Reconstruction of an 8,000-year record of typhoons in the Pearl River Estuary, China G. Huang 1 &...
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Transcript of Reconstruction of an 8,000-year record of typhoons in the Pearl River Estuary, China G. Huang 1 &...
![Page 1: Reconstruction of an 8,000-year record of typhoons in the Pearl River Estuary, China G. Huang 1 & W.W.-S. Yim 2 1 Department of Environmental Sciences,](https://reader035.fdocuments.in/reader035/viewer/2022062421/56649d0a5503460f949dd5a6/html5/thumbnails/1.jpg)
Reconstruction of an 8,000-year Reconstruction of an 8,000-year record of typhoons in therecord of typhoons in thePearl River Estuary, ChinaPearl River Estuary, China
G. HuangG. Huang11 & & W.W.-S. YimW.W.-S. Yim22
11 Department of Environmental Sciences, South China Department of Environmental Sciences, South China University of Technology, Guangzhou, ChinaUniversity of Technology, Guangzhou, China
2 2 Department of Earth Sciences, The University of Hong Department of Earth Sciences, The University of Hong Kong, Hong Kong SAR, ChinaKong, Hong Kong SAR, China
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Classification of typhoonsClassification of typhoonsafter Hong Kong Observatoryafter Hong Kong Observatory
__________________________________________________________
Classification Wind speed* (km/hr) Beaufort scale.
Tropical depression 41 - 62 6 -7
Tropical storm 63 – 87 8 – 9
Severe tropical storm 88 – 117 10-11
Typhoon 118 or above 12
__________________________________________________________
* Averaged over a period of 10 minutes.
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Eye
Philippines
A typhoon originating in the western Pacific off Luzon Fact – Typhoon damage will increase in the future Past record may be useful for prediction to reduce risk
Whystudy?
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Top 10 disasters in Hong Kong’s historyTop 10 disasters in Hong Kong’s history_______________________________________________
Year Type of disaster Death toll .
1937 Unnamed typhoon ~11,000 (1%)
1906 Unnamed typhoon ~10,000 (3%)
1962 Typhoon Wanda 130
1971 Typhoon Rose 110
1925 Po Hing Fong landslide 73
1972 Sau Mau Ping landslide 71
1972 Mid-levels landslide 67
1960 Typhoon Mary 45
1964 Typhoon Ruby 38
1964 Typhoon Dot 26 .
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Methods used for reconstructingMethods used for reconstructingtyphoonstyphoons
Time scales:
(1) 1884 to 2000 – instrumental record of the Hong Kong Observatory (best from 1975 onwards because of satellites)
(2) 700 to 1883 AD – historical documentation of Guangdong
(3) 8,000 years Before Present to 700 AD – offshore boreholes and beach-dune
barriers including radiocarbon and archaeological ages
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Distribution of Neolithic middens in the PearlRiver Estuary showing the location of thecoastline ~6,000 years Before Present
Guangzhou
HK
Macau
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2-dimensional model of sedimentation in the Pearl River Estuary during typhoons. Storm deposits are identified by their foraminiferal
assemblage.
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Location of 6 offshore boreholesLocation of 6 offshore boreholesstudiedstudied
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Cross-section across the Pearl River Estuary showing facies distribution, radiocarbon ages and magnetic susceptibility profiles obtained in the six cores studied
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Air photo of beach-dune barriers at Pui O, Lantau Island. The inner barrier is younger than 2,200 years Before Present based on radiocarbon ages
Inner dune barri
er
Outer dune barri
erLagoon
Lagoon
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Radiocarbon ages and archaeological ages of beach-dune barriers in the vicinity of the Pearl River Estuary
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Classification of AD 700 to 1883 typhoons Classification of AD 700 to 1883 typhoons inferred from historical documentationinferred from historical documentation
_______________________________________________
Category No. of Damage No. of
counties typhoons
I <4 moderate to minimal 149
damage; death toll <100
II 5-8 extensive damage ; death 8
toll 100 to 5,000
III >8 extreme damage; death 4
toll > 5,000 .
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Plot of decadal typhoon distribution based on historical documentation from AD 700 to 1883 and instrumental documentation from AD 1884 to 2000
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Factors affecting storm surge levelsFactors affecting storm surge levels(modified after Lau 1980)(modified after Lau 1980)
(1) Parameters of typhoon
- central pressure - closest approach
- translational speed - path
- size
(2) Coastal parameters
- seafloor topography - coastal configuration
(3) Local factors
- river discharges - seiching
- rainfall runoff - tidal effects
- wind effects
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Tracks of top 10 typhoons affecting the Pearl River Estuary from 1884-2000. Based on Hong Kong Observatory data.
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Sha Tin – unnamed typhoon 1937
Tai Po – Typhoon Wanda 1962 Survivors of 1937 typhoon
Tolo Harbour – location of worst death toll
Tai Po
Sha Tin
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Flooding in Kwai Chung Road 1982Reclamation in Victoria Harbour Flooding in Happy Valley Typhoon Wanda 1962
Reclamations are prone to storm-surge flooding through the trough effect
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Frequency of typhoons in the northwestern Pacific during 1946-2000. From Huang & Yim (2001).
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Main conclusionsMain conclusions(1) Typhoons have occurred since ~8,000
years Before Present.(2) Instrumental documentation provides the best
record of typhoons followed in order by historical documentation, beach-dune barriers and offshore boreholes.
(3) The 5-year running mean of typhoon frequency is found to decline prior to the onset of El Niño years.
(4) Multi-decadal variability in the frequency of typhoons have been found in the northwest Pacific since 1945.
(5) Whether global warming is causing a change in frequency of typhoons in the South China sea
and the northwest Pacific requires further investigation.