Climate risks and adaptation in Asian coastal megacities: A synthesis

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a paper commissioned by JICA (Sugiyama 2008). Asea level rise of 0.27 m by 2050 was also added tothe storm surge for the A1FI and B1 climate changescenarios based on current estimates. All these scenarios(without and with climate change effects)were then modeled to assess the impact in termsof the extent, magnitude, and duration of flooding.Geographic andSocioeconomic ContextsThe geographic area covered in the study is theKolkata Metropolitan Area (KMA), a continuousurban area stretching along the east and west bankof the Hooghly River surrounded by some ruralareas lying as a ring around the conurbation andacting as a protective green belt. KMA has an areaof 1,851 square kilometers and consists of a complexset of administrative entities comprising 3 municipalcorporations (including Kolkata Municipal Corporation,or KMC), 38 other municipalities, 77 nonmunicipalurban towns, 16 out growths, and 445rural areas. KMC, the core of the city, lies along thetidal reaches of the Hooghly and was once mostlya wetland area. The elevation of KMA ranges from1.5 to 11 meters above sea level (masl). The elevationof KMC area ranges from 1.5 to 9 masl with anaverage of 6 masl.With a population of about 14.7 million (including4.6 million in KMC), KMA is one of the 30 largestmegacities in the world (United Nations 2007). Theaverage population density in KMA is 7,950 peopleper km 2 ; in KMC, it is 23,149 per km 2 . The averageper-capita income in KMA in 2001–02 was $341 (at1993–94 prices).The Study AreaA special characteristic of KMA is its large slumpopulation, comprising more than a third of the totalpopulation. These slums not only lack basic infrastructureand services, but are also the hub of manyinformal manufacturing activities, some of which involvehighly toxic industries. Little oversight of suchactivities is carried out by government agencies. Thismixed residential and commercial/industrial landuse in slums make these areas highly vulnerable toextreme weather-related events, especially flooding.MethodologyThe study modeled the impact of climate changeon increased flooding in KMA. The main causes offlooding in KMA are intense precipitation, overtoppingof the Hooghly River due to water inflow fromlocal precipitation as well as that from the catchmentarea, and storm surge effects. Land subsidence—which occurs in a few pockets—was not includedin the study. The study covered three main sourcesthat aggravate flooding in KMA:■■■■■■Natural factors. Natural factors include flattopography and low relief that cause riverineflooding and problems with drainage.Developmental factors. Developmental factors includeunplanned and unregulated urbanization;low capacity drainage; sewerage infrastructurethat has not kept pace with the growth of thecity or demand for services; siltation in availablechannels; obstructions caused by uncontrolledconstruction in the natural flow of storm water;and reclamation of natural drainage areas(marshlands).Climate change factors. Climate change factorsinclude an increase in the intensity of rainfall,sea level rise, and an increase in storm surgecaused by climate change effects.Flooding from intense precipitation was modeledfor three scenarios—30-year, 50-year, and100-year return period flood events—assuming noclimate change effects. The climate change effectswere added to the 100-year flood event using theA1FI and the B1 scenarios.Assumptions about the impacts of climatechange in Kolkata in 2050 (Sugiyama 2008) included(a) a temperature increase of 1.8°C for theA1FI scenario and 1.2°C for the B1 scenario; (b) afractional increase in the precipitation extremes ofabout 16 percent for the A1FI and 11 percent for theB1 scenarios; and (c) sea level rise of 0.27 m by 2050,which was added to the storm surge for the A1FIand B1 climate change scenarios based on current86 | Climate Risks and Adaptation in Asian Coastal Megacities: A Synthesis Report
estimates. All these scenarios (with and withoutclimate change effects) were then modeled to assessthe impact in terms of the extent, magnitude, andduration of flooding.Three separate models were used to capturethe overall effect of natural, developmental, andclimate change factors that lead to flooding in KMA.A hydrological model (SWAT model) was usedto develop the flow series for the whole Hooghlycatchment. The generated data was then fed into ahydraulic model (HECRAS model) to analyze theimplication of the flood passing through the riverstretch. Finally, a storm drainage model (SWMMmodel) was used to determine the flooding that willresult once the river flooding is combined with localprecipitation and drainage capability of the urbanarea under an extreme flood situation.Vulnerability analysisThe models generated the increase in depth, duration,and extent of flooding in Kolkata due to climatechange effects. A separate vulnerability analysiswas done to assess the impact of flooding; this partof the analysis was restricted to only the KMC areabecause of data limitations. The vulnerability analysiswas based on three separate indices: (1) a floodvulnerability index based on the depth and durationof flooding, (2) a land-use vulnerability index basedon the nature of land use, and (3) a social vulnerabilityindex based on the existing infrastructure andthe socioeconomic characteristics of the population.Finally, the three separate indices were combined toform a composite vulnerability index.Vulnerability was assessed at both the ward andsubward levels. To evaluate the impact of flooding inKMC, the analysis identified the 9 most vulnerablewards that may need specific attention in designingadaptation strategies. To assess vulnerabilitywithin each ward in greater detail, the analysis wasextended to the sub-ward level using spatial data.Damage assessmentThe vulnerability analysis was followed by aseparate economic damage assessment. Due todata limitations, this was also restricted to the KMCarea. Damage to stocks measured primarily physicaldamage arising out of water submersion (sectorsincluded residential buildings and property, com-INDIAWEST BENGAL STATEAND THE CITY OF KOLKATAIBRD 37779SEPTEMBER 2010West BengalArea: 88752 sq. km.Population: 80 millionPop. Density: 904/sq. km.Kolkata Metropolitan AreaArea: 1851.41 sq. km.Population: 14.7 millionPop. Density: 7950/sq. km.RiverHooghlyKolkotaI N D I AWestBengalKolkataArabianSeaBay ofBengalKolkata Municipal CorporationArea: 187 sq. km.Population: 4.57 millionPop. Density: 23149/sq. km.HooghlyRiverGarden ReachTiljalaThis map was produced by the Map Design Unitof The World Bank. The boundaries, colors,denominations and any other informationshown on this map do not imply, on the partof The World Bank Group, any judgment onthe legal status of any territory, or anyendorsement or acceptance of such boundaries.INDIAN OCEANVulnerability of Kolkata Metropolitan Area to increased Precipitation in a Changing Climate | 87
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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
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 108 and 109: mercial and industrial establishmen
Page 110 and 111: ADB. The selection and prioritizati
Page 113 and 114: AnnexCAdaptation to IncreasedFloodi
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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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