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2. The natural of arid, semi-arid zones and desertification in the people's republic of China
2.1 Arid semi-arid and dry sub-humid zones cover 2 976 000 km2 in northern China; extreme arid areas cover 697 000 km2. This totals 3 673 000 km2 or 38.3 percent of China's total land mass including 2 080 000 km2 of decertified land (cf. bibl. entry 26). In Xinjiang province alone there are 423 000 km2 of desert-China's largest. Gradual invasion of moving sand is decreasing the size of oasis areas (cf. bibl. entry 8).
2.2 Land degradation caused by poor management has long plagued northern China. Desertification-prone land covers 334 000 km2 176 000 km2 are already decertified lands and 158 000 km2 are at risk. From aerial-surveyed topographic maps desertification-prone land increased by 390 000 km' between 1950 and 1970 (cf. bibl. entry 145). The area of degraded land expanded by 1 560 km2 annually from the end of the 1950s to the mid-1970s and reached 2 100 km2 in northern China during the last decade. The total area of degraded land approximates 197 000 to 226 000 km2 Forty-five thousand km2 of desertification-prone lands were rationally utilized and 2 250 km2 rehabilitated. (cf. bibl. entries 15 144).
2.3 In the "three-north" region the ratio between greening velocity and desertification velocity is one to eight indicating that rehabilitation of decertified land in China is slow (cf. bibl. entry 111).
2.4 There are 818 000 km2 of saline land; 173 300 km2 are threatened with salinisation. To achieve sustainable agriculture in China this vast area of saline land must be improved and utilized (cf. bibl. entry 7).
2.5 China's arid environments have been divided into two types three patterns and 15 zones based on annual aridity coefficients rainfall and accumulated temperature (cf. bibl. entry 106). Regional management strategies and detailed natural resource development utilization and protection measures have been suggested for each area (cf. bibl. entry 1).
2.6 Based upon differences in the desertification process China's decertified lands have been divided into 20 regions' eight showed slight desertification e.g. central plain of northeast China; seven moderate desertification e.g. Bashang in Hebei province; and five severe desertification e.g. northern Shaanxi province (cf. bibl. entry 32).
2.7 Studies on the spatial characteristics of natural disasters divide China into tour Disaster Action territories and 14 Disaster Action regions (cf. bibl. entry 93). Disaster distribution is controlled near the Qingling-Huai He line (34° N). The areas of most frequent disaster action (droughts floods landslides and earthquakes) are located in northern China's Hu line zone. Other disaster centres are Huang He Huai He Hai He the area between Zhengzhou and Wuhan-Dong Ting Lake and the Yunnan-Sichuan-Guangxi border region.
2.8 According to Wu Zheng (cf. bibl. entry 97) desertification patterns and sand deserts in North China have been changing since the glacial activity of the Quaternary period. Between the Quaternary and modern times a sand desert in the broad semi-desert and steppe area of the east part of North China existed intermittently experiencing stable, expansive and retroactive phases. Since 1949 dry climatic conditions, population increases and adverse economic development activities have caused desertification in North China to worsen.
2.9 Trends in desert evolution are determined by climate variation and global climate change. Precipitation in the eastern part of China may increase, thereby alleviating or reversing the desertification process. On the contrary, drought in the western desert region may intensify (cf. bibl. entry 98). If CO' concentrations double and mean annual temperatures increase to 4°C, China's arid zones will expand to 4 630 000 km2 or 48.3 percent of China's total area, including 2 670 000 km2 of desertified land. The rate of land desertification will increase to 6 941 km2 per year (cf. bibl. entry 26).
2.10 Over the past 40 years and particularly during the last decade, China has made great progress in research related to arid zones; certain fields rank among the world's most highly advanced (cf. bibl. entry 130). Topics include:
(a) Inventory and evaluation of land, water, climatic, biological, mineral and other natural resources.
(b) Monitoring and control of natural disasters, including drought, sandstorms and salinisation. It is noteworthy that sandstorm control has been successful.
(c) Evaluation and predictions of geographical and environmental change.
(d) Productivity allocations for industry, agriculture and transportation.
(e) Human population dynamics including national minorities population growth, the population and economy of mountain areas, population and environment relationships and migration.
(f) Regional research and regional development.