher
Economic
centre
Danger
Industry
Typhoon
Institutions that could
shelter the population
Legend
Shanty or vulnerable building
Shelter
Typhoon
Economic centre
Vulnerable area
Industry
Development of
shantytown around
economic centre
Danger