Climate Change related increase

in flood risks for HK and the PRD

Qiwei Yu, Alexis KH Lau, HY Lau, W BarronThe Hong Kong University of Science and Technology

Gabriel NC LauThe Chinese University of Hong Kong

2

Daily maxima sea level at NPQB (1954-2012)

Threshold Number of

case

Approximate

return period

>340 cm 1 60

>330 cm 3 20

>320 cm 7 8

>310 cm 10 6

>300 cm 20 3

>290 cm 56 1

HKO Sea Level Data

Return period is a critical

Engineering design parameter

Threshold Number of caseApproximate

return period

Threshold – 290 cm

(current annual event)

>340 cm 1 60 50 cm

>330 cm 3 20 40 cm

>320 cm 7 8 30 cm

>310 cm 10 6 20 cm

>300 cm 20 3 10 cm

>290 cm 56 1 0

Projected Sea level rise

from 2000

Future annual

maximum sea level

Return period

by 2100

2030 +10 cm 300 cm ~3

2050 +20-25cm 310-315 cm ~6-7

2100 +40-80cm 330-370 cm 20-100+

Rising Sea Level in Hong Kong

Shortening of

Return Period

1957-1984

data

1957-2012 1985-2012

2030 2050 2100

Sea level projections 10cm 20-25cm 40cm-75 cm

Source: IPCCAR5 WG1

What does it mean to have a

100 year flood event ???

Global Active Archive of Large Flood Events

---Dartmouth Flood ObservatoryDuration - Derived from start and end dates.

Known Dead - News reports are usually specific about this, but occasionally there is only mention of 'hundreds' or

'scores' killed

Number Displaced - This number is sometimes the total number of people left homeless after the incident, and

sometimes it is the number evacuated during the flood. News reports will often mention a number of people that are

'affected', but we do not use this.

Damage (US $) - This number is never more than an estimate and we use no independent criteria for determining such.

Instead we accept the latest and apparently most accurate number available in all the relevant sources.

Main Cause - One of eleven main causes is selected: Heavy rain, Tropical cyclone, Extra-tropical cyclone……

Severity Class - 1, 1.5, 2.Class 1: large flood events: significant damage to structures or agriculture; fatalities; and/or 1-2

decades-long reported interval since the last similar event. Class 1.5: very large events: with a greater than 2 decades

but less than 100 year estimated recurrence interval, and/or a local recurrence interval of at 1-2 decades and affecting

a large geographic region (> 5000 sq. km). Class 2: Extreme events: with an estimated recurrence interval greater than

100 years.

Geographic Flood Extents (sq km) - This is derived from our global map of news detected floods. Polygons representing

the areas affected by flooding are drawn in a GIS program based upon information acquired from news sources

Flood magnitude=log(severity *duration*area)9

Flood events 1985/1-2013/7, Totally 4068 cases

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Flood Impact

Deaths

Economic Damage

Displaced

1. Data ellipse outlier

detection-A clear increase trend

and the data is

concentrate in the

ellipse (0.9)

2. From the origin-If flood magnitude is 0,

there has no damage

due to flood

3. Log-linear

regression

estimation

Vulnerability

Difference

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World Development Indicators ( Word Bank, Average of 1985-2012)1

Country damage_rate GDP per capita Urban population (%) ……………. Employment ratio Telephone lines

China 3.0 1518.0 35.6 . 73.3 11.4

United States 3.2 33184.2 78.5 . 61.4 56.4

Philippines 3.0 1167.4 47.8 . 59.8 2.8

Vietnam 2.9 544.5 24.4 . 76.4 5.2

. . . . . . .

. . . . . . .

. . . . . . .

Canada 3.6 27455.5 78.6 . 60.5 58.0

Korea, Rep. 3.7 11849.5 77.7 . 58.9 43.7

Argentina 2.7 6307.0 89.4 . 52.2 17.8

Fiji 3.7 2681.1 46.4 . 56.1 9.9

Japan 2.8 33061.6 81.6 59.5 46.6

New Zealand 3.2 17967.4 85.4 . 61.5 43.9

1. WDI take into consideration only if it has more than 20 years record

Categorized countries by Population density & Urban population (%)

-Deaths/Displaced

-Factor analysis

-Identify the indicators represent

the characteristic of the country

-Where is Hong Kong & PRD

locate?

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Correlated indicators

Death: • Rural population (% of total) (0.58)

• Population density (people per sq. km of land area) (0.48)

Displaced:• Population density (people per sq. km of land area) (0.65)

• Rural population (% of total) (0.52)

Cor (Urban population, Population Density)≈0.28

Economic Damage:• GDP per capita (constant 2005 US$) (0.43)

• Telephone lines (per 100 people) (0.52)

Cor (GDP,per capita & Telephone lines)=0.95

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Impact for Hong Kong 2000 2030 2050 2100

Projected Sea level rise

from 20000 cm +10 cm +20-25 cm + 40-80 cm

Return Period (years)

in the future1.5 1.5 1.5 1.5

Equivalent Return

Period (years) in 20001.5 ~ 3 6 – 7 20 – 100+

Flood magnitude 3.5 3.5+ 4 6 - 7

Number of deaths < 5 ~ 5 ~ 20 20 – 60+

Number of people

displaced< 400 400+ 1,000+ 5K – 150K

Economic loss

(Million HKD)< 25 25+ 60 – 600 800 – 6000+

Impact estimates ASSUMED no protective measure being done in HK

Year 2030 2050 2100

Return period at present 3 6~7 20-100+

Deaths

Hong Kong ~ 10 ~ 20 20 – 60+

PRD ~ 30 ~ 40 100 – 700+

Displaced

Hong Kong Up to 400 Up to 1,000 5000 – 150,000

PRD Up to 4,000 Up to 15,000 0.2 – 2+ million

Economic Damage (HK Dollars)

Hong Kong < 25 million 60-600 million 800–6000+ million

PRD < 10 million 30–150 million 200–3000+ million

Recovery duration

Hong Kong & PRD Several days <1 month Several months

(>4 months)

Projected annual flood damages for Hong Kong & PRD in 2030, 2050

and 2100 without adaptation (flood magnitude: 3.5, 4, [6-7])

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Summary

• Order of magnitude estimates

• Significant impact without adaptation –

need to work hard on that

Thailand 2011

Guangdong 2013