Drainage Services Department

To supplement the department's efforts in improving the drainage system and in maintaining the system in good working order, the efforts of the members of the public are also important to help avoid blockage and misuse of the drainage system.

The Hong Kong Observatory issues warnings on rainstorm and flooding based on its weather condition. It is important for members of the public to familiarize themselves with the meaning of these warnings and take appropriate precautionary measures in good time. These warnings include :

Rainstorm Warnings
Special Announcement on Flooding in the Northern New Territories
Storm Surge Information under Tropical Cyclones Warning Signals

The department has set up a 24-hour hotline 2300 1110 to enable quick response to deal with flooding reports. Please call this number at any time to report any flooding cases. And if there is any risk of personal injury due to flooding, do call the emergency services number 999 immediately.

Rainstorm Warning System

The Government has developed a rainstorm warning system to provide the public with better information about heavy rainstorms.  There are three levels of warning : AMBER, RED and BLACK.

Guide to the rainstorm signals :
 

	Heavy rain has fallen or is expected to fall generally over Hong Kong,exceeding 30 mm in an hour, and is likely to continue.
	Heavy rain has fallen or is expected to fall generally over Hong Kong, exceeding 50 mm in an hour, and is likely to continue.
	Heavy rain has fallen or is expected to fall generally over Hong Kong, exceeding 70 mm in an hour, and is likely to continue.

The rainstorm warning system is designed to alert the public about the occurrence of heavy rain which is likely to bring about major disruptions, and to ensure a state of readiness within the essential services to deal with emergencies.  It is independent of other severe weather warnings, which will be issued separately where necessary.


Click here https://www.hko.gov.hk/en/wservice/warning/rainstor.htm for more details.

Special Announcement on Flooding in the Northern New Territories

A Special Announcement on Flooding in the northern New Territories will be issued by the Hong Kong Observatory whenever heavy rain affects the area and flooding is expected to occur or is occurring in the low-lying plains of the northern New Territories.

The special announcement is intended to prompt the public to take precautionary measures against flooding and to alert farmers, fish farm operators, engineers, contractors and others who are likely to suffer losses from flooding. It is issued irrespective of whether other severe weather warnings, e.g. tropical cyclone signals or rainstorm warning signals, are in force.

Click here https://www.hko.gov.hk/en/wservice/warning/flood.htm for more details

Storm Surge Information under Tropical Cyclones Warning Signals

Low-lying coastal areas are susceptible to storm surge hazards associated with approaching tropical cyclones.  During the passage of tropical cyclones, the associated strong winds pile up the sea water near the coast causing a surge of the sea level.  To a less extent, the low atmospheric pressure of the tropical cyclone also uplift the sea surface on its path.  Such phenomenon is called storm surge.  If storm surge occurs during astronomical high tide, the sea can rise to a high level and flood low-lying coastal areas.

HKO may include information about oncoming storm surge high tide in their tropical cyclone warning messages.  Members of the public staying in low-lying coastal areas should take precautions accordingly.  As an example, Typhoon Mangkhut has brought a record-breaking storm surge in many parts of the territory. The tide level (the sum of astronomical tide and storm surge) recorded was 3.88 m (chart datum) at Quarry Bay and 4.71 m (chart datum) at Tai Po Kau in September 2018 which are the second highest tide level recorded.