Theor Appl Climatol (2009) 95:331–340
DOI 10.1007/s00704-008-0010-z
ORIGINAL PAPER
Atmospheric moisture budget and floods in the Yangtze
River basin, China
Zengxin Zhang & Qiang Zhang & Chongyu Xu &
Chunling Liu & Tong Jiang
Received: 28 July 2007 / Accepted: 12 February 2008 / Published online: 11 April 2008
# Springer-Verlag 2008
Abstract In this paper, we explored the trends of the
atmospheric moisture budget, precipitation, and streamflow
in summer during 1961 to 2005 and possible correlations
between them by using the linear regression method in the
Yangtze River basin, China. The results indicate that: (1)
increasing tendencies can be detected in the atmospheric
Z. Zhang (*)
State Key Laboratory of Lake Science and Environment,
Nanjing Institute of Geography and Limnology,
Chinese Academy of Sciences,
Nanjing 210008, China
e-mail: zhangzengxin77@yahoo.com.cn
Z. Zhang
Jiangsu Key Laboratory of Forestry Ecological Engineering,
Nanjing Forestry University,
Nanjing 210037, China
Z. Zhang
Graduate School of the Chinese Academy of Sciences,
Beijing 100039, China
Q. Zhang : T. Jiang
Nanjing Institute of Geography and Limnology,
Chinese Academy of Sciences,
Nanjing 210008, China
Q. Zhang : C. Liu
Department of Geography and Resource Management
and Institute of Space and Earth Information Science,
The Chinese University of Hong Kong,
Shatin, Hong Kong, China
Z. Zhang : Q. Zhang : T. Jiang
Laboratory for Climate Studies, National Climate Center,
China Meteorological Administration,
Beijing 100081, China
C. Xu
Department of Geosciences, University of Oslo,
Oslo, Norway
moisture budget, precipitation and streamflow in the
Yangtze River basin; however, the significant increasing
trends occur only in the atmospheric moisture budget and
precipitation in the middle and lower Yangtze River basin;
(2) both the ratio of summer moisture budget to annual
moisture budget and the ratio of summer precipitation to
annual precipitation exhibit a significant increasing trend in
the Yangtze River basin. The ratio of summer streamflow to
annual streamflow is in a significant increasing trend in
Hankou station. Significant increasing summer precipitation can be taken as the major controlling factor responsible
for the higher probability of flood hazard occurrences in the
Yangtze River basin. The consecutively increasing summer
precipitation is largely due to the consistently increasing
moisture budget; (3) the zonal geopotential height anomaly
between 1991 and 2005 and 1961 and 1990 is higher from
the south to the north, which to a large degree, limits the
northward propagation of the summer monsoon to north
China. As a result, the summer moisture budget increases in
the middle and lower Yangtze River basin, which leads to
more summer precipitation. This paper sheds light on the
changing properties of precipitation and streamflow and
possible underlying causes, which will be greatly helpful
for better understanding of the changes of precipitation and
streamflow in the Yangtze River basin.
1 Introduction
Global warming, which is due to the enhanced greenhouse
effect, is likely to have significant effects on the hydrological cycle (IPCC 2007). The accelerated hydrologic cycle of
the last two decades is believed to be one of the
consequences of global warming, especially for some parts
of the northern hemisphere (Brutsaert et al. 1998; Karl et al.
332
1996). The increasing temperature leads to the changes of
atmospheric water budget due to the high sensitivity of the
saturation vapor pressure in air to temperature, and
perturbations in the global water cycle are expected to
accompany the climate warming (Allen et al. 2002). The
regional patterns of the surface hydro-climatological
changes due to the currently well-evidenced global warming are more complicated as compared to temperature
changes. However, decreasing and/or increasing runoff or
precipitation can be expected (e.g., Milly et al. 2005).
Precipitation efficiency is the fraction of the average
horizontal water vapor flux over an area that falls as rain.
Summer rainfall, whether forced by synoptic-scale disturbances or by mesoscale mechanisms, is overwhelmingly
subject to moisture transportation and deep convection
(e.g., Heideman and Fritsch 1988).
The Yangtze River, the longest river in China and the
third longest river in the world, plays a vital role in the
social-economic development of China. The river originates
in the Qinghai-Tibet Plateau and flows about 6,300 km
eastwards to the East China Sea. Being affected by the
monsoon climate, flood events occur almost every year in
the Yangtze River basin (Jiang and Shi 2003). During the
most recent 150 years, the greatest floods occurred in 1870,
1931, 1935, 1954, 1996, and 1998 (Wang et al. 2001), and
the most recent example is the greater number of floods in
the Yangtze River basin in the 1990s. Zhang et al. (2006)
and Jiang et al. (2006) also found that there is a significant
positive trend in flood streamflow in the middle and lower
basin in the last 40 years. In 1998, the entire basin suffered
from a tremendous flooding event, resulting in an economic
loss of 20 billion US dollars (Yin and Li 2001).
Impacts of climate change on floods and the possible
underlying causes have been widely discussed. Many
researchers have addressed the changing properties of
meteorological and hydrological components such as
temperature, precipitation, evapotranspiration, streamflow,
and possible correlations between these components in the
Yangtze River basin (Zhang et al. 2006; Xu et al. 2006;
Gong et al. 2006; Jiang et al. 2006), demonstrating the
considerable importance of studying climate changes and
the possible impacts on regional socio-economic development in the Yangtze River basin. Summer (June–Aug) is
the flooding season and much more attention has been paid
to the changes of the summer precipitation in the region
(Zhang et al. 2007a, b; Gong et al. 2000; Zhu and Wang
2001). Summer rainfall in the Yangtze River basin is
closely associated with the East Asian summer monsoon.
The west Pacific (120°E–133°E) and the Bengal Bay are
the sources of atmospheric moisture entering the Yangtze
River basin, and in the summer most of the atmospheric
moisture is coming from the south and west edges, while
the leaving atmospheric moisture usually exits in the east
Theor Appl Climatol (2009) 95:331–340
and north edges (e.g., Li 1999; Huang et al. 1998; Zhou
et al. 1998; Miao et al. 2005).
Although much research has been conducted on the
precipitation and streamflow changes in the Yangtze River
basin (e.g., Zhang et al. 2005; Zhang et al. 2006; Jiang et al.
2006), the atmospheric moisture budget, as one of the key
components in the hydrological cycle, has not yet been
thoroughly analyzed. Studying of the changes in the
atmospheric moisture budget is of great importance in
understanding the spatial and temporal patterns of precipitation in the study region. Therefore, the objectives of this
paper are: (1) to explore the changes of the atmospheric
moisture budget, precipitation, and streamflow in the
Yangtze River basin; and (2) to discuss the circulation
patterns of the wind field and moisture fluxes and streamflow changes across the area. This paper will be helpful for
further understanding the changes of precipitation and
possible relations between atmospheric moisture budget,
precipitation, and streamflow in the Yangtze River basin.
2 Data and methods
2.1 Data
Data of daily precipitation covering the period from 1961
to 2005 from 124 National Meteorological Observatory
(NMO) stations is used in this study. The data are provided
by the National Climate Centre (NCC) of the China
Meteorological Administration (CMA). The location of
the Yangtze River basin and the gauging stations can be
seen in Fig. 1.
Monthly streamflow data are extracted from three major
hydrological stations on the mainstream Yangtze River:
Yichang in the upper basin (1961–2005), Hankou in the
middle basin (1961–2005), and Datong in the lower basin
(1961–2005). Yichang, Hankou, and Datong cover upstream areas of about 1 million km2, 1.49 million km2, and
1.7 million km2, respectively (Fig. 1b). Homogeneity of the
meteorological and the hydrological data are tested by
calculating the von Neumann ratio (N), cumulative deviations (Q/n−0.5 and R/n−0.5), and Bayesian procedures (U and
A) (Buishand 1982). The homogeneity test conducted on
the dataset of 124 meteorological stations and the three
hydrological stations by using these three methods reveals
that the data are homogeneous at >95% confidence level
(Becker et al. 2007).
The whole layer of the atmospheric moisture and related
transport features are explored based on the NCAR/NCEP
reanalysis data from 1961 to 2005 (Trenberth and Guillemot
1998). In the actual atmosphere, the moisture content is
very low above 300 hPa, so that a top of the atmosphere
pressure of 300 hPa will be used in the study (Miao et al.
Theor Appl Climatol (2009) 95:331–340
333
Fig. 1 The location of the
Yangtze River basin (a) and the
location of the rain gauging
stations (b)
2005). The zonal moisture transport flux (QU ), the
meridional moisture transport flux (QV), and the whole
layer moisture budget (QT) at regional boundaries are
calculated based on the following equations:
Z
1 ps
Qu ðx; y; tÞ ¼
qðx; y; p; tÞuðx; y; p; tÞdp
ð1Þ
g p
Qv ðx; y; tÞ ¼
QW ¼
82
X
1
g
Z
ps
qðx; y; p; tÞvðx; y; p; tÞdp
12
X
2.2 Methods
p
Qu ð1 1 ; y; tÞ
QE ¼
81
QS ¼
ð2Þ
where u and v are the zonal and meridional components
of the wind field, respectively; q is the specific humidity; ps is surface pressure; p is atmospheric top pressure;
g is acceleration of the gravity; QW, QE, QS, QN are the
west, east, south and north regional boundaries, respectively; and 81, 82, l1, l2 are the latitude and longitude
according to the regional boundaries (Zhou et al. 1998;
Miao et al. 2005)
82
X
Qu ð1 2 ; y; tÞ
ð3Þ
Qv ðx; 8 2 ; tÞ
ð4Þ
81
Qv ðx; 8 1 ; tÞ QN ¼
11
QT ¼ QW QE þ QS QN
12
X
11
ð5Þ
Simple linear regression is used in this paper to test the
significance of the long-term linear trend. The simple linear
regression is a parametric T-test method that consists of two
steps, fitting a linear simple regression equation with the
time t as the independent variable and the meteorological
variable, Y as the dependent variable, and testing the
statistical significance of the slope of the regression
equation. The parametric T-test requires that the data to be
tested is normally distributed. The normality of the data
series is first tested in the study by applying the
Kolmogorov-Smirnov test (Xu 2001). The method first
334
compares the specified theoretical cumulative distribution
function (in our case normal distribution) with the sample
cumulative density function based on observations, then
calculates the maximum deviation, D, of the two. If, for the
chosen significance level, the calculated value of D is
greater than or equal to the critical tabulated value of the
Kolmogorov-Smirnov statistic, the hypothesis of normal
distribution is rejected. Confidence levels of 95% are taken
as thresholds to classify the significance of the positive and
negative trends. Trends above the threshold are significant,
otherwise are not significant (Niu et al. 2004; Wang and
Zhou 2005; Chen et al. 2007).
The observed trends of individual stations are spatially
interpolated by applying the Inverse Distance Weighted
(IDW) interpolation method. IDW creates a raster surface.
The raster cell values are calculated by averaging the values
of station data in the vicinity of each cell. IDW implies that
each station has a local influence that decreases with
distance (De By. 2001).
3 Study region
The Yangtze River lies 91°E~122°E and 25°N~35°N. In
this study, the whole Yangtze River basin is divided into
two parts based on longitude: (i) the upper Yangtze River
(average altitude of about 2,250 m) with 54 stations, and
(ii) the middle and lower Yangtze River (average altitude of
about 270 m) with 70 stations (Fig. 1b). The location of the
sub-catchments can be seen in Fig. 2. The climate of the
Yangtze River basin is of the subtropical monsoon type.
The southern part of the basin is climatically close to
tropical climate and northern part is near to temperate zone.
The annual mean temperature in the southern and northern
parts of the middle and lower Yangtze basin is 19 and 15°C,
respectively. As the temporal and spatial distributions of the
rain zone are closely related to monsoon activities and
seasonal motion of subtropical highs, the main flooding
Fig. 2 The location of the sub-catchments in the Yangtze River basin.
1 Jinshajiang River, 2 Mintuojiang River, 3 Jialingjiang River, 4
Wujiang River, 5 The upper mainstream section, 6 Hanjiang River, 7
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season for the area is during the summer (Zhang et al.
2007a, b).
4 Results
4.1 Trends of moisture budget, precipitation, and streamflow
Figure 3 illustrates the linear trends of the atmospheric
moisture budget, precipitation and streamflow in the
Yangtze River basin. Figure 3a shows that in the upper
area of the basin the atmospheric moisture budget,
precipitation, and streamflow (Yichang station) in summer
are increasing, but these increasing trends are not significant. For the middle and lower regions, both the atmospheric moisture budget and precipitation show significant
increasing trends. However, this is not the case for streamflow in Hankou and Datong stations (Fig. 3b-c).
Summer atmospheric moisture budget is a crucial factor
for the spatial and temporal distribution of precipitation and
floods in the Yangtze River basin. Positive correlations
have been observed between the atmospheric moisture
budget, precipitation, and streamflow in the Yangtze River
basin. Significant correlations are detected among the
atmospheric moisture budget, precipitation, and streamflow
in the middle and lower basin (Fig. 4d-f). Significant
correlation is also found between streamflow and precipitation in the upper basin (Fig. 4a-c).
Figure 5 illustrates the changes of the ratios of summer
moisture budget (SMB/AMB), precipitation (SP/AP) and
streamflow (SS/AS) to the corresponding annual values.
The ratios show increasing trends in the basin, and the
significant increasing trend of SMB/AMB and SP/AP can
be identified (see Fig. 5). However, the significant
increasing trend of SS/AS occurs only in Hankou station.
Tables 1 and 2 display the considerable differences in SMB/
AMB, SP/AP and SS/AS between the 1960s and 1990s.
The significant increase in the ratio of summer to annual
Dongtinghu Lake, 8 Poyanghu Lake, 9 The middle mainstream
section, 10 The lower mainstream section, 11 Taihu Lake
Theor Appl Climatol (2009) 95:331–340
335
Fig. 3 Linear trend of the summer moisture budget, precipitation, and discharge in the
Yangtze basin. a Upper Yangtze
River basin. b Middle and lower
Yangtze River basin. c Entire
Yangtze River basin. P-values
show the significance level and
when the P-value is smaller than
0.05 meaning that the trend is
significant at >95% confidence
level
precipitation in the 1990s as compared with that in 1960s
might be regarded as the major factor resulting in higher
probability of Yangtze flood hazard occurrences in the
1990s as compared with that of pre-1990s. The consecutively increasing summer precipitation is largely due to the
consistently increasing moisture budget. Jiang et al. (2006)
also found that higher summer precipitation and rainstorms
increased summer runoff and floods in the lower Yangtze
River basin during 1961–2000 by applying the MannKendall trend test.
4.2 Precipitation anomalies
Figure 6a demonstrates the spatial distribution of the
summer precipitation anomalies between 1991 and 2005
and 1961 and 1990. Figure 6a shows that the Jialingjiang
River basin and the upper Hanjiang River basin are
dominated by minus precipitation anomalies, while the
southeastern and the southwestern parts of the Yangtze
River basin are characterized by positive precipitation
anomalies.
336
Theor Appl Climatol (2009) 95:331–340
Fig. 4 Correlations between the moisture budget, precipitation, and
discharge. a-c Upper Yangtze River basin; d-f Middle and lower
Yangtze River basin. R is the correlation coefficient and P is the
significance level. P-values smaller than 0.05 indicate that the
correlation is significant at >95% confidence level
Figure 6b illustrates the spatial distribution of the linear
trend of summer precipitation in the Yangtze River basin
where it can be seen that the basin is dominated by the
increasing precipitation trend. Summer mean precipitation
decreases significantly in the Jialingjiang River basin and
increases significantly in the southern and eastern parts of
the Yangtze River basin, which is in good line with the
spatial distribution of the linear trend of precipitation in the
study region
4.3 Large-scale circulation
As mentioned above, both the atmospheric moisture budget
and the precipitation in summer exhibited coherent increasing trends in the Yangtze River basin from 1961 to 2005.
Figure 7 illustrates the spatial distribution of the summer
moisture flux anomalies between 1991 and 2005 and 1961
and 1990. The moisture flux anomalies show a tendency
from north to south in the central-east China (100–122°E).
Theor Appl Climatol (2009) 95:331–340
337
Fig. 5 The ratios of summer
moisture budget (SMB/AMB),
precipitation (SP/AP) and
streamflow (SS/AS) to the
corresponding annual values in
the Yangtze River basin.
a Upper, b Middle and lower ,
c Entire Yangtze River basin. P
is the significance level and
when the P-value is smaller than
0.05 meaning that the trend is
significant at >95% confidence
level
To detect changes in the circulation patterns between 1991
and 2005 and 1961 and 1990, we analyzed the 500-hPa
geopotential height and wind fields which are considered as
Table 1 Upper, middle, and lower Yangtze River basin
Upper
Middle-lower
Whole basin
Longitude
Latitude
100–110°
111–122°
100–122°
25–35°
25–35°
25–35°
a good proxy for large-scale moisture budget (e.g., Jiang
et al. 2006) (Fig. 8). The lower geopotential anomaly
localized over Japan, while the higher geopotential anomaly
could be found in Mongolia. The zonal geopotential height
anomaly is larger from the south to the north of central-east
China, and the meridional anomaly is lower from the west
to the east of East Asia. A similar large-scale circulation
trend over East Asia has been found by Wang et al. (2005).
When compared with the 1961–1990 period, a northerly
wind anomaly has been found in the lower troposphere over
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Theor Appl Climatol (2009) 95:331–340
Table 2 Changes of the percentage of summer moisture budget to
annual moisture budget (SMB/AMB), the summer precipitation to
annual precipitation (SP/AP), and the summer streamflow to annual
streamflow (SS/AS) in the Yangtze River basin in the 1960s and
1990s (%)
SMB/AMB
SP/AP
SS/AS
Upper Yangtze basin
Mid and lower Yangtze basin
1960s
1990s
1960s
1990s
32
50
25
50
53
26
28
37
39
57
56
44
central-east China in 1991–2005, which limits the northward propagation of the atmospheric moisture and northward propagation of the summer monsoon to north China.
As a result, the summer moisture budget and precipitation
consistently increase in the Yangtze River basin. These
results are in agreement with changes of precipitation and
streamflow in the basin, showing a close relationship
between the atmospheric moisture budget, precipitation,
and streamflow. Yu et al. (2004) and Wang et al. (2005)
also found the annual and summer precipitation would
increase in the middle to lower Yangtze River basin when
the East-Asian summer monsoon began to weaken.
Fig. 6 Spatial distribution of
the summer precipitation
anomalies between 1991 and
2005 and 1961 and 1990 (a) and
the linear trends of summer
precipitation during 1961–2005
(b) in the Yangtze basin
4.4 Discussion and conclusions
We analyzed the trends of the atmospheric moisture budget,
precipitation, and streamflow from 1961 to 2005 in the
Yangtze River basin by using linear regression technique
and the inverse distance weighted (IDW) interpolation
method. Some interesting conclusions can be drawn as
follows:
1. The atmospheric moisture budget, precipitation, and
streamflow in summer are in increasing trends in the
Yangtze River basin, but significant increasing trends
occur only in summer moisture budget and precipitation in the middle and lower Yangtze River basin.
Significant positive correlations can be detected between the atmospheric moisture budget, precipitation,
and streamflow in the middle and lower basin and
between the precipitation and streamflow in the upper
basin.
2. The Jialingjiang River basin and the upper Hanjiang
River basin are dominated by minus precipitation
anomalies between 1991 and 2005 and 1961–1990,
while the southeastern and the southwestern parts of the
Yangtze River basin are characterized by positive
precipitation anomalies. Summer precipitation increases
significantly during 1961 and 2005, especially in the
Theor Appl Climatol (2009) 95:331–340
339
Fig. 7 Spatial distribution of
the summer atmospheric moisture flux anomalies between
1991 and 2005 and 1961 and
1990 (gray regions indicate
>100 kg/m·s, unit: kg/m·s
1990s, which might be regarded as the main factor
leading to the higher probability of flood hazard
occurrences in the 1990s. The consecutively increasing
summer precipitation is largely due to the consistently
increasing atmospheric moisture budget.
3. The zonal geopotential height anomaly between 1991
and 2005 and 1961 and 1990 is higher from the south
to the north, which weakens the summer monsoon and
limits the northward propagation of atmospheric moisture to north China. We also find that an obvious
tendency from the north to the south in the moisture
Fig. 8 Difference geopotential
height and the corresponding
horizontal winds in summer between 1991 and 2005 and 1961
and 1990 at 500 hPa
flux anomalies between 1991 and 2005 and 1961 and
1990 in east China. This results show that it is difficult
for the moisture flux to reach north China and more
moisture has to stay longer in the Yangtze River basin,
which leads to more summer moisture budget and
precipitation in the study region. The results of the
current study shed light on the changing features of the
precipitation and streamflow and the underlying causes,
which will be greatly helpful for better understanding
of the changes of precipitation, streamflow, and their
correlations in the Yangtze River basin.
340
Acknowledgements This paper was financially supported by the
Chinese Meteorological Administration (No. ccsf 2007–35), National
Natural Science Foundation of China (Grant No.: 40701015), and
fully supported by a Direct Grant from the Faculty of Social Science,
The Chinese University of Hong Kong (Project No. 4450183) and by
the Outstanding Overseas Chinese Scholars Fund from CAS (The
Chinese Academy of Sciences). We would like to thank the National
Climate Centre in Beijing and CWRC of the Yangtze River in Wuhan
for providing valuable climate and hydrological datasets. Thanks
should be extended to Dr. Guo Hua, Dr. Zeng Xiaofan, Dr. Liu Bo,
and Dr. Zhai Jianqing for their constructive discussions. Last but not
least, we should extend our cordial thanks to two anonymous
reviewers for their valuable comments and suggestions which greatly
improved the quality of this paper.
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