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

Classification of typhoonsClassification of typhoonsafter Hong Kong Observatoryafter Hong Kong Observatory

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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

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* Averaged over a period of 10 minutes.

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?

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 .

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

Distribution of Neolithic middens in the PearlRiver Estuary showing the location of thecoastline ~6,000 years Before Present

Guangzhou

HK

Macau

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

assemblage.

Location of 6 offshore boreholesLocation of 6 offshore boreholesstudiedstudied

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

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

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

Classification of AD 700 to 1883 typhoons Classification of AD 700 to 1883 typhoons inferred from historical documentationinferred from historical documentation

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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 .

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

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

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

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

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

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

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.