Climate risks and adaptation in Asian coastal megacities: A synthesis

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a 30 percent increase in the flood-prone area. InManila, even if current flood infrastructure plansare implemented, the area flooded in 2050 will increaseby 42 percent in the event of a 1-in-100-yearflood under the high emission scenario comparedto a situation without climate change. In HCMC,the area inundated increases (from 54 percent ina situation without climate change to 61 percentin 2050 with climate risks considered) for regularevents and for extreme (1-in-30 year) events from68 percent (without climate change) to 71 percent(with climate risks considered) in 2050 under thehigh emission scenario. Further, there is a significantincrease in both depth and duration for both regularand extreme floods over current levels in 2050. Theanalysis also highlights areas that will be at greaterrisk of flooding in each metropolitan area. In MetroManila, for instance, areas of high population densitysuch as Manila City, Quezon City, Pasig City,Marikina City, and San Juan Mandaluyong City arelikely to face serious risks of flooding.Increase in population exposed to floodingdue to climate changeIn all three cities, there is likely to be an increase inthe number of persons exposed to flooding in 2050under different climate scenarios compared to asituation without climate change. For instance, inBangkok, in 2050, the number of persons affected(flooded for more than 30 days) by a 1-in-30-yearevent will rise sharply for both the low and highemission scenarios by 47 percent and 75 percentrespectively compared to those affected by floods ina situation without climate change. In Manila, for a1-in-100-year flood in 2050, under the high emissionscenario more than 2.5 million people are likely tobe affected assuming that the infrastructure in 2050is the same as in the base year, and about 1.3 millionpeople if the 1990 master plan is implemented. InHCMC, currently, about 26 percent of the populationwould be affected by a 1-in-30-year event. However,by 2050, it is estimated that approximately 62 percentof the population will be affected under the highemission scenario without implementation of theproposed flood control measures. Even with theimplementation of these flood control measures,more than half of the projected 2050 population isstill likely to be at risk from flooding during extremeevents. How to plan for such large percentages ofpopulation being exposed to future flooding needsto be seriously considered.Costs of damage likely to be substantialin and can range from 2 to 6 percentof regional GDPIn Bangkok, the increased costs associated withclimate change (in an A1FI scenario) from a 1-in-30-year flood is THB 49 billion ($1.5 billion) orapproximately 2 percent of GRDP. These are the additionalcosts associated with climate change. Theactual costs of a 1-in-30-year flood would includecosts resulting from land subsidence and would beeven higher. In Manila, a similar 1-in-30-year floodcan lead to costs of flooding ranging from PHP 40billion ($0.9 billion) given current flood controlinfrastructure and climate conditions to PHP 70billion ($1.5 billion) with similar infrastructure butfuture A1FI climate. Thus, the additional costs ofclimate change from a 1-in-30-year flood wouldbe approximately PHP 30 billion ($0.65 billion) or6 percent of GRDP. The HCMC study adopts a differentmethodology to analyze costs and its resultscannot directly be compared to the costs of Manilaand Bangkok. The HCMC study uses a macro approachand estimates a series of annual costs up to2050. The flood costs to HCMC, in present valueterms, range from $6.5 to $50 billion. The “annualized”costs of flooding would likely be comparableto the costs of Bangkok and Manila.Damages to buildings is an importantcomponent of flood-related costsDamage to buildings emerges as a dominant componentof flood-related costs, at least in Bangkokand Manila. In these cities, over 70 percent offlood-related costs in all scenarios are a result ofdamage to buildings. Cities are, almost by definition,built-up areas full of concrete structures. Itis, therefore, not surprising that the main impactsof floods is on these structures and the assets theycarry. In HCMC, 61 percent of urban land use, 67percent of industrial land use, and 77 percent of76 | Climate Risks and Adaptation in Asian Coastal Megacities: A Synthesis Report
open land use is expected to be flooded in 2050in an extreme event if the proposed flood controlmeasures are not implemented. Future floodingalso has major sector implications. For instance, inthe transportation sector in HCMC, even with theimplementation of the proposed flood protectionsystem, a significant percentage (76 percent of axisroads, 58 percent of ring roads) of the existing andplanned roads will be exposed to increased flooding.Thus, as cities develop over the next 40 years,it would be important to design their commercial,residential, and industrial assets and zones to minimizethese costs.Impact on the poor and vulnerable willbe substantial; however, even better-offcommunities will be affected by floodingIn Bangkok and Samut Prakarn, the study estimatesthat about 1 million inhabitants will beaffected by the A1FI climate change condition in2050. One out of eight of the affected inhabitantswill be those living in condensed housing areaswhere the population primarily lives below thepoverty line. Of the total affected population, approximatelyone-third may have to encounter morethan a half-meter inundation for at least one week,marking a two-fold increase in the vulnerablepopulation. People living in the Bang Khun Thiandistrict of Bangkok and the Phra Samut Chedi districtof Samut Prakarn will be especially affected.In HCMC, in general, poorer areas in HCMC aremore vulnerable to flooding. However, in some ofthe areas, the poor and non-poor are both at risk.The Manila study shows that while low-incomeresidents have devised many coping strategies toextreme events, state and non-state actors need toplay a more proactive role in addressing vulnerabilityof the urban poor.Urban plans and flood protectioninfrastructure need to take climate risksinto accountFlood protection plans are already in place in allthree mega-cities considered. However, in all threecities, these have been prepared without consideringfuture climate-related risks, which need to be consideredfor the infrastructure to provide the expectedlevel of protection from future climate risks. InHCMC for example, which has a long history of respondingto natural disasters, a number of measuressuch as dykes and early warning systems (which arealso important aspects of a climate change adaptationstrategy) have been developed. However, thelikelihood of increasing frequency and intensity ofextreme events has not been built into these disastermanagement plans. Consideration of climate-relatedrisks has also not been sufficiently integrated intourban planning and in various sectoral plans in thecities. As the HCMC case shows, in addition to theurban master plan, there are a number of city-levelsectoral plans with little coordination between them.The main policy implication is that climate changeadaptation measures need to be well-integratedinto urban, sectoral, and flood protection plans andthe coordination between these plans needs to bestrengthened.Reduction of land subsidence should beconsidered an important part of urbanadaptationOne of the main findings of this study is that nonclimate-relatedfactors such as land subsidence areimportant and in some cases even more importantthan climate risks in contributing to urban flooding.In Bangkok, for instance, there is nearly atwo-fold increase in damage costs between 2008and 2050 due to land subsidence. Further, almost70 percent of the increase in flooding costs in 2050in the city is due to land subsidence. While datafor land subsidence was not available for Manilaand HCMC and this issue was not considered inthe hydrological modeling for these two cities,available literature suggests that it is an importantfactor in all three cities and should be consideredin follow-up studies. Even though the megacitieshave already undertaken a number of measuresto slow down land subsidence, further regulatoryand market incentives are clearly required to stemgroundwater losses. City governments need tobetter assess factors contributing to land subsidenceand consider options to reduce it. Based onqualitative information provided in the city studies—the impact of other non climate factors such asConclusions and Policy Implications | 77
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© 2010 The International Bank for
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Figure 4.6 Damage Costs Associated
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AcknowledgmentsThis synthesis repor
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Executive SummaryIntroduction and R
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For each city, complex hydrometeoro
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infrastructure but a high emission
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these include strategies that focus
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policy implications have broader re
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2Methodologies forDownscaling, Hydr
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Table 2.1 ■ Climate Change Foreca
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Return periods considered 18In this
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Figure 2.2 ■ Manila Rainfall-Runo
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Figure 2.3 ■ Estimation of Damage
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sion and distribution lines, and en
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Figure 2.5 ■ Possible Relationshi
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prices and the same prices are appl
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3Estimating Flood Impactsand Vulner
Page 45 and 46: Table 3.2 ■ Bangkok Monthly Avera
Page 47 and 48: Estimation of storm surge in the ca
Page 49 and 50: Climate Change Impact and Adaptatio
Page 51 and 52: Figure 3.5a ■ Affected Condensed
Page 53 and 54: Manila’s current climate—Tropic
Page 55 and 56: Table 3.6 ■ Manila Climate Change
Page 57 and 58: Figure 3.10 ■ Areas of High Popul
Page 59 and 60: is also a key economic and financia
Page 61 and 62: Box 3.3 ■ HCMC in 2050Future land
Page 63 and 64: original swamp land on which the ci
Page 65 and 66: from 68 percent to 71 percent; that
Page 67 and 68: Table 3.15 ■ Districts Affected b
Page 69 and 70: Table 3.16 ■ Effects of Flooding
Page 71 and 72: 4Assessing Damage Costsand Prioriti
Page 73 and 74: Table 4.2 ■ Summary of Flood and
Page 75 and 76: uilt outside the cities and are not
Page 77 and 78: ■■■■■■For the eastern p
Page 79 and 80: Table 4.6 ■ Flood Damage Costs Wi
Page 81 and 82: Table 4.8 ■ Flood Damage Costs in
Page 83 and 84: Figure 4.5 ■ Loss Exceedance Curv
Page 85 and 86: Box 4.3 ■ Increased Time Costs an
Page 87 and 88: Table 4.11 ■ Adaptation Investmen
Page 89 and 90: Marikina River areas through a dam,
Page 91 and 92: Table 4.14 ■ Present Value of the
Page 93 and 94: of reducing vulnerability of the po
Page 95: 5Conclusions andPolicy Implications
Page 99 and 100: hydrometeorological data, yielding
Page 101 and 102: BibliographyAllen, M. R., and W. J.
Page 103: Reduction: Inventory and Prospect.
Page 106 and 107: a paper commissioned by JICA (Sugiy
Page 108 and 109: mercial and industrial establishmen
Page 110 and 111: ADB. The selection and prioritizati
Page 113 and 114: AnnexCAdaptation to IncreasedFloodi
Page 115: of people and institutions to manag
Page 120: THE WORLD BANK1818 H Street, NWWash
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