Common hazards in Hong Kong

What is a landslide?

A landslide is the movement of soil and rocks down a slope due to gravity.

In Hong Kong, landslides often occur near urban areas. They happen mainly on steep slopes during the rainy season.

What are the causes of landslides?

- Heavy rainfall adds weight and washes loose rocks and soil down a slope.

- Hilly relief and steep slopes

- Urban development on hills (e.g. housing and roads) clears the natural vegetation and adds weight onto slopes

- Cutting makes slopes steeper and unstable because soil and rocks are cut out of the slope and removed

- Poor maintenance of man-made slopes allow water to seep into the soil

What are the effects of landslides?

- Injury or death

- Settlements buried

- Damage and disruption to infrastructure

- Collapsing buildings

Ways to avoid slope failure and minimize loss

- Spread cement on slopes to prevent water seepage

- Install weepholes and drainage channels to reduce pressure from water

- Install soil nails to anchor soil to the slope

- Build retaining walls to strengthen cut slopes

- Plant vegetation to protect slopes from erosion

- Proper maintenance to man-made slopes through laws and regulations

- Provide early warnings of landslides to the public

- Educate the public on the importance of slope safety

What are weather and climate?

Weather: Conditions of atmosphere over a short period of time

Climate: Average conditions of atmosphere over a long period of time

What is a monsoon climate?
It is the seasonal wind which changes directions in between winter and summer. Land absorbs and loses heat faster than the sea. In summer the land is generally cooler than the sea, in winter the land is generally hotter than the sea. This temperature difference creates a pressure difference over the land and sea. Wind blows from areas of high pressure to area of low pressure. Wind coming from the sea is wet. This brings heavy rainfall and sometimes major rainstorms in summer.

Why does most of Asia suffer from typhoons?

Typhoons are tropical storms that commonly occur in summer. They are low pressure systems. For typhoons to form they require a plentiful supply of warm moist air and a sustained ocean temperature over 26.5^oC.

These conditions create a low pressure system which combines with the rotation of the earth produce spiraling winds and storm clouds.

Typhoons bring heavy rainfall that may cause flooding or landslides. They occur mostly in the summer.

What are the effects of typhoons?

- Disrupt economic activity and daily life

- Trigger landslides and flooding

- Cause damage and injury

How can people respond?

- Build buildings to withstand strong winds

- Provide early warning systems

- Education