Climate risks and adaptation in Asian coastal megacities: A synthesis

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Accommodate—a traditionapproach in monsoonal Asiato reducing vulnerabilityAccommodation acknowledges that people andassets are exposed to floods, but seeks to minimizevulnerability. In rural Asia, houses located in floodplains and exposed to frequent flooding are usuallybuilt on stilts, which reduces the vulnerability of thepeople and the household assets to flooding. Croppingcalendars designed around annual monsoonfloods and floating varieties of rice are other waysin which rural Asia accommodates floods. In citieswhere ankle-deep flooding occurs regularly, woodenplanks on blocks are common sights to allow passageand access of pedestrians. In periurban areas, landfillis frequently used to elevate new construction sitesalong major roads above the expected flood levels.Accommodation, however, can be applied ona broader scale. Flood losses in urban areas ariseprimarily from damage to buildings, houses, andcommercial/industrial properties. In this regard,risks could be dramatically reduced if buildingcodes specified minimum elevations for the firstoccupied level for housing, commerce, or industry(based on predicted inundation levels for the zonesin the city). These elevations could be reviewed andincreased as warranted with long-term (5 to 10 year)advance projections to developers. Given the timeframe of the study (40 years), this gradual approachgives urban planners a powerful tool to reduce riskswith minimal economic impact.Accommodation also relates to measures to“flood-proof” structures and building exteriors thatmay be exposed to floods. Flood-proofing dramaticallyreduces damages from floods. These standardsshould be included in urban building codes as partof an adaptation program. The study has demonstratedthat traditional accommodation methodsmay not reduce vulnerability in 2050. In HCMC, forexample, areas with frequent ankle-deep floodingwill be facing knee-to-waist-deep floods, which arenot easily managed by pedestrians. This will reduceaccess and increase losses. Similarly, many housesand buildings that have been built with main floorsabove the current 1-in-30-year flood levels will beinundated by 1-in-30-year floods in 2050.Retreat—when risks aretoo high, retreat reducesexposureRetreat as planning option to reduce exposure can beapplied in urban areas through urban land use plansand zoning codes. The social, environmental, and economicimplications need to be carefully studied. In urbanareas with high property values, it is usually onlyapplicable where the risks of loss of life or assets arehigh enough to warrant the action. In rural areas, retreatis common practice vis-à-vis flood embankmentsas rivers modify courses and erode embankments.Forced retreats are occurring in Bangkok’s coastal areadue to coastal erosion and land subsidence.Used in conjunction with restoring naturalecosystems that provide flood protection benefits,retreat can be a useful adaptation planning tool. Incoastal areas, land that becomes untenable due toSLR could be converted to natural systems (e.g.,mangroves) that can help capture sediment andprotect against SLR and storm surges. In urbanareas, reclaiming land along rivers and convertingthese to linear parks that will inundate during floods(increasing hydraulic capacity and lowering theflood profile) help beautify the city while providinga range of benefits. Similarly, agricultural landsthat may become unviable due to flooding couldbe purchased and converted to wetlands. Retreatsometimes occurs following major disasters whenthe perceived risks outweigh the desire to reconstructamong the private sector. Planners shouldseize such opportunities and develop the lands fortheir ecological and flood protection potential.In addition to the retreat from section of a cityor coast line, facilities that are critical in disastersituations or at particular risk (like schools) can beretired and moved as part of a longer term adaptationprogram.Improved management—building capacity to reducerisksFlooding needs to be considered in the context ofoverall water basin management and the capacity94 | Climate Risks and Adaptation in Asian Coastal Megacities: A Synthesis Report
of people and institutions to manage the resource.Experience has shown that piecemeal or ad hoc approachesare at risk of causing significant adverseimpacts elsewhere. For example, flood embankmentsprotect one area by aggravating the flood inanother area. Water uses and hazards need to beaddressed holistically for the water basin to maximizebenefits.With the hazard of flooding increasing, adaptationmeasures aimed at improved managementcan focus on (a) reassessing operational rule curvesfor reservoirs, given the increasing precipitationvariability; (b) increasing awareness and community-basedadaptation initiatives (e.g., shelters andearly warning systems); and (c) strengthening theplanning and risk-sharing mechanisms related tocontrolled flooding of agriculture lands to attenuateflood peaks when protecting cities.Adaptation to Increased Flooding: Brief Overview | 95
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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
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Table 3.2 ■ Bangkok Monthly Avera
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Estimation of storm surge in the ca
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Climate Change Impact and Adaptatio
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Figure 3.5a ■ Affected Condensed
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Manila’s current climate—Tropic
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Table 3.6 ■ Manila Climate Change
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Figure 3.10 ■ Areas of High Popul
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is also a key economic and financia
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Box 3.3 ■ HCMC in 2050Future land
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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
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Page 91 and 92: Table 4.14 ■ Present Value of the
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Page 95 and 96: 5Conclusions andPolicy Implications
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Page 101 and 102: BibliographyAllen, M. R., and W. J.
Page 103: Reduction: Inventory and Prospect.
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Page 108 and 109: mercial and industrial establishmen
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Page 113: AnnexCAdaptation to IncreasedFloodi
Page 120: THE WORLD BANK1818 H Street, NWWash
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Climate risks and adaptation in Asian coastal megacities: A synthesis

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