Climate risks and adaptation in Asian coastal megacities: A synthesis

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dumping of solid waste into the city’s canals andwaterways, poor dredging of canals, siltation ofdrains, deforestation and soil erosion in the upperwatershed, and land use patterns—are also criticaland should be part of a broader and multisectoralapproach to addressing urban adaptation.Important to consider variation in climaterisks and factors contributing to floodingAn important finding of this study is that whilea combination of climate-related factors can contributeto urban flooding, some factors are muchmore important than others in different cities. Forinstance, in HCMC, storm surges and sea levelrise are important factors contributing to flooding.However, in Bangkok these factors seem tobe relatively less important. In part this has todo with the location, elevation, and topographyof the city. The policy implication is that adaptationmeasures need to be designed based on thespecific hydrological and climate characteristicsof each city.Need for greater emphasis on ecosystembasedapproachesIn all of the cities considered, an important focusof flood management and control is on hardinfrastructure solutions. However, the studies(Bangkok and HCMC) show that ecosystem-basedapproaches are also important and can be usefullycombined with infrastructure interventions. TheHCMC study, for instance, argues for combiningconstruction of dykes (as approached by theplanned flood control measure) with managementand rehabilitation of the mangrove systems in CanGio, reforestation of the Dong Nai River Basin upperwatersheds, river and canal bank protection,and implementation of basin-wide flow managementstrategies. Urban wetlands provide a rangeof services, including flood resilience, allowinggroundwater recharge and infiltration, and providinga buffer against fluctuations of sea level andstorm surges. Rehabilitation of urban wetlands istherefore critical. Upstream protection of watershedsthrough reforestation is also important inmanaging the release of runoff into the reservoirsthat serve urban residents. These options need tobe considered in developing a comprehensive approachto urban adaptation. Dykes themselves aresusceptible to erosion by rainfall and storms. Assuch, it is also important to consider protection ofdykes through planting.Importance of locally induced climatechange factorsEven though this report does not take into accountlocally induced climate change factors, these arevery significant (Grimm et al. 2008). For example,the rate of increase of temperature in HCMC is almostdouble that of the surrounding Mekong Deltaregion. Between 1997 to 2006, the average temperatureof HCMC increased .34° C compared to .16° Cfor the Mekong Delta region. This increase in temperaturefor HCMC has coincided with increasingurbanization in the city. In HCMC, the heat islandeffect is changing the climate and urbanization ishaving a significant effect on increases in temperature,rainfall, and flooding in and around HCMC.Further analysis is needed to better understandthis issue.Lessons on Methodologyfor Follow-up StudiesEven though analysis similar to that undertakenin this report has been carried out for cities in developedcountries (Rosenzweig et al. 2007), it hasso far not been done in developing country cities.Moreover, preparation of this report has spurredsimilar studies in other cities in the Africa andMiddle East and North Africa regions. It is importanttherefore to conclude with a few lessons forfollow-up studies.Approaches to downscalingIn this study two different approaches to downscalingwere used, namely statistical scaling usedby JICA and use of a dynamic regional model asdone by the HCMC study. Each method has itsstrengths and limitations. Dynamic regional modelscan simulate daily information on a broad range of78 | Climate Risks and Adaptation in Asian Coastal Megacities: A Synthesis Report
hydrometeorological data, yielding information onfloods and droughts and on the joint occurrence ofvariables, like the pattern of precipitation over alarge watershed. Dynamic models that are nestedin AOGCMs are necessarily bound to the parentmodel’s intrinsic biases. There is, for example, awide variation in the results of the AOGCMs inforecasting extreme precipitation, and use of onemodel alone can yield unreliable results. Statisticalmodels yield single parameters and shed little lighton the joint probability of occurrence. Nevertheless,because the results are based on a correlationwith the results of many models, the downscaledparameters have less intrinsic bias than those generatedby a single model. These constraints need to beconsidered in undertaking similar city-level studies.Need to forge stronger links betweenmethodologies developed by disaster riskreduction community and climate changeadaptationThere is a strong global consensus on the increasinglyurgent need to address the underlying causes of climatechange and its impacts through mitigation ofgreenhouse gas emissions and development of effectiveadaptation strategies. This has been underscoredat the recent United Nations Framework Conventionon Climate Change (UNFCCC) Conferences of Parties(COP) in Copenhagen (COP-15), which againhighlighted the need to foster better linkages betweenclimate change adaptation (CCA) and disaster riskreduction (DRR). The Hyogo Framework of Action,signed by 168 countries in 2005, is the guiding documentfor the DRR initiatives to mainstream DRR intothe national, sectoral, and local-level developmentplanning process. The DRR community has wellestablishedprocedures and terms of reference for riskassessment, including probabilistic risk assessment,that allow assessment of risks based on an analysisof hazards, exposure, vulnerability, and capacity(ECLAC 2003). The use of simulation models to developevent-loss relationships are likewise commonlyapplied in the DRR work (e.g., hydrometeorological,earthquake, storm surge, tsunami, and landslidemodels). In addition, the DRR community has thelocal networks and knowledge management systemsthat will provide significant benefit for climatechange adaptation studies. These synergies need tobe recognized and strengthened.Lessons with respect to damage costanalysis and prioritizing adaptation optionsThe three studies were based on available data. Thismeant that various assumptions had to be maderegarding the number of households affected, the“damage rate” or extent of damage to various assetsas a result of floods of different intensity, and thecosts associated with these damages. The underlyingdata and valuation would be much improved ifthere was scope for survey-based data collection. Arather important gap in the studies is the analysisof health impacts. Floods do have serious healthconsequences and while the studies have attemptedto estimate these, the full importance of these impactshas not been captured. To carefully examinethe health impacts of floods would require first anestimation of disease prevalence in the future (takinginto account climate and economic conditions)and second, application of robust dose-responserelationships to establish the extent of flood-relatedillnesses. This is an impact issue that requires morecareful consideration. In terms of adaptation toclimate change, the Bangkok and Manila studiesare unable to incorporate “soft options” such aschanges in legal and institutional issues into theircost-benefit analyses. Thus, it is possible that thereare less costly policy changes that might bringabout the same type of results as the engineeringsolutions identified. However, identifying the fullimplications of different policy reforms and thenincorporating these into a cost-benefit frameworkis difficult. Future studies would do well to lookat behavioral change options, zoning possibilities,legal and institutional reforms, and conservationpossibilities carefully and rank them relative toengineering solutions.Need for detailed institutional analysis infuture studiesIn undertaking similar studies in the future, a moredetailed analysis of institutional and organizationalcapacity for urban adaptation is suggested. Whileall three city studies considered in this report doConclusions and Policy Implications | 79
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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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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
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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 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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Climate risks and adaptation in Asian coastal megacities: A synthesis

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