Climate changes and sea level rise: Implications on coastal area utilization and management in South-east Asia

Ocean & Shoreline Management 15 (1991) 205-232

Climate Changes and Sea Level Rise: Implications on Coastal Area Utilization and Management in South-east Asia James N. Paw & Chua Thia-Eng International Center for Living Aquatic Resources Management, MC PO Box 1501, Makati, Metro Manila 1299, Phillipines (Received 10 October 1989; accepted 8 October 1990)

ABSTRACT By the next century, global warming due to an intensifying greenhouse effect could cause profound climate changes and accelerate sea level rise. These may have significant effects on the coastal areas of South-east Asia. These areas are densely populated and support a broad range of diversified economic activities. The physical environment of the region is briefly reviewed as well as the various socio-economic activities in the coastal areas. The physical impact of sea level rise include coastal erosion and inundation of low-lying areas, salt intrusion, flooding due to storm surges and high tides as well as habitat loss. Possible economic impact of sea level rise include the destruction of properties along the coast, changes in land use patterns, water management systems, navigation and waste management. In addition, climate changes will alter precipitation and evaporation patterns, increase cyclone frequency and drought stress which could compound the impact of sea level rise on the coastal zone. Some strategies for the mitigation of sea level rise impact such as zoning and land use management, erosion and flood control, water management, reinforcement of existing coastal structures and waste management are discussed. It is advisable to include climate risk factors in coastal management strategies in order to cushion climate changes and sea level rise impact attributed to a greenhouse effect. INTRODUCTION Since the onset of the Industrial A g e in the 1850s, the concentration of carbon dioxide due to combustion of fossil fuels and, recently, of trace 205 Ocean & Shoreline Management 0951-8312/91/$03-50 © 1991 Elsevier Science Publishers Ltd, England. Printed in Northern Ireland

James N. Paw, Chua Thia-Eng

206

gases like methane and nitrous oxide in the atmosphere, have steadily increased. These gases, known as greenhouse gases, have an important effect of trapping infrared (IR) radiation (thermal radiation) leading to the warming of the earth's surface, called the greenhouse effect, t-s Compilations made by scientists of the University of East Anglia (UK) pointed to a global surface temperature increase by about 0-5°C between 1861 and 1984. Although the warming effect caused by emission of greenhouse gases has some inherent uncertainties as in all climate observations, several observations indicate that the earth is warmer now than in the past century. 2.3,6 At the 1987 Villach Workshop in Austria, global projected temperature rise ranged from 0.06°C to 0.8°C per decade beginning in 1985 (see Fig. 1). 4 Due to non-linear interactions of the atmosphere, oceans and landmass including the ice caps, warming is not uniform but will vary significantly with latitude, altitude and season. Such non-uniform warming patterns will alter the general circulation of the atmosphere and the oceans. L7 Projected temperature rise by the middle of the next century for the humid tropical region (latitudes 00-30 °) may be 0-3 to 5 °C of global average, 4 with likely mean values of 1-2 °C. Overall, the hydrologic regime of evaporation and precipitation may rise under increased greenhouse gases concentration and the mean rates of evaporation and precipitation are expected to increase by 2 to 3% per degree of global warming. Thus, in the tropical region, precipitation will probably be p / Upper scenario 4

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enhanced in areas currently receiving heavy rainfall. 4,6 Despite the difficulty in predicting precipitation patterns due to greenhouse effect, rainfall increase in the tropical region is likely to range from about 5 to 20% and possibly with more drought stress. 4 With global warming, the present sea level will rise due to ocean thermal expansion and an increase in glacial melting. 4,s-1° Although eustatic sea level rise has been estimated at 1.0-1.5mm per year for the past 100 years, it will accelerate due to the greenhouse effect. 8." Projected sea level rise by year 2050, as shown in Fig. 2, could range from 23 to 30 cm (low scenario) to 116.7 to 150 cm (high scenario). 4'5 There is indication that the greenhouse effect is intensifying, but multidisciplinary research on trace gases, deglaciation, climate and ocean circulation is necessary in order to produce better climate models. Uncertainty in measuring relative sea level has to be resolved so that eustatic rise projections can be made with greater accuracy. Forecasting the effects of global warming and consequent sea level rise can then be precisely estimated.8-to,~2.13

IMPACT OF SEA L E V E L RISE ON T H E C O A S T A L Z O N E Accelerated sea level rise in the next century due to the greenhouse effect may have significant impact on the coastal zone, especially on coastal resources, ecosystems and the myriad socio-economic activities

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therein. Sea level rise impact includes coastal erosion, inundation of low-lying coastal areas and saltwater intrusion. Such an impact could be exacerbated by the projected increased rainfall, cyclone frequency, drought stress and geographical shifting of rainfall patterns. Damage along coastal areas, especially along deltaic plains could be severe if high tide coincides with storm surges during heavy rainfall.~Z'14-16 Coastal erosion

Coastal erosion due to accelerated sea level rise may affect coastline configuration, especially along sandy beaches. In general, rapid erosion usually results in shore retreat and narrowing of beaches. 15 In some cases, loss of beaches might occur, particularly beaches that are already narrow or highly eroded due to human activities (e.g. mining). Inundation

Inundation of wetlands and low-lying coastal areas could be a significant effect of high sea level rise. Inundation can occur in these areas in the absence of adequate flood control mechanisms. Inundation can also alter shoreline configuration and some habitats like estuaries. In the event of storm surges, flooding could occur in areas previously secure from coastal flooding. ~2'~5'16 Apart from that, it can also cause backwater flow in tidal rivers causing extensive flooding and damage. Deltaic plains can erode where no protection from a rising sea level is built. The changes in rainfall patterns could reduce sediment load of rivers flowing into these plains and at the same time increase erosion in these deltas. Deltaic plains are low-lying areas and are prone to inundation, especially during spring tides and storm surges. 14-16 Saltwater intrusion

High sea level rise is likely to increase saltwater intrusion into coastal aquifers, especially those that are sources of potable water. Certainly, some island freshwater lenses could be affected. In continental coastal aquifers, saltwater is confined to saltwater wedges which boundary between the lighter freshwater and the heavier saltwater progressively below ground further inland. T M As the level of the water table is determined by sea level, a high sea level rise will cause the freshwater/seawater boundary to rise also. Thus, some coastal aquifers could become salty.

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Along estuaries and rivers where tidal influence is strong, saltwater could move upstream increasing the salinity. Aquifers along these rivers could also become salty. Saltwater intrusion will most likely intensify during drought and storm surge. It is anticipated that severe drought and increased frequency of cyclones will exacerbate saltwater intrusion inland. 4,16

IMPLICATIONS OF F U T U R E SEA L E V E L RISE ON T H E C O A S T A L A R E A S OF S O U T H - E A S T A S I A The South-east Asian region extends from 15°S to 26°N latitude and from 93°E to 149°W longitude, covering an area of 26-1 million km 2 with approximately two-thirds of the area occupied by seas.17 Table 1 shows the land area and coastlines of South-east Asian countries. The region is geologically active, being located in the junction of three major lithospheric plates: the Eurasian, the Indo-Australian and the Pacific Plates with two lesser ones, the Philippine and Molucca Sea Plates. Island arc systems are well-developed along convergent margins where active subduction zones occur forming deep trenches. Many of the arc systems are active volcanic island chains associated with shallow to deep earthquakes. These processes, which are still active in some form or another throughout the geological history of the region, have determined its present physical environment, 23-25 and earthquakes and volcanic eruptions occur in them. A large part of the coastal areas of South-east Asia is characterized by high population density and diversified economic activities. This is because natural resources in the coastal zones are vast and varied. Although sea level has been slowly rising for the past 100 years, exact measurement of sea level changes is difficult for various reasons (e.g. limitations and geographical distribution of tide gauges) including TABLE 1

Areal Extent and Coastlines of Selected South-east Asian Countries Country

Brunei Darussalam Indonesia Malaysia Philippines Thailand Source: Refs 18-22.

Areal extent (kin")

Coastline (kin)

5 699 1 491 564 329 735 300 000 514 000

161 80 791 4 675 17 460 2 960

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geological factors such as uplift or subsidence. 7.t3,26 In some areas, subsidence will exacerbate the impact of future sea level rise while along convergent margins as in Indonesia and the Philippines, tectonic uplifts may keep up with the rise in sea level and possible direct impact could be minimal. Subsidence in some areas is attributed to anthropogenic activities like hydrocarbon extraction and groundwater pumping. 27 In Bangkok, for instance, subsidence due to groundwater pumping was more than 10 mm/year in some areas. 27"28

Impact on the physical environment The South-east Asian countries have numerous coastal features which can be vulnerable to sea level rise, particularly in low-lying coastal areas. In Brunei Darussalam, coastal features such as sandy beaches occur from Muara Jetty to Kuala Belait while mangrove swamps are mostly found in Brunei Bay. The country's major estuaries are Belait Estuary with tidal effects extending 90 km upstream, Tutong Estuary which has a tidal limit of 4 6 k m from its fiver mouth and the large

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Brunei Bay. ~9 Figure 3 shows the physical environment of Brunei Darussalam. 3° Flat areas with slopes not more than 3% elevation are found in the coast which include sandy beaches and mangrove areas. 3t These may not only be vulnerable to erosion but also to inundation at high sea level rise. At present, significant tidal flooding occurs during November to January in Brunei Darussalam. This is exacerbated when high tides coincide with storm surges or strong wind conditions. Tidal flooding occurs in low-lying areas of the Sungai Brunei Basin, Mulaut Plain and the lower reaches of S. Temburong Basin. Severe backwater effects occur in the upper catchment areas if river flooding coincides with high tides, particularly during inclemental weather conditions. :9 Figure 4 shows the areas prone to flooding in Brunei Darussalam. The severity of the impact of sea level rise on these areas in the next century depends both on its degree and on the adequacy of flood control schemes. At present, flooding is compounded by channel obstruction and inadequate waterways. Saltwater intrusion in the upper catchment areas occurs where tidal influence extends further upstream. In Brunei Darussalam, saltwater [

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intrusion in Belait River is 40-50 km upstream while in T u t o n g River, it can reach up to 30-40 km. 32 Unless some structures are made (e.g. dams), rising sea level will most likely increase saltwater intrusion much further upstream than today, particularly during drought periods. Indonesia has more than 13 700 islands. Extensive coastal plains are found in these islands as well as tidal and mangrove swamps, ls'33`3a Figures 5 and 6 show the coastal environment of Indonesia. s4 Areas that will be vulnerable to erosion due to high sea level rise are sandy beaches and mudflats as well as deltas. Tidal swamps and estuaries are

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particularly prone to inundation or frequent flooding during storm surge as well as backwater flows. Tidal ranges in Indonesia are generally less than 2 m but may reach up to 4 m locally on the southern coast of Irian Jaya? 5 Thus, there might be local variations in response to high sea level rise. Peninsular Malaysia and the states of Sabah and Sarawak in Borneo Island have numerous sandy beaches, mangrove swamps and estuaries (Figs 7a and 7b). 36 Along the eastern coast, beaches are marked by low sandy ridges locally known as p e r m a t a n g . 3v The coastal features of Malaysia have been described by Kam, 3s Teh 39 and Valencia2 ° Tidal pattern along the east coast of Peninsular Malaysia is semi-diurnal with mean daily range of about 1.83 m and m a x i m u m of 3.05 m during north-east monsoon. In Sarawak, the m a x i m u m tidal range recorded was 2 m ? 7'3s Like Indonesia, low-lying coastal areas in Malaysia can be affected by high sea level rise with variable responses due to differences in tidal pattern. The Philippines is an archipelago of 7100 islands. Coastal plains with slopes of not more than 3% elevation and which sometimes extend inland along river basins, are extensive. Figure 8 shows some coastal features in the Philippines. 4~ Sandy beaches of volcanic and coralline origins are found in nearly all the islands. Tidal patterns are diurnal and semi-diurnal with range generally less than 2 m. 42"~3 High sea level rise could inundate low-lying areas and estuaries as well as cause erosion of beaches where no protective structures are found. Saltwater intrusion could occur in coastal aquifers as underscored earlier. In Thailand, low-lying areas, particularly deltaic plains and mudflats are located along the Bight of Bangkok and in the Upper South region. 2° Figure 9 shows the various coastal features in Thailand. As with the rest of the South-east Asian countries, Thailand's low-lying areas are likely to be vulnerable to erosion, inundation and saltwater intrusion under high sea level rise. Along Chao Phraya delta where elevation ranges from 1 to 2 m above mean sea level, these areas can easily be inundated or even submerged if a sea level rise of l m occurs.~5'~ Figure 10 shows the possible extent of sea level rise in the delta. ~5 Impact on coastal resource utilization

Due to rapid economic development in the region, coastal resources are heavily utilized. Some of the resources with socio-economic importance on the coastal communities which could be affected by accelerated sea level rise are mangrove exploitation, salt making and fishing.

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Exploitation of mangrove resources in the region is well-known. 33.45"47 Sea level rise will most likely transpose mangroves further inland provided there are available lands to colonize. 14 Some mangroves may disappear in areas where there are no colonizable lands or in areas already very much disturbed by human activities. In general, mangroves in managed areas or reserves will remain intact but may shift slowly inland in response to sea level rise. Exploitation of mangroves by

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coastal communities may not be affected very much as long as it is done on a sustainable basis. Solar salt making is an important small-scale industry in many coastal areas of the region. 14 Salt is produced in very shallow ponds of not more than 5 cm in depth and are generally located along the coast. Production is seasonal mainly during the dry season. With the rising sea level, salt ponds sited along the seashore could be subjected to erosion and flooding unless adequate protection is in place (e.g. revetments or dikes). Otherwise, salt ponds will have to be abandoned or moved further inland unless owners are willing to install protective structures

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which may entail considerable cost. Agricultural lands that will be affected by tides due to rising sea level will either be abandoned or converted into brackishwater ponds. ~5 In the Philippines, as shown in Fig. 8, some brackishwater pond areas that are vulnerable to sea level rise are located in Pangasinan, Pampanga-Bulacan and Capiz. Stakes and on-bottom culture methods used in molluscs and seaweeds may have to adjust to the rising sea level, t' However, it is possible that coastal water productivity might be depressed. Hence, mollusc and seaweed production may be negatively affected. The change in rainfall pattern may affect the settlement of spats and propagation of seaweeds including availability of nutrients. Thus, some operations may have to be abandoned or sited elsewhere. The distribution and abundance of broodstock and fry of cultivable species could be altered as a result of climate changes and sea level rise impact on coastal habitats. Thus, catch and availability of broodstock and fry for hatchery and growout production could be affected.

Urban and industrial development Major coastal urban centers like Bangkok, Jakarta, Manila and Penang Island are characterized as densely populated where major commercial and industrial activities are concentrated. 4a-51These coastal megalopoles will likely remain centres of activity despite current planned expansion of economic activities into the rural areas. Population is expected to increase in these centres, especially migration from rural areas. For instance, the doubling time of the population of south-east Asia is presently estimated at about 29 years, 2z a time span shorter than the occurrence of a very noticeable sea level rise. Thus, basic services will have to be expanded to cater for the burgeoning populations. Currently, these centres have inadequate water and waste management systems including housing facilities) 1 Riverine flooding is common during heavy rains. In Manila, overflowing of the numerous rivers found within the metropolis have inundated low-lying areas due to obstruction of waterways by solid wastes and proliferation of illegal shanties (Fig. 11): 2-64 Although pumping facilities are available, these are inadequate. Movement of operations further inland can only be made if adequate lands are available and also if such lands are alienable. In most cases, this may not be so. The change in precipitation due to climatic change may shorten the salt production period in some areas or lengthen during drought periods. Many of the coastal communities in the region are highly dependent on fishing with the majority of those involved being sustenance

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fishermen. At present, the increase in coastal marine fishery production is not very high and many fishing grounds are heavily exploited. 21.53.5~ Climate changes and even a moderate sea level rise could affect important habitats such as estuaries, coral reefs and wetlands. Distribution and abundance of important fish stocks associated with these habitats will also be affected. Some of these species may migrate or relocate to other areas where environmental conditions will be favourable. As a consequence, there may be some geographical shifting of fishing grounds. Changes in hydrologic regime, current and tidal patterns could also depress biological productivity of coastal waters, t4 This means that catch could diminish in some areas. Thus, such conditions could compound the socio-economic problems that may be existing in these areas (e.g. conflict between trawlers and sustenance fishermen, poverty, lack of alternative livelihood, etc.).

Coastal tourism and recreation Coastal tourism has become a very important industry in many countries in the region. In Thailand, tourism contributed to about 3.4% of the country's gross domestic product in 1986. 55 Tourism provides substantial foreign exchange earnings for the Philippines, Indonesia and Malaysia. Important coastal tourist resort areas are Bali, Indonesia; Johore and Sabah, Malaysia; Puerto Galera, Boracay and El Nido, Philippines; and Pattaya, Phuket and Ko Samui, Thailand. ~9'5~4s The rise in sea level, as mentioned earlier, is expected to erode many beaches if no protective structures are built. At present, many of the coastal resorts are built very close to the shore and protective structures like breakwater are haphazardly installed. Many of these beaches are highly eroded or the beach topography has changed (e.g. La Union, Philippines; Pattaya, Thailand). Resorts have high real estate values. ~4 Those that will be situated in the open coast may experience rapid erosion not to mention potential damage from storm surges. Thus, costly protective structures or beach nourishment may have to be made to counter these forces or else abandonment of the sites may be the alternative recourse.

Coastal aquaculture Coastal aquaculture is a very important economic countries of the region. It contributes substantially exchange earnings, particularly through the culture of Pond culture is the dominant culture system employed

activity in many to their foreign penaeid shrimps. which is typically

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constructed by reclaiming mangrove areas. Major species cultured are penaeid shrimps and milkfish. Other culture systems employed are marine net-cages for sea bass and grouper and stakes and raft methods for mussels and oysters. Mudflats are generally utilized for blood cockle culture such as those in Malaysia and Thailand. Seaweeds are cultured in reefs fiats like those in Bohol, Philippines? 9 Future sea level rise caused by the greenhouse effect may readily affect brackishwater ponds followed by stakes and on-bottom types of culture methods. The least affected are most likely to be those floating types (marine cages and rafts). 14'~5 Brackishwater ponds are easily eroded where no protective dikes are built to counter wave actions such as those in Citarum Delta in Indonesia or where no fringing mangroves are found. It is safe to assume that the majority of the ponds will still be the earthen type rather than those made of concrete and they will be prone to erosion. In a deltaic plain such as the Chao Phraya delta, the rising sea level may force some owners to abandon ponds that are sited at low elevations (1-2 m of present mean sea level) as these ponds may be frequently inundated or submerged? ~'52,6" About 10 natural and artificial rivers flow through the coastal fiat plain where Jakarta is currently sited. Flooding on low-lying areas occur during rainy seasons (Fig. 12). 51 The rising sea level is not expected to directly cause the inundation of low-lying coastal areas within these metropolises. However, if adequate pumping facilities as well as other flood control measures (levees, good waterways) are not available, severe backwater effects may cause flooding during high tides and storm surges. Due to changes in rainfall pattern, flooding frequency may be high. Such a situation may cause

River and canal Flood prone area (usually) ,.. : . . . ~ . .... ::::::::::::::::::::::::::

~:j: :::~:~ Flood prone area (unusually)

dakarta

Fig. 12.

Flood prone areas of Jakarta, Indonesia. Adapted from Ref. 51.

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extensive damage to properties not to mention life. Health hazards due to water borne diseases may intensify in depressed areas. Another aspect of coastal settlements is the so-called 'fishing villages' or 'water villages' where houses are built on stilts. Some of these settlements are located within urban waterways and port areas. A notable example of a 'water village' is Kampong Ayer in Brunei Darussalam. The rising sea level is likely to force these villages to build houses with longer stilts or retreat further nearshore. In either case, these villages could be vulnerable to storm surges and other inclemental weather conditions due to change in cyclone and rainfall patterns. Moreover, retreat may be costly not to mention the availability of space to settle. Port facilities such as those in Manila, Penang, Jakarta and other coastal urban centers throughout the region may have to adjust to the rising sea level. ~a'6° Adequate structures to offset the gradual sea level rise may have to be built so that these ports remain viable. Industrial establishments would not probably be severely affected except those that might be sited along the seashore (power plants, refineries). Industrial facilities like oil refineries and depots may also be affected. Adjustment to the rising sea level may be necessary if these facilities are already sited at low elevation coastal areas (less than 3 m above mean sea level). Rainfall pattern changes may generate storm surges that could also damage these facilities. By the next century, if government plans are successfully implemented, most of the industrial establishments would have been relocated outside urban centres and further inland. The likely effect on these establishments even if sited inland would be availability of freshwater for operation. It is expected that climate change will bring about drought stress and intense rainfall. Reservoir and water management systems may have to adjust to these conditions as they are made to meet the requirement of population expansion and economic development. Water management covering drinking water and for general purposes including irrigation, would have to be managed properly. At present, many of the urban centres have an acute shortage of potable water and many still rely on groundwater pumping which are increasingly contaminated with waste leachates and salt. Groundwater pumping is a major concern as it will lead to land subsidence and salt intrusion, especially aquifers that are located along coastal areas. 7"16 The subsidence in Bangkok due to excessive groundwater pumping is a classic example. 28 Waste management in the region is, in general, very poor. Much of

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the solid and liquid wastes are dumped into the sea or close to the seashore as well as along waterways. These lead to obstruction and siltation of waterways and increase the risk of flooding during heavy rains. Solid wastes and hazardous materials dumped close to the seashore could create countless problems under a rising sea level condition and climate change. Flooding, for instance, can affect the waste drainage systems of coastal settlements. Storm, shore retreat and changes in water tables can affect waste facilities or waste dumping sites that are located close to the seashore and along river banks. As a result, leaching of waste materials into the nearby areas and soil as well as possible washout during floods and storm surges can occur. 6t Moreover, potential health risks would involve the release of pathogenic organisms and toxic substances like heavy metals from waste materials. CONCLUSION The varied and rich natural resources of the South-east Asian region are partly attributed to its complex geology. Important coastal activities include fishing, navigation, aquaculture, tourism and mining. Coastal population is high and many important urban and industrial centres are located within the coastal zone. Population pressure and rapid economic development in the region have led, and are likely to continue to lead, to heavy exploitation of coastal resources and environmental degradation? 3 In general, a future sea level rise may bring about extensive land use changes, particularly within large urban centres. There will be areas prone to high erosion, frequent flooding, salt intrusion, inundation or submergence which could create numerous economic setbacks, unemployment, population migration and disruption of social amenities as underscored earlier. The intensity of these effects will, of course depend on the degree and the rate of climatic change and the ensuing sea level rise but under the prevailing circumstances even a moderate rise may have serious consequences especially if it happens faster than anticipated. Climatic change will probably bring about changes in rainfall patterns and increase drought stress which may have severe repercussions in the many economic activities in the region. Some of the strategies regarding mitigation of climate changes and future sea level rise impact due to the greenhouse effect have been described by Jaeger, 4 Titus e t a l . , ~2 and Sorensen et al. 16 Strategies include zoning of high risk and low risk coastal areas that may be vulnerable to sea level rise. In high risk zones, coastal development

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should either be stopped or restricted such that industrial establishments and hazardous material dumping facilities should not be located in these zones. Apart from that, waterways should be cleared of obstructing materials and structures so that flooding can be minimized as well as improving flood control facilities like pumping stations and channels. In areas where land subsidence is already a problem, groundwater pumping should be stopped. Water management systems should be instituted (e.g. expand piped water service) and existing ones improved (e.g. improve reservoir capacity) so that dependence on phreatic sources, especially within residential areas, can be minimized. Climate risk factors should be included in water management planning to provide flexible absorptive capacity of water management facilities, particularly in urban areas. 62 No doubt, these improvements will be costly. However, problems of coastal erosion and other deterioration are already existing within the region, particularly in large urban areas. Actions to address the above issues have been incorporated in the national plans of many countries in the region but projections are based on the assumption that climate change will not be a factor that will exacerbate or ameliorate future developments. At present, environmental considerations in development plans are readily evident.63 However, these are focused on sustainability of natural resources in their present state or condition since a large part of the natural resources in the region are heavily exploited. The climatic change possibly brought about by the greenhouse effect and an ensuing sea level rise in the coming century have not been considered in any of the current development plans. This phenomenon is still relatively new and as yet no clear observational evidence is available that will convince policy-makers in the region to regard this as a serious problem. Considering the present state of information on the greenhouse effect beset with uncertainties as it is a future climatic change and the sea level rise following it could have profound impacts on the economies of the countries in the region. It is obviously necessary to resolve the uncertainties regarding climatic changes and sea level rise projections on a regional basis so that policy-makers may be able to consider these in their national development plans. It may, in fact, be wise to consider expected lifetimes of the various components of these plans and to include in them, wherever possible, contingencies for a sea level rise that would not increase the costs of the measures envisaged. ACKNOWLEDGEMENTS The authors would like to thank Mrs Absornsuda Siripong, Marine Science Department, Chulalongkorn University, Thailand, and Dr

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Chou Loke Ming, Zoology Department, National University of Singapore, for providing useful reference material, to colleagues at I C L A R M , for many productive discussions, to Ms Ma. Angelina A. Agulto for copy-editing, Ms Eloisa Espiritu for typing the draft manuscript and Ms Rachel Atanacio for the artwork. REFERENCES 1. Ramanathan, V., The greenhouse theory of climate change: a test by an inadvertent global experiment. Science, 240 (1988) 293-9. 2. Baes, C. F., Jr, Goeller, H. E., Olson, J. S. & Rotty, R. M., Carbon dioxide and climate: the uncontrolled experiment. In Climates Past and Present, ed. B. J. Skinner. W. Kaufmann, Inc., California, 1981, pp. 86-96. 3. Hansen, J., Lacis, A. & Rind, D., Climate trends due to increasing greenhouse gases. In Coastal Zone '83. Proceedings of the Third Symposium on Coastal and Ocean Management, ed. O. T. Magoon & H. Converse. American Society of Civil Engineers, New York, 1983, pp. 2796-810. 4. Jaeger, J., Developing policies for responding to climatic change. A summary of the discussions and recommendations of the workshops held in Villach (28 Sept.-2 Oct. 1987) and Bellagio (9-13 Nov. 1987), under the auspices of the Beijer Institute, Stockholm. World Meteorological Organization and the United Nations Environment Programme. Stockholm, Sweden, 1988. 5. Titus, J. G., Rising sea level, storms, and coastal erosion at Ocean City, Maryland, In Coastal Zone '85. Proceedings of the Fourth Symposium on Coastal and Ocean Management, ed. O. T. Magoon, H. Converse. D. Miner, D. Clark & L. T. Tobin. American Society of Civil Engineers, New York, 1985, pp. 2538-55. 6. Kerr, R. A., Is the greenhouse here? Science, 239 (1988) 559-61. 7. Rodgers-Miller, L. & Bardach, J. E., In face of a rising sea. In Ocean Yearbook 7, ed. E. M. Borgese, N. Ginsburg & J. R. Morgan. University of Chicago Press, Chicago, 1989, pp. 177-90. 8. Barnett, T. P., Global sea level: estimating and explaining apparent changes. In Coastal Zone '83. Proceedings of the Third Symposium on Coastal and Ocean Management, ed. O. T. Magoon & H. Converse. American Society of Civil Engineers, New York, 1983, pp. 2777-82. 9. Hoffman, J. S., Projecting sea level rise to the year 2100. In Coastal Zone '83. Proceedings of the Third Symposium on Coastal and Ocean Management, ed. O. T. Magoon & H. Converse. American Society of Civil Engineers, New York, 1983, pp. 2784-92. 10. Thomas, R. H., Thompson, D. E., Bindschadler, R. A. & MacAyeal, D. R., Ice-sheet melting and sea level. In Coastal Zone '83. Proceedings of the Third Symposium on Coastal and Ocean Management, ed. O. T. Magoon & H. Converse. American Society of Civil Engineers, New York, 1983, pp. 2846-57. 11. Peltier, W. R., Global sea level rise and earth rotation. Science, 240 (1988) 895-901.

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62. Riebsame, W. E., Adjusting water resources management to climate change. Climatic change, 13 (1988) 69-97. 63. Chua, T. E., Developing coastal area management plans in the Association of Southeast Asian Nations (ASEAN). Paper presented at the Sixth Symposium on Coastal and Ocean Management, Charleston, South Carolina, 11-14 July 1989. 64. DPWH, Revised Project Proposal for the Retrieval of Flood Prone Areas in Metro Manila. Department of Public Works and Highways, Manila, Philippines. Unpublished manuscript (with map), 1988.