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close this bookFreshwater Resources in Arid Lands (UNU, 1997, 94 p.)
close this folder4: Water resources and agricultural environment in arid regions of China
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View the documentIntroduction
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View the documentImproving water management for sustainable agricultural development
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(introduction...)

Wang Tao and Wu Wei

Introduction

In arid regions, water is one of the most challenging current and future natural-resources issues. For a sustainable agriculture and, hence, a healthy economy, water is the key to success. The importance of water in arid regions is self-evident indeed.

The arid regions occupy a vast area in north-western China that mainly includes the Alxa Plateau in the western part of Inner Mongolia, the northern part of Ningxia Hui Autonomous Region, most of Qinhai and Gansu provinces and the Xinjiang Uygur Autonomous Region - about 2.5 million km² or one-quarter of the Chinese territory. In these regions, mean annual rainfall is less than 250 mm, and even less in the western plains (50-150 mm) and the Taklimakan Desert (less than 25 mm). The annual evaporation is more than 1,400 mm in general, and about 2,000-3,000 mm in desert areas. Because of the arid climate, about 70 per cent of the total arid regions are unusable areas such as sandy deserts, gravel deserts, and other wildernesses. Although there are enough wasteland, light, and heat resources, the local economy depends only on irrigated agriculture and animal husbandry because of the limited water supply.

Water is not only the most precious natural resource in arid regions but also the most important environmental factor of the ecosystem. Human impact on the water supply will certainly cause a chain reaction within the ecosystem. Since ancient times, water utilization has always had a decisive impact on local socioeconomic development. But the increased intensity of human activities and overuse or misuse of water resources caused, and quickly spread, agroenvironmental degradation, including salinization, vegetation degeneration, and sandy desertification. Water resources are already under great pressure to support agricultural production in the arid regions and will face a much more difficult situation in the future. Therefore, understanding the relationships between water and environment, and water and development, and recognizing how to practice sound water management, are crucial subjects to study for sustainable agriculture and a stable environment in the arid regions.

Water resources

In the arid regions of China, the water resources are present as rainfall, glaciers, surface water, and groundwater. Rainfall is the basic supply source for all kinds of water resources. Its variation in time and space controls the water conditions and glacial development, as well as directly influencing the formation and distribution of surface water and groundwater. Additionally, there are frequent transformations and interactions between surface water and groundwater.

Rainfall Resources

Rainfall varies from place to place in the arid regions of China (fig. 1). Most parts of the plains receive less than 100 mm annually, but some plains, like the Yinchuan Plain, the eastern part of the Hexi Corridor Region in Gansu, and the northern area of Xinjiang, receive from 100 to 250 mm. The extremely arid centres in China, as shown in table 1, obtain no more than 25 mm yearly. However, the mountain areas share much more rainfall during some periods. For instance, there are 500 mm or even 1,000 mm of rainfall in the western part of the Tianshan Mountains, and about 400 x 108 m³ surface run-off are formed and come down to the plains. In the Qilian Mountains of Gansu, 350400 mm can be expected, which results in 70 x 108 m³ of water being supplied to the Hexi Corridor Region every year.

According to the isohyets, the annual precipitation in China's arid regions (including mountain areas) is estimated at over 5,000 x 108 m³, which converts into an average rainfall of 175 mm and which constitutes the only reliable guarantee for subsistence and development in these regions.

Glacial Resources

Glaciers and permanent snow are special water resources preserved in the mountains of the arid regions, and they play an important role in regulating run-off. The glaciers cover a wide area of about 26,000 km² from the Qilian Mountains in the east to the Tianshan Mountains in the west, and from the Altayshan Mountains in the north to the Kulunshan Mountains in the south, with water reserves of 29,000 x 108 m³ (Qu 1986) supplying 230 x 108 m³ of water to the run-off annually (Gao and Shi 1992). The glacial run-off percentage of the surface run-off is 20.8 per cent in Xinjiang, 12.0 per cent in the Hexi


Figure 1 Precipitation Isogram of the Arid Regions of China

Table 1 The Centres Extreme Aridity in the Arid Regions of China

Arid centre

Annual precipitation(mm)

Minimum recorded a(mm)

Maximum recorded a(mm)

Period

Tuksun

7.1

0.5 (1968)

23.8 (1979)

1957-1979

Naomaohu

11.7

5.2 (1977)

28.5 (1964)

1960-1979

Lenghu

17.6

3.2 (1961)

44 5 (1972)

1957-1980

Ruoqiang

18.4

3.9 (1957)

42.0 (1953)

1953-1979

a. Year recorded, in parentheses.

Table 2 River Run-off Resources in the Arid Regions of China

Region

Run-off volume(108 m³)

Percentage of total run-off volume (%)

Flow in from outside regions (108 m³)

Flow out to outside regions (108 m³)

North Xinjiang

439.40

31.3

30.12

220.98

South Xinjiang

444

31.7

60.74


Gansu

187.15

13.3



Qinhai

322.54

23.0



Ningxia

8.89

0.6


344.00

Alxa, Inner Mongolia

0.24

Total

1,403.12

100.00

93.83

564.98

Source: Gao and Sui (1992).

Corridor Region, and 15.6 per cent in Qinghai Province. So it can be said that the glacial resources serve not only to store water in a certain quantity but also to improve the stability of the water supply and the efficiency of water utilization in the regions.

River Run-off-Resources

The rainfall in the mountains and melt water from the glaciers are the major supply sources to the surface run-off in the regions and can be used as water resources once they have been transformed to surface run-off and have flowed into the plains and basins. In other words, the usable water resources in the arid regions are the surface water and the groundwater in the plains. Based on the average annual runoff volume flowing through the mountain passes to the plains and basins, the amount of surface run-off was estimated at about 1,400 x 108 m³ (Gao and Shi 1992) in the arid regions of China (table 2).

The natural river flow in the regions provides high-quality fresh water that can meet any purpose of water use. The degree of mineralization generally ranges from 0.1-0.3 g/litre at the river heads in the mountains to 0.1-0.5 g/litre at the mountain passes. Table 3 shows the degree of mineralization in some rivers in Xinjiang in 1982 (Tarim River in 1983). The degree of mineralization obviously increases to 1.0-5.0 g/litre if the water is used for irrigation in the plains and permeates the ground, especially in the low reaches of rivers like the Tarim, Heihe, and Ulungurhe rivers. At present, although in some cities waste water is discharged directly into the nearby rivers and lakes and causes water quality pollution in varying degrees, industrial pollution is not yet serious in the regions

Table 3 Annual Changes of Degree of Mineralization in Some Rivers in Xinjiang



Degree of mineralization (mg/litre)

River

Station

Jan-Apr

May-Aug

Sep-Dec

Toutun

Hadibe

440

191

318

Urumqi

Yingxunqiao

242

142

208

Dina

Dinahe

1,310

456

784

Karakax

Uluwati

624

250

547

Tarim

Aral

2,040 (Jan-May)

576 (Jun-Sep)

1,020 (Oct Dec)

Source: CAS (1989).

Groundwater Resources

Groundwater is a very important component of the water resources, and an indispensable form of movement, transformation, and utilization of water in the regions. Because of the arid climate conditions, only a very small part of the groundwater is supplied as rainfall and the largest portion stems from the permeation of surface water. When the rivers come down to the plains from the mountains, a great quantity of water seeps through the ground to become groundwater, and the groundwater spills over as springs in lower-lying areas. Such "seeping-spilling" forms the basic pattern of the water cycle between surface and groundwater in the arid regions. For example, in Xinjiang, about 185 x 108 m³ of river water seeps into the ground, and 60 x 108 m³ overflows to the surface again every year. Sometimes, the cycle seems to repeat itself in some places.

The groundwater resources are widely dispersed in the Piedmont plains, basins' fluvial plains, and desert areas. In the four biggest Piedmont plains, the annual natural supply of water to groundwater is about 316 x 108 m³ (table 4) and 60-90 per cent of that is transformed from surface water (Gao and Shi 1992).

The groundwater in lake basins and fluvial plains is provided mostly by underground flow and permeation of surface water. In the eight largest areas there are about 33 x 108 m³.. Since those areas are located in the lower reaches of the water supply and are seriously affected by human activities, some problems, such as the lowering of the groundwater level, the contraction of lake basins, and the exhaustion of groundwater supplies, have recently become more and more severe.

There are other kinds of water resources, such as soil water and phreatic water. Soil water depends on the water exchanges between rainfall, surface run-off, and groundwater in the soil, which are so complex that it is difficult to make a quantitative evaluation. The phreatic water can be found in deserts. Since most of the interior basins in the arid regions are occupied by deserts more than 694,000 km² and it is impossible for surface and groundwater from the outside to enter, rainfall is the main source for phreatic water here, which is estimated at about 50 x 108 m³ each year.

Table 4 Groundwater Resources in the Piedmont Plains of the Arid Regions of China

Plains

Recharged from river canal and field( x 108 m³)

Ground run-off( x 108 m³)

Permeated from rainfall( x 108 m³)

Total recharged volume( x 108 m³)

Hexi Corridor Region, Gansu

39.83

2.52

2.42

44.77

Caidam Basin, Qinhai

23.30

5.65

1.02

29.98

Junggar Basin, Xinjiang

53.27

3.77

5.84

62.88

Tarim Basin, Xinjiang

161.92

10.72

6.08

178.72

Total

278.32

22.66

15.36

316.35

Source: Gao and Sui (1992).

Water utilization and agricultural environment

Water Utilization

In the arid regions of China, water utilization has a long history because of irrigation agriculture. Since the Han Dynasty (206 B.C. 220 A.D.), the regions have been opened up on a large scale. The people have accumulated rich experience and achieved phenomenal success in the development, utilization, and protection of water resources. A very good example is an ancient water conservation measure used in Xinjiang, the karez well, an irrigation system of wells connected by underground channels. This system can draw water automatically into the fields, just like artesian springs. There were more than 1,;'00 channels of the karez well, with an overall length of 5,000 km (3-4 km on average and 30 km the longest) in Xinjiang in the 1950s. According to 1985 statistics (CAS 1989), there were still 1,016 channels used to distribute 4 x 108 m³ of water to irrigate 20,000 ha of farm land (table 5).

Before the 1950s, there were just a few water-conservation facilities in the regions, and the total irrigated land area was only about 1.3 million ha in 1949. Since the 1950s, the construction of water-conservation facilities has achieved quite good results. Excepting the two biggest reservoirs of Liujiaxia and Longyangxia along the Yellow River, there are 1,168 reservoirs of different types with a storage capacity of 77 x 108 m³. Among them are 195 large and middle-sized reservoirs with a storage capacity of 67 x 108 m³.. Many different installations have been built, including 4,300 projects for diverting water automatically, 1,300 engineering facilities for pumping water, 75,700 power-driven wells, and 250,000 km channels on different scales (Gao and Shi 1992). Those installations can effectively irrigate 4.5 million ha of farm land, 127,000 ha of range land and 429,000 ha of orchards and gardens. Table 6 shows the situation of water utilization in the arid regions of China in the 1980s

Table 5 Distribution and Flow Capacity of Karez Wells in Xinjiang in 1985

County

Channel

Flow capacity (108 m³)

Turpan

366

1.29

Toksun

80

0.55

Shanshan

254

1.00

Hami

280

0.70

Yiwu and Barkol

15

0.19

Muri

36

0.39

Total

1,016

4.03

Source: CAS (1989).

Agricultural Environment

In the arid regions, the decisive factor in the ecosystem is water, which will directly affect the environment by the changes in its quantity, quality, and regional distribution. The reclamation and utilization of the water resources in the arid regions played a key role in the development of society and the economy. Certainly, the impact of human activities on water management has improved the environment to be favorable for agricultural development on a large scale, especially thanks to the construction of reservoirs and of irrigation and drainage systems. Several dreams have come true, such as expanding the agricultural areas of the old oases, exploiting the wasteland, and increasing the artificial woodland and range land. Those changes have brought about a great advance in agricultural production. But the management of water resources is still the most important task for sustainable development in the arid regions, not only because the promotion of economic prosperity is limited by water scarcity but also because water management is involved in exploiting other natural resources and protecting the environment. In view of the laws governing water movement, transformation, and circulation, and the role of water in the arid ecosystem and in sustainable agriculture, there have been many harmful effects on the agricultural environment from poor water management, which can be summed up as follows.

Shortened Rivers, Shrunken or Dried Lakes and Degenerated Water Quality

Every continental river basin in the arid regions is a unit composed of surface water and groundwater forming an independent water-resources system and an integrated ecosystem. Given the limitation of water resources, if the channels and water storage were increased excessively in the upper reaches this would cause not only a decrease in the water supply, a river shortened in many cases, and the deterioration of water quality in the lower reaches, but also an imbalance in the ecosystem, degradation of the environment, and destruction of other resources.

Table 6 Water Utilization in the Arid Regions of China

Province

Agricultural irrigation(108 m³)

Range-land irrigation(108 m³)

Industrial water use(108 m³)

City use(108 m³)

Countryside use(108 m³)

Surface water use(108 m³)

Groundwatera use(108 m³)

Xinjiang

387.98

9.50

7.49

0.43

2.05

335.6

63.38

Hexi Corridor Region, Gansu

63.81

3.95

2.01

0.09

0.69

48.5

24.10

Qinhai

5.07

2.33


0.05

0.46

8.09

0.06

Inner Mongolia

5.35


0.23

0.06

0.57

1.84

4.37

Yellow Riverb

120.00

2.00

8.00

1.00

2.60

106.00

2.90

Total

582.21

17.78

18.18

1.63

6.37

500.03

94.81

Percentage

93.0

2.8

2.9

0.3

1.0

84.1

15.9

Source: Gao and Sui (1992).
a. Includes water diverted from springs.
b. Up to the Hekou hydrometric station, Lanzhou.

Unfortunately, many rivers, such as the Tarim, Keriya, Hotan, Yarkant, Konqi, Shule, Heihe, and Shiyan, in the arid regions are facing such problems. For example, the Tarim River valleys converge to a river system originating from the Kulun and Tianshan Mountains. There used to be enough run-off so that Lake Taitema could survive for a long time at the end of the river. But, during the last five years, owing to a sharp increase in the water consumed for agriculture in the upper reaches, the water supply to the lower reaches has decreased constantly, as table 7 shows. The artificial Daixihaizi Reservoir has become "the end of the lake." Each decade, the lower reaches received less and less sluice water from the reservoir. From table 7 it can easily be seen that, during the last three decades, the run-off volume has shown only small variations compared with the average volume of 49.2 x 108 m³ at the Aral Hydrometric Station, which represents the volume of water supply contributed to the upper reaches of the Tarim River by its tributaries, but has decreased station by station from the upper to the lower reaches until only about one-quarter of its original volume of 1957-1960 remains at Qara Station in 1986.

Even worse was the fact that more than 300 km of river bed and all of Lake Taitema have been dried up for many years. The groundwater level on both sides of the river bed declined quickly from 3-5 m to 8-10 m or more below the ground surface. For instance, the groundwater levels were 3-5 m in two wells of the Aragan Region in the 1950s and descended to 11-13 m in 1985 (Wang 1986). Table 8 displays another example of shortening of a seasonal section of the Keriya River in Xinjiang.

In the 1950s, there were 52 lakes of over 5 km² in area in Xinjiang, totalling 9,700 km², but that number had decreased to 4,700 km² by the early 1980s. The famous Lake Lup Nur (3,000 km²) dried up in 1964 and others, such as Lake Manas (550 km²) in 1960, Lake Taitema (88 km²) in 1972, and Lake Aydingkol (124 km²) in the 1980s, dried up in succession. Lake Ebinur (1,070 km²) and Lake Ulungur (745 km²) have been reduced to one-half and one-tenth their original size, respectively, since the 1950s. In the Alxa Plateau of Inner Mongolia, the Gaxun Nur Lake (262 km²) dried up in the 1970s and the Sogo Nur Lake in the 1980s.

Since expansion of the irrigation areas in the upper reaches has increased the proportion of backwater (recharged from the irrigated land), the degree of mineralization has increased in the lower reaches, which has caused water-quality deterioration. The degree of mineralization has changed at the Aral Station as follows: initially, 0.33-1.28 g/litre, with an average of less than 1 g/litre year-round except in May (the driest season) before the upper area was irrigated on a large scale; subsequently, more than 1 g/litre year-round except in the flood season, with 2.5-5.5 g/litre in the dry season. The degree of mineralization for groundwater from Aragan to Lake Taitema was raised from less than 1 g/litre in the 1950s to 2-10 g/litre in the 1980s along the Tarim River, and reached over 400 g/litre at Lake Taitema in 1982 (Zhou 1983). In

Table 7 Run-off Volume (108 m³) Passing the Main Hydrometric Stations (Points) along the Tarim River







Station (point)

Period

Aral

Qiman

Taba Luntai

Confluence one a

Confluence two b

Qara

Sluice from Daxihaizi Reservoir

Yengisu

Argan

Luobuzhuang Lake Taitema

1957-1960

49.4

43

32.4

(28)

(19)

13.3

(8-9)

Run-off perennial

(4-5)

1961-1970

51.3

44.7

33.2

(17)

(11)

9.4

3.6

flood water only

2 m³/s (Oct. 1965)

1971-1980

44.0

35.2

26.8

(15)

(8)

6.3

0.5


Dried up (1974)

1981-1985

46.2

37.7

24.6

(13.5)

(3.8)

3.7

0.6 (1985)


Dried up

Dried up

1986

48.0

35.0

20.9

(11.0)

(2 6)

3.4

No sluice

Dried up

Dried up

Dried up

Source: CAS (1989).
a. Run-off flowed in the Tarim river from the Wushiman river.
b. From the Ogan river.

Table 8 Shortening Situation of a Seasonal Section of the Keriya River

Period

Type of run-off

Place reached

Distance from Yutian (km)

Extent of shortening (km)

1950s

Flood water

Xiabulak

305



Normal run-off

Tobkargan

265


1960s

Flood water

Xiaderan

255

50


Normal run-off

Yirake

250

15

1970s

Flood water

Aktuzi

245

60


Normal run-off

Xiakshimu

241

24

1980s

Flood water

Daiheyan

200

105


Normal run-off

Lianmaza

115

150

Source: Tian (1986).

Table 9 Irrigation in Southern Xinjiang in 1985

Region

Water use(108 m³)

Irrigation area(ha)

Irrigation quota(m³/ha)

Canal utilization coefficient

Kizilsu

8.34

49,800

16,747

0.43

Kashgar

87.00

521,100

16,695

0.39

Nongsanshi

10.22

48,400

19,080

0.45

Hotan

39.70

212,100

18,717

0.38

Bayingolin

27.64

186,180

14,846

0.40

Lake Borten (1,019 km²), the degree of mineralization changed from 0.39 g/litre in the 1950s to 1.5 g/litre in the 1970s, and to over 1.8 g/litre in the 1980s; the lake level has descended from an elevation of 1,048.5 m in the 1950s to 1,047.5 m in the 1960s, 1,046.0 m in the 1970s, 1,045.6 m in 1985, and 1,044.8 m in 1986, a total drop of 3.70 m.

Salinization

Water conservation is an essential prerequisite for constructing new oasis agriculture in the arid regions. A vast area of wasteland has been opened up, dependent solely on the water-supply system. But if the water management is poor and inappropriate, the new productive oasis could become wasteland again. For a long time in the past, much attention was paid to broadening water sources, but less to reducing water wastage. The waste of water, or overuse of water resources, was a very common irrigation practice, resulting from the backwardness of such systems as flood irrigation. Channel permeation wasted water in great quantities, too, since only 0.5-1.0 per cent of the total number of channels had been treated to be waterproof. Under those conditions, a high irrigation quota was impossible to avoid. Table 9 shows the situation of irrigation in the southern part of Xinjiang in 1985. The gross irrigation quota in the area was more than 14,850 m³/ha and even reached 19,000 m³/ha. Very disadvantageous also was the fact that many of the irrigated areas were not fitted with drainage systems. Such a practice not only wasted water resources but also did not meet the water need for crops in good time and sufficient quantity, and caused the rising of groundwater levels and the creation and expansion of land affected by salinization. Up to the late 1980s, about 1.15 million ha of land had been salinized to a serious degree, one-third of the total irrigated farmland in the arid regions of China.

Table 10 Degradation of Populus Diversifolia Woodland in the Lower Reaches of Some Rivers in the Arid Regions of China


Period


River

1950s(ha)

1980s(ha)

Percentage decrease

Heihe

67,000

-

100.00

Shiyang

72,000

2,300

68.10

Yarkant

171,300

94,000

44.70

Tarim

54,000

16,400

69.60

Kaxgar

70,000

28,600

59.10

Kaxakax

10,700

1,170

89.00

Vegetation Degeneration

The unfavourable changes in the water supply and the degree of mineralization resulted in serious vegetation degeneration, especially of woodlands (mostly composed of Populus diversifolia), in the regions. Of course, felling the trees to open up wasteland and to gather firewood for heating and cooking destroyed the woodland even more quickly. But in the lower reaches of the rivers, a more important factor was the water. Table 10 shows examples of the degradation of P. diversifolia woodland in the lower reaches of some rivers in the region.

Vegetation has also been degraded by overuse of groundwater in oases that are located at the lower reaches of rivers. Take the Minqin Oasis of the Shiyang River as an example. Because the surface run-off to the oasis has been lowered continuously (5.46 X 108 m³ in the 1950s, 4.49 x 108 m³ in the 1960s, 3.23 x 108 m³ in the 1970s, and 2.22 x 108 m³ in the 1980s), groundwater has been pumped extensively since the 1970s (1-3 x 108 m³ annually), and the accumulated total for the following 15 years amounted to 36.28 X 108 m³, which greatly exceeded the quantity of recharged water in the same period. The utilization ratio of groundwater for agriculture has increased from 4-5 per cent in the 1950s to 50 per cent in the 1980s. For these reasons, the groundwater level has declined by a large margin, by about 4-17 m from place to place at the oasis. The natural and artificial vegetation has withered and died. There were 220,000 ha of arboreal and shrub woodland in the late 1950s, of which 72,600 ha in good growth were left in the late 1980s; thus, about 67 per cent of the woodland has degraded. The vegetation cover has decreased from 44.8 per cent to 15 per cent (Zhu and Chen 1994).

Sandy Desertification

Sandy desertification is a major part of environmental degradation in the arid regions of China (Zhu and Chen 1994), and is mainly caused by excessive human activities facilitating wind erosion. Wind erosion damages the structure and composition of soil and leads to a rapid decline of biomass production and potential productivity of the land. The features of the land surface will deteriorate under the impact of wind erosion. Wind erosion occurs after the vegetation has been destroyed by overcultivation, overcollection of fuel wood, overgrazing, and misuse of water resources.

A very good example here can illustrate what constitutes misuse of water resources. Salinization was caused principally by the overuse of water in the upper and middle reaches of the rivers, while the sandy desertification spread because there was no more water available in the lower reaches. Many areas of farm land had to be abandoned along the lower reaches since the water supply had been cut off. Those areas were subject to erosion by wind and became decertified land some years later. Since the 1950s, more than 132,000 ha of farm land have been decertified in the regions along the lower reaches of the Tarim River and Konqi River, 25,400 ha along the Shiyang River and 30,000 ha along the Hotan River. Also, much range land and woodland has been degraded in the same period. In total, 343,000 ha of abandoned land have been decertified in the southern part of Xinjiang (Wang 1996) and much more in the arid regions as a whole. The degradation of the agricultural environment because of misused water resources in the arid regions can be seen in summary in figure 2.

Improving water management for sustainable agricultural development

Water resources are the most important condition for agricultural development and hence economic development and progress of the society in arid regions. Water management and utilization have made great contributions to agriculture, but were accompanied by some environmental and social problems because of the misuse of water resources. At present, developing agricultural production is limited by the degree to which the water supply occurs in the right amount and at the right moment in the arid regions of China. Consequently, the urgent challenge before us is the improvement of water management and utilization, which not only is required to ensure the sustainable development of the economy, but also is needed to protect the agricultural environment. Some suggestions based on typical examples of good water management in the region can be made as follows.

1. Take the Continental River Basin As an Integrated Ecological System to Unify Water-Use Planning with Due Consideration for All Concerned

In the arid regions, the formation, distribution, and transformation of water resources originate from each continental river basin through the link between surface run-off and groundwater, which constitute an integrative valley ecosystem from the upper to the lower reaches of the river. The oasis agriculture in the river basin depends on the water supply. Any unsuitable water use will cause an imbalance of the ecosystem and environmental degradation, and consequently endanger the agricultural production. So it is a vital task to take the river basin as a whole ecosystem to unify the water-use plan. In accordance with the principles of overall consideration of all factors in the upper, middle, and lower reaches of the river, of unified management and utilization of surface and groundwater resources, and of centralized distribution of water supply along the river, the former intensive water use should be regulated and the scope of land use should be maintained at the level of the maximum water capability for irrigation. A good example is the well management of the Manas River basin in the south-western fringe of the Gurbantunggut Desert in Xinjiang in the aspects of water use and water-conservation projects.


Figure 2 Diagram of Degradation of the Agricultural Environment by the Misuse of Water Resources in the Arid Regions of China

2. Increase the Utilization Ratio of Water Use and Establish a Stable and Highly Efficient Artificial Ecosystem in Each River Basin

In the arid regions, agriculture can be practiced only in the oases, and over 90 per cent of farmland relies on irrigation. The average grain yield is 2,100-2,500 kg/ha, but 3,700-4,000 kg/ha in many high-yield fields (Wang and Zhu 1989).

The land's productivity has a great potential to be exploited. Under the present conditions of available water and favourable heat and light resources, along with gigantic efforts to increase the production so as to increase the multiple crop index, to choose crops in the light of water-supply variation in different seasons, to ameliorate the soil, and to control salinization, a stable and highly efficient artificial ecosystem will not be so difficult to establish. Again, the example is the artificial oasis ecosystem in the Manas River basin in Xinjiang. Here, the utilization ratio of water use was increased to as high as 85 per cent in the 1980s. The areas of artificial oasis agriculture expanded from 1,200 km² in the 1950s to 7,200 km² in the 1980s.

3. Improve the Conveyance System and Irrigation Technique

Although many water-conservation facilities have been constructed, most of them still need to be completed by adding conveyance systems, and the trunk and branch canals also have to be treated with seepage-proof materials, so that more benefits of water use can be obtained. For example, in the Shihezhi reclamation area of Xinjiang, the irrigation system with over 40 per cent seepage-proof canals has effectively saved water since the canal utilization coefficient reached 0.63 and the irrigation quota decreased to 5,460 m³/ha.

The irrigation techniques, such as flood and string irrigation, are very backward in the arid regions, too, which results in the large gross quota of irrigation (table 9); capital construction on farmland and better techniques (furrow and border method of irrigation) should therefore be carried out. A series of experiments on the Yarkant River of Xinjiang shows that the gross quota of irrigation could be decreased on average to 2,300 m³/ha when the better technique was practiced, and about 3.87 x 108 m³ of water could be saved annually over a total of 167,000 ha land if spring-sown crops were adapted to the border method of irrigation along the river only. Information regarding the advanced technique of spray and drip irrigation should be spread and applied, although we would not expect that to be on a large scale at present because of the higher cost.

4. Protect the Natural Vegetation and Develop an Artificial Shelter Belt for a Better Agricultural Environment

The oasis is the foundation of agriculture. But only 3-15 per cent of the river basin area is constituted by oases in the arid regions, which are surrounded by deserts and face many natural disasters such as drought damage, frost injury, hail, flooding, sandstorms, dry and hot winds, and wind erosion. Vegetation serves to withstand these disasters; thus, on the one hand, it is a foundation to safeguard the stability of the oasis and on the other hand it is the most stable part of production in the arid ecosystem. It is, consequently, very necessary to ensure a volume of water for use on woodland and range land, which will certainly have the effect of protecting the oasis ecosystem.

Based on the experience of oasis shelter-belt construction in the arid regions, the forestry should keep a certain proportion in the oasis area. In the Shihezhi reclamation area of Xinjiang, the shelter-belt covers 7-15 per cent of the irrigation area on the edge of deserts and 5-10 per cent in the oases. In the Hexi Corridor Region the proportion is 5-10 per cent. Under normal conditions, the shelter forest is planted along the canal or around the crop land, so the seepage water from the canal and land can be used by the forest. That being the case, the forest can fully save and utilize the farmland irrigation water, as well as providing biological drainage to avoid salinization. At present, the total forest land in the arid regions comprises about 5-10 per cent of irrigation land, which still should continue to increase. The water supply for the shelter-belt and woodland should be about 10 15 per cent of total irrigation water in the oases.

Conclusions

Water is one of the most challenging current and future natural resources issues in the arid regions of China. For sustainable agricultural development and, hence, economic growth and society's progress, water is the key to success. Although there are vast wastelands and light and heat resources, the local economy depends only on irrigated agriculture and animal husbandry because of the water limitations. In the arid regions of China, water utilization has a long history and human activities in water management have improved the agricultural environment to be favourable for subsistence and development on a large scale. Along with the construction of reservoirs, irrigation and drainage systems, and other water-conservation facilities, the old oases have been expanded and new oases and artificial woodland and range land have been created. These have brought about great advances in agricultural production. But, owing to increased human requirements and overused and misused water resources, agro-environmental degradation, such as salinization, vegetation degeneration, and sandy desertification, has been caused and spread quickly. The existing water resources are already under great pressure from agriculture, and will face a much more difficult situation in the future. However, some typical examples have proved that agricultural development could be sustained if water management was improved. But how to conduct sound water management is still the most important question for sustainable development when we face agriculture that is limited by water.

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