reconstruction of an 8 000 year record of typhoons in the pearl river estuary china
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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

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

classification of typhoons after hong kong observatory
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.

slide3

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

top 10 disasters in hong kong s history
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 .

methods used for reconstructing typhoons
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

slide6

Guangzhou

HK

Macau

Distribution of Neolithic middens in the Pearl

River Estuary showing the location of the

coastline ~6,000 years Before Present

slide7

2-dimensional model of sedimentation in the Pearl River Estuary

during typhoons. Storm deposits are identified by their foraminiferal

assemblage.

slide9

Cross-section across the Pearl River Estuary showing facies distribution,

radiocarbon ages and magnetic susceptibility profiles obtained in the six

cores studied

slide10

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

slide11

Radiocarbon ages and archaeological ages of beach-dune barriers in the

vicinity of the Pearl River Estuary

classification of ad 700 to 1883 typhoons inferred from historical documentation
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 .

slide13

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 levels modified after lau 1980
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

slide15

Tracks of top 10 typhoons affecting the Pearl River Estuary from

1884-2000. Based on Hong Kong Observatory data.

slide16

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

slide17

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

main conclusions
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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