Climate risks and adaptation in Asian coastal megacities: A synthesis

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2.1.2 Land Subsidence 2.1.2 Land SubsidenceFrom observed data, From the observed average land data, subsidence the average rate land in subsidence the Bangkok rate Metropolitan in the Bangkok Region Metropolitan (BMR) Region (BMR)has gradually reduced has gradually from 10 cm reduced per year from to 101-2 cm cm per per year year to from 1-2 cm 1978 per to year 2007. from Furthermore, 1978 to 2007. Furthermore,during the last 5 years during (2002-2007), the last 5 years the average (2002-2007), land subsidence the average rate land has subsidence reduced to rate 0.97 has cm reduced per to 0.97 cm peryear. Therefore, it year. is expected Therefore, that it the is expected land subsidence that the rate land would subsidence reduce rate by 10% would per reduce year. by Thus, 10% per year. Thus,the accumulated land the accumulated subsidence during land subsidence 2002-2050 during (48 years) 2002-2050 would (48 spatially years) vary would from spatially 5 to 30 vary from 5 to 30cm depending on location cm depending as shown on location in Figure as 2.1-3. shown in Figure 2.1-3.Figure 3.2 ■ Land Elevations, 2002 versus 2050 Land Subsidence640000660000640000680000660000700000680000640000700000660000640000680000660000700000680000700000!(Pathum Thani!(Pathum Thani!(Pathum Thani!(Pathum Thani!(Nonthaburi!(Bangkok!(Samut Prakan14800001480000150000015000001520000152000015400001540000!(Nonthaburi!(Bangkok!(Samut Prakan14800001480000150000015000001520000152000015400001540000!(Nonthaburi!(Bangkok!(Samut Prakan14800001480000150000015000001520000152000015400001540000!(Nonthaburi!(Bangkok!(Samut Prakan14800001480000150000015000001520000152000015400001540000640000660000640000680000660000700000680000640000700000660000640000680000660000700000680000700000Legend!( ProvinceProvince BoundaryRiver/Canal Network-1 - 00 - 11 - 2Legend8 - 10 !( Province10 - 15 Province Boundary15 - 20 River/Canal Network-1 - 00 - 11 - 28 - 10Ê10 - 150 1.5 3 6 9 1215 - 20Legend!( ProvinceProvince BoundaryÊ-1 - 00 - 1River/Canal 0 1.5 Network 3 6 9 121 - 2Legend8 - 10 !( Province10 - 15 Province Boundary15 - 20 River/Canal Network-1 - 00 - 11 - 2Ê8 - 1010 - 150 1.5 3 6 9 1215 - 20Ê0 1.5 3 6 9 12Elevation (m.MSL)-7 - -5-5 - -3-3 - -12 - 33 - 44 - 55 - 820 Elevation - 25 (m.MSL)25 - 35-7 - -5-5 - -3-3 - -12 - 320 - 25Kilometers3 - 425 - 35Land Elevation in 20024 - 5(Surveyed 5 - 8 benchmark)Elevation (m.MSL) Kilometers-7 - -5Land Elevation in 2002-5 - -3(Surveyed benchmark)-3 - -12 - 33 - 44 - 55 - 820 Elevation - 25 (m.MSL)25 - 35-7 - -52 - 320 - 25 KilometersKilometers3 - 425 - 35Land Elevation in 2050 Land Elevation in 2050-5 - -34 - 5(Forecasted -3 - -1 land 5 - 8 subsidence) (Forecasted land subsidence)Source: Panya Consultants (2009).Source: Royal Thai Survey Source: Department Royal Thai (RTSD) Survey and Department Panya Consultants’ (RTSD) and forecast Panya Consultants’ forecastdistribution patterns (1995). There is an implicitassumption that the underlying variability (timingand location) will remain the same in 2050. This isconservative in the sense that increased variability(worse floods and droughts) around the mean wouldgenerate greater losses than estimated in the study.Main Findings fromHydrological Analysis andGIS Mapping for BangkokFlood-prone area likely to increase inBangkok in the futureFigure 2.1-3 Land Figure Elevation 2.1-3 in Land 2002 Elevation and 2050 in due 2002 to Land 2050 Subsidence due to Land Subsidence2.2 CLIMATE 2.2 CLIMATE2.2.1 General 2.2.1 General2-2remain under water for over a month. The increaseis likely to be in the western areas, where existingflood protection infrastructure is likely to be insufficient.There is also an increase in the maximumwater depth between the base year and 2050 forevents of different return periods. Figure 3.3 forexample, shows a comparison of the maximumdepths of flooding for the 1-in-30-year flood under2008 and the 2050 A1FI scenario. The implication isthat the people living in Bangkok will be facing morefrequent events that significantly disrupt daily life.2-2A flood frequency graph obtained by plottingthe inundated area versus return frequency for theBangkok City case study results for the 2008 and 2050The climate of the The Chao climate Phraya of River the Chao Basin Phraya belongs River to the Basin tropical belongs monsoon. to the tropical The average monsoon. annual The average annualrainfall over the basin rainfall is 1,130 over the mm, basin varying is 1,130 from mm, 1,000 varying to 1,600 from mm 1,000 and to registering 1,600 mm higher and registering in the higher in thenortheastern region northeastern of basin. region According of the to basin. the rainfall According pattern, to the about rainfall 85% pattern, of the average about 85% annual of the average annualrainfall occurs between rainfall May occurs and between October. May Tropical and October. cyclones Tropical occur between cyclones September occur between and September andOctober and may October strike the and basin. may In strike this the case, basin. rainfall In this continues case, rainfall for a long continues period for of time a long in period a of time in arelatively wide area. relatively The peak wide river area. discharge The peak is river registered discharge in October, is registered the end in of October, the rainy the season, end of the rainy season,and severe flood and damage severe may flood arise damage with high may tide arise in with this period. high tide The in mean this period. temperature The mean ranges temperature rangesfrom 26 o C to 31 o C. from Its 26 maximum o C to 31 o temperature C. Its maximum is in temperature April and its is minimum April and is in its December. minimum The is in December. Theevaporation (Class-A evaporation Pan) in (Class-A the basin Pan) is normally in the basin at its is highest normally in April at its and highest lowest in April in October and lowest in Octoberwith an average annual with an value average of about annual 1,700 value mm. of about 1,700 mm.The hydrological analysis shows that for events ofdifferent return periods, the area inundated willincrease in 2050 for both the B1 and the A1FI scenarios(Table 3.4).For instance, the current (2008) estimated annualinundated area in Bangkok and Samut Prakarn isabout 550 km 2 , which will increase to 734 km 2 in 2050under the A1FI scenario for a 1-in-30-year flood. Thatis an increase of 184 kms, or approximately a 30 percentincrease in the area inundated. The inundationcould be for varying depths and varying number ofdays, but about 7 percent of these provinces couldTable 3.4 ■ Bangkok Inundated Areaunder Current Conditionsand Future ScenariosFrequency2008(km 2 )Scenario2050 B1(km 2 )2050 A1FI(km 2 )1/100-year 737 893 9271-in-30-year 550 719 7341-in-10-year 359 481 518Source: Panya Consultants (2009), Appendix k, Table K2.4-1.28 | Climate Risks and Adaptation in Asian Coastal Megacities: A Synthesis Report
Climate Change Impact and Adaptation Study for Bangkok Metropolitan RegionFinal ReportChapter 3: Model Development and SimulationFigure 3.3 ■ Maximum Water Depth for 1-in-30-year event, 2008 and 2050, A1FI62000064000066000068000070000062000064000066000068000070000015600001560000156000015600001580000158000015800001580000!(Pathum Thani!(Pathum Thani15400001520000!(Nakhon Pathom!(Nonthaburi!(Bangkok1540000152000015400001520000!(Nakhon Pathom!(Nonthaburi!(Bangkok154000015200001500000!(Samut Sakhon!(Samut Prakan15000001500000!(Samut Sakhon!(Samut Prakan15000001480000Legend620000!( ProvinceProvince BoundaryRiver/Canal NetworkDikeElevation (m.MSL)-7 - -5-5 - -3Source: Panya Consultants’ calculationSource: Panya Consultants (2009).640000-3 - -1-1 - 00 - 11 - 22 - 33 - 46600005 - 88 - 1010 - 1515 - 2020 - 25> 254 - 5 Max. Water Depth (cm)6800000 - 1010 - 5050 - 100100 - 200200 - 300300 - 400> 400700000Ê0 2 4 8 12 16KilometersMax. Water DepthC2008-T301480000Figure 3.2-2 illustrates the maximum water surface profile along the Chao Phraya River from theA1FI river further mouth demonstrates to Bang Sai how district, the flood Ayutthaya hazard will at 10, 30 Figure and 100-year 3.4 flood ■ Bangkok return periods. Flood Comparing Hazardincrease Case dramatically C2008-T100 in and Bangkok. C2050-LS-T100, As the graph it reveals in that the maximum Relationshipwater level will be reducedFigure due 3.4 to below land illustrates, subsidence a of flood about event 0.20 in m, 2008 considering the sea level at the river mouth is not1,000with increased. an inundated Comparing area of 625 Case kmC2050-LS-T100 2 has a frequency and C2050-LS-SR-A1FI-T100,900the maximum waterof 0.02 level or will return be period increased of due 1-in-50 to the years. increasing By 2050 of flood water 800 from the upper basin ~39% and increase the sea level700Increased625underrise.theComparingA1FI scenario,CasefloodC2050-LS-SR-A1FI-T100events inundatingand C2050-LS-SR-SS-A1FI-T100, the maximum600water level will be increased at the river mouth due to storm surge,frequencybut the effect willareas of 625 km 2 would be expected to occur with an500Increased appear up toabout 50 km from the river mouth.400450 Intensityincreased frequency of 1-in-15 years. The corollary of300this is that the intensity of flooding for a 1-in-15-year200event would increase from about 450 km 2 to 625 km 2 .1001/50–year1/15–year00.00 0.02 0.04 0.06 0.08 0.10 0.121480000LegendInundated area (km 2 )620000!( ProvinceProvince BoundaryRiver/Canal NetworkDikeElevation (m.MSL)-7 - -5-5 - -3640000-3 - -1-1 - 00 - 11 - 22 - 33 - 45 - 86600008 - 1010 - 1515 - 2020 - 25> 254 - 5 Max.Water Depth (cm)6800000 - 1010 - 5050 - 100100 - 200200 - 300300 - 400> 400700000Ê0 2 4 8 12 16KilometersMax. Water DepthC2050-LS-SR-A1FI-T30Figure 3.2-1 Maximum Water Depth of Case C2008-T30 and C2050-LS-SR-A1FI-T301480000Population exposed to flooding will increasefor 1-in-30-year flood for both A1FI and B1scenariosSource: Panya Consultants (2009).Flood frequency2008 2050 A1FISevere floods inundate the lower Chao Phrayafloodplain in which Bangkok is situated. The hugevolume of water (over 31,000 million cubic metersfor a 1-in-30-year event) associated with thesefloods can take months to drain as Bangkok acts asa “bottleneck” to the discharge reaching the Gulfof Thailand. This can leave many areas flooded formore than 30 days. The flood protection schemes forBangkok are generally designed to protect againstEstimating Flood Impacts and Vulnerabilities in Coastal Cities | 29
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: Estimation of storm surge in the ca
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
Page 99 and 100:
hydrometeorological data, yielding
Page 101 and 102:
BibliographyAllen, M. R., and W. J.
Page 103:
Reduction: Inventory and Prospect.
Page 106 and 107:
a paper commissioned by JICA (Sugiy
Page 108 and 109:
mercial and industrial establishmen
Page 110 and 111:
ADB. The selection and prioritizati
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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