Post on 20-Jan-2016
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