1. Types of natural hazards and their distribution
Figure 14 shows data relating to cyclones, floods, earthquakes
and volcanic eruptions likely to cause damage. Besides the principal
cyclone tracks, lines of equal frequency built out of data standardised over
a hundred years have been represented (after NEUMANN, 1993 in ROUX &
Statistically two types of cyclone tracks dominate: the ESE-WNW
ones that mainly affect the Philippines, Vietnam: the cyclones of the ESE sector
strengthening as they go over the positive thermal anomaly in the South China
Sea; the others correspond to a displacement of cyclones in the SSW sector and
affect preferentially Bangladesh or the northern Myanmar coast. The cyclones
also grow stronger as a result of intense evaporation arising from the positive
thermal anomaly in the Gulf of Bengal waters. Figure 15 illustrates the high
frequency of the cyclones which affect preferentially the low deltaic coast of
Bangladesh. The cyclones also affect the Arakan plains and mountains causing
strong rains because of the orographic effect. The effective tracks of certain
cyclones like the Forrest typhoon (November 1992) and to a certain extent the
Colleen typhoon (October 1992) recall that major events can be left out by
In addition to wind and rain effects, cyclones are characterised
by destructive storm surges which affect the more highly exposed coastal
fringes in Vietnam, Myanmar and particularly Bangladesh and the Philippines.
Figure 15 shows that cyclones cause storm surges which can go upstream for more
than 100 kilometres. Certain parts of the coast are more frequently subject to
storm surge effects than others; this depending on the topography and the
possibilities of shelter. Figures 16 and 17 illustrate this phenomenon in the
Philippines and Vietnam.
The easily inundated areas and, moreover, those prone
to mass movements or droughts cannot easily be represented at this
scale, hence the drawing up of national maps. Figures 17 and 18 give some of the
examples in Vietnam and Bangladesh. Floods and landslides are favoured in
sectors statistically most affected by cyclones though they depend notably on
the relief, lithology and the development of vegetation.
The areas prone to earthquakes with a magnitude greater
than 5 are given by the Swiss Reinsurance Company (1992) and four zones of
decreasing exposure have been identified. All the coasts of the region under
study are exposed to tsunamis and particularly those nearest to
earthquake epicentres. Here again, as shown in figure 19, the topography and
shelter conditions may cause locally differences as concerns exposure. The data
related to volcanism have also been taken from the Swiss Reinsurance
Company and RANTUCCI (1994). The affected zones, are directly related to the
regional geodynamic framework. South East Asia lies in the area of the planet
where the Indian, Eurasian and Pacific plates come into contact. These contacts
correspond to the destruction of the lithosphere by subduction, hence a high
deep focus earthquake frequency. Their epicentres surround this southern
extension of the Eurasian plate constituted by the continental part of South
The map of potential threats (figure 14) and figure 20
showing the possibilities in terms of variety and hazard intensity , highlight
three groups of countries.
Fig. 14 - Hazards map
Key to figure 14
1. Lines of equal frequency of cyclones using data
normalized over 100 years.
- 1945-1988 on the North West Pacific
1891-1989 on the Bay of Bengal
Source: Neumann (1993), in Roux et Viltard
2. Principal tracks of the major cyclones .
Neumann (1993), in Roux et Viltard (1997)
3. Observed and/or partly estimated paths of three
Eli, Colleen and Forrest (1992).
After data from the "Water
Resources Journal", June 1993, No. 177.
4. Areas vulnerable to river floods.
sources: Asian Development Bank (1991), DHA (1994), etc.
Exposure to earthquakes
5. Zones prone to very high
6. Zones prone to high exposure
7. Zones prone to
8. Zones prone to low exposure Source: Swiss
Reinsurance Company (1992)
9. Areas of recent or active
Sources: Swiss Reinsurance Company (1992), Rantucci (1994)
* The Philippines and Bangladesh
These two countries both have a very high degree of exposure to
several threats but show notable differences. Bangladesh is affected almost only
by hydro-meteorological phenomena (cyclones, floods, and droughts), while all
hazard types are potentially present in the Philippines.
* Myanmar, Vietnam and Laos
Myanmar, Vietnam and to a certain extent Laos are affected by
most of hydro-meteorological and induced (mass movements) phenomena and have a
potentially high degree of exposure. The earthquake threat is low except in
Myanmar. Volcanic activity does not exist.
* Thailand and Cambodia
The principal threat in these countries is flooding.
Historical data on natural disasters in the areas affected by
hazards will supplement the information given above.
Fig. 15 - Cyclone and storm surge
hazardareas in Bangladesh
(Source: Asian Development Bank, "Disaster
mitigation in Asia and the Pacific", Manila, 1991, p. 142.)
Fig. 16 - Historical storm surges
in the Philippines
(Source: Asian Development Bank, "Disaster mitigation in
Asia and the Pacific", Manila, 1991, p.250.)
Fig. 17 - Areas subject to flooding
(Source: DHA, "Strategy and action plan for mitigating water
disasters in Viet Nam", 1994, p. 1.0.)
Fig. 18 - Flood types in
(Source: Asian Development Bank, "Disaster mitigation in Asia and
the Pacific", Manila, 1991, p. 144.)
Fig. 19 - Tsunami prone areas in
(Source: PHTVOLCS, "Geologic hazards and disaster
preparedness systems", 1987, p.53.)
Fig. 20 - Types and relative
intensity of hazards faced by the seven countries
(According to our hazard
analysis and "Economic and Social Commission for Asia and the Pacific", 1995, p.