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Reconstruction of an 8,000-year record of typhoons in the Pearl River Estuary, China

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, South China University of Technology, Guangzhou, China 2 Department of Earth Sciences, The University of Hong Kong, Hong Kong SAR, China.

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Reconstruction of an 8,000-year record of typhoons in the Pearl River Estuary, China

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  1. Reconstruction of an 8,000-year record of typhoons in thePearl River Estuary, China G. Huang1 & W.W.-S. Yim2 1 Department of Environmental Sciences, South China University of Technology, Guangzhou, China 2 Department of Earth Sciences, The University of Hong Kong, Hong Kong SAR, China

  2. Classification of typhoonsafter 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.

  3. Why study? 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

  4. Top 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 .

  5. Methods used for reconstructingtyphoons 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

  6. Guangzhou HK Macau Distribution of Neolithic middens in the Pearl River Estuary showing the location of the coastline ~6,000 years Before Present

  7. 2-dimensional model of sedimentation in the Pearl River Estuary during typhoons. Storm deposits are identified by their foraminiferal assemblage.

  8. Location of 6 offshore boreholesstudied

  9. Cross-section across the Pearl River Estuary showing facies distribution, radiocarbon ages and magnetic susceptibility profiles obtained in the six cores studied

  10. Lagoon Inner dune barrier Lagoon Outer dune barrier 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

  11. Radiocarbon ages and archaeological ages of beach-dune barriers in the vicinity of the Pearl River Estuary

  12. Classification of AD 700 to 1883 typhoons inferred 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 .

  13. Plot of decadal typhoon distribution based on historical documentation from AD 700 to 1883 and instrumental documentation from AD 1884 to 2000

  14. Factors affecting storm surge levels(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

  15. Tracks of top 10 typhoons affecting the Pearl River Estuary from 1884-2000. Based on Hong Kong Observatory data.

  16. Sha Tin Tai Po Tolo Harbour – location of worst death toll Sha Tin – unnamed typhoon 1937 Tai Po – Typhoon Wanda 1962 Survivors of 1937 typhoon

  17. Reclamations are prone to storm-surge flooding through the trough effect Reclamation in Victoria Harbour Flooding in Happy Valley Typhoon Wanda 1962 Flooding in Kwai Chung Road 1982

  18. Frequency of typhoons in the northwestern Pacific during 1946-2000. From Huang & Yim (2001).

  19. Main 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.

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