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close this bookNatural Disasters in South East Asia and Bangladesh - Vulnerability Risks and Consequences (Centre for Research on the Epidemiology of Disasters - International Center for Training Exchanges in the Geosciences, 1998, 83 p.)
View the document(introduction...)
Open this folder and view contents1. Criteria used to identify territories prone to risks
Open this folder and view contents2. Five types of territories prone to risks
View the document3. National distribution of the territories prone to risks
View the document4. From a typological to a hierarchical classification of the territories prone to risks


The synoptic evaluation of risks aims at identifying the criteria that can be used to differentiate the types of territories prone to risks, and also at drawing up a key suitable for all the countries in order to obtain a series of maps.


Both the criteria concerning the types of dangers and those of the population types are considered. These data, together, enable the identification of the different types of territories prone to risks.

1.1. Hazards

Other than volcanism (the Philippines) and the effects due to earthquakes (the Philippines, Bangladesh, Myanmar and Vietnam) there are 8 hazards (see key for the maps of the territories prone to risks). As mentioned above, floods and cyclones are the most dominant. Floods are subdivided into river floods, which have an annual frequency because of the effects of the monsoon winds, and flash floods of the mountain rivers

Cyclones affect preferably coasts, deltas, coastal plains but also the mountains exposed to winds such as the Annamitic mountain chain in Vietnam, the Arakan Yoma mountains in Bangladesh and Myanmar which will be called coastal mountains.

Floods related to great rivers affect deltas and inland basins. The latter often protected from high intensity cyclones by coastal mountains are not sheltered from droughts because they are practically exposed to wind (Mekong Laotian plains, Menam Chao Phraya and Irraouadi middle basins). The same is true for inland mountains which are preferentially affected by mud slides, landslides and flash floods.

Storm surges and high tides may increase the effects of the annual floods or the floods associated with cyclones in coastal plains and deltas to which one can add the subsidence of deltas. For example the meteorological department in Thailand reported that in 1996 "continuing floods due to high tides remained in several locations of the lower central" (terminal part of the Chao Phraya delta) "especially along the Chao Phraya River banks until November" (13).

13 In: Damage caused by floods, drought, tropical cyclones and other severe weather events in Asia and the Pacific during 1996. Water Res. Journ., June 1997, p. 3

In drawing up an assessment (cf. key to maps of territories prone to risks) it has been possible to identify five national sub-types areas associating, though unequally, the different types of dangers. It is also possible to regroup deltas and coastal plains on one side, and both inland and coastal mountains on the other, the inland basins being notably different from the two preceding groups.

The interest of this approach lies in the fact that the national sub-types groupings correspond to human groups that are also differentiated, and therefore enables the identification of the different types of territories prone to risks.

1.2. Different population types and consequences as concerns vulnerability

Two types of central areas (centres) and three types of peripheral areas (margins) can be distinguished. This depends on the establishment of national territories and their present development.

* Central areas

The two types of centres concern the inland basins and the deltas. The countries have been constituted either around inland fluvial basins or from the head of a delta. This has been revealed by the downstream historical displacement tendencies of the capitals. This is the case for Burma (Mandalay and Rangoon), Thailand (Ayutthaya-Bangkok), and Laos (Louang Phrabang-Vientiane). The capitals are in the inland and associated to the principal rivers; Dhaka is situated 200 km from the Bay of Bengal on the Burhiganga river, which name evokes a sacred river; Bangkok lies along the Menam Chao Phraya which means "mother water" (DE KONINCK, 1994, p. 231); Hanoi is 100 km away from the sea, but indirectly associated to the Red River and its delta. At last, the Royal palace of Phnom Penh "lies at the exact confluence of the Mekong and Tonle Sap rivers where, twice a year, the latter reverses its course" as a result of the Mekong floods (DE KONINCK, 1994, p. 266).

Historically, the roots of this part of Indochina underline the great significance of the attachment to land and fluvial waters. The successive migrations that constituted the populations in question, apart from the Philippines, came principally from South China. They got to Indochina by simply going down the valleys of the major rivers. The centres today are therefore composed of one or several inland fluvial basins and their deltas associated to their agrarian cities. The populations involved in foreign trade, particularly the Chinese, unequally transformed these cities. Apart from Laos and the Philippines, the current capitals are found in the deltas which are characterised by a concentration of international investments. Inland basins and deltas are particularly populated by the dominant ethnic group in power.

The consequences of all that has been mentioned above, for these two types of central territories, tend to increase the vulnerability to the various risks for two reasons:

- On one hand, the physical dangers, particularly in the deltas, often have a high frequency and intensity yet there is an obvious increase in the activities and infrastructures in the different capitals despite the strong disparities from one country to another. The international openings, logically, promote the urban growth (PIGEON, 1994) but they also favour the vulnerability for a number of reasons.

First of all it is because of the growing pre-eminence of the "commercial" districts over the "agrarian" ones (CLEMENT-CHARPENTIER, 1995). This signifies an increase in the population density in areas close to water bodies where, historically, the minority trader communities are found, among which the Chinese communities. Then the same evolution as observed in Bangkok takes place. Historically, the Thai people are known to have used canals (khlongs) as a means of transport but people from the Western countries who lived in the South closer to the sea supposedly had the first street built in 1861. This street was rapidly occupied by the Chinese "compartments" (14) (CLEMENT-CHARPENTIER, 1995, p. 115).

14 Buildings used for both commercial and dwelling purposes.

This development leads to and favours the filling of the canals, which plays a role in the floodings that affect the Thailand capital.

Moreover, the river dikes are weakened by the heavy construction of buildings close to the rivers. This was observed in 1995 at Hanoi by DRAKAKIS-SMITH & DIXON (1997) who stated: "recently, in Hanoi, uncontrolled buildings within the restricted limits adjacent to one of the city's main dykes was blamed for serious cracks appearing in this major flood control measure. Typically, instead of total demolition, only construction within 5 metres of the dyke was demolished, leaving some houses without any fronts, and even this was bitterly contested by private investors".

At last the spreading of urbanization in the delta tends to destroy the community relationships, does not encourage traditional agricultural activities, and partly explains the degradation of dykes, canals, which also play a major role in flood management.

On the other hand, the cultural heritages tend to aggravate this vulnerability by minimizing the damages related notably to floods. In these societies, except in the Philippines, farmers dominate. Therefore they have been led to manage water, (maybe because of physical constraints since the inland basins are principally sheltered from the monsoon winds) and have obviously a particular, ambiguous, approach of the effects of floods on which agriculture depends fundamentally.

In Bangladesh local populations refuse flood disappearance: "the majority of the practising farmers were against the idea of preventing flooding entirely, perhaps because of the way they adjusted their agricultural practices to normal flood regimes" (RASIN & MALLIK, 1995). Even more, "these authors indirectly state that the farmers were not totally surprised by the exceptional floods of 1987. On one hand they were able to empirically predict the occurrence of a more intense flood ("As heavy monsoon rainfall coincided with such rapidly rising river levels, many farmers could predict the impending high-magnitude flood"). On the other hand, they developed at least 19 different techniques in order to minimize crop damages which makes the exceptional aspect of the flood relative, as it was experienced by the local populations and despite the importance of both human and material damages. In Thailand, awakening to the environment-related problems is not so much linked than to floods as to possible droughts like the one that occurred in 1994 (RIGG, 1995): 'Perhaps, it is this ancient link between water, happiness and prosperity which accounts for the fervent discussion which has accompanied Thailand's most recent water crisis". Finally, the Khmers adapted their way of life to seasonal floods of the Tonle Sap thanks to pile-dwelling, or even floating houses.

This therefore underlines the relativity of perception of risks, if not disasters, by the local populations despite the significance of the damages in case of floods with intensities above the mean values. This fact should be taken into account in order to interpret the relatively few statistics concerning the countries like Laos and Cambodia. It reveals the limits of a purely technical response to the risks of flooding in a country like Bangladesh, as mentioned by THOMPSON and SULTANA (1996).

* The outlying areas

Mountainous and coastal peripheral areas are in complete contrast to centre areas and fluvial basins.

It is in the mountains that one can find the minority ethnic groups, called the tribal groups, who generally practice agriculture considered as less intensive, are of different religions and speak differently. In Laos, the Lao majority represents only 55% of the population but is concentrated in the Mekong plains. These Lao Lum (low Laos), Buddhists, differ from the Laos Soung (Laos of the summits) who arrived last from China and are animists.

The contrasts are often strong between the summit populations where shifting agriculture is practised and the populations living in the valleys, where it is possible to find a more intensive agriculture. For example this is the case in the north of Thailand.

The coasts have been, historically, considered as areas of little interest which is manifested in the population aspects and distribution. The city of Rangoon in Burma is an ancient Mort that was partially transformed into a garrison by the Burmese, and developed by the British, so much so, that the present Burmese in Rangoon "have never seen the sea" (LUBEIGT, 1997, p. 27). The Bengal coast proves to be associated to real pioneer fronts, such is the case with the Thailand "Eastern Seaboard Development Programme". In Vietnam, despite the anteriority of the Khmer presence, the Saigon area (Ho Chi Minh-city), though associated to the Mekong delta, "provided but a base for a wharf and a fort" at the time when the Vietnamese took over the city in the 17 century (DE KONINCK, 1994). However, at 200 km north-west, the significance is known of the angkorian vestiges around the Mekong and Tonle Sap valleys just upstream of the apex to the delta and in a territory that continually attracted the greed of the Vietnamese.

As a matter of fact, the opposition between the centres and the outlying areas favours a definite trend in political instability, be it in the framework of both civil or international wars. Tensions divide the dominant ethnic groups from the "tribal" ones, but also the dominant groups amongst themselves. The international powers have not hesitated to capitalize on these structural weaknesses within the framework of colonial policies or the rivalry between the United States of America, ex-USSR and China. The historical heritages are heavy, the suspicious attitude of these peoples in front of their neighbours persists. At last, everybody knows how much the badly controlled borders promoted all kind of illicit trading, in particular, in the famous gold triangle.

There again, the consequences of this tends to increase the vulnerability in view of risks.

Risk management is obviously influenced by this partition of the population types. The vulnerability of the major populations and that of the marginal ones does not have the same significance in that the Governments will be even less inclined to intervene in order to handle the risks concerning the populations often considered inferior and badly assimilated. But these populations are one of the poorest in the country and show, from estimations, high illiteracy rates; they are, yet, established in the mountains or associated to the coasts in the areas where the hazards generally have higher intensities and frequencies. It is clear that cyclones and earthquake induced effects (tsunamis for example) hit the coastal areas and the Arakan Yoma mountains open to the Bay of Bengal more than the centre of Bangladesh or that of Burma. These areas are, yet, very difficult to get to by road and the Ngapali station, on the Arakan coast, is served by aeroplane on a daily basis only in the dry season (LUBEIGT, 1997, p. 37). These are also areas which are not under the central governmental control at the time when the effects induced by deforestation are being denounced with lots of ulterior geopolitical motives. The Lao News (April-June 1997) reported that "planning the eradication of slash-and-burn practices: in the Lao P.D.R, shifting cultivation is causing an alarming amount of forest destruction. According to the government's plan for the stabilization of slash-and-burn cultivation, it will try to resettle about 100,000 swidden families by the year 2000".

But at the same time, an increased political will has been observed as regards opening-up to international trade, which induces to develop infrastructures and to increase the human presence in these marginal areas. The international opening-up is wished not only by the Chinese diaspora and the former colonial powers but also by central governments. It therefore seems to be following the development desired by Thailand and particularly China since the Open-door policy of 1979. It is worth recalling that Vietnam changed its attitude in relation to international investments by the so-called "doi moi" policies in 1986 (DRAKAKIS-SMITH & DIXON, 1997), and joined the ASEAN in 1995. In November 1996, Laos, Cambodia and Burma were accepted into the ASEAN, this admission being effective from July 1997 (Lao News, July 1997). The year 1996 was declared by Burma as the year of tourism. Some international development projects appear such as the gold quadrilateral "intended to increase trade within the highlands adjacent to Laos, Chinese Yunnan, Thailand and Burma" (DE KONINCK, 1994).

The consequences as far as vulnerability is concerned are numerous. These plans show a renewed interest for the mountainous valleys of the principal rivers which may regain their privileged main-live function of trade with China, their historical function (TAILLARD, 1989). This gave rise to the railway projects in Laos. In February 1997, the Laotian government authorized a joint-venture agreement with a company called "Pacific Transport Company" whose aim was to make a train pass over the Friendship Bridge and extend the section to Louang Phrabang then to China. The April 1997 bulletin of the Lao News adds: "in addition to the construction of railways, the agreement talks about other projects, including developing industrial zones". The increased international opening-up also shows a renewed interest for the coasts, on which shrimp breeding for export and also touristic infrastructures are found very unequally distributed depending on the country (Bangladesh, Burma). Within such physical frameworks, the increase in land value means, inevitably, an increase in the vulnerability and suggests an interest to associate preventive measures against certain physical hazards to economic development.

The above considerations allow the identification and justification of five territories prone to risks.


The key of the maps enclosed (figures 34 to 37) is based on them.

2.1. Deltas

The deltas are characterised by very high population densities and major cities, quite often capitals, and are associated with intensive rice-growing. This does not exclude, for reasons mentioned above, the existence of rapidly developing pioneer fronts close to the coastal lines. The dominant ethnic groups make the majority in the deltas. Yet we can find there pockets of minorities: foreigners in the cities, if not people who represent the remainder of a late assimilation of the deltas in the centre of the countries. This dense human presence is yet associated to a physical environment which increases the dangers by the conjunction of cyclones, floods, high tides, storm surges and if not, local tsunamis. International openings increase the vulnerability while modifying the previous danger management measures as can be seen by the development of Hanoi that has been faced with an evolutive management of the dykes network.

2.2. Inland basins

The inland basins, too, have high population densities associated with the historical or present (Laos) capital cities and irrigated rice-growing. The majority ethnic group of the countries largely dominates especially in the countryside whereas the minority groups, often Chinese, are found in the urban areas linked to trade. The international opening-up is more restricted though variable depending on the country. The bridge over the Mekong river, that facilitates the links between Vientiane and Thailand, has been, in a quite characteristic way, called the "Friendship bridge". This type of territory is therefore still largely dominated by rural agricultural activity which probably reduces and minimizes the perception of flood risks while droughts are mentally dreaded (RIGG, 1995).

2.3. Coastal plains

With the exception of Vietnam, the minority groups represent there a high percentage of the population. The access to these areas remains limited and often difficult and international investments are limited and selective, for example touristic enclaves and shrimp breeding. On a local level, the presence of commercial cultivation can be more significant like in the South of Thailand where it is associated with a minority Malay community. Although the predominant dangers obviously vary according to the latitude, the coast orientation, and the immediate back country, they are linked to cyclones and floods which can be aggravated by storm surges and high tides.

2.4. Coastal mountains

Directly concerned by cyclones and flash floods, the coastal mountains are still associated with, and named after, the minority ethnic groups living there and who often use their knowledge of the relief to oppose the central power and illegally trade with the neighbouring countries. These minority ethnic groups frequently practice "slash and bum" agriculture. The access to these mountains remains difficult even though the proximity to the coasts has sometimes given rise to the development of commercial cultivation. This is the case in Myanmar with the small rubber plantations "on the well-irrigated sides of the Arakan relief (BRUNEAU, 1995, p. 159).

2.5. Inland mountains

The inland mountains are also occupied by minority ethnic groups. These groups are numerous and poorly controlled by the central powers. The population density is there obviously limited and the mountains are far from being easily accessible. They are only concerned with scarce selective projects liable to open the area especially towards China. The fulfilment of such projects will however depend on the development of international relationships that are often strained in the area. According to ESCAP, the principal advantage of the Mekong Committee lies in "strengthening co-operation, mutual understanding and trust among the riparian countries" (15). While these mountains are not subject to the most intense cyclones, however they may experience droughts and suffer from flash floods and mass movements, which makes the access still more difficult.

15 In: ESCAP and the Mekong cooperation. Water Res. Jour., Sept 1997, p. 4.

Key to the maps showing territories prone to risks. (Figs. 34 - 35 - 36 - 37)

Fig. 34 - Territories prone to risks in Bangladesh and Myanmar

Fig. 35 - Territories prone to risks in Thailand

Fig. 36 - Territories prone to risks in Laos, Cambodia and Vietnam

Fig. 37 - Territories prone to risks in the Philippines

3. National distribution of the territories prone to risks

The five types of territories prone to risks happen to be unequally arranged in the seven target countries (figures 34 to 37).


This country was formed, though late (1947 and 1971) around the delta of the Ganges and the Brahmapoutra but the historical capitals of Bengal were progressively moved towards the east: "the movement of the capitals is connected to the colonisation of the delta jungles by clearing" (SILBERSTEIN, 1995, p. 412). This displacement of populations towards the east is shown in figure 34, the coastal plains of Sundarban remaining associated with the mangroves contrary to the plains in the eastern part of the country whose development resembles that of the live deltas. The structure of the country reveals a symbiosis with the delta which moves itself towards the east; hence, a population that tends to expose itself to accumulated effects of cyclones and floods, the Bay of Bengal being marked by a positive anomaly of mean annual temperatures.

Floods are, indeed, an annual phenomenon in the Bangladesh with at least one third of the country that proves to be liable to flooding (BIMAL KANTI, 1997). In 1988, nearly 65% of the total surface area of the country was flooded (HOFER et alii, 1996, figure 38). During the 1987 floods, 51% of the precarious housing settlements of Dhaka were flooded, and the houses in these settlements were all practically destroyed (NAZRUL ISLAM, 1996, p. 381). Moreover, the mean track of the cyclones tends to deflect towards the North east, thereby affecting particularly the Chittagong coastal plains and the coastal mountains. The coastal mountains are populated by Buddhist, Animistic and Christian tribes that are in conflict with the Bangladesh army which is trying to find a way to control the very sensitive border with the Indian Union.


Myanmar perfectly illustrates the five territories prone to risks and the cultural polarization of the dominant populations on an inland basin. We find here the ancient capital cities of Burma like Mandalay, that are associated to Irraouadi, while the present capital, Rangoon, is an ancient Mort partially transformed into a garrison by the Burmese (LUBEIGT, 1997). It is worth noting that the Mthnic group is mainly found around Mulmein port in the Salouen delta. This is where "the only Mwho have kept their language and a certain nationalism referring to their brilliant pest" are to be found (BRUNEAU, 1995, p. 145). On the map and for these reasons, the Salouen delta, despite its physical characteristics, belongs to the marginal areas and resembles the coastal plains.

There is therefore a contrast shown between a present deltaic centre - the Irraouadi one that holds the capital city, is associated to intensive rice-growing and is exposed to danger of high frequency and intensity - and the coastal margins that show numerous minority ethnic groups. Mountains have been called according to minorities names: Chin mountains, Arakan mountains, Shan plateau (DE KONINCK, p. 206). A certain number of these ethnic groups occupy the mountain chains on the borders with the neighbouring countries. For example the Karen with Thailand, the Nagas with the Indian Union. This causes geopolitical problems. The geopolitical problems may be aggravated by the existence of ethnic groups belonging to the dominant cultures in the neighbouring countries: Bengalis Rohingyas of the Arakan plains of which 200,000 are political refugees in Bangladesh, Thais of the Shan mountains. BRUNEAU (1995, p. 163) points out that Thailand which was invaded by the Burmese in the 15 and 18 centuries "voluntarily favours a buffer zone along its border that is avoided by the Burmese army". The consequences of risk management by the Burmese government can be imagined. It happens that plains and coastal mountains are particularly exposed to cyclones, yet it concerns territories that are partially open to international trade (rubber, tin).


Just as in the case of Myanmar, Thailand illustrates the five territories prone to risks. The capitals moved from the inland basin, - with Sukhotai (1220-1377) then Ayutthaya, that was destroyed by the Burmese in 1767 - to the Menam Chao Phraya delta around the two forts of Thonburi and Bangkok. According to BRUNEAU (1995) "the central plain" -that is the inland basin - became the periphery of the centre". The Siamese dominate in the inland basin just like the delta and their Thai language is in reality the Siamese or "Thai of the centre".

This development as well as the predominance of the capital city increased the vulnerability to floods. The floods aggravated by the subsidence of the delta constitute a danger that slightly worries the local populations. They tend to culturally and economically value the presence of river water and make the best of floods. According to CLEMENT-CHARPENTIER (1995), on the initiative of people from western countries - who settled to the south of Bangkok, on the riversides -, the first street was laid out in 1861 on which Chinese trade rapidly grew. Up to then, all movements were by water, using the khlongs. According to a survey carried out by DANIERE and TAKAHASHl (1997) among 515 inhabitants from the shanty towns of Bangkok, flooding did not appear as one of the nuisances in the area. However, they insisted on the problems caused by bad water quality and the presence of rats and mosquitoes.

The minority ethnic groups are present on the territory margins: Laos of the Khorat plateau, 1.5 million from South Malay, 700 to 800,000 Khmers at the Cambodian border. It must be underlined that the coasts are affected by the development of international trade. Tourism, rubber plantations, aqua culture and fishing, particularly in the south, lead the Thailand government to develop the transport infrastructure, notably that near the Songkhla port on the Bay of Siam. These coasts are exposed to cyclones.


Laos shows a clear subdivision of two groups: the inland mountains in which the numerous minority ethnic groups dominate and the plains of successive basins of the Mekong where the low Laos are majority. The Mekong plains are associated to floods with the same culture ambiguities as those elsewhere in the continental South-east Asia. The country can be affected by tropical storms which result from the progressive attenuation of cyclones having crossed Vietnam. Difficulties in communication and ethnic group opposition - the country has experienced 30 years of civil war - render almost utopic every management of risk in a mountainous environment. Nevertheless, as was observed above, trying to open up the country to international trade, particularly with China and Thailand, is likely to improve the transport infrastructure in the axis of the high Mekong valley.

Fig. 38 - Percentage of the national territory of Bangladesh affected by floods between 1954 and 1993 [Source: Hofer et alii (1996)]


The five territories prone to risks identified in Myanmar and Thailand are found in this country. The Mekong delta starts, according to DE KONINCK (1994) to open itself at about 100 km to the north east of Phnom Penh, and at more than 400 km from the sea. Upstream, there is an inland basin around the Tonle Sap which is affected by the Mekong floods, whose waters force back those coming from the Tonle Sap. Once again, the Khmers, who are the dominant ethnic group here, developed, in a rather selective way, this central basin; they built so-called hydraulic or agrarian cities among which Angkor, while trying to get to the Mekong delta. Significantly, the present capital is found at the confluence of the Mekong and the effluent from Tonle Sap. The Khmer culture here again develops the river waters (ZEPHYR, 1997) which leads the populations to minimizing the effects of so-called abnormal floods (abnormal because of their intensity or frequency).

And there again, peripheral areas associated with minority ethnic groups, with coastal lines and highlands, can be identified. These are the coastal plains and mountains with Cham, Chinese and Khmer Islam minorities, the Chinese representing, despite the consequences of the Red Khmers period, one third of the coastal population. Here also the development of international trade, which promoted the Chinese minority, led the Cambodian government to develop the infrastructures: the Sihanoukville (Kompong Som) port was fully created in 1955 and linked up to the capital by rail. In the north, the plateaus have low population densities of the minorities called "Austro-asiatic mountain" people (BRUNEAU & GRUNEWALD, 1995, p. 180).


Vietnam, once again, shows a duality between territories populated by the Viets -two deltas, an inland basin in the prolongation of Cambodia, and coastal plains- and mountain territories that are the domains for minority ethnic groups. The two deltas are associated to the rival major cities of which one is the present capital, knowing that Hanoi is historically the first and that the Mekong delta was developed by a wave of successive colonisations. The southern peripheral parts of the delta remain associated to the mangrove coast and correspond to the limits of the pioneer fronts. Saigon even became the provisional capital of the Union in 1887.

The two deltas, particularly their cities, are primarily affected by the effects of the international opening-up and by the distribution of urbanization which results (DRAKAKIS-SMITH & DIXON, 1997). According to these authors, the effects of the opening-up, that are very unequally distributed, increase the vulnerability (fig. 39). They suggest that urbanization tends to weaken the management, and maintenance of the dyke networks, which, despite the numerous effects induced, protect the two cities from floods. Yet these cities, like the populations in the coastal plains, are hit by a high frequency of cyclones which can add their effects to those of floods. Ho Chi Minh-city "suffers the effects of the tides and faces a season of tropical rain causing flooding of large parts of the urbanized territory... The metropolis really lives with its feet in the water" (BOLAY et alii, 1997, p. 192).

Fig. 39 - Vietnam growth and distribution of investment [Source: Vietnam Economic Times and Asian Development Bank - in: Drakakis-Smith and Dixon (1997)]


The map shows a very different territorial structure distinguishing the very limited, small inland basins, and a domination of coastal mountains leaving little space to the coastal plains. Deforestation would therefore have, for the whole country, direct and major consequences on the dangers downstream. According to PARAGAS & CACANINDIN (1997, p. 29): "the destruction of forests and uplands endangers the watersheds and results in massive soil erosion, decline of soil productivity, sedimentation of river channels... catastrophic floods and acute water shortages during the dry season". These floods are favoured by a very high annual frequency of cyclones, between 5 (five) and 50 (fifty) during the period 1951-1985, even though they preferentially affect Lu and the side of this island exposed to the east. Moreover, earthquakes indirectly contribute to the floods that affect the coastal plains by way of tsunamis or by landslides. Landslides may temporarily block the rivers before giving way, thereby aggravating the intensity of the flood.

The floods here do not have the same cultural value as in continental Asia and the populations did not focus themselves on one or two principal hydrographic basins which we can straightaway understand from the name of the country. PARAGAS & CACANINDIN (1997, p. 31) notably insisted on the negative aspects of floods and cyclones: "flood damage is incalculable... the main effect of flood is to retard development". This has partly led the Philippines government to be much more vigilant to risk management. It leads to a better understanding of the shift observed in the intensity and frequency of natural hazards and the relatively lower number of victims recorded.

4. From a typological to a hierarchical classification of the territories prone to risks

It is difficult to establish a hierarchy in terms of risks of the five territories. Each of the territories has specific types of natural hazards and particular forms of vulnerability even though it is easy to regroup the deltas and coastal plains on one side, and the coastal mountains and inland mountains on the other, and distinguish the inland basins. Therefore a typological classification of zones prone to risks is proposed here more than an attempt of hierarchical organization based on risk levels. This approach aims at providing a basis of reflection and decision-making for some of the solutions that would reduce the risks and cannot be standardised on a national scale but be adapted to the different types of situations.

This being stated, it might be possible to establish priorities. Taking all the human and physical criteria together, the deltas are logically within the very highest risk zones. For the other territories, the hierarchical organization depends on the criterion considered.

Considering the demographic criteria (population size and densities), the inland basins are of main concern. On the other hand, the risks in the coastal plains appear more significant given the striking diversity and potential intensity of the natural hazards alone. Basing on the socio-political factors ^among others the minorities groups), it is the coastal or inland mountains that appear to be the areas of high risk because of the vulnerability. From this point of view the reduction of the vulnerability can not be a simple technical task. The determination of the priority sectors prone to risks cannot therefore be based on scientific, physical or human criteria only, but also on political choices and considerations.