Zhang Guang-xin and Deng Wei are associate professors at Changchun Institute of Geography, the Chinese Academy of Sciences, Changchun, P.R. China.undefined
With an area of 9.6 million square kilometers, China possesses 28,124 * 108 m3 of total water resources. The annual average runoff is 27,115 * 108 m3 and the annual average groundwater amount is 8,788 * 108 m3. Although China ranks sixth in the world in total water resources, there is a shortage. The average water resources per capita is 2,300 m3, making it only one fourth of the world average per capita, while the unit plantation area of water resources is only one half the world’s average value.1
In northern China, the 15 provinces, municipalities and autonomous regions have an area of 5.70 million km2, accounting for 59.4 percent of the total area of the country. However, the total water amount of this area (5,745 * 108 m3) is only 20.5 percent of the whole country. The allocation of land resources compared to water resources is very undesirable.
The groundwater withdrawal is over 20 percent of the total water supply of the entire country.2 Overall in northern China, the groundwater withdrawal is 710.17 * 108 m3 with the utilization rate being 48.79 percent.
Current agricultural water use
China mainly uses supplementary irrigation. Eighty-percent of the food is grown in irrigated farmland. The irrigated area is 50 million hm2 or 50 percent of the total planting area and ranks as the largest in the world. The water used for irrigation accounts for 80 percent of the total water use in China and 17 percent of the total water use in the world. About 95 percent of the irrigated farmland is done with overflow and ditches.4 With a utilization rate of only 30–40 percent, wasted water is a very serious issue. In Northwestern China (Xinjiang, Ningxia, Gansu and Qinghai) the utilization coefficient is 0.4–0.5. In the Haihe basin it is 0.45. Even in areas irrigated by wells, the rate is not more than 0.6–0.7.5
In northern China, groundwater is the main water source for industry, agriculture and life. About 70 percent of the groundwater withdrawal is used to irrigate farmland. According to 1982 data from the water conservancy department, there were about 2.2 million wells that were used for irrigation. The area irrigated is about 19.72 percent of the total irrigated area in China. The utilization rate of groundwater in the five main northern river basin plains (excluding the inland river basin plains) are over or near the exploiting limit (Table 2).6 These data clearly show that the groundwater withdrawal surpasses the permitted exploiting power.
Negative ecological and environmental effect of groundwater withdrawal
There are 56 falling funnels with a total area of 87,000 km2 in China, and most of them lie in the North. At the beginning of the 1990s, the water tables for most of the North China Plain (which produced about 40 percent of the total food of the country) was decreasing at an average rate of 1.5 m per year. Some aquifers were almost dry. The water resources reserve decreased dramatically. Wanghe Chen, a professor at the Hebei Geological and Mining Bureau, estimated that the volume of water drained and exhausted in the Hebei plain was 340 * 108 m3 only in the years between 1975 and 1988. Compared to 1959 levels, the water tables of shallow groundwater have fallen 10–20 m. By 1992, the water tables of deep groundwater in the mid-eastern part of this region had fallen below sea level. For example, in Changzhou City, the center of the groundwater funnel was 80 m below sea level.
The central government plans to increase the food output for the whole country by 50 billion kg. In order to increase the production output both the Jilin and Heilongjiang provinces have launched alteration work for saline-alkaline land and low production farming. This practice has resulted in the water table lowering at an average rate of 0.125 m per year, while deteriorating the ecological environment. A report on the future of China’s agriculture has showed that in almost all of the plains in China, the groundwater tables continually have fallen. The people have to drill deeper wells in order to irrigate their farmland. Once the aquifers are exhausted, most of the farmland will become dry agricultural land or abandoned. What is worse is that the food output would actually decrease by about one-half or two-thirds, threatening the food supply of China and the world.
Surface sinking and cave ins
In the North China Plain, the area that subsides over 0.1 m is 3.39 km2. In Tianjin City, the maximum sinking value is 2.69 m covering an area of 9,080 km2. Problems brought about by sinking land include, water log in the city, cracks in houses and roads, rising river levels, sinking bridges and houses, etc. Since the groundwater tables fall dramatically and land dehydrates and constricts, ground crannies are produced. Since the 1960s more than 200 ground crannies have formed in the Huabei plain. The crevices mainly are distributed in Xingtai, Handan, Shijiazhuang and Hengshui. The dimensions of crannies range from several meters to several hundred meters by length and 5–40 cm in width, with the maximum depth being 9.8 m. Ground crannies destroy buildings and means of transportation. Over-exploiting groundwater can cause the ground to cave in. According to a survey covering 18 provinces, there are more than 700 cave ins and more than 30,000 cave-in pits.
In many coastal regions of northern China, seawater intrusion is very serious due to the over-exploitation of groundwater. According to mid-1980s data, in Huabei and Jiaodong, the area of seawater intrusion was 400 km2, at a rate of 16–22 m/a. The census and surveillance of the 1990s showed that in 705 wells that lie in sand and igneous rock in Liaoning, Hebei and Shandong provinces, the concentrations of chlorine ion in groundwater are more than 250 mg/L. The seawater intrusion area includes the Shandong peninsula, coastal region of Eastern Hebei Province, Eastern Liaoning Peninsula and Western coastal region.
The seawater intrusion in the coastal areas of Yantai and Dalian are the most serious, with intrusion areas of 495 km2 and 434 km2, respectively. In these areas, seawater usually intrudes 5–8 km toward inland. Because of this intrusion, more than 5,000 mechanical wells were destroyed, the output of food on 300,000 acres of irrigated farmland decreased by 50 percent and 900,000 people and 250,000 livestock were deficient in drinking water. The direct loss of industry and agriculture was 0.43 billion yuan.
Salinification and desertification
Improper use of groundwater can lead to secondary salinification. For example, in many coastal areas along the Bohai Sea, seawater intrusion resulting from over-pumping the groundwater caused secondary salinification of the coastal area. In the basin located downstream of the Shiyang River in Gansu province, farmland was salinized because the mineralized groundwater pumped from deep aquifers was used for irrigation. In addition, the over-exploitation of groundwater will result in the groundwater table falling in the entire region, declining vegetation and land desertification. This is a fatal threat to the northern arid plant ecosystem that depends on soil water and groundwater. Such phenomena can be found in Gansu and Western Jilin.
Solving the crisis
The groundwater crisis and the accompanying negative effects not only restrict the development of sustainable agriculture but also threaten the safety of food output. Therefore, it is urgent to solve this problem. Presented are four methods to achieve this goal.
Water saving agriculture and efficient water utilization
Developing water-saving agriculture is an important first step. The irrigation methods currently used are inefficient at best. Whereas in developed countries the water utilization rate is 80–90 percent, the rate in irrigated areas of China is only 30–40 percent. In China, the food output is 0.8 kg per cubic meter of water, compared to 2.32 kg in Israel. In much of Northern China’s irrigated areas, three to six times the actual water needed by crops is used. It is estimated that wasted agricultural water is over 1,000 x 108 m3. Therefore, it is imperative to practice economical irrigation, utilize water resources efficiently and develop water-saving agriculture.
There is a great potential in enhancing the economical use of agricultural water and production power. Given that agricultural water use is 4,000 * 108 m3, if irrigation improvements are implemented and the water utilization rate is increased by 10–20 percent, about 4,000 to 8,000 * 108 m3 of water can be saved. If comprehensive economical measures are implemented to decrease the invalid wastage, the production efficiency of irrigating water is expected to increase from 0.8 kg/m3 to 1.5 kg/m3 and more food can be produced. Therefore, there is a far-reaching practical significance in developing water-saving agriculture and efficiently utilizing water resources.
Water transfer from south to north
Due to precipitation patterns, the spatial and temporal distribution of water resources in China is very disproportionate. Rainfall in southern China is 800 to 2,000 mm, compared to the North where rainfall is only 200 to 800 mm. Unfortunately, the water resources distribution is a poor match with the distribution of farmland. However, as a controllable resource, water can be managed by human behavior. Macroscopically controlling water resources in river basins and optimally arranging water and land resources can help guarantee sustainable agricultural development.
Implementing the transfer of water from the south to the north not only is an important measure to solve the disproportionate distribution of water resources but to solve the groundwater crisis as well. The economic, social and environmental benefits of the completed Changiang East-line water project are immeasurable (similar Mid-line and West-line projects are proposed). Success of this project shows that water transfer from south to north plays an important role in alleviating the stress on water resources in northern China and developing agriculture. In addition, other regional water transfer projects that are across provinces or districts such as the Yellow River into Qingdao in Shandong, the Datonghe to Qinchuan in Gansu and the Yellow River to supply Tianjin play an undeniable role in regional water transfer.
We also must reinforce the regional management of water resources (i.e., cooperation between different provinces, cities and districts and its internal management). Water supply power must be reinforced. Especially in northern China, dams and catchworks should be built and wells should be properly collocated to pump groundwater as supplementary water resources.
In addition, technological, economical, administrative and legal means must be taken to comprehensively manage water resources. The branches as well as even the draining areas of the main river must be coordinated between upstream, midstream and downstream in order to avoid conflicts. For example, in the past, river disconnection often occurred because of the over exploitation of water upstream of the Yellow River. This practice seriously influenced the development of sustainable agriculture in the midstream and downstream areas. This past year, because of the macroscopic administration of the central government, overall plans and economic leverage, there is no disconnection. Such measures not only guarantee the agriculture along the river but also replenish the groundwater system.
Water pollution in China is a very serious problem. According to 1990 statistics, the total sewage discharged was 35.4 billion tons (24.9 billion tons from industry and 10.5 billion tons from life use). Most of this polluted water was discharged into waters directly or indirectly without treatment. According to data from the Food Peasant Organization of the United Nations, of the 50,000 km of rivers in China, 80 percent are polluted and do not meet water quality standards for fishing use. Some rivers cannot even be used to irrigate the farmland. Such rivers are not only unusable but pollute the groundwater. According to “Monitoring of Water Environment in China,” the farmland irrigated by sewage will be up from 4.2 to 4.4 million hm2 by 2000. Four big rivers in northern China (Haihe, Liaohe, Yellow and Huaihe) account for 85 percent of the total area irrigated by polluted water.
Pollutants can be accumulated in the crops and impair one’s health. Currently, in the Yellow River drainage area within Shanxi province it was discovered that the content of lead and chromium are above standards. Cabbages grown in the area also were found to contain chromium. In addition, pesticides and chemical combinations used by farmers enter into aquifers through the leaching and infiltration of rain and surface water.
Development of research on multi-water sources
As China rapidly develops agriculture, the demand for water is increasing. However, just utilizing one of the four water sources (rain, surface, ground or soil) is not a good way to develop sustainable agriculture. We must systematically research the belt and regional attributes of the water cycle and balance them, comprehensively exploit multi-water-source resources and guarantee the sustainable development of agriculture.
Much research has been launched into the utilization of multi-water sources. Some of this research includes the following.
These research projects not only provide the scientific foundation for deeper research into the mechanism and rearrangement of the water cycle but also technically support the development of water-saving agriculture.
These water sources link, transform and depend on each other. Therefore, we must study their relationships to establish comprehensive systematic management models. By using these models and some of the factors, water resources can be used optimally.
The extremely poor matching of water and land resources and the development of agriculture at the expense of the over-exploitation of groundwater inevitably has brought about a series of ecological and environmental problems in China. This paper presents four strategic counter-measures in order to solve the groundwater crisis, guarantee the sustainable development of agriculture, secure a safe food supply for a population of 1.6 billion and finally realize the strategy of sustainable development for society and the economy.
This paper was jointly founded by the National Natural Science Foundation of China (No. 40171017) and Project of Chinese Academy of Sciences (No. KZCX2-SW-320-2).