Download Water problems and hydrological research in the Yellow River and

HYDROLOGICAL PROCESSES
Hydrol. Process. 18, 2197– 2210 (2004)
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/hyp.5524
Water problems and hydrological research in the Yellow
River and the Huai and Hai River basins of China
Changming Liu1,2 * and Jun Xia1,3
1
Institute of Geographical Sciences and Natural Resources, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China
2 Beijing Normal University, Beijing 100875, People’s Republic of China
3 Wuhan University, Wuhan 430072, People’s Republic of China
Abstract:
This paper deals with hydrological research in regard to the water resources crisis in the vulnerable areas found in
the northern part of China. This area includes three main river basins, namely the basins of the Yellow (Huang)
River, the Hai River and the Huai River. Several water problems are becoming very severe. Among them, two are
the most critical: the Yellow River has been drained dry in the main course of its lower reaches and along its major
tributaries, and the groundwater table has rapidly declined in the floodplains of the three rivers’ downstream areas.
To counter the problems, particularly the critical issues mentioned above, hydrological research, which serves as the
basis of water development and management, has been carried out in the last two decades. This paper addresses three
basic scientific problems in North China, namely: (a) water consumption and the capacity for saving water; (b) the
changes in hydrological processes and water resources caused by natural change and human activities; and (c) the
ability to supply water resources and water safety in terms of both quantity and quality within a changing environment.
However, opportunities and challenges for ameliorating the problems exist, and new ideas and methodology to solve
the problems have been proposed, such as the interface process study on the interactions in the soil–root interface,
the plant–atmosphere interface, the soil–atmosphere interface, and the interface of soil water and groundwater. In
order to manage water resources in a sustainable manner, the study of water resources’ renewal ability as affected
by natural change and human activity is addressed from the viewpoint of both water quantity and quality, and their
integration. To reduce the vulnerability of water resources in regional water management, a paradigm of sustainable
water resources utilization is also proposed, using water–heat balance, water–salt balance, water–sediment balance,
and water supply–demand balance. This approach may help reveal the basic problems and point to possible approaches
to solving the water problems in North China in the 21st century. Copyright  2004 John Wiley & Sons, Ltd.
KEY WORDS
water problems; North China; hydrological processes; water resources
INTRODUCTION
Many countries of the world have been faced with increasing problems in managing their water resources
for decades (WMO–UNESCO, 1988; Plate, 1993; Simonovic, 1996; Falkenmark, 1997; Loucks, 1997;
Kundzewicz, 1997; World Bank, 1997; Huang and Xia, 2001). The imperative of sustainable economic
development demands sound water management and more research on hydrological processes. China is an
example of a country where water-related problems are multifold, ranging from water shortage and ecoenvironment degradation to food safety. It is well known that the drying up of the lower reaches of the
Yellow (Huang) River has almost become an annual event since 1972. And the crisis of shallow groundwater
depletion on the alluvial plains of the Yellow, Huai and Hai Rivers in the last two decades is no less serious
(Chen, 1985; Liu and Wei, 1989; Chen, 1995; Liu and He, 1996; Lou and Le, 1996; Xia, 1997; Xia and Hu,
1997; Lou, 1998; Wu et al., 1998; Chen and Xia, 1999; Chen et al., 1999; Liu and Cheng, 2000; Liu and
* Correspondence to: Changming Liu, Institute of Geographical Sciences, Natural Resources Research, CAS Building 917, Dahin Rd, Anwai,
Beijing 100101, China. E-mail: [email protected]
Copyright  2004 John Wiley & Sons, Ltd.
Received 20 December 2002
Accepted 30 July 2003
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C. LIU AND J. XIA
Yu, 2001; Xia and Chen, 2001; Xia et al., 2001; Liu et al., 2002). In order to manage water resources in a
sustainable manner, it is imperative to study the hydrological processes associated with the water problems
to understand the causes of the existing vulnerability of water resources and to try to increase water safety.
Since the completion of a nationwide assessment of water resources by China’s Ministry of Water Resources
(MWR) in 1986 (MWR, 1987, 1992), a number of research papers from national perspectives have appeared
in Chinese journals that have become major references on a variety of issues related to water resources (Qian,
1991; Liu and He, 1996; Zhang, 1999). Recently, the Chinese Academy of Engineering has completed a 2 year
project and produced a series of volumes on strategic studies of water resources for sustainable water resources
development in China (e.g. Liu and Chen, 2001; Qian and Zhang, 2001). This series of publications addresses
a wide variety of important issues, including: the assessment, analysis and forecasting of the nation’s water
resources; water supply and demand relationships; flood prevention and hazard mitigation; agricultural water
demands and water conservation for effective farming; sustainable development and the utilization of urban
water resources; and pollution prevention and the control of river, lake and ocean waters. These research efforts
have also discussed ecosystem restoration and water resources protection and utilization, rational reallocation
of water resources in the light of North China’s water shortages, namely the south-to-north scheme of water
transfers, as well as water resources development and utilization in western China.
Responding to international research programs (IGBP-BAHC, WCRP, GEWEX/GAME, etc.) and the
demands for social and economic development in China, a series of key projects on hydrological processes
and water resources management have been supported by the National Natural Science Foundation of China
(NNSFC), the Chinese Academy of Sciences (CAS), the MWR, and the Ministry of Science and Technology
(MOST), particular in the last 10 years. Most of the key projects focus on a better understanding of the role
of hydrological processes in environmental change or water resources variation caused by climate change and
human activity in water-vulnerable regions, such as North China and Northwest China.
This paper reviews water problems and the progress of hydrological process research in the North China
region. The main discussion is focused on three key issues:
1. The water crisis in North China, where there is a mismatch between water resources and the distribution
of population. Two key water problems, namely the drying up of the main course of the lower Yellow
River reaches and eco-environmental degradation, are addressed.
2. Recent progress in hydrological process research associated with water problems in North China, where
the two main drivers of climate change and human activity, including population growth and economic
development, were analysed in terms of practical observations and case studies in this regions.
3. The scientific problem and new challenge of water issues in North China were discussed. These include
how to understand the hydrological cycle and water resources vulnerability in a changing environment
and how to manage water resources in a sustainable manner.
In contrast to past publications on water issues covering the whole nation (Chen and Xia, 1999; Xia and
Chen, 2001), this paper focuses on the urgent water crisis and the scientific problems linked with hydrological
process research in the regions of the Yellow River, Huai River and Hai River. After a discussion of the role
of the hydrological sciences, the challenges and opportunities for hydrologists in the development of new
scientific knowledge and engineering practices for water resources management in China’s water-vulnerable
regions will be highlighted.
THE MAIN PROBLEMS ASSOCIATED WITH THE WATER RESOURCES CRISIS
Of the several major river fluvial plains of China, the Yellow–Huai–Hai River fluvial plain is the largest
(Figure 1). In a general sense, it lies in the area north of the Huai River’s main course, which drains an area
of about 400 000 km2 . The Yellow River flows across the middle of the plain and has shifted its main courses
Copyright  2004 John Wiley & Sons, Ltd.
Hydrol. Process. 18, 2197– 2210 (2004)
HYDROLOGICAL RESEARCH IN THE YELLOW RIVER
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Figure 1. A map of the Yellow–Huai–Hai River fluvial plain in China
26 times over a large 250 000 km2 area lying between the main courses of the Huai and Hai Rivers, reaching
Tainjin City in the north and Huaiying County in the south. Geomorphologically, it is the Yellow River that
has produced the floodplain during China’s long historical and geological past.
Because of the fertility of the fluvial sediments deposited by the Yellow River over this vast area, the
plain is of prime importance as a major farming, urban and industrial region of China, and it supports a vast
population. The plain has 175 ð 106 ha of cultivated land. The population was 213Ð9 million in 1998, with
41Ð4 million in urban areas that include several mega-cities, such as Beijing, Tianjin, Jinan, Shijiazhuang
and Zhengzhou. However, a number of water quantity and quality problems are associated with the region’s
rapid growth and development. These problems have reached the stage of crisis and challenge the wisdom of
hydrologists and decision makers at the present time and in the near future.
The severity of drying up of river courses
Since the 1970s, the flows in the Yellow River and the Hai River have ceased frequently in their lower
reaches traversing the fluvial plain. For instance, during the 27 years from 1972 to 1998, the lower Yellow
River has dried up, on average, in 4 years out four times every of every 5 years (Table I). The condition
became more severe in the 1990s, when the channels of the lower Yellow River dried up every year, with
the drying up appearing unusually earlier and earlier and lasting longer and longer in the years of occurrence.
Moreover, the segment of the river’s dried-up channel has continuously extended towards the upper reaches
(Table I). The length of the dried-up segments in the lower reaches during the 1970s averaged 242 km; this
increased to 256 km in the 1980s and 392 km in the 1990s. In 1997, parts of the river dried up almost
completely throughout the entire year. According to the hydrological observations at the river estuary, the
interruption lasted for 330 days without any freshwater flowing into the sea. In 1997, the dried-up segments of
the river course extended upwards to Liuyuankou in Kaifeng City, Henan Province. The length of the dried-up
segments was 704 km, accounting for 90% of the river course length in the lower reaches. Furthermore, in the
middle reaches of the river, the flows of the primary tributaries, such as the Qinhe River, Yihe River, Fenhe
River, Dawenhe River, Yanhe River and Weihe River, were also drained dry subsequently. The Yellow River
is now shrinking. As for the Hai River courses traversing the fluvial plain, they have also dried up since the
1970s due to increasing upstream water use and decreasing reservoir water storage.
Copyright  2004 John Wiley & Sons, Ltd.
Hydrol. Process. 18, 2197– 2210 (2004)
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C. LIU AND J. XIA
Table I. Records of the dried-up channels in the lower reaches of the Yellow River at Lijin hydrological station
Year
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
Dried-up channels
Occurrences
Duration
(days)
3
0
2
2
1
0
4
2
3
5
1
1
0
0
19
0
20
13
8
0
5
21
8
36
10
5
0
0
Length (km)
310
0
316
278
166
0
104
278
104
662
278
104
0
0
Year
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
Dried-up channels
Occurrences
Duration
(days)
0
2
2
3
0
2
5
5
4
3
7
13
16
6
0
17
5
24
0
16
83
60
74
122
136
226
142
42
Length (km)
0
216
150
277
0
131
303
278
308
683
579
704
142
42
From the bearing supply capacity of the Yellow River and the social and economic development of the
provinces that lead to withdrawal of water from it, we may conclude that it is time to control the water
diversions along the upstream river courses. Otherwise, with further development, the demand for water will
increase more quickly, leading to continuous drying up of the river channels downstream. Moreover, as a result
of increasing competition among all sectors of water utilization, such as water for economic development,
sediment transport, soil conservation, ecological protection in the river’s estuary and delta areas, the drying
up of the channel will lengthen and the situation will become extremely serious if no action is taken soon. In
summary, the lack of water and the drying up of the lower Yellow River courses demand immediate attention
and action.
The severity of groundwater exhaustion
Since a great deal of water has been used for the rapid development of industry and urbanization, the
supply of water resources for agriculture has greatly declined. Rapid development of cities and industries and
the increase in farmland irrigation has doubled water demand. The consequence is excessive withdrawal of
groundwater in the areas.
Over the western part of the plain, the groundwater table has been dropping at an accelerating rate. The
shallow groundwater table declined from a depth of 3 to 4 m in the 1950s to more than 20 m in the 1980s and to
about 30 m in the 1990s. The decline of the shallow groundwater table observed along the Beijing–Guangzhou
railway line in North China is shown in Figure 2. In such a case, if the excessive extraction of groundwater
persists at this rate, then the obvious result would be a sharp rise in irrigation cost with deeper water table. If
the irrigation water supply cannot be assured, then high-output agriculture in the plain area is not sustainable.
A degradation of groundwater quantity and quality would take place over wide areas. Located in the lower
section of the plain, the Heilonggang River basin, which consists of low-lying flat lands, has suffered from a
shortage of surface water. People have extensively mined the limited groundwater from deep aquifers. Deep
wells in the areas have been sunk to pump deep groundwater since the beginning of the 1970s. The result
has been a persistently high rate of excessive withdrawal, leading to a deep groundwater table decline of 2
to 3 m year1 and to the formation of large depression cones over a wide area. Up to now, the groundwater
table has failed to about 80 m below sea level in Chaozhou Prefecture of Hebei Province. Over-pumping in
both rural and urban regions and the lowering of the groundwater table have caused severe impacts on both
Copyright  2004 John Wiley & Sons, Ltd.
Hydrol. Process. 18, 2197– 2210 (2004)
HYDROLOGICAL RESEARCH IN THE YELLOW RIVER
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Buried depth of groundwater table (m)
Baoding Zhuozhou
Jumahe
Dingxing
Zhanghe Handan Yongnian Xingtai Lincheng Gaoyi Shijiazhuang Dingzhou
0
5
10
15
20
25
30
35
40
April, 1964
May, 1984
May, 1993
May, 1998
45
Figure 2. Decline of the groundwater table observed along the Beijing–Guangzhou railway line in northen China
the groundwater itself and the environment. Firstly, the quality and quantity of groundwater have declined.
Secondly, these have resulted in problems of land subsidence in a number of places, as well as seawater
intrusions in the coastal plain area along the Bohai Gulf. Moreover, in a large part of Heilonggang in Hebei
Province, deep groundwater contains high levels of fluoride and more than one million people are drinking
the high-fluoride water. This severely harms the health of the local people.
KEY FEATURES OF THE PROBLEMS
Vulnerability of water
The plain crossed by the three rivers lies in a transitional zone between semi-humid regions and a semi-arid
region. The annual precipitation of 500–600 mm is much lower than the annual evaporative capacity. The
aridity index is between 1Ð3 and 1Ð5, which climatologically means that there is a certain degree of water
scarcity in this area. In addition to this, being under the influence of the southeastern Asian monsoon, the
region’s precipitation varies greatly from season to season and from year to year. On the other hand, the arable
land ratio in the northern part of China is significantly higher than that in the south. In the four major basins in
the north (the rivers Liao, Hai, Yellow, and Huai), farmland covers 40Ð2 ð 106 ha, accounting for 41% of the
total farmland area in China, but the annual amount of river runoff is only 163 km3 , which is only 6% of the
national total. The per capita annual runoff volume here is only 431 m3 , which is far lower than the volume
of 1700 m3 per capita generally recognized worldwide as a water shortage criterion. The available water
volume per unit farmland area is low, i.e. only 4050 m3 ha1 , which is only 15% of the national average of
26 400 m3 . Consequently, water resource availability in time and space is very uneven, which points to poor
availability of water supply under heavy demand due to rapid population growth and economic development.
Water overuse and water pollution have increasingly combined with negative systematic feedbacks to increase
the vulnerability of the region’s water resource systems.
Influence of climate change
The water resources of the rivers traversing the great fluvial plain are mainly derived from their upstream
watersheds. For instance, 96Ð5% of the lower Yellow River water comes from its middle and upper reaches.
Therefore, the hydrological response of the lower Yellow River to climate change is extremely dependent on
the climate change occurring in the middle and upper reaches. Long-term climatic records for the last five
decades and geographical information system mapping suggest that there is a geographical differentiation in
precipitation that corresponds with temperature. In the middle and upper river basins, the annual temperature
anomaly has remained positive as a general tendency since the 1970s, as would be expected if global
Copyright  2004 John Wiley & Sons, Ltd.
Hydrol. Process. 18, 2197– 2210 (2004)
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C. LIU AND J. XIA
warming were occurring. At the same time, the annual precipitation in the basin has shown a decrease, with
continuously negative anomalies since the 1970s. In the 1970s, in the middle reaches of the Yellow River
basin, the annual precipitation anomaly had a negative value. In the 1980s, an obvious negative anomaly of
the annual precipitation appeared in the Ningxia Hui Autonomous Region of the upper Yellow River. During
1990–97, the annual precipitation changed, with a negative anomaly that was close to 0Ð1 10% at the
maximum being apparent. Annual precipitation has been decreasing as annual temperature has risen in the
basin; consequently, a reduction in river runoff has occurred (Figure 2). This demonstrates that such change
is non-linear in nature.
Impact of human activities
During the 1990s, water consumption by industry and agriculture increased dramatically and the contrast
between upstream and downstream reaches became increasingly apparent. Each water consumption area
expanded their projects, so that the water-withdrawing capability of the projects along the river totalled
6000 m3 s1 , which amounts to 3Ð4 times that of the average annual runoff 1830 m3 s1 . This amount of
water-withdrawing capacity has exceeded the available amount of the natural runoff. The Yellow River plays
an important role in water supply for wide areas in northern and northwestern parts of China. With a rapidly
developing economy in these regions, water demand has increased greatly. Up to the 1990s, annual water
withdrawal from the river for domestic use and production amounted to about 30 ð 109 m3 , which was 1Ð6
times more than that of the 1950s (Table II). For these regions, agricultural irrigation is the main sector, which
makes up about 91% of the total water consumption in the basin. The irrigated area in the basin had been
expanded from 1 402 700 ha in the 1950s to 4 870 700 ha in the 1990s, an increase of almost 3Ð5 times during
the last five decades. Consequently, water utilization has increased by 4Ð2 times in the same period. In the
basin, especially in its fluvial plain in the lower reaches, water diversions and withdrawals for irrigation and
industrial production increased more rapidly. These have not only sharpened the contradiction between water
supply and demand, but have also intensified the negative impact on the river’s water system in the wake of
a reduction in runoff. Moreover, the reservoirs on the tributaries and the main courses have intercepted flows
from the upstream area. Thus, the downstream courses in the fluvial plain have been shrinking.
The analyses based on the hydrological data show that there were successive dry years in the Yellow River
basin in the period from 1922 to 1932, and that the average annual flow of the Yellow River during this period
was reduced by 34%. There were no records to show that drying up occurred in its lower course. However,
in the dry-year period of the 1990s, the average annual flow was reduced only by about 12% and the river
course has dried up almost every year. Comparisons between the above two periods suggest that the dominant
factors affecting the drying up of the river courses are highly likely to be related to human activities.
NEW CHALLENGES FOR HYDROLOGICAL RESEARCH IN NORTH CHINA
As the most populous country in the world, China faces many resource problems and challenges, among them
water being a critical issue. Understanding water-cycle behaviour in a changing environment and establishing
Table II. Annual average amount of water utilized and irrigation areas during different periods of different segments
Water utilized 108 m3 Irrigation areas 104 ha
Items
Period
1950s
1960s
1970s
1980s
1990s
1950s
1960s
1970s
1980s
1990s
Upper reaches
Middle reaches
Lower reaches
Whole river
73Ð4
30Ð0
18Ð9
122Ð3
95Ð2
49Ð4
33Ð1
177Ð7
102Ð9
63Ð4
83Ð5
249Ð8
121Ð1
62Ð1
112Ð9
296Ð1
131Ð7
60Ð2
107Ð8
299Ð6
68
42Ð29
30Ð0
140Ð29
88Ð46
80Ð22
33Ð3
201Ð98
112Ð7
114Ð4
100Ð0
327Ð1
130Ð3
130Ð1
146Ð81
407Ð2
131Ð5
133Ð3
148Ð27
487Ð07
Copyright  2004 John Wiley & Sons, Ltd.
Hydrol. Process. 18, 2197– 2210 (2004)
HYDROLOGICAL RESEARCH IN THE YELLOW RIVER
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a comprehensive strategy on water resources in the wider context of regional economic growth are two priority
topics of research for Chinese hydrologists. To mitigate serious water problems in North China, the Chinese
Government is considering the feasibility of large water-diversion projects from south to north (Zhang, 1999).
But the priority strategy is saving water and sustainably managing local water resources. The government
has addressed three priority principles related to water resources management, i.e.: (a) saving water prior to
diverting water; (b) waste-water treatment prior to transporting water; and (c) environment protection prior to
using water. As far as the hydrological basis for water resources management in North China is concerned,
the most urgent issues are likely to be as follows:
1. Understanding why the hydrological regime and associated water resources in this region have experienced
such a significant change; comparing climate change and human activities and determining the primary
cause; quantifying how water-cycle processes are impacted and changed by human activity.
2. Determining the capacity for saving water in North China in the agricultural and urban–industrial sectors;
clarify in this problem in relation to the wasting of water resources by the main sector of agriculture
irrigation.
3. Developing a decision-support system for ensuring water supply security, focusing on how to assess water
availability precisely in terms of quantity and quality and how to reallocate water resources spatially in
an optimal manner.
With support from the MOST, the CAS, the MWR, the NNSFC and other foundations, a number of key
projects on North China have been carried out and some outcomes are selected for the present special issue.
New opportunities and challenges for hydrological research will focus on (1) field-scale studies, (2) regionalscale studies and (3) eco-environmental equilibrium.
Field-scale studies
The senior author of this paper once proposed the concept of ‘five states of water interaction’ in 1988
(Liu and Wei, 1989). This idea involves the study of the interaction between atmospheric water, plant water,
surface water, soil water and groundwater. Water movement in the field is linked to all of the hydrological
states under natural or artificial conditions. In the soil system, the inputs of soil water include atmospheric
precipitation, groundwater capillary rise and artificial input of surface water (e.g. irrigation), and the outputs
are the evaporation directly from the soil surface and from plant transpiration to the atmosphere through root
absorption, and seepage from the soil to a groundwater aquifer. It is clear that the study of the ‘five states of
water interactions’ has expanded the scope of soil–vegetation–atmosphere transfer (SVAT). The total system
framework is shown in Figure 3. The five hydrological states are water in the air (P), soil (S), surface (R),
underground aquifers (G) and plants (V). In other words, the study is a kind of detailed analysis of the water
cycle at the field scale. Based on such an idea, a theoretical deduction can be employed for deriving an
interaction matrix of five hydrological states (Table III).
Obviously, the components P/G or G/R can be seen as interactions between surface and ground waters.
It must be pointed out that the coupled interaction systems in Table III are all simple couplings linking two
hydrological states. Moreover, from such a deduction we can also extend it for more combinations with more
links in the water coupling systems. The various combinations can be simple coupling of two hydrological
states (as shown in Table III), or the linkage of three, four or five hydrological states. For instance, by
linking three hydrological states there will be combinations of 10 varieties. For example, S, V and P form
the soil–plant/vegetation–atmosphere system (SVAT or SPAC). Apparently, in linking the four hydrological
states of P, R, S and G there will be five varieties, which would make an excellent research topic. In China,
we call this ‘water interactions among four hydrological states’, based on which the regional water resources
in North China have been assessed since the 1980s. As for linking five hydrological states, there will be just
one combination regarding the water cycle, which is now being employed for studies on agricultural water
management in the fluvial plain areas.
Copyright  2004 John Wiley & Sons, Ltd.
Hydrol. Process. 18, 2197– 2210 (2004)
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C. LIU AND J. XIA
Radiation
Wind speed
Temperature
Evapotranspiration
Precipitation
Humidity
Atmosphere
Gradient of temp.
Evaporation
Gradient of humidity
Direct radiation
PAR
Transpiration
Interception
Plant height
Leaf water potential
Root water
Uptaken rate
Water/heat
flow in
Soil-Plant
-Atmosphere
Continuum
Stomatal conductance
Leaf distribution
Canopy
LAI.
Soil water
movement
Albedo
Biomass
Root water potential
Root radium
Root system
Water flow
Resistance from
Soil-toot-leaf
-Atmosphere
Root distribution
.along soil profile
Soil heat flux
Infiltration
Subsurface water
replenishment
Soil surface evaporation
Soil physical characters
Soil hydrological
characters
Soil
Changs in
Subsurface water
Soil water content
Soil matric potential
Groundwater
Figure 3. The five states of water transfer and the associates physical processes
Table III. A theoretical deduction matrix of the coupled interaction
systems of the five hydrological states
P
R
S
G
V
P
R
S
G
V
1
R/P
S/P
G/P
V/P
P/R
1
S/R
G/R
V/R
P/S
R/S
1
G/S
V/S
P/G
R/G
S/G
1
V/G
P/V
R/V
S/V
G/V
1
Copyright  2004 John Wiley & Sons, Ltd.
Hydrol. Process. 18, 2197– 2210 (2004)
HYDROLOGICAL RESEARCH IN THE YELLOW RIVER
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Obviously, the above deduced coupling systems will be useful to control water interaction through the
interfaces between any two coupled hydrological states. Because of the complexity of water movement at the
interfaces between the systems, detailed measurements are required. Accordingly, field observations have to
be carried out in the study areas (Figure 3). The following major interfaces in the experimental sites have
been selected for study:
ž soil–root interface,
ž plant–atmosphere interface,
ž soil–atmosphere interface, and
ž interface of soil water and groundwater.
For example, the results of soil–atmosphere interface measurements undertaken at Lancheng eco-hydrological
station showed that, in a wheat field, direct evaporation from the soil surface and transpiration from the wheat
canopy contribute 30% and 70% respectively. This result will provide a potential figure of 30% for controlling
soil water evaporation from the soil–atmosphere interface.
Regional-scale studies
In the past, there was little concern for the renewability of water in studying the process of developing
water resources. Considering the water cycle in the hydrosphere, the transformations of hydrological states are
continuously happening, exhausting and renewing water quantity and quality. These processes are remarkably
complex. Dynamically, the transforming processes are changeable not only as a result of fluctuations in natural
conditions’ states, but they are also sensitive to human intervention in terms of water resources development.
In general, the water cycle in the hydrosphere always follows the law of mass conservation. Water exchanges
D in the hydrosphere or in its separate hydrological states can be changed quantitatively by the volume of
water storage V and water discharge Q in a given hydrological state:
D D V/Q
1
The value of D in Equation (1) can be defined as the water detention period, providing an indicator of the
water renewability, namely the time period needed to renew water in the given hydrological state. Obviously,
its reciprocal, 1/D, represents the frequency of water exchanges.
In the light of the problem of groundwater resource exhaustion, water-balance models and isotopic methods
have been employed as an important approach. Using 14 C determinations for dating groundwater storage, we
have learnt that the age of groundwater in the fluvial plain varies from 5000 years in the western piedmont
plain to 20 000 years in the eastern low-lying plain. This identification is important for controlling deep
groundwater mining at present and in the future.
In considering the drying up of the courses of the lower Yellow and Hai Rivers, the renewability of their
water is also of great significance in harnessing the rivers. For example, to alleviate drying up of the Yellow
River course, to rehabilitate the ecology and to protect the environment, there is an urgent need to keep
a sound water cycle in terms of maintaining the renewability in river water resource systems. Thus, the
MOST established a national key project regarding ‘The evolving law and maintaining mechanism of water
renewability of the Yellow River’ known as the Chinese ‘973’ project.
Different approaches can be adopted to investigate the natural hydrological cycle and the influence of human
activities in order to find the answers to such important questions as ‘What are the key factors controlling
the renewable capacities of water resources in a watershed like the Yellow River basin?’ and ‘How can a
quantitative evaluation of the renewability of water resources and their variations resulting from both natural
change and human impact be made?’
Renewability of water quantity can be characterized as the replenishment and recovery of water resources
from precipitation supply after losses through evaporation, runoff and withdrawal. It is directly related to
Copyright  2004 John Wiley & Sons, Ltd.
Hydrol. Process. 18, 2197– 2210 (2004)
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the periodicity of the hydrological cycle and the replacement rates of water bodies. Water renewability is
always limited by many factors, chief among which is a low precipitation total due to the characteristics of
regional climate. When water withdrawal exceeds the rate of replenishment and recovery, the renewability of
water resources is partially reduced or completely destroyed, causing damage to regional hydrological cycles
and ecosystems. Maintenance and protection of water renewability can only be achieved when consumption
of water is controlled within the limits of the mean annual availability of water resources. Obviously, water
renewability is closely related to water use and yield in a basin within a certain time period. Therefore, factors
such as climate, topography, soils, vegetation and human activities would affect water renewability in various
ways.
Renewability of water quality relates to the ability of water bodies to carry out self-purification after being
polluted by contaminants. Similarly, the concept indicates that water has an assimilative capacity and the
polluted water may be recovered by either self-purification or treatment. When the assimilative capacity is
not exceeded by pollutants or sewage discharge, water quality is able to recover and hence the renewability
of water quality is maintained. Otherwise, water quality will deteriorate and the renewability of water quality
will be damaged. Naturally, being closely tied to hydrological and water resources systems, the renewability
of water quantity and quality cannot be evaluated without a full understanding of the hydrological cycle. In
essence, the renewability of water resources reflects the effect of the hydrological cycle, and is thus controlled
by all elements influencing the water balance at various temporal and spatial scales. The basin defined by
natural drainage boundaries is scientifically and practically important as a system for studying the hydrological
cycle and managing water resources. Analyses of the system components and their interactions (Figure 4) help
hydrologists formulate fundamental rules and relationships which, in turn, can lead to a better understanding
of water problems.
It should be pointed out that a basin’s hydrological cycle consists of natural and manmade components at
the regional scale, but analysts should consider land and atmosphere interaction processes with a macro view.
Regional hydrological response to global change should be determined for projection of water resources in
the future.
Eco-environmental equilibrium
One of the most important concepts in water resources safety is its vulnerability, which is an indicator
or measurement used to gauge the ability of water systems to cope with changes in the eco-environment.
Vulnerability assessments are increasingly recognized as an essential scientific basis for integrated water
Evapotranspiration
Precipitation
Irrigation
Evaporation from water
Total
consumption
Impacted area
Transpiration
Surface water storage
Surface runoff
Evaporation
Soil moisture storage
Interflow
Groundwater storage
Groundwater flow
Stream channel storage
Transpiration
Evaporation
External water
Water supply
Water use system
Drainage system
Stream flow
Groundwater runoff
Figure 4. A conceptual model of the hydrologic cycle and water resources assessment under environmental change (Xia and Chen, 2001)
Copyright  2004 John Wiley & Sons, Ltd.
Hydrol. Process. 18, 2197– 2210 (2004)
HYDROLOGICAL RESEARCH IN THE YELLOW RIVER
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resources management. These assessments evaluate the combined effects of multiple stresses and potential
adverse outcomes for water systems at all scales, ranging from global to regional. Water resources are exposed
to the combined effects of climate change, land-use change and increased water use and water pollution. The
strength of these effects and the sensitivity of regional water resources determine their vulnerability to change.
Any adaptation and mitigation measures have to take into full account such integrated assessments of change.
The ultimate goals are a reduction in vulnerability, the return to sustainable use and the protection of regional
water resources. Targeted vulnerability research and application projects can provide a scientific basis for
planning and decision making. Specific pilot studies in the participating areas will be designed to demonstrate
the usefulness of the methodology and possible limitations, building upon ongoing integrated water resource
management assessments. This effort will also help fill gaps in our knowledge, as such studies will add more
regional analyses and applications to the limited number of examples of systematic studies that have been
carried out within the general framework of vulnerability assessments.
In China, the concept of vulnerability of water resources is less commonly used than that of the supply
capacity of water resources. How to reduce the vulnerability of water resources in a region is a big question.
Based on our long-term experience and research, we propose here a hydrological concept called the four
balances for water resources research.
The four balances represent an integrated hydrological concept incorporating the elements of climate, land,
ecology and socio-economy. The four balances are water–heat balance, water–salt balance, water–sediment
balance and water supply–demand balance. These balances are all closely related to the hydrological processes.
Water–heat balance. The latent heat of water vaporization is one of the more important factors in the
land-surface energy balance. We use the energy heat balance equation:
Rn H G LE P0 D 0
2
where Rn is net radiation, H is the sensible heat transfer in the atmosphere, G is the heat transfer through soil,
L is the latent heat of vaporization, E is the mass of the vaporized water, and P0 is the energy conversion of all
chemical syntheses. Combining Equation (2) with the average annual water balance equation, the water–heat
composed equation is obtained as follows:
ED
Rn H G
L
3
The water–heat balance is of significance in water conservation. The water–heat index, namely radiation
aridity Rn /(LP), can be used for regional water projects. Actually, R n /(LP) is the ratio of potential evaporation
to precipitation P for the reason that, in the heat-balance equation, Rn /L represents the upper limit of potential
evaporation PE PE D Rn /L. A regional wetness index is obtained by subtracting direct surface runoff Rs
from the precipitation P : Wh D P Rs . Using this, we define an index Cr to express the suitability of the
regional water–heat balance:
PE
Rn
E0
Cr D
D
³
LP Rs Wh
Wh
where E0 is an approximation of the evaporative capacity. When E0 /Wh D 1 the regional water is in a
suitable condition and the ecology of the region is in a sound state, namely no drought and no waterlogging.
This is an index used to plan China’s south-to-north water transfer projects. Thus, the water resources
development programme should be implemented in order to make the value of the E0 /Wh water index
approach unity, namely
E0
Cr D
!1
Wh C T
where T is water amount to be supplemented.
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C. LIU AND J. XIA
Water–salt balance. The following equation for regional water–salt balance is employed:
S B D C 1 P C C 2 Ri C 3 R0 S i C S r C S w
where SB is the regional water–salt balance, C1 t m3 is the total ion content in precipitation water P,
C2 t m3 is total ion content in the runoff entering the region Ri , C3 t m3 is the total ion content in
runoff draining out of the region R0 , Si and Sr (t) are the total salt contents absorbed and excreted by the
biota, and Sw (t) is the salt resulting from weathering of parent rock. The problem of unbalanced water and
ion flows in the fluvial plain of the Haihe River is a major reason for the development of regional salinization.
The annual salinity flushing into the sea from the plain depends on the total ion runoff into the sea. According
to measured data over the last 30 years, the annual runoff into the sea has decreased year after year owing to
high water withdrawal from the rivers. The salinity brought by runoff has therefore accumulated within the
plain.
Water–sediment balance. When rivers flow into downstream regions, sediments are deposited due to
the slope becoming more gentle and the declining flow velocity. The river courses are often clogged by
large deposits of sediment. In order to maintain the channel capacity for flood-flows, there is a need for
water–sediment balance in the river courses. For instance, after a series of drying-up periods along its
courses, the lower Yellow River has developed a much-reduced carrying capacity for transporting the hyperconcentrated sediment loads. This has resulted in channel aggradation and has raised the level of the river
bed. Consequently, there is an increasing threat of floods in the area along the lower Yellow River. A study
has shown that the lower Yellow River courses need an annual flow of 15–20 ð 109 m3 to maintain a proper
water–sediment balance.
Water supply–demand balance. There are many water-related problems in the study areas. The most critical
issue is the severe contrast between water supply and water demand in cities and rural areas. The latest estimate
of deficit between water supply and demand in the Yellow–Huai–Hai River basins is 24Ð2 ð 109 m3 . In this
case, we must consider that the development and utilization of water resources should meet not only the
requirements of social and economic development, but also keep water resources continuous and sustainable.
These two attributes are mutually dependent: without the sustainable development of water resources there
will be no sustainable and stable development of society and the economy; similarly, without the support of
the water resource system the requirement of social economic development will put a severe strain on the
water resource system and might destroy the renewability of the water resources system.
CONCLUDING REMARKS
This paper has shown that the northern part of China faces a number of water problems, including the
drying up of the region’s river courses and a declining groundwater table over a wide area. Such problems
have caused severe degradation of the eco-environment. Obviously, the main reasons for such problems are
inappropriate development of water resources and the anomalous oscillation of climate change.
From a hydrological point of view, a water body is in a hydrological state linked to both the hydrosphere
and the eco-environment. Thus, better understanding of water resources systems must be based upon the
hydrological concept.
The importance of hydrological research in managing water resources can be seen from the following three
perspectives: (1) accurate assessment of water quantity and quality requires precise hydrological measurements
and observations covering all components of a water body; (2) the rational development and utilization of
water resources at various scales in time and space requires a healthy hydrological cycle that can help maintain
water and energy balance and water renewability in the regional natural water system; (3) the harmony between
regional water development and the maintenance of a sound eco-environment requires improved understanding
Copyright  2004 John Wiley & Sons, Ltd.
Hydrol. Process. 18, 2197– 2210 (2004)
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of environmental hydrology. Hydrologically, it is essential to maintain the four balances in a region, namely
water–heat balance, water–salt balance, water–sediment balance and water supply–demand balance. The
maintenance of the four balances is highly important for the development of any regional economy.
ACKNOWLEDGEMENTS
In the last few decades, North China has experienced severe water crises. A number of research projects on the
region’s water issues have been organized by the MOST, the NNSFC and the CAS. In addition, the provinces
in northern China have also supported a number of local projects. This special issue of the international
journal Hydrological Processes reports on selected facets of hydrological studies regarding water resources
management in northern China. We wish to thank the support offered by the Key Project of Science Research
Program, G1999043601, by the key projects of the CAS, KZCX-SW-317/CX10G-E01-08, KZ951-A1-203,
and by the Hebei Province key project, 002207030.
REFERENCES
Chen JQ. 1994. Water resources in China. In Water Resources Development in China, Qian ZY (ed.). China Water and Power Press: Beijing;
1–42 (in Chinese).
Chen JQ, Xia J. 1999. Facing the challenge: barriers to sustainable water resources development in China. Hydrological Sciences Journal
44(4): 507–516.
Chen XD, Li XM, Lu GQ. 1999. Drying up courses of lower Huanghe River and variable characteristic of water resources. In Research and
Practice on Sustainable Management of Water Resources. Wuhan Mapping University of Science and Technology Press: Wuhan: 23–28
(in Chinese).
Chen ZK. 1985. China’s water resources and its utilization. GeoJournal 10(2): 167–171.
Falkenmark M. 1997. Society’s interaction with the water cycle: a conceptual framework for a more holistic approach. Hydrological Sciences
Journal 42(4): 451– 466.
Huang GH, Xia J. 2001. Barriers to sustainable water quality management. Journal of Environmental Management 61(1): 1–23.
Kundzewicz ZW. 1997. Water resources for sustainable development. Hydrological Sciences Journal 42(4): 467–480.
Liu CM, Chen ZK. 2001. Assessment of Water Resources Status and Trend of Water Demand and Supply in China. China Water Power Press:
Beijing (in Chinese).
Liu CM, Cheng L. 2000. Analysis on runoff series with special reference to drying up courses of lower Huanghe River. Acta Geographica
Sinica 55(3): 257– 265 (in Chinese).
Liu CM, He XW. 1996. China’s Water Problems and Strategies in the 21st Century. Science Press: Beijing (in Chinese).
Liu CM, Wei ZY. 1989. Agricultural Hydrology and Water Resources in the North China Plain. Science Press: Beijing (in Chinese).
Liu CM, Yu JJ. 2001. Groundwater exploitation and its impact on the environment in the North China Plain. Water International 26(2):
265–272.
Liu CM, Zhang XY, Zhang YQ. 2002. Determination of daily evaporation and evapotranspiration of winter wheat and maize by large-scale
weighing lysimeter and micro-lysimeter. Agricultural and Forest Meteorology 11: 109– 120.
Lou CZ, Le JX. 1996. Hazardous Floods in China. China Bookstore: Beijing (in Chinese).
Lou XC. 1998. Handbook of Water Resources and Water Treatment for China. China Environmental Science Press: Beijing (in Chinese).
Loucks DP. 1997. Quantifying trends in system sustainability. Hydrological Sciences Journal 42(4): 513–530.
MWR. 1987. Water Resources Assessment for China. Chinese Water and Power Press: Beijing (in Chinese).
MWR. 1992. Water Resources Assessment for China. Chinese Water and Power Press: Beijing (English translation).
Plate EJ. 1993. Sustainable development of water resources: a challenge to science and engineering. Water International 18(2): 84–93.
Qian ZY. 1991. Water Resources in China. Chinese Water and Power Press: Beijing (in Chinese).
Qian ZY, Zhang GD. 2001. Strategic Studies of Water Resources for Sustainable Development in China, volume 1. Chinese Water Resources
and Hydropower Press: Beijing (in Chinese).
Simonovic SP. 1996. Decision support systems for sustainable management of water resources: 1, general principles. Water International
21(4): 223–232.
WMO–UNESCO. 1988. Water Resources Assessment. Handbook for Review of National Capabilities. WMO: Geneva.
World Bank. 1997. Clear Water and Blue Skies: China’s Environment in the New Century. World Bank: Washington, DC.
Wu K, Xue YQ, Liu EM. 1998. Characteristics, variations and forecasting of dry-up episodes of the Huang River. Geographical Research
17(2): 125–129 (in Chinese).
Xia J. 1997. Advances in management of sustainable water resources system. Advances in Water Science 8(4): 370– 376 (in Chinese).
Xia J, Chen YQD. 2001. Water problems and opportunities in hydrological Sciences in China. Hydrological Sciences Journal 46(6): 907–922.
Xia J, Hu BQ. 1997. Water-related environmental problems and sustainability of water resources: a case study of the San Hua region, China.
In Sustainability of Water Resources under Increasing Uncertainty, Rosbjerg D, Boutayeb N-E, Gustard A, Kundzewicz ZW, Rasrossen PF
(eds). IAHS Publication no. 240. IAHS Press: Wallingford.
Copyright  2004 John Wiley & Sons, Ltd.
Hydrol. Process. 18, 2197– 2210 (2004)
2210
C. LIU AND J. XIA
Xia J, Chen Z, Huang GH, Rong X. 2001a. An integrated hydro-ecological modeling approach applied to the Lake Bositeng Basin in China.
Water International 26(1): 105–118.
Xia J, Huang GH, Chen Z, Rong X. 2001b. An integrated planning framework for managing flood-endangered Regions in the Yangtze River
Basin. Water International 26(2): 153–161.
Xia J, Wang Z, Wang F. 2001c. Eco-environment quality assessment: a quantifying method and case study in Ning Xia, arid and semi-arid
region in China. In Hydro-ecology: Linking Hydrology and Aquatic Ecology, Acreman M (ed.). IAHS Publication No. 266. IAHS Press:
Wallingford; 139–150.
Xia J, Zuo Q, Pang J. 2001d. Enlightenment on sustainable management of water resources from past practices for the Bositeng Lake basin
in Xinjiang, China. In Regional Management of Water Resources, Schumann A, Xia J, Marino M, Rosbjerg D (eds). IAHS Publication
No. 268. IAHS Press: Wallingford 41–48.
Zhang GL. 1999. Water Supply and Demand in China in the 21st Century. Chinese Water Resources and Hydropower Press: Beijing (in
Chinese).
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Hydrol. Process. 18, 2197– 2210 (2004)