From the viewpoint of annual changes, there are great differences between the years with a high amount of precipitation and the years with a low amount. For example, in 1963 when the sea and rivers had high water content, the amount of water resource was as much as 53.3 billion cubic meters, which is 440% more than 9.9 billion cubic meters in 1972. Thus, the annual fluctuation is considerable, and tends to cause flood or drought damage, affecting agricultural production.
The distribution of water and land in China also lacks balance. The small amount of per-capita water resources is the greatest hindrance to the development of agricultural production. The area to the south of the Changjiang River has 70% of the national water resources, yet its farmland area accounts for only 31% of the national total. On the other hand, the area to the north of the river has 30% of the national water resources, but its farmland area amounts to 69% of the national total. Accordingly, the average water contents per hectare are substantially different from south to north. Those in Guangdong and Fujiang in the south are 90,000 cubic meters and 105,000 cubic meters respectively, while that in Hebei and Shanxi in the north is only 5,800 cubic meters. Even though the absolute quantity of China's water resources may not be small, its per-capita quantity is merely 2,700 cubic meters, equivalent to a quarter of the world average amount of water resource per capita. It is forecasted that the total demand for water in China in 2000 will be approximately 700 billion cubic meters, 80% of which is for agricultural irrigation. However, the amount of water resources available in a semi-drought year is 650 billion cubic meters, leaving a short-fall of 50 billion cubic meters. According to agricultural sector statistics, the shortage of water has forced the irrigation area or the effective frequency of irrigation to be decreased, causing a reduction of about 5 billion kilograms food production.
In the meantime, a considerable amount of industrial effluent and domestic sewage are discharged to pollute the surface and ground water.
