Climate risks and adaptation in Asian coastal megacities: A synthesis

More documents

Recommendations

Info

Table 3.12 ■ Climate Change Parameter Summary for HCMCIPCC ScenarioTemperatureincrease (oC)Precipitation 24-hreventPrecipitation 3–5days Sea Level Rise (m) Storm Surge (m)Land subsidence(m)B2 +1.4 –25% Insignificant change 0.24 1.08 (from 0.53 2008) Not consideredA2 +1.4 +20% +20% 0.26 1.08 (from 0.53 2008) Not consideredfor the A2 and B2 scenarios, respectively. The studyalso notes that the city’s low topography creates asituation where a tipping point 42 of around 50 cmswould considerably increase the impact of SLR, withsignificant areas potentially becoming permanentlyflooded. For storm surge, the study assessed thatthe historic storm surge lasts about 24 hours andreached about 0.5 m. For storm surge from intensifiedtyphoons in 2050, the study examined adjustedhistoric tracks that would increase the storm surgeand estimated future storm surges associated withextreme events at 1.08 m, which would be associatedwith a track making landfall at HCMC.Flood simulations limited to regular andextreme 1-in-30-year flood events for currentand the 2050 A2 high emission scenarioIn assessing the impact of extreme flooding inHCMC, the study focused mainly on the 1-in-30-yearextreme event for 2008 and the 2050 scenario. Also,the study focused mainly on the A2 scenario becausethe team found that the extreme precipitation eventsunder the B2 scenario were not significantly differentthan 2008 events. A summary of the simulationsconducted is provided in Annex B. A significantadvantage of the dynamic downscaling techniqueis that it gives temporal and spatial information onprecipitation patterns on a daily basis, which allowsassessment of not only floods, but also droughtevents. While this was not defined as a focus of thestudy for the four cities, it is important in the contextof HCMC. Drought scenarios also were modeled.Main Findings fromHydrological Analysis andGIS Mapping for HCMCFlood hazard increases, for both regularand extreme events and number of personsexposed to flooding rises dramaticallyLarge areas of HCMC (1,083 km 2 ) 43 flood annually;extreme floods (1-in-30-year) inundate 1,335 km 2 .Similarly, much of HCMC’s population alreadyexperiences regular flooding with about 48 percentof the communities affected annually. Table3.13 shows a comparison of regular (annual) andextreme (1-in-30-year) flooding under the currentand the 2050 A2 scenario for inundated areas andcommunities affected. The analysis shows that thearea inundated increases for regular events from 54percent to 61 percent in 2050, and for extreme events42A point at which the changes or impacts rapidly increase,possibly irreversibly.431 km 2 = 100 ha.Table 3.13 ■ Summary of Flooding at Present and in 2050 with Climate ChangeNumber of communes affected(from a total of 322)Present 2050Regular flood Extreme flood Regular flood Extreme flood154 235 177 265Area of HCMC flooded (ha) 108,309 135,526 123,152 141,885% of HCMC area affected 54 68 61 71Source: ADB (2010).44 | Climate Risks and Adaptation in Asian Coastal Megacities: A Synthesis Report
from 68 percent to 71 percent; that is, an increaseof 7 percent and 3 percent for regular and extremeevents respectively in 2050. This is also indicatedthrough GIS maps (Figures 3.13a and 3.13b).Figure 3.13a ■ HCMCCity Case Study:Comparison of 1-in-30-year Flood for 2008Significant increase in both flood depth andduration for regular and extreme events in2050A key finding of the hydrological analysis is thatthere is a significant increase in both depth andduration for both regular and extreme floods overcurrent levels in 2050. The average maximum flooddepth in HCMC is about 35 cm and the averagemaximum flood duration is 64 days. As a rule ofthumb, more than 50 cm of flood water is consideredthe threshold for safe operation of vehiclesand bikes. Flood duration of more than three daysat 50 cm depth is considered to cause significantdisruption in the city. Results from the hydrologicalanalysis estimate that there will be a 20 percent and43 percent increase in average maximum depth forregular and extreme events respectively, and a 21percent and 16 percent increase in average maximumflood duration during regular and extremeevents respectively in 2050. That is, the averagemaximum flood duration increases from 64 to 86days for regular events, and from 18–22 days forextreme events. Similar to past events, the depthof extreme floods in 2050 throughout the city willbe higher (72–100 cm) compared to the depth forregular flooding (35–44 cm).Figure 3.13b ■ HCMCCity Case Study:Comparison of 1-in-30-year Flood for 2050 A2ScenarioIncrease in populations at risk from floodingby regular and 1-in-30-year event in 2050Results from the hydrological modeling and GISmapping show that an increasing number andproportion of the population 44 will be affected byflooding from regular and extreme events in 2050(Table 3.13). For regular floods, about 15 percentof HCMC’s population is affected for the baselinescenario (in 2007). This increases to 49 percentwithout implementation of proposed flood controlmeasures. With the implementation of the proposedflood control measures, the percentage of affectedpopulation is reduced to 32 percent (ADB 2010).Climate change will also impact daily life in HCMCSource: ADB (2010).44As mentioned earlier, the official population of HCMCin 2007 was 6.4 million people and about 8 million if unregisteredmigrants are included. The team considered two(high and a low) population growth scenarios, but assumeda high population growth scenario for the vulnerabilityanalysis. The high case includes unregistered migrants intothe baseline; that is, it assumes current population to beabout 8 million. This seems more realistic compared to theassumption in the low-growth scenario, which does not assumeunregistered migrants currently in the city. Further,the existing rate of 2.4 percent population growth assumedin the low-case scenario is low compared to the experienceof other large cities in the region.Estimating Flood Impacts and Vulnerabilities in Coastal Cities | 45
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 and 48: Estimation of storm surge in the ca
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: original swamp land on which the ci
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
show all

Climate risks and adaptation in Asian coastal megacities: A synthesis

Create successful ePaper yourself

Delete template?

Save as template?