Climate risks and adaptation in Asian coastal megacities: A synthesis

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Why these three cities? The three developingcountry cities selected for this study are all coastalmegacities with populations (official and unofficial)ranging from 8 to 15 million people. Two are capitalcities and all three are centers of national and regionaleconomic growth contributing substantially to theGDP of the respective countries. However, being lowlyingcoastal cities situated in the deltas of major riversystems in the East Asia region, all three are highlyvulnerable to climate-related risks and rank high inrecent rankings of exposure and vulnerability. HoChi Minh City and Bangkok are among the top 10cities in terms of population likely to be exposed tocoastal flooding due to climate-related risks in 2070,according to the first global assessment of port cities(Nicholls et al. 2008). Further, Manila has been identifiedas particularly vulnerable to typhoon damage,and HCMC ranks fifth by population exposed tothe effects of climate change (Nicholls et al. 2008). Arecent study also identifies Manila, Ho Chi Minh City,and Bangkok among the top eleven Asian megacitiesthat are most vulnerable to climate change (Yusufand Francisco 2009). 2 Devastating floods in Manilain 2009 only confirm the vulnerability of this city toextreme weather events. For instance, flooding inManila from tropical storm Ketsana in Septemberwas the heaviest in almost 40 years, with flood watersreaching nearly 7 meters. More than 80 percent ofthe city was underwater, causing immense damageto housing and infrastructure and displacing around280,000–300,000 people. 3 All of this highlights theneed to better understand and prepare for such climaterisks and incorporate appropriate adaptationmeasures into urban planning.While there is a growing literature on cities andclimate change, as yet there is limited research onsystematically assessing climate-related risks at thecity level. This report aims to fill this gap. Further,it aims to provide evidence-based information tosupport urban policy and planning as these issuesare debated at the local, national, and global levels.ObjectiveThe main objective of this report is to strengthenour understanding of climate-related risks and impactsin coastal megacities in developing countriesusing case studies of three cities that are differentin their climate, hydrological, and socioeconomiccharacteristics. Specifically, it draws on an in-depthanalysis of climate risks and impacts in Bangkok,Manila, and Ho Chi Minh City to highlight to nationaland municipal decision makers (a) the scaleof climate-related impacts and vulnerabilities atthe city level, (b) estimates of associated damagecosts, and (c) potential adaptation options. Whilethe report focuses on three cities in East Asia, thepolicy implications resulting from the comparativeanalysis of these cities has broader relevance forassessing climate risks and identifying adaptationoptions in other coastal areas.Approach and MethodologyThe approach to assessing climate risks and impactsconsists of the following sequential steps: (1)determining climate variables at the level of thecity/watershed through downscaling techniques;(2) estimating impacts and vulnerability throughhydrometeorological modeling, scenario analysis,and GIS mapping; and (3) preparing a damage/loss assessment and identification/prioritizationof adaptation options.As a first step, each of the city-level studiesconsidered two IPCC scenarios, a high- and a lowemissionsscenario, 4 and estimated climate risksto 2050. The 2050 time horizon for the study is appropriategiven city-level planning horizons andthe typical time frame for major flood protectionmeasures. The downscaling analysis allowed estimationof changes in temperature and precipitationin 2050. These parameters were used as inputs to thehydrological modeling. In addition to this, assumptionsand estimates were also made about changesin sea level rise and storm surge in 2050 based onpast historical data and available estimates.2Vulnerability in the scorecard was understood interms of exposure, sensitivity, and adaptive capacity ofthe cities. See also http://www.idrc.ca/uploads/user-S/12324196651Mapping_Report.pdf.3http://edition.cnn.com/2009/WORLD/asiapcf/09/27/philippines.floods/index.html.4Different scenarios were considered to assess impact dueto the uncertainties in projecting future climate conditions.xii | Climate Risks and Adaptation in Asian Coastal Megacities: A Synthesis Report
For each city, complex hydrometeorologicalmodels were then developed using a whole hostof local information. These included (a) climatevariables such as changes in temperature, precipitation,sea level rise, and storm surge; (b) socioeconomicand developmental factors such as landsubsidence, land use, and population increases;and (c) local topographical and hydrologicalinformation. Flooding in the metropolitan areaswas chosen as the key variable to assess impact.The hydrological analysis allowed determinationof the area, depth, and duration of flooding underdifferent scenarios. This information was used toidentify the scale of risks and vulnerability of sectors,local populations, and districts (representedin GIS maps), as well as estimate damage costs.Two of the three studies undertook cost-benefitanalysis to prioritize adaptation options, whilethe third approached the issue of adaptation morequalitatively. To understand the impact of climatechange in 2050 in each city, an important assumptionmade by all teams was that without climatechange, the climate in 2050 would be similar to the2008/ base-year climate. Various climate scenariosare overlaid on this assumption.Process of PreparationThe analysis was carried out over a period of oneand-a-halfyears. The synthesis team and the citylevelteams met periodically and worked closely todevelop common terms of reference to guide thecity-level studies, as well as share methodologicalissues and ongoing findings. These discussions andthe analysis undertaken for each city have formedthe basis of this report. Further, each city-levelteam worked with their respective country/urbancounterparts to build ownership and capacity forthe analysis. For instance, the main counterparts inHCMC were the HCMC People’s Committee andthe Department of Natural Resources and Environment(DoNRE). The study sought to inform thepreparation of HCMC’s citywide adaptation plan.In Bangkok, the main counterpart was the BangkokMunicipal Authority. In Metro Manila, the maincounterpart was Metro Manila Development Authority(MMDA). At the global level, a preliminaryversion of the study has been presented at severalinternational forums.Uncertainties, Limitations,and Interpreting theFindings of this StudyAny study forecasting conditions four decadeshence will be faced with large uncertainties andthese need to be borne in mind in interpreting theresults of this study. One uncertainty concernsthe pathway of GHG emissions. To address thatissue, the city case studies examined both a highand a low GHG emissions scenario to bracket thelikely future conditions. In the climate changedownscaling methodologies, there are uncertaintiesin forecasting the increase in extreme andseasonal precipitation under the different scenarios.The techniques applied in the statisticaldownscaling examined the results from sixteenatmosphere-ocean general circulation models(AOGCM). Robust relationships were identifiedfor temperature (with a ~ 10 percent internalerror) and precipitable water increases (with a ~10–20 percent error) (Sugiyama 2008). Hydrologicmodels can simulate flood events with relativelysmall errors (
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: Executive SummaryIntroduction and R
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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
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Page 49 and 50: Climate Change Impact and Adaptatio
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Page 55 and 56: Table 3.6 ■ Manila Climate Change
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Page 61 and 62: Box 3.3 ■ HCMC in 2050Future land
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from 68 percent to 71 percent; that
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Table 3.15 ■ Districts Affected b
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Table 3.16 ■ Effects of Flooding
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4Assessing Damage Costsand Prioriti
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Table 4.2 ■ Summary of Flood and
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uilt outside the cities and are not
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■■■■■■For the eastern p
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Table 4.6 ■ Flood Damage Costs Wi
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Table 4.8 ■ Flood Damage Costs in
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Figure 4.5 ■ Loss Exceedance Curv
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Box 4.3 ■ Increased Time Costs an
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Table 4.11 ■ Adaptation Investmen
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Marikina River areas through a dam,
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Table 4.14 ■ Present Value of the
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of reducing vulnerability of the po
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5Conclusions andPolicy Implications
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open land use is expected to be flo
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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
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mercial and industrial establishmen
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ADB. The selection and prioritizati
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AnnexCAdaptation to IncreasedFloodi
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of people and institutions to manag
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THE WORLD BANK1818 H Street, NWWash
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