ENG-1983 — Page 314

THE ENVIRONMENT

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10 000 years ago; since that time there have been sporadic depositions of sedimentary material eroded from the hills.

This erosion of the hills and deposition in the valleys increased rapidly following the widespread colonisation of the Hong Kong area during the Song Dynasty (960-1279).

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 throughout the territory.

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 establishing hardy pines with some deciduous trees. While Hong Kong does possess some deposits of iron, lead, zinc, tungsten, beryl and graphite, they have been mined only 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 continuing around the Deep Bay area where brackish fishponds have been successfully established in areas that once were mud flats, mangrove swamp or salt-water rice paddies.

Climate

Although Hong Kong lies just inside the tropics it has a remarkably temperate climate for nearly half the year. During November and December there are pleasant breezes, plenty of sunshine and comfortable temperatures, and many regard these as the best months of the year. During January and February there is rather more cloud and occasional cold fronts followed by dry northerly winds which can at times be too cold for comfort. 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 sometimes disrupted by the reduced visibility. May and June are hot and humid with frequent showers and thunderstorms, particularly during the mornings. Afternoon temperatures often exceed 32°C and nights are humid with temperatures generally around 26°C. There is usually a fine spell in early July which may last for one or two weeks.

On average, 31 tropical cyclones form in the western North Pacific or China Seas every year and about half of them reach typhoon strength (maximum winds of 33 metres per second or more). September is the month during which Hong Kong is most likely to be