Climate risks and adaptation in Asian coastal megacities: A synthesis

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1-in-30-year floods. There are steep increases inpersons affected as inundation levels exceed the2008 1-in-30-year design standards. For example,the number of persons who would be affected by1-in-100-year flood event in 2008 is nearly doublethe number affected by a 1-in-30-year flood, asshown in Table 3.5. Similarly, the number of personsaffected in 2050 by a 1-in-30-year event will rise sharplyfor both B1 and A1FI scenarios, with 47.2 percent and74.6 percent increases, respectively.Areas in Bangkok vulnerable to floodingAlthough Bangkok’s flood embankment andpumped drainage will continue to offer substantialprotection for the interior area, land outside the embankmentto the north and the southwest is likely toexperience significantly worse flooding. These areareas which are undergoing housing, commercial,and industrial development. Within BMR, Bangkokand Samut Prakarn are the two provinces that aremost affected by climate change. In a C2050-LS-SR-SS-A1FI-T30 scenario, almost 1 million people inBangkok and Samut Prakarn would be impactedby floods. The impact will be profound for peopleliving on the lower floors of residential buildings.Nevertheless, people living on higher floors in theBang Khun Thian district of Bangkok and the PhraSamut Chedi district of Samut Prakarn might alsobe impacted. District-wise, Don Muang district innorth Bangkok has the highest number of peopleaffected by floods (approximately 90,000) owing toits higher population density. In the western part ofthe Chao Phraya River, about 200,000 people in BangKhun Thian, Bang Bon, Bang Khae, and Nong Khamdistricts might be impacted. The maps in Figure 3.5aand 3.5b below show the differences in flooding forthe 1-in-30-year event, currently and in 2050.Table 3.5 ■ Exposure of BangkokPopulation to FloodingFrequencyPopulation affected for >30 days2008 2050 B1 2050 A1FI1-in-100 year 1,002,244 1,187,803 1,271,3061-in-30 year 546,748 805,055 954,389Source: Panya Consultants (2009).Impact of the floods on people living incondensed housingFigures 3.5a and 3.5b show the impact of floodingunder the 1-in-30-year A1FI flood in 2050 in comparisonto 2008, with an overlay of poor housingin Bangkok. It shows increased flooding in severalcondensed housing areas where the poor live. Asthe study points out, “ about 1 million inhabitantsof Bangkok and Samut Prakarn will be affected bythe A1FI climate change condition in 2050. One ineight of the affected inhabitants will be from the condensedhousing areas where most live below the poverty level.One-third of the total affected people may be subjected tomore than a half meter inundation for at least one week.This marks a two-fold increase of that vulnerablepopulation. The impact will be critical for the peopleliving in the Bang Khun Thian district of Bangkokand the Phra Samut Chedi district of Samut Prakarn”(Panya Consultants 2009).Key sectors likely to be affected by floodingin 2050 but buildings and housing mostaffectedThe most significant impacts will be felt by theresidential, commercial, and industrial sectors withmore than a million buildings being affected by a1-in-30-year event in 2050. About 300,000 buildingsin areas to the west of Bangkok—like BangKhun Thian, Bang Bon, Bang Khae, Phra Samut,and Chedi districts—will also be impacted. Forthe 1-in-30-year event, approximately 1,700 kmof roads would be exposed to flooding. The LatKrabang water supply distribution station andthe Nongkhaem solid waste transit station wouldboth be subject to 50–100 cm inundation, althoughthe main water and wastewater treatment facilitiesare protected. In addition, 127 health care facilitieswould be subject to flooding, with inundation levelsranging from 10 to 200 cm.Storm surge and sea level rise haverelatively small role in contributing toflooding in BangkokAnalysis carried out in the Bangkok study founda linear relationship between future precipitation30 | Climate Risks and Adaptation in Asian Coastal Megacities: A Synthesis Report
Figure 3.5a ■ Affected Condensed (Poor) Community of Case C2008-T30Figure 3.5b ■ Affected Condensed (Poor) Community of Case C2050-LS-SR-SS-A1FI-T30Source: Panya Consultants (2009).and flood volume in the Chao Phraya River. However,it found that flood peak discharge in the ChaoPhraya River will increase by a larger percentagethan precipitation, due to unequal travel times offloods from upstream catchments. Further, whilestorm surges and sea level rise are important, theywill have less effect on flooding in Bangkok. Whilestorm surges do occur in the Gulf of Thailand andcontribute to flooding the BMR area, it was estimatedthat the flood-prone area in Bangkok andSamut Prakarn will increase by about 2 percentdue to a storm surge striking the western coast ofthe Gulf of Thailand.Estimating Climate-relatedImpacts in ManilaThe Manila study (Muto et al. 2010) focuses onMetro Manila and includes Manila and 16 munici-Estimating Flood Impacts and Vulnerabilities in Coastal Cities | 31
Page 4 and 5: © 2010 The International Bank for
Page 7 and 8: Figure 4.6 Damage Costs Associated
Page 9: AcknowledgmentsThis synthesis repor
Page 13 and 14: Executive SummaryIntroduction and R
Page 15 and 16: For each city, complex hydrometeoro
Page 17 and 18: infrastructure but a high emission
Page 19: these include strategies that focus
Page 23 and 24: policy implications have broader re
Page 25: 2Methodologies forDownscaling, Hydr
Page 28 and 29: Table 2.1 ■ Climate Change Foreca
Page 30 and 31: Return periods considered 18In this
Page 32 and 33: Figure 2.2 ■ Manila Rainfall-Runo
Page 34 and 35: Figure 2.3 ■ Estimation of Damage
Page 36 and 37: sion and distribution lines, and en
Page 38 and 39: Figure 2.5 ■ Possible Relationshi
Page 40 and 41: prices and the same prices are appl
Page 43 and 44: 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: Climate Change Impact and Adaptatio
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 and 96: 5Conclusions andPolicy Implications
Page 97 and 98: open land use is expected to be flo
Page 99 and 100: hydrometeorological data, yielding
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BibliographyAllen, M. R., and W. J.
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Reduction: Inventory and Prospect.
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a paper commissioned by JICA (Sugiy
Page 108 and 109:
mercial and industrial establishmen
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ADB. The selection and prioritizati
Page 113 and 114:
AnnexCAdaptation to IncreasedFloodi
Page 115:
of people and institutions to manag
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THE WORLD BANK1818 H Street, NWWash
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Climate risks and adaptation in Asian coastal megacities: A synthesis

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