International Conference on Climate Change

Impact of Sea Level Rise on storm surge in Hong Kong and the Pearl River Delta

by

WONG, Agnes K.M.LAU, Alexis K.H.GRAY, Joseph P.

(The Hong Kong University of Science and Technology)

31 May 2007

• Did you know that the Pearl River Delta is already under threat from severe flooding?

Guangzhou in flood due to heavy rain.

Guangzhou in flood due to astronomical tide: School is cancelled for 100,000 students

190 flood events have been recorded in PRD over the last 40 years(Huang et al, 2004)

June 2005NOT rain related

Coastal FloodingCoastal Flooding

• Astronomical tide• Shape of coast• Accumulated rain water• Tropical cyclone• Global warming (sea level rise)

Storm surge

The abnormal rise in the ocean level associated with typhoon landfall.

Storm SurgeStorm Surge

Global SituationGlobal Situation

Intergovernmental Panel on Climate Change (IPCC) report in 2007:

An average rate of 1.8mm/yr for 1961-2003 Faster rate of 3.1mm/yr for 1993-2003 Total sea level rise for 20th century is estimated

to be 0.17m

Time series of global mean sea levelIPCC 2007

10cm

22cm

Local SituationLocal Situation

The observed rate of sea level rise in Hong Kong is faster than the global average report by the IPCC (2007)

Rate of sea level rise

(mm/yr)

HK Global (IPCC, 2007)

1961 – 2003 2.8 1.81993 – 2003 7.2 3.1

(HKO, 2004)

IPCC (2007) ReportIPCC (2007) Report

Storm surges are especially serious when they coincide with high tide. Changes in the frequency of occurrence (i.e. return period) are affected both by changes in mean sea level and in the meteorological phenomena causing the extremes. There is evidence for an increase in the occurrence of extreme high water worldwide related to storm surges

HKO’s findingsHKO’s findings

Hong Kong Observatory (HKO) research in 2004:

The 50 yr return period would be shortened to about 3 yrs if the sea level rises by 48cm in 2100

A 50yr event could even become an annual event if sea level rises by 88cm

Practical use of return periodPractical use of return period Formation levels for reclamations - str

eets and pavements Flood defence levels for critical facilities

- building basements, MTR Crest levels for seawalls and river banks Tailwater levels and other hydraulic design

- stormwater and sewage systems

S. Buttling & M.L. Chalmers

Normally, the extreme environmental conditions for structures having a design life of 50 years should be taken as those having return periods of 100 years.

Design Life Design Life

Port Works Design Manual : Part 1

Objective of this studyObjective of this study

• To see how the probability of destructive flooding (return period of extreme flooding events) changes with increasing mean sea level

• To understand the relationship between sea level rise and storm surge

DataData Sea Level records around HK from HKO Period: 1965 - 2006

MethodologyMethodology Gumbel cumulative distribution

- extreme value type I Parameter estimation with the moment method

It is used to find the maximum of a number of samples of various distributions. It is useful in predicting the chance that an extreme flood will occur.

North Point

300

310

320

330

340

350

360

370

380

0 50 100 150 200 250

Return period (years)

Extre

me

valu

e (c

m)

1965-2006

1965-1985

1986-2006

20 yr

100 yr

Significant increase in extreme value in last 20 years

Extreme value ranged between 3 to 4 meters

Current 20 year event

NPT - Extreme tide level (324.5cm)

0

5

10

15

20

25

original +5 +10 +15 +20 +25 +30

MSL rise from present level (cm)

Ret

urn

Per

iod

(yrs

)

IPCC Sea level rise estimate for 2050

IPCC Sea level rise estimate for 2100

If the MSL reaches the lower limit of IPCC’s predication for 2050, a 20-yr event would become a 10-yr event

If the MSL reaches the lower limit of IPCC’s predication for 2100, the return period would be decreased to less than 5 yrs

Current return period for a 3.2 m event (20 yr)

Current 100 year event

NPT - Extreme tide level (347.3cm)

0

20

40

60

80

100

120

original +5 +10 +15 +20 +25 +30

MSL rise from present level (cm)

Ret

urn

Per

iod

(yrs

)

IPCC Sea level rise estimate for 2050

IPCC Sea level rise estimate for 2100

If the MSL reach the lower limit of IPCC’s predication for 2050, the structure’s design life would be halved

Event level used for a marine work with a 50yr design life

If the MSL reach the lower limit of IPCC’s predication for 2100, the structure’s design life would be reduced by roughly 75%

Population annually affected by flood

Robert J. Nicholls 2004

Constant Protection

In Phase Evolving Protection

Land Use Map in PRDRed – highly developed area Current Situation

Land Use Map in PRDRed – highly developed area Flooding of 3m

Land Use Map in PRDRed – highly developed area Flooding of 4m

Economic ImpactsEconomic ImpactsRegion Predicted

losses for a 30cm rise

(2000)in RMB

Predictedlosses for a

30cm rise (2030)

in RMB

Predictedlosses for a

1m rise (2000)

in RMB

Predictedlosses for a

1m rise (2030) in

RMB

PRD 22.6 Billion 56 Billion 104.4 Billion 262.5 Billion

Economic Losses from sea level rise in the PRD

Warrick, Barrow & Wigley

Summary & DiscussionSummary & Discussion

• The PRD is already susceptible to severe flooding

• The observed sea level rise in the region is faster than the global average

• The sea level rise projected by the IPCC results in a significant decrease in the return period in the region, implying a significant reduction of the design life of coastal constructions

• We need to act swiftly to mitigate the flooding potential caused by climate change

Action ItemsAction ItemsBuilding regulations should be reviewed to

reflect the potential risks related to climate change

Environmental responsible policies should be adopted to reduce our contribution to Global Warming

Further research work should be done to better understand the rise of sea level and its impact on the region

Acknowledgment

Prof. S.C. Kot for his guidance Dr. Jimmy Chan for his graphics Hong Kong Observatory for provision of

historical sea level data around Hong Kong