ENG-1973 — Page 248

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THE ENVIRONMENT

Due to the hilly terrain, agricultural land is restricted. The most important area is the flat alluvium around Yuen Long in the Deep Bay area. Outside the alluvial areas, soil cover is usually thin, sometimes no more than two or three inches. In general the natural residual soils are acidic and of low fertility, needing the addition of lime, potash and superphosphates. However, given intensive labour input, water supply rather than soil condition tends to be the controlling factor in farming. The predominantly crystalline character of the rock formations unfortunately makes them unsuitable for underground storage and this makes it necessary to concentrate on the collection of surface run-off for all water supplies. The highly variable rainfall of the area has led to periodic water shortages. Most of Hong Kong's surface water supply has now been captured through the construction of catchments and reser- voirs. After completion of the High Island reservoir scheme, desalination on a large scale will become necessary.

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processes

Hong Kong lies in the frost-free double-cropping rice zone of East Asia, but more profitable vegetable crops have increasingly displaced rice during the past 25 years and it is now grown on only 31 per cent of the area being used for agriculture. Fish ponds are also an important form of rural land use. The upland areas are mostly grass-covered and in several places, as in the Castle Peak area, severely eroded. Afforestation has been developed since 1945 but the area covered is still relatively small. The most important economic function of the uplands is for water catchment areas, which must be reconciled with needs of the crowded urban areas for recrea- tional space.

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Climate and the Year's Weather

Climate

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Although Hong Kong lies within the tropics it experiences seasonal weather conditions, unusual for tropical countries. The winter monsoon blows from the north or north-east and normally begins during September. It prevails from October until mid-March but can persist until May. Early winter is the most pleasant time of the year when it is generally dry and sunny. After New Year there is often more cloud and although rainfall remains slight, it is often persistent. Coastal fog and drizzle occur from time to time in early spring-during breaks in the monsoon-when warm south-easterly winds may temporarily displace the cool north-easterlies.

The summer monsoon blows from the south or south-west and can occur from mid-April until September, but it is not as persistent as the north-east monsoon of winter. Summer is the rainy season and is almost continuously hot and humid. The annual rainfall measured at the Royal Observatory has varied between 901.1 mm in 1963 and 3,100.4 mm in 1973, the wettest year since 1889, but the mean value is 2168.8 mm.

Mean daily temperature ranges from about 15°C in February to about 28°C in July and the average for the year is 22°C. February is normally the coldest month and July the hottest. The absolute minimum and maximum temperatures ever re- corded at the Royal Observatory were 0.0°C and 36.1°C respectively. However,