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

2. Classification of typhoons after Hong Kong Observatory __________________________________________________________ Classification Wind speed* (km/hr) Beaufort scale. Tropical depression41 - 62 6 -7 Tropical storm63 – 87 8 – 9 Severe tropical storm88 – 117 10-11 Typhoon118 or above 12 __________________________________________________________ * Averaged over a period of 10 minutes.

3. 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 Why study?

4. Top 10 disasters in Hong Kong’s history _______________________________________________ YearType of disasterDeath toll. 1937Unnamed typhoon~11,000 (1%) 1906Unnamed typhoon~10,000 (3%) 1962Typhoon Wanda130 1971Typhoon Rose110 1925Po Hing Fong landslide73 1972Sau Mau Ping landslide71 1972Mid-levels landslide67 1960Typhoon Mary45 1964Typhoon Ruby38 1964Typhoon Dot26.

5. Methods used for reconstructing typhoons 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. Distribution of Neolithic middens in the Pearl River Estuary showing the location of the coastline ~6,000 years Before Present Guangzhou HK Macau

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 boreholes studied

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

10. 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 barrier Outer dune barrier Lagoon

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 II5-8 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 – unnamed typhoon 1937 Tai Po – Typhoon Wanda 1962 Survivors of 1937 typhoon Tolo Harbour – location of worst death toll Tai Po Sha Tin

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

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.