Journal of Hydrology (2008) 353, 215– 227
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/jhydrol
Spatial and temporal variability of precipitation
maxima during 1960–2005 in the Yangtze River basin
and possible association with large-scale circulation
Qiang Zhang a,b,c,*, Chong-Yu Xu
Chun-ling Liu a, Hui Lin a
d,e
, Zengxin Zhang f, Yongqin David Chen a,
a
Department of Geography and Resource Management and Institute of Space and Earth Information Science,
The Chinese University of Hong Kong, Shatin, Hong Kong, China
b
Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China
c
Laboratory for Climate Studies, National Climate Center, China Meteorological Administration, Beijing 100081, China
d
Department of Geosciences, University of Oslo, Norway
e
Department of Earth Sciences, Uppsala University, Sweden
f
Jiangsu Key Laboratory of Forestry Ecological Engineering, Nanjing Forestry University, Nanjing, China
Received 8 April 2007; received in revised form 16 November 2007; accepted 20 November 2007
KEYWORDS
Precipitation maxima;
Mann–Kendall trend;
Large-scale circulation;
The Yangtze River basin
Summary This study investigated spatial and temporal patterns of trends of the precipitation maxima (defined as the annual/seasonal maximum precipitation) in the Yangtze
River basin for 1960–2005 using Mann–Kendall trend test, and explored association of
changing patterns of the precipitation maxima with large-scale circulation using NCEP/
NCAR reanalysis data. The research results indicate changes of precipitation maxima from
relative stable patterns to the significant increasing/decreasing trend in the middle 1970s.
With respect to annual variability, the rainy days are decreasing and precipitation intensity is increasing, and significant increasing trend of precipitation intensity was detected
in the middle and lower Yangtze River basin. Number of rain days with daily precipitation
exceeding 95th and 99th percentiles and related precipitation intensities are in increasing
tendency in summer. Large-scale atmospheric circulation analysis indicates decreasing
strength of East Asian summer monsoon during 1975–2005 as compared to that during
1961–1974 and increasing geopotential height in the north China, South China Sea and
west Pacific regions, all of which combine to negatively impact the northward propagation
of the vapor flux. This circulation pattern will be beneficial for the longer stay of the Meiyu front in the Yangtze River basin, leading to more precipitation in the middle and lower
* Corresponding author. Address: Department of Geography and Resource Management and Institute of Space and Earth Information
Science, The Chinese University of Hong Kong, Shatin, Hong Kong, China. Tel.: +852 2609 6639; fax: +852 2603 5006.
E-mail address: zhangqiang@nju.org.cn (Q. Zhang).
0022-1694/$ - see front matter ª 2007 Published by Elsevier B.V.
doi:10.1016/j.jhydrol.2007.11.023
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Q. Zhang et al.
Yangtze River basin in summer months. The significant increasing summer precipitation
intensity and changing frequency in the rain/no-rain days in the middle and lower Yangtze
River basin have potential to result in higher occurrence probability of flood and drought
hazards in the region.
ª 2007 Published by Elsevier B.V.
Introduction
Extreme climatic events have drawn more and more concerns from public, government and academic circles because of the tremendous impacts of floods, droughts,
storms and extreme temperatures on human society (Founda et al., 2004; Nasrallah et al., 2004; Beniston and Stephenson, 2004). One of the most significant potential
consequences of climate changes may be alterations in regional hydrological cycles and subsequent changes in river
flow regimes, e.g. flood or low flow. The tremendous importance of water in both society and nature underscores the
necessity of understanding how a change in climate could
affect regional water supplies (Xu and Singh, 2004). Hydrologists and meteorologists suggested that an increase in surface temperature leads to higher evaporation rates and
enables the atmosphere to transport higher amounts of
water vapor, which, in turn, leads to accelerated hydrological cycle (e.g. Menzel and Bürger, 2002). The present global warming led to changes of the global hydrological
cycle and to the amplitude of the increase of global and
continental runoff (Labat et al., 2004; Semenov and Bengtsson, 2002). These results will be helpful for the understanding of the current increase of flood/drought hazards over
the world under current well-evidenced global warming
(e.g. Herschy, 2002; Mirza, 2002). Climatic changes because
of global warming might result in increase and intensification of extreme events (WMO, 2003). Groisman et al.
(1999) indicated that the probability of daily precipitation
exceeding 50.8 mm in mid-latitude countries (the USA, Mexico, China and Australia) increased by about 20% in the later
20th century. Suppiah and Hennessy (1998) pointed out that
the heavy precipitation events in most parts of Australia
have increased. Zhai et al. (1999) indicated that the intensive precipitation events have increased in the western China since 1950. Increasing extreme precipitation events can
also be found in the south-eastern China (e.g. Liu, 1999).
Wang and Zhou (2005) studied the spatial distribution of extreme precipitation during 1961–2001 and demonstrated
that the annual mean precipitation increased significantly
in southwest, northwest, and east China, and decreased significantly in central, north and northeast China. The
increasing trends in east China occurred mainly in summer,
while the decreasing trends in central, north, and northeast
China occurred in both spring and autumn.
The Yangtze River, being the longest river in China and
the third longest river in the world, plays an important role
in the sustainable development in economy and ecology of
China. However, frequent floods in the Yangtze River basin
inflicted considerable loss on economy and human life. In
1998, disastrous floods occurred to the entire Yangtze River
basin, which was the largest flood since 1954. The economic
loss was 166 billion yuans (about 20 billion US dollars). This
flood hazard was the direct result of unusually high precipitation that occurred between June and August (670 mm)
due to a strong El Niño event (Yin and Li, 2001). Therefore,
more and more investigations have been performed on the
floods and possible mechanisms (e.g. Zhang et al., 2006,
2007). Extreme precipitation events are the main causes
for the flood hazards in the Yangtze River basin (Zhang
et al., 2005). Some investigations have focus on the statistical characteristics of extreme precipitation in the Yangtze
River basin (e.g. Su et al., 2005). However, the large-scale
circulation behind these statistical features of precipitation
extremes in the Yangtze River basin has not been investigated. Studying large-scale circulation and exploring its impact on regional precipitation will be helpful for further
understanding the statistical properties of precipitation extremes and possible mechanisms behind climatic extreme
events in the Yangtze River basin. Therefore, the objectives
of this paper are: (1) to explore spatial and temporal
changes of precipitation maxima and precipitation intensity
over the Yangtze River basin for 1960–2005 based on daily
precipitation dataset using Mann–Kendall trend test; (2)
to investigate large-scale circulation behind the observed
changes of precipitation extremes with the help of NCEP/
NCAR reanalysis data of the same time period for better
understanding of possible mechanisms behind the changing
patterns of the precipitation maxima in the Yangtze River
basin; and (3) to discuss the possible association of the observed trends of precipitation maxima in the Yangtze River
basin with large-scale circulation patterns.
Data and methods
Study region and data
The Yangtze River (Fig. 1 upper panel) lies between 91E–
122E and 25N–35N and has a total drainage area of
1 808 500 km2. The mean annual discharge at Hankou Station
(at Wuhan, in the middle Yangtze River) is 23 400 m3 s1.
The river originates in the Qinghai-Tibet Plateau and flows
about 6300 km eastwards to the East China Sea (Zhang
et al., 2006). The climate of the Yangtze River basin is of
the subtropical monsoon type (Zhang et al., 2005). 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 River basin is 19 C
and 15 C, respectively. Summer (June–August) is the main
flooding season for the Yangtze River basin (Zhang et al.,
2007).
Daily precipitation data of 147 rain gage stations during
1960–2005 were collected in the current study, which were
provided by the National Climate Center (NCC) of the China
Meteorological Administration (CMA). The distribution of
Spatial and temporal variability of precipitation maxima during 1960–2005
217
Figure 1 Location of the Yangtze River basin (upper panel) and location of the rain gage stations and sub-catchments in the
Yangtze River Basin (lower panel). 1: Jinshajiang River; 2: Mintuojiang River; 3: Jialingjiang River; 4: Wujiang River; 5: The upper
mainstream section; 6: Hanjiang River; 7: Dongtinghu Lake; 8: Poyanghu Lake; 9: The middle mainstream section; 10: The lower
mainstream section; 11: Taihu Lake.
rain gage stations over the Yangtze River basin is shown in
Fig. 1 (lower panel). The missing data (mostly in the dry season which have little influence on the findings of the current
study that focuses on annual/seasonal maxima precipitation) of one day or two days are replaced by the average
precipitation values of the neighbouring stations. The
homogeneity of the precipitation series was analyzed by calculating the von Neumann ratio (N), the cumulative deviations (Q/n0.5 and R/n0.5), and the Bayesian procedures
(U and A) (Buishand, 1982). The data sets of all stations
which have been used in the present study are homogeneous
at >95% confidence level.
In this paper, precipitation maxima were defined as: (1)
annual maximum precipitation and seasonal maximum precipitation in summer; (2) daily precipitation exceeding
99th and 95th percentiles. Here, the one-day maximum precipitation within one year, spring, summer, autumn and
winter denotes annual maximum precipitation and seasonal
maximum precipitation respectively. The number of rainy
days, days with daily precipitation exceeding 99th and
95th percentiles, and mean daily precipitation intensity
(we will just mention precipitation intensity thereafter)
(PI = Total precipitation/days) for the whole year and for
the summer are defined for exploring precipitation variability in the Yangtze River basin. For further understanding of
the atmospheric circulation patterns behind the spatial
change patterns of precipitation maxima, the horizontal
wind field, geopotential height at 850 and 500 hPa from
the National Centers for Environmental Prediction/National
Center for Atmospheric Research (NCEP/NCAR) reanalysis
data (http://www.cdc.noaa.gov) were analyzed.
To have a brief idea on the climate of the study region,
the Yangtze River basin is divided into three parts along
the longitude from west to east, which correspond well with
the decrease in altitude (Xu et al., 2006). The upper region
(104E) has a mean altitude of 2551 m above sea level
(m.a.s.l), and the middle (104–113E) and lower regions
(113E) have a mean altitude of 627 and 113 m.a.s.l,
respectively (Xu et al., 2006).
Method
The Mann–Kendall trend test (MK) (Mann, 1945; Kendall,
1975) is used to analyze the trends of the frequency of
the maximum precipitation events for all the 147 stations
in the Yangtze River basin. The influence of serial correla-
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Q. Zhang et al.
tion in the time series on the results of MK test has been discussed in the literature (e.g. Yue et al., 2002; Yue and
Wang, 2002). Prewhitening has been used to eliminate the
influence of serial correlation (if significant) on the Mann–
Kendall (MK) test in trend-detection studies of meteorological time series. However, the study conducted by Yue and
Wang (2002) demonstrates that when trend exists in a time
series, the effect of positive/negative serial correlation on
the MK test is dependent upon sample size, magnitude of serial correlation, and magnitude of trend. When sample size
and magnitude of trend are large enough, serial correlation
no longer significantly affects the MK test statistics. In this
study, before the MK test was applied, the series of the annual and seasonal precipitation maxima were tested for persistence by the serial correlation analysis method presented
in Haan (2002) using the following equation:
qm ¼
CovðX t ; X tþm Þ
¼
VarðX t Þ
1
nm
nm
P
tþm XÞ
ðX t XÞðX
t¼1
1
n1
n
P
;
2
ðX t XÞ
t¼1
where Xt (t = 1, 2, . . .) is the tested time series; Xt+m is the
same time series with a time lag of m; X is the mean of the
time series. The equation shows that 1 6 q 6 1; if m = 0
then q = 1. For a purely random (stochastic) series, qm 0
for all m 5 0. If the series of qm (for m 5 0) falls between
the 1p
a confidence interval calculated by ul ¼ ð1
ffiffiffiffiffiffiffiffiffiffiffi
z1a=2 n 2Þ=ðn 1Þ (n is the length of the tested time series, l and u are the lower and upper limits, a is the significance level, z is the critical value of the standard normal
distribution for a given a), the tested series is an independent series at 1 a confidence level. Confidence levels of
95% were taken as threshold to classify the significance of
positive and negative MK trends. Trends at significance below the 95% confidence level were not considered.
Results
Spatial distribution of MK trends of the
precipitation maxima
Fig. 2 demonstrates the spatial distribution of MK trends of
annual precipitation maxima events in the Yangtze River basin. It can be seen from Fig. 2A that most stations show no
significant trends of the annual maximum precipitation over
the Yangtze River basin. Significant increasing annual maximum precipitation is found in four stations, and three stations show significant decreasing trends. Fig. 2B shows
that the majority of stations in the Yangtze River basin
are dominated by significant decreasing trends in the number of rainy days at >95% confidence level. These stations
are mostly located in the middle and lower Yangtze River
basin. Two stations in the upper Yangtze River basin are
characterized by significant increasing trends in the number
of rainy days. Fig. 2D illustrates the trends in the number of
no-rain days, showing similar changing patterns (but with
opposite sign) when compared with those of the number
of rainy days (Fig. 2B). Most stations of the Yangtze River
basin at <104E show no significant trend in frequency of
rainy days at >95% confidence level (Fig. 2D). Fig. 2C indicates that significant increasing MK trend in precipitation
intensity can be identified in the southeast Yangtze River
basin. Specifically, Dongtinghu Lake, Poyanghu Lake, the
lower mainstream section, the middle mainstream section
and the Taihu Lake region (refer to lower panel of Fig. 1)
are dominated by significant increasing trend at >95% confi-
Figure 2 Mann–Kendall trend of annual extreme precipitation events in the Yangtze River basin (1960–2005) calculated for the
147 stations. A: MK trend in the annual maximum precipitation; B: MK trend in the frequency of the days with rain; C: MK trend in the
precipitation intensity; D: MK trend in the frequency of the days with no-rain. m denotes significant increasing trend; s denotes no
trend; . denotes significant decreasing trend.
Spatial and temporal variability of precipitation maxima during 1960–2005
dence level. A majority of regions in the north and west part
of the Yangtze River basin show no significant MK trends in
precipitation intensity. It is concluded from Fig. 2 that the
Yangtze River basin was dominated by the significant
decreasing MK trend in rainy days and increasing MK trend
in no-rain days. And most of the stations showing significant
increasing/decreasing rainy/no-rain days are located in the
middle and lower Yangtze River basin. The significant
increasing precipitation intensity mainly occurred to the
south-east corner of the Yangtze River basin and the Yangtze Delta.
Fig. 3A indicates that most stations in the Yangtze River
basin show no significant trend of the summer maximum
precipitation. Only nine out of 147 stations are dominated
by significant increasing summer maximum precipitation.
Wherein, seven stations are located in the middle Yangtze
River basin. More stations, when compared with what is
shown in Fig. 3A, are characterized by significant decreasing
trend in number of rainy days in summer (Fig. 3B), and these
stations are mostly located in the upper Yangtze River
basin. Three stations in the lower Yangtze River basin show
significant increasing trends. As for the changes of no-rain
days, opposite changing patterns can be observed in
Fig. 3D when compared to those in Fig. 3B. Significant
increasing trend in summer precipitation intensity can be
detected in the lower Jinshajiang, upper Wujiang, upper
Hanjiang, and the Taihu lake region (Fig. 3C). The stations
with significant increase of summer precipitation account
for 25.9% of the total stations studied in the Yangtze River
basin. Fig. 4 illustrates changes of precipitation maxima in
summer defined by 99th and 95th percentiles. It can be seen
from Fig. 4 that the number of days with precipitation
exceeding 99th percentile (Fig. 4A) and 95th percentile
219
(Fig. 4C) and related precipitation intensity (Fig. 4B for
99th percentile and Fig. 4D for 95th percentile) are observed in no significant trends in most of the stations in
the Yangtze River basin. Significant increasing trends in
the number of days with precipitation exceeding 99th percentile can be found mainly in the north Yangtze River basin, and related precipitation intensity is in significant
increasing trend in the south Yangtze River basin. In comparison with Fig. 4A and B, more stations are dominated
by significant increasing number of days with precipitation
exceeding 95% percentile (Fig. 4C), accounting for 12% of
the total stations. Only three stations show significant
increasing precipitation intensity, and one station shows significant decreasing precipitation intensity (95% percentile)
in summer (Fig. 4D).
Time series of MK trends of the precipitation
maxima
Figs. 5 and 6 demonstrate temporal changes of MK trends of
the annual and summer precipitation maxima in the Yangtze
River basin. The annual precipitation maxima in the lower
and upper Yangtze River basin are in decreasing trend during 1960–1985 and in increasing trend after 1985
(Fig. 5A). The increasing trend in the upper Yangtze River
basin becomes significant at >95% confidence level after
1998. The annual precipitation maxima in the middle Yangtze River do not show any obvious trend. Fig. 5B indicates
that the frequency of rainy days has no obvious changing
patterns during 1960–1975. After 1975 the frequency of
rainy days is decreasing in the whole Yangtze River basin
and these decreasing trends are significant at >95% confidence level after middle 1980s. The trend of frequency of
Figure 3 Mann–Kendall trend of the extreme precipitation events of summer in the Yangtze River basin (1960–2005). A: MK trend
in the summer maximum precipitation; B: MK trend in the frequency of the days with rain; C: MK trend in the precipitation intensity;
D: MK trend in the frequency of the days with no-rain. m denotes significant increasing trend; s denotes no trend; . denotes
significant decreasing trend.
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Q. Zhang et al.
Figure 4 Mann–Kendall trend of the summer precipitation extremes defined as daily precipitation exceeding 99th and 95th
percentiles. A: MK trends in the number of days with precipitation exceeding 99th percentile; B: MK trend in the precipitation
intensity (99th percentile); C: MK trends in the number of days with precipitation exceeding 95th percentile; D: MK trend in the
precipitation intensity (95th percentile). m denotes significant increasing trend; s denotes no trend; . denotes significant
decreasing trend.
Figure 5
Temporal changes of the MK trend Z-value of areal-averaged annual extreme precipitations in the Yangtze River basin.
no-rain days (Fig. 5D) shows an opposite pattern as compared with the trend of frequency of rainy days (Fig. 5B).
The precipitation intensity in the Yangtze River basin has
no obvious changing pattern during 1960–1975 (Fig. 5C).
After 1975 the precipitation intensity in all three regions
of the Yangtze River basin is increasing and the increasing
Spatial and temporal variability of precipitation maxima during 1960–2005
Figure 6
221
Temporal changes of the MK trend Z-value of areal-averaged summer precipitation in the Yangtze River basin.
trend in the middle and lower Yangtze River basin is significant at >95% confidence level after about 1985. This figure
confirms the findings obtained in Fig. 2 that the lower and
middle parts of the Yangtze River basin are experiencing
more rapid increase in precipitation intensity and have
therefore higher risk of flood hazards. Fig. 4 also shows that
1975 is the turning point for the changes of the annual precipitation maxima from a relative stable pattern to the significant increasing/decreasing trend.
The results of the similar study conducted for summer
precipitation maxima are shown in Fig. 6, which reveal a
similar changing pattern as the annual precipitation changes
in some cases. It can be seen from Fig. 6A that the summer
maximum precipitation in the upper and lower Yangtze River basin is decreasing during 1960–1985, and is increasing
thereafter. The middle Yangtze River basin has no significant changing pattern at >95% confidence level. The frequency of rainy days is decreasing in upper Yangtze River
basin and this decreasing trend is significant at >95% confidence level after 1985. However no significant changing
trend can be detected in the frequency changes of rainy
days in the middle and lower Yangtze River basin
(Fig. 6B). Conversely, the frequency of no-rain days is
increasing in the upper Yangtze River basin, and this
increasing trend is significant after 1980. No significant
changes can be observed in the frequency of no-rain days
in the middle and lower Yangtze River basin. Fig. 6C shows
that the summer precipitation intensity in the Yangtze River
basin is increasing after about 1980, and the increasing
trend becomes significant after 1990 in the middle and lower Yangtze River basin. Fig. 7 indicates that the number of
days with precipitation exceeding 95th percentile (Fig. 7A)
and 99th percentile (Fig. 7C) and precipitation intensity
for 95th percentile (Fig. 7B) and for 99th percentile
(Fig. 7D). It can be seen from Fig. 7 that the frequency
and the precipitation intensity are generally increasing in
the Yangtze River basin after about 1980. The number of
days with precipitation exceeding 95th percentile is in significant increasing trend after 1990 in the lower Yangtze
River basin, but no significant changes can be found in the
middle and upper Yangtze River basin (Fig. 7A). Significant
increasing trend of precipitation intensity exceeding 95th
percentile can be detected in the upper Yangtze River basin
after 1990, no significant trend can be found in the middle
Yangtze River basin. The precipitation intensity for the
95th percentile is in significant decreasing trend in the lower Yangtze River basin (Fig. 7B). As for the precipitation
maxima defined by 99th percentile, the number of days with
precipitation exceeding 99th percentile is increasing after
1980 and this increasing trend is significant after 1995 in
the lower Yangtze River basin. No significant trend can be
observed in the middle and upper Yangtze River basin
(Fig. 7C). Similar changing characteristics can be identified
in the precipitation intensity (Fig. 7D). The difference is
that significant increasing trend of precipitation intensity
for the 99th percentile is found in the middle Yangtze River
basin, and no significant trend is detected in the upper and
lower Yangtze River basin at >95% confidence level
(Fig. 7D).
In order to have a direct view of the development of frequency and intensity of annual maximum precipitation for
individual stations, an example is shown in Figs. 8 and 9 that
demonstrate changes in frequency and intensity of precipitation maxima of Nanjing station (32N, 118.8E). It can be
222
Q. Zhang et al.
Figure 7 Temporal changes of the MK trend Z-value of areal-averaged precipitation extremes defined by 99th and 95th percentiles
in summer in the Yangtze River basin. A: Changes of the number of days with precipitation exceeding 95th percentile; B: changes of
the related precipitation intensity; C: changes of the number of days with precipitation exceeding 99th percentile.
seen from Fig. 8 that no significant trend can be detected in
annual maximum precipitation (Fig. 8A) and annual total
precipitation (Fig. 8C). However the number of rainy days
is in significant decreasing trend (Fig. 8B) and significant
increasing trend can be observed in the precipitation intensity (Fig. 8D). As for the precipitation maxima (for 99th and
95th percentiles), no significant trends can be observed for
this particular station. The number of days with precipitation exceeding 99th and 95th percentiles (Fig. 9B) and related total precipitation (Fig. 9A) are increasing with
insignificant trend at 95% confidence interval. The resulting
precipitation intensity is slightly decreasing with insignificant trend at 95% confidence interval (Fig. 9C).
Large-scale atmospheric circulation
To explore large-scale circulation patterns behind the
changing trends of seasonal and annual maximum precipitation events, we examine and compare the horizontal
wind anomaly between 1961–1974 and 1961–2005 and between 1975–2005 and 1961–2005 at 850 hPa (Fig. 10) and
500 hPa (Fig. 11), respectively. These periods are chosen
because earlier results (see Time series of MK trends of
the precipitation maxima) have shown that a turning point
in the precipitation maxima exists in the middle 1970s.
Fig. 10 compares the wind anomaly between 1961–1974
and 1961–2005 (Fig. 10A) and that between 1975–2005 and
1961–2005 at 850 hPa (Fig. 10B). Fig. 10A demonstrates an
obvious northward wind component, indicating a stronger
East Asian summer monsoon during 1961–1974 as compared
to that during 1961–2005. However Fig. 10B shows an obvious southward wind component, suggesting a weaker eastern Asian summer monsoon during 1975–2005 as
compared to that during 1961–2005. Wind field changes at
500 hPa shows similar characteristics (Fig. 11). The northeasterly wind tendency will weaken the southwesterly summer monsoon flow and limit the northward extension of the
summer monsoon to north China. This atmospheric circulation will make the rainfall belt stay longer in the middle and
lower Yangtze River basin, leading to increasing precipitation in the Yangtze River basin (Wang and Zhou, 2005; Yu
et al., 2004). The onset and northern development of eastern Asian summer monsoon will decide the northward movement of the rainfall belt. Weaker eastern Asian summer
monsoon will not be beneficial for northern movement of
the rainfall belt, resulting in more precipitation in the middle and lower Yangtze River basin and in southern China.
However, stronger eastern Asian summer monsoon will be
beneficial for the northern movement of the rainfall belt
and resulting in more precipitation in northern China and
less precipitation in the Yangtze River basin and southern
China (Qian et al., 2003; Wang and Zhou, 2005).
Fig. 12 shows the linear trend of the geopotential height
at 850 hPa (Fig. 12A) and 500 hPa (Fig. 12B) in the Eurasia
Spatial and temporal variability of precipitation maxima during 1960–2005
223
Figure 8 Annual changes of precipitation extremes at Nanjing station (32N, 118.8E). (A) Annual maximum precipitation; (B)
changes of number of rainy days; (C) annual total precipitation and (D) precipitation intensity.
Figure 9 Changes of precipitation extremes defined by 99th and 95th percentiles at Nanjing station (32N, 118.8E). (A) Total
precipitation exceeding percentiles; (B) number of days with daily precipitation exceeding percentiles and (C) precipitation
intensity.
continent and the west Pacific regions. Fig. 12A indicates
that the Eurasia is covered with dense contours in the
north–south direction. The significant increasing trend of
geopotential height in northern China and increasing geopotential height in the South China Sea and west Pacific regions will exert negative influences on the northward
transportation of the vapor flux, and more vapor flux will
stay longer in the Yangtze River basin. Furthermore, the
decreasing geopotential height in the South China Sea indicates weakening summer monsoon which will also lead to
the longer stay of the Meiyu fronts (quasi-stationary fronts
with heavy rainfall systems elongated mainly in the east-
224
Figure 10
850 hPa.
Q. Zhang et al.
Horizontal wind anomaly between 1961–1974 and 1961–2005 (A), and between 1975–2005 and 1961–2005 (B) at
northeast to west-southwest orientation over East Asia from
late spring to mid-summer (Ding, 1994) in the Yangtze River
basin and will result in more precipitation. Fig. 12B indicates the significant increasing geopotential height in the
Baikal region and the decreasing geopotential height in
the north-western Pacific Ocean, Japan islands, northern
Korea peninsula, and these spatial distribution characteristics of the geopotential height usually lead to more precipitation in the Yangtze River and north parts of the south
China (Chen, 1994).
Conclusion and discussion
In this paper, we studied the spatial and temporal changes
of the precipitation maxima in the Yangtze River basin during 1960–2005 using Mann–Kendall trend test and possible
association with large-scale circulation. Some interesting
conclusions can be drawn as follows:
(1) Extreme precipitation is enhanced in the Yangtze
River basin, especially after about 1975, which is elucidated by significant increasing no-rain days, significant decreasing rainy days and significant increasing
precipitation intensity. The mid-1970s can be
accepted as the starting point for pattern change of
precipitation maxima. Extreme precipitation events
as measured by frequency and intensity are in significant increasing trend after about 1975–1985 in the
Yangtze River basin.
(2) The significant increasing trend of precipitation intensity occurred mainly in the south-east and south-west
part of the Yangtze River basin and the Yangtze River
Delta. The trend in the precipitation intensity in other
parts of the Yangtze River basin is not significant at
>95% confidence level. The precipitation intensity in
summer is in significant increasing trend in the south
and north part of the Yangtze River basin and the Yan-
Spatial and temporal variability of precipitation maxima during 1960–2005
Figure 11
500 hPa.
225
Horizontal wind anomaly between 1961–1974 and 1961–2005 (A), and between 1975–2005 and 1961–2005 (B) at
gtze River Delta. Therefore, the middle and lower
Yangtze River might face higher risk of flood hazards.
It should be noted that, in the middle and lower Yangtze River basin the frequency of no-rain days is in significant increasing trend and the frequency of rainy
days is in significant decreasing trend. No significant
trend of precipitation maxima can be identified in
the upper Yangtze River basin.
(3) Analysis of large-scale circulation during 1961–1974,
1975–2005 and 1961–2005 indicates that weaker East
Asian summer monsoon can be identified during
1975–2005 as compared to 1961–1974. Linear trend
of geopotential height at 500 hPa and 850 hPa indicates that the spatial distribution patterns of the geopotential height in the Eurasia and west Pacific Ocean
are not beneficial for the northward transportation of
the vapor flux and result in longer stay of the Meiyu
front in the Yangtze River basin, which will lead to
more precipitation in the middle and lower Yangtze
River basin. The relationship between precipitation
changes in the Yangtze River basin and the large-scale
circulation can be explained by the physical mechanisms involved, which lead to a general increase in
the atmospheric moisture content accompanied by
warming and also lead to changes in evaporation, circulation, and other processes (Khon et al., 2007).
Model study shows increasing extreme precipitation,
particularly over land areas in middle and high latitudes of the Northern Hemisphere, and a decrease
of rainy days in the latitudinal belt around 40N during
summer (Khon et al., 2007). One possible cause for
changes in precipitation intensity would be changes
in relative contributions of precipitation originating
from convective mechanisms (Gregory and Mitchell,
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Q. Zhang et al.
Figure 12 Linear trend of the mean geopotential height of JJA at 850 hPa (A) and 500 hPa (B). The contours indicate the
correlation coefficient between time and the geopotential height. Values of the contours larger (smaller) than 0.3 (0.3) are
statistically significant at >95% confidence level.
1995). Under the increasing CO2 scenarios, some global climate models (GCMs) demonstrate enhanced
mid-latitude precipitation intensity (e.g. McGuffie
et al., 1999; Osborn et al., 2000). Furthermore,
altered atmospheric moisture, temperature fields,
shifts in strength of Asian monsoon could have driven
across the board changes in the precipitation intensity, with no shift in the importance of the various
mechanisms (Osborn et al., 2000).
(4) Changes in precipitation maxima are likely to have
greater immediate impact on human society than
any likely small change in the mean rainfall amount.
Changes in the precipitation intensity may have
important implications for flood risk/control in the
Yangtze River basin. The research results of this paper
indicate that increasing flood may risk the middle and
lower Yangtze River basin. The significant increasing/
decreasing trends of no-rain/rainy days in the middle
and lower Yangtze River basin have potential to result
in higher variability of flood risk and dry events in the
middle and lower Yangtze River basin. It should be
mentioned here that the middle and lower Yangtze
River basin is heavily populated and economically
developed, therefore the middle and lower Yangtze
River basin is also the risk-prone region. The effective
measures should be taken to reduce huge damage due
to extreme climatic events in the middle and lower
Yangtze River basin.
Acknowledgements
This study was financially supported by the National Natural
Science Foundation of China (Grant No. 40701015) and by
the Laboratory for Climate Studies, National Climate Center, China Meteorological Administration, China (Grant No.
CCSF2007-35), Outstanding Oversea Chinese Scholars Fund
from CAS (The Chinese Academy of Sciences) and by a Direct
Grant from the Faculty of Social Science, The Chinese University of Hong Kong (Project No. 4450183). Great thanks
should be extended to two anonymous reviewers and to
Prof. Dr. Marios Sophocleous, the editor, for their crucial
comments which greatly improved the quality of this paper.
Spatial and temporal variability of precipitation maxima during 1960–2005
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