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Detailed Information on Landslip Warning System

Shum Wan Road Lanslide in 1995

Each year, on average, approximately three to four hundred landslides are reported to the Geotechnical Engineering Office (GEO).  Most landslides in Hong Kong are caused by heavy rainfall. By using a combination of real-time rainfall data and rainfall forecasts from the Hong Kong Observatory (HKO), and based on our study on the landslip/rainfall relationship, the GEO is able to identify instance when landslide danger is high and when it would be appropriate to issue the Landslip Warning jointly with the HKO. The issuing of the Landslip Warning also triggers an emergency system within government departments, which mobilizes staff and other resources to deal with landslide incidents.

Landslip Warning Symbol

The purpose of the Landslip Warning is to alert the public and reduce their exposure to possible danger from landslides.  It is different from the Amber, Red and Black Rainstorm Warnings that are issued by the HKO to alert the public to the occurrence of heavy rain.  Most landslides are small, but occasionally large ones occur. Landslides, particularly when large, can cause casualties, damage property and block roads.  Therefore, the public should keep vigilant against landslide danger when the Landslip Warning is in force.

GEO raingauge
GEO raingauge system

Considerations for Issuing the Landslip Warning

The GEO has been operating an extensive network of automatic raingauges providing real-time rainfall data for use in the Landslip Warning System since 1984.  Real-time rainfall data of the GEO raingauges are transmitted via 3G mobile network, which provides a reliable and flexible telecommunication system. The data capture, control and processing system receives data from the 90 GEO raingauges and from an additional 31 automatic raingauges operated by the HKO and other government department. The raingauge system utilises modern, advanced data logging and processing equipment and software.

Decisions as to whether to issue or cancel the Landslip Warning are made jointly by the Director of the HKO and the Head of the GEO. The Landslip Warning will be issued if the 24-hour rainfall is expected to be heavy enough to cause numerous landslides. The criterion for the issue of the Landslip Warning is related to the size of the area receiving heavy rainfall, the rainfall intensity and the number of slopes in the affected area. The latest weather information available including short-term rainfall forecast is also considered.

In order to issue timely warnings to the public, the HKO proactively monitor the weather conditions in and around Hong Kong. In addition to data from raingauges, the HKO uses radars to monitor continuously the movement and development of rain-bearing clouds. High-resolution meteorological satellite images also provide information on cloud patterns around Hong Kong.

Neither weather forecasting nor landslide prediction can be regarded as exact sciences. There will inevitably be occasions when the Landslip Warning is raised and not many landslides occur. On the other hand, if heavy rain develops suddenly and unexpectedly, landslides can occur before the Landslip Warning is issued.

The criteria for the issue and cancellation of the Landslip Warning are reviewed regularly to take account of the gradual improvement in slope safety and technology.

Keep away from slopes Watch out for the Landslip Warning

When the Landslip Warning is in Force

When the Landslip Warning is issued, the Warning is broadcasted to the public by local radio, television channels, government websites and mobile apps, together with advice on the precautions that should be taken. The Hong Kong Slope Safety Website ( http://hkss.cedd.gov.hk ) also publishes the warning message and the number of landslide incidents reported to the GEO at regular intervals.

When the Landslip Warning is in force, the public should stay away from slopes and be cautious of landslide danger. The Home Affairs Department opens temporary shelters for the public including anyone whose dwelling is endangered by unstable slopes or boulders. Pedestrians should avoid walking or standing close to steep slopes, especially where landslip warning signs are erected. When the landslide situation is becoming serious, members of the public are advised to cancel non-essential appointments and to stay at home or in a safe shelter. Motorists are advised to avoid driving in hilly areas or on roads with landslip warning signs.

For an update on the situation with respect to weather warnings, members of the public can use the HKO’s “My Observatory” mobile app and the HKO Dial-a-weather service at 187 8200. Weather information is also available on the HKO's Internet Homepage ( http://www.weather.gov.hk ).