hidden vulnerability of mega cities · 2018. 12. 10. · land subsidence in asia location, country...

Hidden Vulnerability of Mega cities

Srikantha HerathEnvironment and Sustainable Development

United Nations University

[email protected]@hq.unu.edu

United Nations UniversityUnited Nations University

ContentSafety from floodsCities and Natural Disasters

Inherent risks due to geology and geographyIncreased vulnerability

Increased Resource consumption: ground water Urbanization and increasing risk

Changes to hydrological cycle Increase FloodsUrban infrastructure

Some features from reconnaissance surveysVenezuela, Sri Lanka, Viet Nam, Tokyo

Catastrophic Floods The hidden vulnerability : UNU Programme



Cities and Floods

Cities have traditionally evolved along rivers because of stable water supplyIrrigation in alluvial planes, amenity have made rivers close to peoples daily livesThis increased productivity also has associated risks



Source: UN DHA, 1997/07

Flood Damage 1987-96 in Million DollarsTotal Damage - 250658

0.14%

35.33%

54.06%

9.84%0.63%Africa 1576

Americas 24656

Asia 135509

Europe 88568

Oceania 349

Deaths from Floods 1987 - 96 by ContinentTotal Number of Deaths 245355

0.17%1.58%

92.77%

2.95%2.53%

Africa 6200Americas 7249Asia 227612Europe 3878Oceania 416

Number of Floods 1987-96Number of Floods 982

6%10%

44%

27%

13%Africa 124 Americas 270Asia 432Europe 100Oceania 56

Floods 1987-1996

• Casualties in Asia is highest among the world



Populated Areas and Past floods

Tectonic zones

Flood events reported from 1990-2000



Urbanization and flood risk

The risks increase with urbanization1. Increasing demand and over utilization of

resources (ex. Ground water extraction)2. Urbanization affect hydrology – increasing

flood potential3. Rapid development – risks are unknown for

rare events

Area below normal low tide

Area below normal high tide

Area below abnormal high tide

Increased flood vulnerability due to land subsidence in Tokyo

Present embankment to protect subsided areas

Ground water is easily over exploited to meet growing industrial demands

Land subsidence in AsiaLocation, country

Area, km2 Depth range of compaction, m

Time of occurrence

Maximum subsidence, m

Osaka, Japan

120 (1960) 10-500 1948-1965 3-4 (1965)

Tokyo, Japan

230 (1974) 10-500 1938-1975 4.6 (1975)

Taipei Basin, Taiwan

100 30-200 1961-1975 1.8

Bangkok, Thailand

285 (1980) 10-200 1950-1980 0.80 (1980)

Source: Das Gupta, Ashim (1997) Groundwater and the Environment, in Water Resources



Insufficient Drainage

HANOI, Viet NamBeijing, China, July 10

Rapidly urbanizing cities experience urban floodsUrbanization outpaces drainage infrastructureHolistic approach is required in solving the problem

Urbanization and flood disasters

It is well established that urbanization increase bothflood magnitude and flood frequencyIn addition to infrastructure: taking care of water at the location through infiltration and detention are recognized to be effective in reducing urban floods.

These measures need to be incorporated in City Planning and disseminated Slow down:

Reduce:

+

The recent underground urban expansion creates new flood risks. Fukuoka flood: June 29th, 1999.

Experience of high intensity rainfall

more than 100mm/hr

75-100 mm/hr

Year

(River information center)

NumberTokyo has experienced frequent UG floods – 17 events only in 3 years.

Maximum hourly rainfall varies from 44mm/hr to 131m/hr . (average 60mm/hr)



Urban Expansion and increasing risks

Risk = F (Hazard, Vulnerability) Urbanization increases both the hazard and vulnerabilityExtremely rapid urbanization processes have made it difficult to ‘experience’ the consequences of catastrophic eventsVaries according to concentration of people at different times and facilities

Utility: Transport facilities, Public hallsThe day of the week and time of the day

Dynamic Assessment is necessary

Salient features:•Grid size: 20m•With DEM and DSM•Period: June 29, 1999:01.00 –24:00 hrs.•Rainfall data: 10 min. interval•Number of entrances for water to go in – 25

Safety ofUnderground

space

1999Maximum hourly rainfall is 77 mm/hr, total rainfall is 164mm. Subway was suspended for about 3.5 hours. :Water into subway is estimated about 2,000m3

2003Heavy rain in upstream of Fukuoka.104mm/hr at Dazaifu, less than 20mm/hr in FukuokaSubway stopped at 19th, resumed completely at 20th.:Water into subway is estimated about 10,000m3



The Hidden Vulnerability

Urbanization increases vulnerability to floods.The rapid pace of urbanization makes it difficult to adjust for extremes.Major urban expansions give rise to whole new satellite cities. They grow very rapidly and can be devastated by a severe rainfall event.

The greatest danger is if an extreme event strike an Urban Center



Venezuela floods and debris flow 1999 December30,000 persons lost lives.Over 480,000 people were affected.Us$ 2 million65,000 houses were damaged and over 24,000 houses were destroyed.

DS/DS/DicDic. 99. 99



Development in vulnerable areas

Nepal - 1993

Venezuela - 1999

Therefore it is important to focus on Catastrophic Flood impacts where rare and extreme floods cause huge economic and human losses.This would happen when the floods exceed the design standards of flood control infrastructure, or if the infrastructure fail due to unexpected reasons

• The Venuzuela floods is not an isolated case. The extreme damage was caused by a rare event

• The last major rainfall was 50 years ago (though less in magnitude) when urban expansion has not started.

• The rarity, more than the absolute intensity increase losses

Catastrophic Flood Impacts



Some near misses !In 1992 there was a large flood in Colombo Sri LankaA record rainfall – 1/1000 Rainfall 493 mm -> Total discharge 29 million cubic m.Drainage capacity 2 mil. cu. m, and it took 10 days to discharge the floodThe rainfall was only limited to Colombo – No river overflow. If a river embankment breach occurs A catastrophic loss

Maradana Pumping Station andImprovement of GalleFace Outfall

Restoration of Existing Mutwal Tunnel

New Mutwal Tunnel

North Lock Pumping Station

Construction of Storm WaterRetention Facilities in UrbanArea

Improvement of WelawattaAnd Kirilapone Canals

Madiwela South Diversion

Gotatuwa Pumping Station

Kelani Ganga

Beira Lake

Indian Ocean

Scale

ParliamentLake

N

Marsh

Marsh

Storm Water Retention Areain Bolgoda Basin

PStorm Water Retention Areas

P

Marsh

P

Conceivable Structural Measures for Weras Ganga

2002 July Flooding in Kathmandu

2002 floods in Kathmandu, Nepal has created severe damage

The inundation was caused by flow capacity restriction downstream of Katmandu

The rainfall that produced the flood was not the largest expected

What is the ‘worst case’ rainfall? This is one of the biggest problems for Nepal and elsewhereFrom DHM Nepal



Asia Pacific Initiative on Catastrophic Flood Risk ReductionBangkok Resolution:

The need for an Asia Pacific Initiative on Catastrophic Flood Risk Reduction, and pledged support for the mission and goals of this

initiative by representatives from:

Bangladesh, Cambodia, China, Fiji, India, Indonesia, Lao PDR, Malaysia, Nepal, Pakistan, Philippines, Singapore Sri Lanka, Thailand and Vietnam

at this Regional Workshop “Ensuring Flood Security for Sustainable Urbanization in the Asia Pacific Region”, 2003



Asia Pacific Initiative on Catastrophic Flood Risk Reduction

Mission: GOALTo integrate

Prior risk assessment (catastrophic flood scenario)Basic framework for response (action plan)

into urban development and planning process for sustainable urban futures



Asia Pacific Initiative on Catastrophic Flood Risk Reduction

Components:1. Clarifying Catastrophic Floods and relations to

physical and social conditions2. Estimating extreme Rainfall for the basin3. Inundation modeling and prediction4. Risk Assessment (socio-economic) : response5. Community participation

Focus on those who are subjected to hazardThe whole area of social vulnerability should receive strong attention

6. Capacity development: Institutional needs



ChallengesAs urban centers grow and develop, there will always be new risks

Increased floods, underground space flooding, etc.Ensuring human security in urban areas for sustainable urban communities – from ‘fail-safe’ to ‘safe-fail’

Infrastructure development considering vulnerabilityGuide lines for ‘catastrophic flood’ resistant urban communities

Why catastrophic flood risk assessment?Methods to assess losses consensus

Cost benefit analysis to mobilize investmentMethods that would be useful not only in managing extreme floods but also ordinary floods.

Thank you

for your attention

hidden vulnerability of mega cities · 2018. 12. 10. · land subsidence in asia location, country...

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