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Irrigation and drainage
Evolution of irrigation development
China has a long history of irrigation and drainage. The first canals to divert and wells to lift water for irrigation were constructed 4 000 years ago. Since the founding of the People’s Republic of China in 1949, irrigation has experienced a period of vigorous development. From 1958 to 1985, about 64 368 million Yuan have been spent on irrigation and drainage projects. The area equipped for irrigation increased from 16 000 000 ha in 1949 to 62 938 226 ha in 2006 of which 62 559 130 in Mainland China, 378 096 ha in Taiwan and 1 000 ha in Hong Kong (Table 10 and Table 11).
After 1949, irrigation using groundwater was developed rapidly to promote agricultural production. In north China, insufficient surface water resources have meant that since 1950 the Government has had to rely on groundwater for the development of irrigation projects. In 1985, an area of 11.1 million ha was irrigated using tubewells. In 2006, groundwater irrigation using around 4.8 million tubewells was an estimated 19 million ha, 31 percent of the total area equipped for irrigation was 63 million ha (Figure 3). In addition, 17 million ha is power irrigated using surface water. This means that 57 percent of the total area equipped for irrigation, or 36 million ha, used power irrigation (Table 12). In 1995, the power irrigation area was 29 million ha and the total installed capacity of water-lifting machines for irrigation and drainage was 68 240 MW.
China can be divided into three irrigation zones:
- The zone of perennial irrigation, where annual precipitation is less than 400 mm and irrigation is necessary for agriculture. It covers mainly the northwest regions and part of the middle reaches of the Huang river.
- The zone where annual precipitation ranges from 400 to 1 000 mm, strongly influenced by the monsoon, with a consequently uneven precipitation distribution. Irrigation here is necessary to secure production. This zone includes the Hangh Huai Hai plain and northeast China.
- The zone of supplementary irrigation, where annual precipitation exceeds 1 000 mm. Irrigation is still necessary for rice (especially to improve cropping intensity), and supplementary irrigation is sometimes required for upland crops. This zone covers the middle and lower reaches of the Chang, Zhu and Min rivers and part of southwest China.
The irrigation potential is roughly 70 million ha. The maximum possible area that could be equipped for irrigation by 2050 isabout 66 million ha, of which 63 million ha for annual or food crops (Zhanyi Gao, 2009). China uses the expression effective irrigation to indicate the area of food (annual) crops, not to be confounded with the area actually irrigated.
In 1996, the total area equipped for irrigation, including farmland (area regularly ploughed for growing agricultural crops, also called the area under effective irrigation in China), forests, orchards and pastures, was 52.9 million ha. The total area equipped for irrigation is an estimated 62.9 million ha (2006). The area equipped for irrigation represents just over half of the total cultivated area. The area actually irrigated in 2006 was 54.2 million ha, which accounts for 86 percent of the total area equipped for irrigation.
Surface irrigation, mainly for cereals, vegetables and cotton, is practised on 59.3 million ha (59.0 million ha in Mainland China), which was 94.3 percent of the total area equipped for irrigation in 2006 (Table 10,Table 13 and Figure 4). Sprinkler irrigation was introduced into China in the early 1950s. The first sprinkler irrigation project was constructed in Shanghai in 1954. Sprinkler and localized irrigation were considerably developed in the late 1970s. In 1976, the area of sprinkler irrigation was about 67 000 ha. It increased until 1980, but then large areas were abandoned owing to the poor quality of equipment and poor management. Then, in 2006, the area expanded to about 2.8 million ha, which is 4.5 percent of the total area equipped for irrigation. Localized irrigation was practiced on about 0.8 million ha or 1.2 percent.
China uses the following categories (1 ha = 15 mu):
- very large irrigation schemes: > 500 000 mu or > 33 333 ha
- large irrigation schemes: 300 000 – 500 000 mu or 20 000 – 33 333 ha
- medium irrigation schemes: 10 000 – 300 000 mu or 667 – 20 000 ha
- small irrigation schemes: < 10 000 mu or < 667 ha
The very large, large and medium irrigation schemes are generally administrated by special governmental organizations. The small ones are usually farmer-managed. Some small ponds, wells and pumping stations are owned by individuals. In 2006, very large schemes covered 10.6 million ha (10.5 million ha in Mainland China), large schemes 4.1 million ha (4.1 million ha in Mainland China), medium schemes 12.7 million ha (12.6 million ha in Mainland China) and small schemes 35.6 million ha (35.3 million ha in Mainland China) (Table 10, Table 14 and Figure 5).
Role of irrigation in agricultural production, the economy and society
China makes a distinction between the area irrigated for annual or food crops, and the area under other crops, which include irrigated forests, orchards and pasture. In 2006, of the 62.6 million ha, which was the total area equipped for irrigation in Mainland China, 57.1 million ha were under annual or food crops, 1.6 million ha forests, 2.0 million ha orchards, 1.2 million ha pasture and 0.7 million ha other crops. This means that 91.2 percent of the area equipped for irrigation was covered by annual or food crops.
In Mainland China, of the total area, 62.6 million ha equipped for irrigation, 53.9 million ha or 86 percent was actually irrigated in 2006. Of the 57.1 million ha area equipped for irrigation for annual or food crops, 49.0 million ha was actually irrigated, which is also 86 percent.
In 2006, the total harvested irrigated crop area in Mainland China was about 93.4 million ha, meaning an irrigated cropping intensity of 1.72 (Table 10 and Figure 6). The most important harvested irrigated crop is rice, followed by wheat and maize. The importance of irrigated vegetables is increasing. In 2005, almost three-quarters of grain production was irrigated. According to a nationwide survey in the early 1980s, the average paddy rice yield of irrigated farmland was 7.3 tonnes/ha and the average yield of non-irrigated paddy rice was 2.1 tonnes/ha. In 1995, the International Rice Commission estimated an average yield of 6 tonnes/ha for irrigated paddy rice.
There is no available figure on total harvested irrigated crop area in Taiwan, where rice is the main crop. Other crops are also irrigated, such as sugarcane, vegetables, sweet potato, wheat, maize, sorghum, tobacco, rape seed, beans, melons, citrus, banana, pineapple, tea, cassava, peanuts and jute.
Status and evolution of drainage systems
In 1996, the area subject to waterlogging was 24.6 million ha, of which 20.3 million ha were controlled by drainage. In 1995, the power drained area was 4.2 million ha, while in 2006 it was an estimated 4.5 million ha (Table 12).