Flooding

Low pressure troughs or tropical cyclones bring torrential rainfall to Hong Kong from time to time, placing the city among those with the highest rainfall in the Pacific Rim.  The rainy season comes in summer from May to September, when rainfall is the highest and accounts for almost 80% of the annual total.  Heavy downpours may overwhelm the sewage system and cause flooding; typhoons may drive tidal levels above normal, leading to storm surges and flooding of low-lying coastal areas.  The public should take note of locations with flooding history, especially the blackspots, and take precautions. 
The Drainage Services Department (DSD) has put in place local flood warning systems in flood-prone villages.  The systems will give a warning to village representatives by way of flood sirens or automatic telephone calls when flood water reaches a predetermined alert level.  They serve to alert villagers ahead of floods, allowing sufficient time for evacuation or precautionary measures.

In parallel with the DSD's warning systems, the Hong Kong Observatory (HKO) will issue corresponding tiered rainstorm signals to give the public a heads-up on the major disruptions heavy rainfall may cause to the territory, including flooding.  In addition, when the weather warrants it, the HKO will also issue a Special Announcement on Flooding in the Northern New Territories on account of the presence of farmlands and fish farms in the area, which are susceptible to heavy rainfall.  Apart from alerting the public, these warning systems are also aimed at ensuring preparedness and timely responses of government departments and other emergency service providers in the event of emergencies.

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The symbols and meanings of rainstorm signals

The amount of rain as specified below has fallen or is expected to fall generally over Hong Kong in an hour, and heavy rain is likely to continue.

Symbols	Meaning of signals
	Exceeding 30 mm
	Exceeding 50 mm
	Exceeding 70 mm

 The symbol of Special Announcement on Flooding in the Northern New Territories .

 

Emergency Information

Preparation

• Stay tuned to weather reports to see if there has been a tropical cyclone-induced storm surge or a severe rainstorm.
• Check the flood barriers regularly to make sure they are secure.
• Take the following precautions if you live in or near low-lying areas or places with poor drainage systems and flood-prone watercourses which are susceptible to flooding:
  • Plan ahead of evacuation;
  • Have a waterproof bag/container readily available.  In case of evacuation from flood, put your important identification documents, mobile phone and keys in it;
  • Safekeep your personal belongings and put your valuables at a higher place.

 

During flooding

• Stay tuned to latest weather reports.
• Move to the highest place of the house if flood water keeps running into the house.
• Take refuge on the high ground immediately if you are outdoors.
• Stay away from bridges over flood water or those already submerged under flood water.
• Stay as far away as possible from flood water, watercourses or hill slopes.
• Do not try to wade in flood water.  Rapid currents as shallow as six inches are strong enough to sweep people away.  If you are left with no choice, use a rigid, long object to gauge the depth of water and the firmness of ground in front of you. 
• Do not drive to a flooded place.  Two feet of water is deep enough to float a car. 
• Stay in the car if your car is trapped in a flood.
• If water is running into the car, climb onto its roof.
• Do not try to slosh, swim or drive through flood water.

 

After flooding

• Beware of electrocution.
• Look out for snakes, insects or other animals in trapped water or sludge to avoid their bites.
• Do not drink water that may have been contaminated by floods as this could expose you to diseases.