Climate risks and adaptation in Asian coastal megacities: A synthesis

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activities that are being considered in the Royal IrrigationDepartment master plan are infrastructureactivities (such as construction and improvement ofcanals, dikes, pumping stations, etc.). Flooding ofagricultural lands upstream of Bangkok is utilizedduring major floods to help attenuate the flood peak,lowering the flood profile in Bangkok.Current and planned land use and urbanplanning in Bangkok—Bangkok in the futureThe Bangkok study projected what the city wouldlook like in the future based on a wide range ofavailable data about population and growth and anumber of sectoral and urban development plans(Box 3.1). Modern urban land use planning inBangkok started in the 1950s. Bangkok’s inner citycontains the Grand Palace, government offices, majoruniversities and educational establishments, and2-to-4-story row houses that are used as commercialand residential units. The inner city is a nationalhistoric conservation area where construction ofhigh-rise buildings is prohibited. Urban growth inBangkok, however, has progressed in a sometimesad hoc manner and without a unified plan linkingit to the surrounding areas. To remedy this problem,the government has developed a 50-year regionalspatial plan (finished in 2007) that foresees growthof the surrounding areas. This plan also providesfor significant environmental protection and wetlandareas.Climate change parameters—statisticaldownscalingFor the 2050 simulations, the Bangkok City casestudy applied the statistical downscaling factorsestimated by the University of Tokyo’s IntegratedResearch System for Sustainability Science (IRS3)discussed in chapter 2. Given the size of the ChaoPhraya watershed and the long time it takes upperwatershed rainfall to reach Bangkok as stream flow,the team applied the mean increase in seasonalprecipitation (3 percent and 2 percent for A1FI andB1 respectively) to the three-month rainfall eventsfor the corresponding 1-in-10, 1-in-30 and 1-in-100-year precipitation events for the watershed. Thesetotal precipitation levels were distributed over thewatershed using spatial and temporal patterns fromhistoric flood years. The forecasted temperatureincreases of 1.9 ° C and 1.2 ° C for the A1FI and B1scenarios respectively for 2050 were used in the hydrologicalmodeling. The SLR estimates used were0.29 m and 0.19 m for the A1FI and B1 scenariosrespectively. This was based on IPCC AR4 (WorkingGroup 1, Chapter 10, Table 10.7) estimates. It wasdecided to use half of the 2099 increase for the 2050estimates; namely, 0.29 m and 0.19 m for the A1FIand B1 scenarios respectively.Box 3.1 ■ The Bangkok MetropolitanRegion (BMR): SomeAssumptions about theFutureBangkok is changing rapidly and some of these changes havebeen taken into account in modeling the future. Bangkok isincreasingly “suburbanizing.” Between 1998 and 2003, BMR sawa 74 percent increase in urban development. The city’s housingstock has doubled in the last decade. This trend is expected tocontinue. The Government’s Land Use Plan for 2057 is used toproject the number of commercial, residential, and industrialbuildings in Bangkok in 2050. Available government plans aretaken into account in establishing future road and transportationnetworks. Plans suggest tightened urban areas within a networkof expressways bounded by large environmental protection areasto divert any floods from the centers.Based on existing trends, the city of Bangkok is not expectedto grow a lot, while neighboring suburbs will continue to grow.For instance, suburban Nonthaburi increased its population by47 percent during 2002–07. Bangkok City is expected to have apopulation of 10.55 million (4.65 million households) and BMR apopulation of nearly 16 million by 2050. To forecast the populationin 2050 for BMR, information on population projections for Thailand2003–30 prepared by the government (NESDB) was used as a base.The NESDB report projects population to the year 2030 for the wholekingdom and to 2025 and 2020 for Bangkok and other provincesrespectively. In projecting the population to 2050, a regressionfunction was applied.In terms of the BMR economy, regional GDP is projected for twoareas (Bangkok and Samut Prakarn) of BMR most likely to be affectedby flooding. GDP for Bangkok and Samut Prakarn in 2050 is expectedto be six-fold higher than the current GDP. In terms of poverty inthe cities, in Bangkok in 2007 only 88,361 people (0.6 percent ofthe total) in the BMR were officially considered poor. However, thisnumber excludes some 768,220 people living in 133,317 condensedhousing units. In the flood impact assessment, the higher, moreaccurate number was used.Source: Adapted from Panya Consultants (2009).26 | Climate Risks and Adaptation in Asian Coastal Megacities: A Synthesis Report
Estimation of storm surge in the case ofBangkokFor storm surge, the team examined historic stormsurges in the Gulf of Thailand. There have beenthree events since 1962 along the coast of southernThailand. No recorded typhoon or cyclone has had atrack that approached the mouth of the Chao Phrayaat the north of the Gulf of Thailand. Nevertheless,one typhoon created wind patterns that drove 2 to 3meter waves near the mouth and drove up sea levels.As a result, the team used a storm surge of 0.61 m forthe study. It needs to be noted that the time frame forthe storm surge would be on the order of 24 hours,and only one event has been recorded in 30 years.The hydrometeorological processes driving theseevents have little or no correlation. To have a jointimpact, the storm surge effect would have to occurnear the peak storm discharge for the Chao Phrayawatershed. The joint probability of occurrence, althoughnot calculated in detail, is less than 1/1000.Table 3.3 summarizes the climate change parametersused to model the 2050 impacts in Bangkok.Land subsidence – a significant contributorto future floodingAlthough land subsidence is not driven by climatechange, its impact on flooding in Bangkok needs tobe considered for the 2050 simulations. The teamundertook a comprehensive assessment of historicand forecasted land subsidence for Bangkok, andheld technical consultations with the concernedagencies. Historic land subsidence in Bangkok hasreduced from highs of 10 cm/year to 1 to 2 cm/yearover the period of 1978 to 2007, and from 2002 to2007 the rate had declined to 0.97 cm/year. The teampredicted that due to government efforts to controlgroundwater pumping, the average subsidence ratewould continue to decline by 10 percent/year, assumingthat current efforts to reduce groundwaterextraction continue. As a consequence, the team’sestimate of land subsidence by 2050 varied from 5 to30 cm depending on the location. Figure 3.2 showsland elevations in 2002 versus projected land elevationsin 2050 as a consequence of land subsidence.Simulation events modeledThe study ran simulations for 1-in-10, 1-in-30, and1-in-100-year flood events for 2008 as the baselinefor the inundation hazard. The study then ran simulationsapplying only the land subsidence expectedby 2050 without applying the climate change factorsfor precipitation or SLR. This was done to allow differentiationof the contribution of land subsidenceto the flood hazards and risks. Then simulation runswere made for 1-in-10, 1-in-30, and 1-in-100-yearflood events in 2050, applying either the A1FI or B1forecasted variables (precipitation and SLR). Finally,simulation runs were made for the impact of stormsurge on the 1-in-30-year A1FI and 1-in-100 A1FIand B1 simulations.Infrastructure scenarios were assumed as follows.For the 2008 base year calculations, it wasassumed that the existing and nearly completedflood protection infrastructure was in place. For thefuture 2050 calculations, it was assumed that theplanned flood protection infrastructure will havebeen implemented (Panya Consultants 2009).Conservative values were used in forecastsThe use of the mean increase in seasonal precipitationfor the Chao Phraya watershed is appropriate, as itmatches the time to concentration for the floodingin Bangkok. Mean seasonal increases were appliedto the 1-in-10-year, 1-in-30-year, and 1-in-100-yearprecipitation events and distributed across the watershedspatially and temporally using historical rainfallTable 3.3 ■ Climate Change and Land Subsidence Parameter Summary for BangkokIPCC ScenarioTemperature increase( o C)Mean SeasonalPrecipitation Increase (%) Sea Level Rise (m) Storm Surge (m) Land subsidence (m)B1 1.2 2 0.19 0.61 0.05 to 0.3A1FI 1.9 3 0.29 0.61 0.05 to 0.3Estimating Flood Impacts and Vulnerabilities in Coastal Cities | 27
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: Table 3.2 ■ Bangkok Monthly Avera
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 and 96: 5Conclusions andPolicy Implications
Page 97 and 98:
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
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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