While China's water resources are substantial compared with those of many other countries, its population is even larger, and its water resources are not evenly distributed across the country or across important agricultural regions. China ranks fifth in total water resources among the countries of the world. On a per capita basis, however, its water resource availability is among the lowest. Moreover, the nation's water resources are overwhelmingly concentrated in southern China; northern China has only approximately 25% of the water endowment of the south and 10% of the world average (Ministry of Water Resources, 2000). The lower levels of rainfall in northern China are also much more seasonal than in the south, with more than 70% of the rain occurring between June and September. Northern China, however, remains an important agricultural region and the site for much of China's industrial production. Although it has only 24% of the nation's water resources, northern China contains more than 65% of China's cultivated land and produces roughly half of its grain (nearly all of its wheat and maize) and more than 45% of the nation's gross domestic product (China National Statistical Bureau, 2000; Ministry of Water Resources, 2000).
Groundwater resources in China are both unevenly distributed and unevenly used across regions. According to the latest estimates generated by the Ministry of Land Resources, the annual natural recharge of fresh groundwater resources in China is 884 billion cubic meters, about one-third of the nation's total water resources (Ministry of Land Resources, 2005). Of this, about 70% are in southern China, and only about 30% in northern China. However, the intensity of groundwater use occurs in a very different pattern. Of all the known groundwater resources, rural and urban users are using more than 70% in northern China, whereas less than 30% of the known groundwater resources in southern China are being used.
Despite the fact that most groundwater resources are located in southern China, it is fortunate that they exist across wide expanses of northern China's river basins and that these resources are relatively abundant and accessible. Alluvial deposits consisting primarily of sand, loess silt and clay extend to a depth of more than 500 m below the surface in some areas (Kendy et a/., 2003). These deposits comprise the aquifers that supply groundwater to regions in all major river basins in the North China Plain. The aquifers, however, vary greatly across northern China. For example, in the North China Plain, unlike the south where villages in mountainous areas can tap groundwater resources, mountainous areas are often groundwater-deficient.5 In the flat plains, the aquifers are multilayered. The multilayered aquifers in the Hai River basin (NCP) typically have 2-5 layers; the first and third layers are the most water-abundant. The first layer is typically an unconfined aquifer made up of large-grained homogeneous sand and gravel. The other layers are typically confined aquifers. In some areas, especially in the eastern parts of the Hai River basin, there is a naturally occurring saline layer. Created during a previous ice age, the second layer often contains saline water, is confined and has a salt content high enough that it is typically unusable for agriculture without treatment.
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