THE ENVIRONMENT
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water catchment areas where a policy of afforestation has succeeded in establishing hardy pines and some deciduous trees. Hong Kong possesses some deposits of iron, lead, zinc, tungsten, beryl and graphite, but these have been mined only in small quantities.
As Hong Kong lacks large rivers, lakes and underground water supplies, reservoirs have had to be constructed in large valleys such as Tai Lam Chung and in the coastal inlets of Plover Cove and High Island, where large dams have been built. These reservoirs have a dramatic impact on the environment and their water catchments form a part of the territory's 21 country parks.
The most important agricultural area Hong Kong possesses is the flat alluvium around Yuen Long in the New Territories. These alluvial lowlands have emerged from the sea only within the last 3 000 years, and some areas are still prone to flooding when heavy rainfall coincides with high tides. The natural deposition of sediment is continuing around the Deep Bay area, where brackish fish ponds have been established successfully in areas that were once mudflats, mangrove swamps or saltwater rice paddies.
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On average, only two or three earthquakes are felt by the public each year. However, hundreds are detected by a seismometer network, comprising three short period seismome- ters at Cheung Chau, High Island and Tsim Bei Tsui. Long period seismographs record tremors from all over the world, and strong motion accelerographs are installed at two locations with different soil properties. This network is operated by the Royal Observatory. In recent years, about 150 earthquakes have been detected annually within 320 kilometres of Hong Kong.
Climate
Hong Kong lies just inside the tropics, but has a remarkably temperate climate for nearly half the year. During November and December there are pleasant breezes, plenty of sunshine and comfortable temperatures. Many people regard these as the best months of the year. January and February have rather more cloud, with occasional cold fronts followed by dry northerly winds. It is not uncommon for temperatures to drop below 10°C in urban areas. The lowest temperature recorded at the Royal Observatory is 0°C, although sub-zero temperatures and ice occur at times on high ground and in the New Territories.
March and April can also be very pleasant except for occasional spells of high humidity. Fog and drizzle can be particularly troublesome on high ground exposed to the southeast, and air traffic and ferry services are occasionally disrupted by reduced visibility.
May to August are hot and humid with frequent showers and thunderstorms, partic- ularly during the mornings. Afternoon temperatures often exceed 32°C; at night tempera- tures generally remain around 26°C, with high humidity. There is usually a fine dry spell in July, which may last for one or two weeks, or even longer in some years.
September is the month during which Hong Kong is most likely to be affected by tropical cyclones, although gales are not unusual at any time between May and November. On average, about 30 tropical cyclones form in the Western North Pacific or China Seas every year, and about half of them reach typhoon strength (maximum winds of 118 kilometres/ hour or more).
When a tropical cyclone is about 700 to 1000 kilometres southeast of Hong Kong the weather is usually fine and exceptionally hot, but isolated thunderstorms sometimes occur in the evenings. If the centre moves closer to Hong Kong, winds increase and rain can become heavy and widespread. Heavy rain from tropical cyclones may last for a few days and consequent landslips and flooding sometimes cause more damage than the winds.