Hydrology for the Water Management of Large Riva- Basins (Proceedings of the
Vienna Symposium, August 1991). IAHS Publ. no. 201, 1991.
THE WATER BALANCE OF CHINA AND ITS
LARGE RIVER BASINS
LIU GUOWEI AND GUI YUENG
Nanjing Institute of Hydrology and
Water Resources China
ABSTRACT The Yangtze River, Yellow River and other five large
river basins are the largest ones in China, with a total area amounting to about 4 333 687 km2 and covering both humid and arid/semiarid regions. Based on the computation of atmospheric vapour
transport, precipitation, évapotranspiration and runoff, water balance models for the whole country and its seven large river basins
have already been developed. Through analyses with the models,
some characteristics of hydrologie cycles in the river basins, including the origins and routes of atmospheric moisture flux, the water
circulation coefficients, etc., have been determined. The results
provide a hydrologie basis for water resources assessment and
management in China.
INTRODUCTION
China is located in the East Asian monsoon region, where the hydrologie cycle
presents a monsoon climate regime. Every year in May, with the monsoon onset,
the rainy season begins in the region south of 25 °N in China. During June to
July, the rain band advances to the south of 35°N, and in the whole country the
rainy season has developed by August. From November to March of the next
year, it is a dry season, and there is a transient season from April to September.
The whole country can be divided into three hydrologic-climatic zones: humid,
semi-arid and arid zone.
There are many rivers in China, including more than 1500 rivers with a
catchment area larger than 1000 km2, among which the Yangtze River, the
Yellow River, the Zhujiang River, the Hui River, the Hai River, the Liao river
and the Songhua River are the largest. There are also many inland rivers in the
arid region of west China (Department of Hydrology, Ministry of Water
Resources P.R.C, 1987).
For the study of the water balance, the river basins are divided into six
groups as shown in Table 1, according to their locations and hydrologic-climatic
characteristics. For example, the Yellow River, Hai River and Hui River are in
North China.
For convenience, the boundaries of the six areas and mainland China are
approximated by meridians and latitudes (Fig. 1).
153
154
Lui Guowei & Cui Yifeng
Table 1.
The Main River Basins of China,
ltfhn2
Hydro-climatic
characteristics
124.6
semi-arid region
78.8
180.2
humid region
humid region
84.1
humid region
Area
Area
Northeast China
(I)
South China
(II)
Yangtze River
w>
Southwest China
(IV)
North China
(V)
Northwest China
(VI)
Main River
Songhua River
Liao River
Yalu River
Zhujing River
Qfantang River
Min River
Yangtze River
Lanchang River
Lujing River
Yaluzangbu River
Yellow River
Hai River
Huai River
Talimu River
Eergisi River
Ili River
166.2
semi-arid region
342.3
arid region
Atmospheric vapour transport and water balance components for each area
including atmospheric vapour budget, precipitation, évapotranspiration and
runoff, are calculated. Based on the results of the computations, a water balance
model for each area can be developed and some features of the hydrologie cycle
for the river basins can be determined.
Fig. 1.
The simplified boundaries of China and its large river basin.
Water balance and large river basins of China
155
ATMOSPHERIC VAPOUR TRANSPORT
The atmospheric vapour passing through a vertical section of unit length and
height associated with change in atmospheric pressure from p„ to p z can be
calculated by the following formula (Liu, 1985).
Q==
g fpï
J^
Uqdtdp
(1)
where, U is the wind velocity vector (m/s); q is the specific humidity (g/kg); g is
gravitational acceleration (m/s2); p„ and pz is the atmospheric pressure on ground
surface and at an arbitrary height (hPJ; tj and tj are the beginning and end of a
computational time interval.
Introducing two averaging operations [ ] and { }
™=tr^ ^ u d t
{[U]}=
P7^
*P!'
M
[U]dp
=
^ri^
{[q]}=
P^P7
tf
M*?
equation (1) can be written as
Q =
|
(p. - vu (h -1.) {[qu]}
(2)
The physical quantities U and q or [U] and [q] can be broken down into:
U = [U] +U 1 ,
[U] = {[U]} + [UP
(3)
q = [q] + q1,
M = {[q]} + [ql*
(4)
where
U1, q1, [U]*, and [q]* are the deviations from [U], [q], {[U]} and {[q]}
respectively. Introducing equalities (3) and (4) into equation (2), we get:
£ {[Uq]} = £ {[U]}{[q]} + 1 [{U]*[q]*} + | {[U'q1]}
(I)
(II)
(III)
(5)
(IV)
With (I) denoting the total transport flux of atmospheric moisture, (II) the
mean transport flux, and (III) and (IV) the eddy transport, the total transport flux
of atmospheric moisture passing through an arbitrary vertical section equals the
sum of mean transport and eddy transport (Liu, 1985).
Applying equation (5), atmospheric sounding data collected at 150
meteorological stations where observations of wind, moisture and other
météorologie elements are made at 0800 h and 2000 h (Beijing time) every day at
Lui Guowei & Cui Yifeng
156
1000, 850, 700, 500, 200 and 100 hpa levels, the total transport, mean transport
and eddy transport over 1983 (also in every month) were calculated. The spatial
distributions of the atmospheric moisture fluxes are shown in Fig. 2 and Fig. 3.
Fig. 2 shows that the routes of total transport are in the latitude direction,
and that the atmospheric moisture enters China from the south and west and
leaves China eastwards. In Fig. 3, the routes of eddy transport shows meridionality. The direction of eddy transport is similar to that of the moisture gradient.
Atmospheric moisture is transported to the arid region in the northwest of the
country from its southeast. This phenomenon is very important to maintain the
humidity of the atmosphere over the inland region in northwest China.
CALCULATION OF THE COMPONENTS OF THE WATER BALANCE
The components of the water balance for an area, including the inflow of
atmospheric moisture from its outer boundary I, the outflow of atmospheric
moisture O, precipitation P, évapotranspiration E and runoff R, are shown in
Fig. (4).
Inflow, outflow and netflow
According to equation (1), by integrating along the boundaries of the area, and
by using the above mentioned data in 1983 from 150 météorologie stations, the
amounts of atmospheric moisture of inflow and outflow, including the total
transport, the mean transport and the eddy transport, have been calculated and
listed in Table 2 where the sign of inflow is taken as positive and that of outflow
negative, the netflow is taken as the difference between inflow and outflow.
Precipitation
Based on the data of ]precipitation observed at 13,000 stations, isohyetal
maps for the country have been drawn, and by the isohyetal method the amounts
of precipitation for each area have been calculated.
Evapotranspiration
Based on the data of evaporation observed at 1500 stations, isolines of evaporation from water surfaces can be drawn. These evaporation values from open
water surfaces were transformed into évapotranspiration values by using empirical formulas (Tan, 1984) for each area. Finally, évapotranspiration for each area
was calculated similar to the isohyetal method.
157
Water balance and largeriverbasins of China
Fig. 2.
The spatial distribution of moisture fluxes by total transport (average over 1983).
Fig. 3.
The spatial distribution of moisture fluxes by eddy transport (average over 1983).
158
Lui Guowei & Cut Yifeng
t
/CTSW "
_R
Fig. 4.
The scheme of water balance components.
Table 2.
Atmospheric moisture budget (1983).
whole
country
Area
Term
(I)
Total transport:
Inflow
(km'}
Outflow (km3)
Netflow (km'}
Eddy transport:
Inflow
(km')
Outflow (km3)
Netflow (km3)
Mean transport:
Inflow
(km3)
Outflow (km3)
Netflow (km3)
2806.1
2651.0
155.1
472.7
330.5
142.2
2333.4
2320.5
12.9
(II)
(III)
(TV)
(V)
(VI)
10272.5 6955.3 4393.73654.4 3647.5
9430.8 5816.4 3856.2 3496.7 3540.7
841.7 1138.9 537.5 157.7 106.8
983.6
879.5
1060.2 1394.8
-76.6 -515.3
265.8
229.6
36.2
980.8
783.9
196.9
15308.3
12362.7
2945.6
716.8
528.8
188.0
1527.0
1555.6
-28.6
9288.9 6075.8 4127.9 2673.6 2930.7
8370.6 4421.6 3626.62712.8 3011.9
918.3 1654.2 501.3 -39.2 -81.2
13781.3
10807.1
2974.2
Runoff
Based on the data of runoff observed at 47 basic hydrologie stations which cover
77.2% of the total area except northwest China, the runoff of the control area can
be calculated directly. Runoff not controlled by those stations can be calculated
according to the relationship between precipitation and runoff.
The amounts of precipitation, évapotranspiration and runoff in 1983 are
listed in Table 3.
WATER BALANCE MODEL AND ANALYSIS OF THE HYDROLOGIC
CYCLE
The water balance equation for a defined area can be written as:
P - E - R + AS = 0
(6)
Water balance and largeriverbasins of China
159
while the atmospheric vapour balance equation can be written as:
N - P + E + AW = 0
Table 3.
(7)
Amount of precipitation, évapotranspiration, and runoff (1983).
Term
Area
(I)
P (mm)
E (mm)
R (mm)
558.2
417.2
124.3
(II)
(III)
whole
country
(IV)
(V)
1851.6 1157.7 1023.8 538.0
836.8 587.6 546.9 541.7
1060.8 643.4 661.4 110.7
(VI)
159.6
152.8
30.2
671.5
405.0
308.0
where, AS is the change in water storage in the area, AW is the variation of
atmospheric moisture storage over the area. Over many years in the average, AS
= AW = 0. The state in 1983 is near the average of many years, so from (6)
and (7), a equation can be obtained:
(8)
N = R
where, N is taken as the difference between inflow and outflow of atmospheric
moisture transport, i.e. N = I - O.
According to Table (2) and (3), the water balance models for each area
and the whole country can be developed as shown in Fig. 5.
From the water balance as mentioned above, some characteristic coefficients of the water cycle can be calculated and are listed in Table 4.
Table 4.
Characteristics of the water cycle (1983).
Area
Term
(I)
P (mm)
E (mm)
I (mm)
W (mm)
Pg (mm)
Pe (mm)
Ke (l<r2)
Kg (l<r2)
T (day)
556.2
431.6
2253.9
12.9
507.5
48.6
8.7
109.6
8.4
(II)
(III)
whole
country
(TV)
(V)
(VI)
1871.2 1181.5 1114.5 543.7 164.7
803.0 540.9 475.4 433.6 133.6
13036.2 3911.9 5224.4 2550.2 1062.9
8.6
38.1
14.2 17.2
24.1
1814.9 1105.2 1066.5 501.1 154.9
9.8
48.0 42.6
56.3
76.3
5.9
4.3
7.8
3.0
6.4
103.1 106.9 104.5 108.5 106.3
19.3
5.1 11.7
7.5
8.0
679.2
369.8
1608.0
16.3
609.1
70.1
10.3
111.5
8.9
160
Lui Guowei & Cui Yifeng
/&Ç7?
2028,9
„ ..
1 —
2303.1
P
692.51
1
E
I 314.4
279.4 I
2851.
(537.4
155,1
1954.0
— 0
155.
4,4
-•
R
417,51
0(413,2
47,3
( i ) Nortteast China
10272.5
P
632.1
1474,5
4531,4^110
•0
9430.!
TTTTO?
841.7
0_J
841,7
= = R
150.4
L i i i L , 4953.1
5373.1 f I
Oi 249,4
1071,910
1)312.2
274,0
( I I ) South Oiira
1881.1
— 0
5816.4
2193.71
93.7
P
932,31
*W77
1331..
E
0—|
1133,9
8.2
4833.9 H
^=R
( 1 ) Yangtze River Basin
— 0
3356,2
2703.0
4575.5
H-o
1138,9
147.6
01160.8
612.410
1)82.3
,
m a
— 0
537.5
0 _
(399,8 537,5
=
R
as
1487.9 i I
0 171.4 117.5
(BOSouttoest China
1843.9^111
— 0
3483.7
3854.4
779.11
(621.4
0—I
108.2
157.7
R
2897.2
~0
157.7
1223.0 n
01266,5
195.2)0
1)793.1
117.6
( V ) North China
I —
5347.5
— 0
3540.7
P
555.3
AVAVA " '
2565.5
1453.5 106.1
t:R
2851.3
f— 0
103.1
26.5
253.9 I I
0 f 467.7
— I
35.0
( VI ) tërtfirest China
9,910
— 0
12332,7
15308,3
3520.6
7*TO^r
2945.6
= R
1)1205,9
2945.6
0 —
7333,0(1
ÔT72872
(\|) t ô l e country
Fig. 5.
10974,8
1—0
Estimated water balance of China and its large river
basins.
463.1
161
Water balance and large river basins of China
In this table W is the atmospheric moisture content (Liu, 1984); Pg is the
precipitation formed by atmospheric vapour inflow from outside the area,
Pg=P/(l+E/2I); Pe is the precipitation formed by local évapotranspiration,
Pe=P/(l+2I/E); Ke=Pe/P is called local hydrologie circulation coefficient;
Kg=P/Pg is the general hydrologie circulation coefficient; T is the period of
hydrologie circulation.
Table 4 shows that: the coefficient Ke <0.1 and Kg > 1.0 in all the areas,
implying that the amount of precipitation Pe is less than 10 per cent of the total
precipitation P, and 90 per cent of precipitation is formed by general hydrologie
circulation. At the same time we find that (i) the proportion of Pe/P in humid
regions, for example, in southwest and south China, is 2-3 times larger than that
in arid/semi-arid regions, e.g, in north-west and north China, and that (ii) the
duration of atmospheric moisture staying over the humid region is about 5 to 7
days, and over the arid/semi-arid region about 11-19 days. These results indicate
that the hydrologie cycle in the humid region is active in comparison with that in
the arid/semi-arid region.
Table 2 shows different contributions of the mean and eddy transport
atmospheric moisture in different area. In northeast and southwest China, they
both contribute with a positive sign; in south China and in the Yangtze River
Basin, the mean transport has positive contribution; in north and northwest
China, the mean transport has negative contribution while the eddy transport has
negative contribution.
Of course, there are obvious seasonal variations both in atmospheric
moisture transport and in the components of the water balance (Liu, 1989). It
shows the effects of the monsoon climate on the hydrologie cycle in East Asia
(Liu, 1990).
CONCLUDING STATEMENTS
China is a country with water resources shortage. Especially, the distribution of
water resources over the country is seriously uneven in space and time. For
example, water shortage often occurs in the Yellow River Basin and north China.
These regions account for almost 50% of the total area of China, but the water
resources are just 14% of the total amount. However, the Yangtze River and
south China are rich in water resources, being 81% of the total amount of the
country.
For tackling the problem of the water shortage in north China, one of the
most ambitious water resources projects, the South-North Water Transfer Project
(SNWTP), has been under consideration in China for about 10 years. The project
necessitates the transport of water from the Yangtze River to the Yellow River
and North China, forming the largest water resources system in China.
For evaluating the feasibility of the SNWTP, a lot of scientific problems
have been formulated. For example, how will the water balance components,
such as precipitation, évapotranspiration, runoff and ground water level, be
changed? What are the impacts of the changes on the environment?
All these scientific problems call for answers by hydrologists, as the water
Lui Guowei & Cui Yifeng
162
balance models and hydrological cycle analysis constitute the important bases for
them.
REFERENCES
Department of Hydrology, Ministry of Water Resources of P.R.C. (1978) Water Resources Assessment
of China, Water Resources Electric Power Press, Beijing, 8-10 (in Chinese).
Liu, (1985) Water vapour transport over mainland China, Journal of Hydraulic Engineering, No. 11,
1-13 (in Chinese).
Liu, (1984) The time - space distribution of atmospheric moisture content over mainland China,
Journal of Hydraulic Engineering, 5, 1-9 (in Chinese).
UNESCO, (1978) World Water Balance and Water Resources, Unesco press, Paris, 71-73.
Liu, (1990) Atmospheric moisture transport and water balance over China, Nanjing Institute of
Hydrology and Water Resources Press, Nanjing, China, 13-15 (in Chinese).
Tan (1984) An inspection of the formulae calculating the evaporation from land surface, ACTA Meteorologica SINICA. Vol. 42 No. 2.