ENG-1979 — Page 276

THE ENVIRONMENT

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Large volumes of sedimentary material are brought regularly to Hong Kong by the Zhu Jiang (Pearl) River, but this process has been accelerated in recent years by extensive reclamation projects along the coastline. Hong Kong's granitic and volcanic rocks are deeply weathered and are prone to landslides if disturbed, but they can be excavated quite easily for use as reclamation material. Much of the natural landscape is changing as hills are removed and the fill is used at reclamation sites on Hong Kong Island and in Kowloon and the New Territories.

Apart from providing decomposed rock material as fill for reclamation, the hills that make up most of the total land area of Hong Kong have little economic value. Soils are thin and nutrient-deficient, supporting only a sparse cover of grass or scrub except in protected valleys or in water catchment areas where a policy of afforestation has succeeded in estab- lishing hardy pines with some deciduous trees. While Hong Kong does possess some deposits of iron, lead, zinc, tungsten, beryl and graphite, they have only been mined in small quantities.

Because Hong Kong lacks large rivers, lakes and underground water supplies, reservoirs have had to be constructed in large valleys such as Tai Lam Chung, in the New Territories, and in coastal inlets such as Plover Cove and High Island where the land has been reclaimed from the sea. The areas surrounding Hong Kong's reservoirs and their water catchment areas have become part of the government's Country Parks Scheme.

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 2,000 to 3,000 years, and some coastal areas are still prone to flooding when heavy rainfall coincides with high tides. The natural deposition of sediment is con- tinuing around the Deep Bay area where brackish water fishponds have been successfully established in areas that were once mud flats, mangrove swamp or salt-water rice paddies.

Climate

Hong Kong lies within the tropics but, unlike other tropical places, it experiences distinct seasonal changes in weather. The winter months are characterised by frequent outbreaks of cold and often dry air originating from the Asian continental anticyclone. It is not uncommon during January, February and March for temperatures to drop below 10 degrees Celsius although the mean temperatures from December to March are around 15 to 18°C. During outbreaks of cold air, the winds often become strong from the north or east. The prevailing wind during winter and also for most of the year is moderate easterly.

In summer, the weather is tropical: hot and humid with occasional showers or thunder- storms. Winds are generally moderate in strength and rather variable in direction, although the south-west monsoon is the prevailing wind affecting Southeast Asia. Afternoon tem- peratures frequently exceed 32°C between June and September, with mean temperatures around 27 to 29°C.

Tropical cyclones are most common from July to September. In an average year, about five can be expected to cause strong winds and one to cause gale-force winds or higher in Hong Kong. Tropical cyclones occur in the Pacific and the South China Sea throughout the year, although none has ever caused gales in Hong Kong during the five months between December and April. When a tropical cyclone is about 700 to 1,000 kilometres from Hong Kong, the weather is usually fine and very hot. As it moves closer, winds increase and rain becomes heavy and widespread. The severe weather associated with a tropical cyclone usually affects Hong Kong for one to three days. Heavy rainfall from tropical cyclones often causes more damage and casualties than the wind.