Quaternary International 226 (2010) 44–53
Contents lists available at ScienceDirect
Quaternary International
journal homepage: www.elsevier.com/locate/quaint
Multiscale streamflow variations of the Pearl River basin and possible
implications for the water resource management within the Pearl River
Delta, China
Yongqin David Chen a, b, Qiang Zhang c, *, Chong-Yu Xu d, Xixi Lu e, Shurong Zhang e
a
Department of Geography and Resource Management, The Chinese University of Hong Kong, Hong Kong, China
Centre of Strategic Environmental Assessment for China, The Chinese University of Hong Kong, Hong Kong, China
Department of Water Resources and Environment, Sun Yat-sen University, 135 Xingangxi Road, Guangzhou 510275, China
d
Department of Geosciences, University of Oslo, P O Box 1047 Blindern, N-0316 Oslo, Norway
e
Department of Geography, National University of Singapore, Arts Link 1, 117570 Singapore
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 8 September 2009
Long monthly streamflow series of three control hydrological stations of the Pearl River basin were
analyzed by using the scanning t-test and the scanning F-test. Possible implications of the changing
properties of streamflow variations for the water resource management of the Pearl River Delta are also
discussed. The results indicated that: 1) more complicated changes were observed in terms of the second
center moment when compared to the first original moment. More significant abrupt changes of the
second center moment imply more sensitive response of streamflow stability to climate changes and
human activities; 2) abrupt behaviors of the first (second) center moment of the streamflow variations
tend to be more sensitive to climate changes and/or human activities in the larger river basin when
compared to those in the smaller river basin. These phenomena are attributed to buffering functions of
more storage space of longer river channel, and more complicated and longer runoff yield and
concentration processes in the river basin of larger drainage area; 3) annual minimum streamflow of the
Pearl River basin tends to be increasing. This will be helpful for better human mitigation of the salinity
intrusion in dry seasons across the Pearl River Delta. Annual maximum streamflow, when compared to
annual minimum streamflow, shows larger-magnitude variability reflected by larger standard deviation,
implying unfavorable conditions for flood mitigation in the Pearl River Delta. The results of this paper are
of scientific and practical merits for water resource management and sound human mitigation to water
hazards across the Pearl River Delta, and also are a good case study for similar researches in other river
deltas in the world under the changing environment.
Ó 2009 Elsevier Ltd and INQUA. All rights reserved.
1. Introduction
The altered hydrological cycle and changed spatial and temporal
distribution of water resource as a result of the increasing
temperature attracted considerable concerns from hydrologists,
meteorologists and also policy makers due to the tremendous
importance of water in both society and nature (e.g. Xu and Singh,
2004), and which also poses a new challenge for the actual practice
of basin-scale water resource management under the changing
climate. Research results indicated that water resources are sensitive to climate changes, and this is particularly true for the ground
* Corresponding author. Tel./fax: þ86 20 84113730.
E-mail address: zhangqnj@gmail.com (Q. Zhang).
1040-6182/$ – see front matter Ó 2009 Elsevier Ltd and INQUA. All rights reserved.
doi:10.1016/j.quaint.2009.08.014
surface water resources (WMO, 1987). Small perturbations in
precipitation frequency and/or quantity can result in significant
impacts on the mean annual discharge (Risbey and Entekhabi,
1996). Any alterations in the hydrologic cycle will affect energy
production and flood control measures (Xu and Singh, 2004) to
such an extent that water management adaptation measures will
very likely be brought in (Minville et al., 2008). Therefore, climatic
changes and associate impacts on global/regional water resources
are receiving increasing concerns from academic circles (Loukas
et al., 2002; Camilloni and Barros, 2003; Zhang et al., 2008a).
Xu (2000) thoroughly investigated the influences of climate
changes on flow regimes of twenty-five catchments in central
Sweden by using a conceptual monthly water balance model,
suggesting that significant increase of winter flow and decrease of
spring and summer streamflow were resulted from most scenarios.
Y.D. Chen et al. / Quaternary International 226 (2010) 44–53
More and more hydrologists and meteorologists have focused
attention on variability and availability of regional water resources
under current climatic changes (e.g. Zhang et al., 2009a). Study of
impacts of climate changes on hydrological processes heavily relies
on trend detection of hydro-climatic variables such as precipitation
and streamflow. Due to complex changing patterns of precipitation,
temperature, and other meteorological variables, it is still unclear
how exactly these changes in meteorological variables may affect
streamflow variations (Birsan et al., 2005). Streamflow integrates
the various influences of atmospheric variables, human activities
such as land use changes, urbanization, over watershed, and all
these impacts are combined to reflect hydrological processes in the
outlet of the river basin. Thus, numerous studies attempted to
address variations of streamflow of the river basins over the world
(Pekarova et al., 2003; Kahya and Kalayci, 2004; Birsan et al., 2005;
Zhang et al., 2006). Zhang et al. (2008) studied annual streamflow
and sediment load series of the Pearl River basin. The current study
attempts to address statistical properties of streamflow variations
of the Pearl River basin and discuss associated implications for
water resource management within the Pearl River Delta based on
long monthly streamflow dataset.
The Pearl River (3 410 N- 29150 N; 97 390 E- 117180 E) (Fig. 1) is
the second largest river in terms of streamflow in China with
a drainage area of 4.42 105km2 (PRWRC, 1991), which involves
three major tributaries: West River, North River and East River. The
West River is the largest tributary accounting for 77.8% of the total
drainage area of the basin. The North River is the second largest with
a drainage area of 4,6710 km2. The East River accounts for 6.6% of the
total area of the Pearl River Basin. The annual mean temperature
ranges between 14 and 22 C and the precipitation mainly occurs
during April–September (Zhang et al., 2008b), accounting for 72–
88% of the annual precipitation (PRWRC, 1991). The streamflow
variations of the Pearl River basin have considerable influences on
the hydrological processes of the Pearl River Delta, one of the most
complicated deltaic drainage systems in the world (Chen and Chen,
2002). Flat terrain at low-lying altitude and downstream location,
together with rapid economic development and population growth
over the past three decades have made the PRD region more and
more vulnerable to natural hazards such as flood, salinity intrusion
and storm surge. In recent years, engineering facilities and other
modifications of the Pearl River network have been designed to
45
strengthen flood protection and to cater for huge requirements of
building materials. Since the mid-1980s, intensive channel dredging
and levee construction have significantly affected flood stages and
caused serious hydrologic alterations in the study region. Altered
streamflow allocation between North River and West River was also
seen as a major cause for the hydrological alterations of the Pearl
River Delta (Chen et al., 2008). Hydrological alterations led to
abnormally-high water level in the flooding seasons and more
frequent salinity intrusion events in dry seasons, which posed new
challenges for effective water resource management across the Pearl
River Delta. However, better understanding of hydrological
processes of the Pearl River basin will be of great scientific and
practical importance for effective water resource management
within the Pearl River Delta, and this is the major motivation for this
study. With these in mind, the objectives of this study are: 1) to
understand abrupt behaviors of streamflow variations in terms of
first and second center moments; 2) to detect abrupt changes of
annual minimum and maximum streamflow series based on
monthly streamflow dataset; 3) to reveal possible implications for
water resource management in the Pearl River Delta.
This study analyzed long hydrological series, more than 50
years. The results of this paper should be important for effective
water resource management in the Pearl River Delta under
changing climate and also provide good case study for the water
resource management for other river deltas of the world.
2. Data and methodology
This study analyzed long hydrological series of three control
hydrological stations: Gaoyao, Shijiao and Boluo. More detailed
information of these three hydrological stations is presented into
Table 1. Fig. 1 illustrates the location of these stations considered in
this study. The hydrological data are of good quality without
missing data. The hydrologic data before 1989 are extracted from
the Hydrological Year Book (published by the Hydrological Bureau
of the Ministry of Water Resources of China) and those after 1989
are provided by the Water Bureau of Guangdong Province.
Abrupt changes of hydrological and meteorological series are
often of considerable importance (Lund et al., 2001; Lund and
Reeves, 2002). In this study, abrupt changes were analyzed using
the scanning t-test technique on different time scales. Stable or
Fig. 1. Location of the study region and three hydrological stations.
46
Y.D. Chen et al. / Quaternary International 226 (2010) 44–53
Table 1
Detailed information of hydrological stations along the mainstream and tributaries
of the Pearl River basin.
Tributaries
Station name
Length of series
Basin area
(103 km2)
West River
North River
East River
Gaoyao
Shijiao
Boluo
Jan. 1956–Dec. 2007
Jan. 1956–Dec. 2007
Jan. 1954–Dec. 2007
351.5
38.4
25.3
unstable status of hydrological variations is another important
statistical property of the hydrological series since that unstable
water supply may seriously impact making procedure of water
resource management measures. Steady or unsteady variations of
the hydrological series were evaluated by the change in the standard deviation, which was analyzed by the F-test technique.
Jiang et al. (2002) extended the definition of student t-test and the
F-test (Cramer, 1946) by identifying change points on different time
scales. The scanning t-test attempts to detect significant changes in
the first moment (subseries mean or average) on different time scales
within a long time series; while the scanning F-test attempts to
analyze significant changes in subseries variance (the second
moment) on various time scales. These two techniques were introduced in Jiang et al. (2007). For the sake of completeness of this study,
a brief introduction of these two methods is presented here.
Statistic t(n, j) in the scanning t-test is defined as the difference
of the subsample averages between every two adjoining subseries
of equal subseries size (n):
1=2
tðn; jÞ ¼ xj2 xj1 n1=2 s2j2 þ s2j1
where xj1 ¼ 1=n
Pj1
i ¼ jn
xðiÞ, xj2 ¼ 1=n
256
Pjþn1
i¼j
(1)
xðiÞ,
s2j1 ¼ 1=n 1
s2j2 ¼ 1=n 1
Pj1
¼ jn
Pijþn1
i¼j
ðxðiÞ xj1 Þ2 ,
ðxðiÞ xj2 Þ2 , in which subsample size n may
vary in this way as n ¼ 2, 3,., <N/2. The j ¼ n þ 1, n þ 2,., N n þ 1
is the reference time.
The Table-Look-Up Test (Von Storch and Zwiers, 1999) was used
to modify the significance criterion of statistic t(n, j) with lag-1
autocorrelation coefficients of the pooled subsample and the
subsample size n in that hydrological series usually subject to
persistence. Criterion t0.05 for the correction of the dependence was
accepted as the significance level on time scales considered. For
shorter subsample sizes, the critical values are overly restrictive.
The significance level varies with n and j, and so the test statistic
was normalized as:
tr ðn; jÞ ¼ tðn; jÞ=t0:05
(2)
When jtr(n,j)j > 1.0, the abrupt change is significant at the 0.05
significance level. tr(n,j) < 1.0 denotes significant decrease and
tr (n, j) > 1.0 significant increase.
The scanning F-test defines significant changes of subseries
variances. Statistic Fr(n,j) is defined as:
8 .
>
2
2
>
Fa ; for Sj2 < Sj1 ;
>
< Sj1 =Sj2
0; for Sj2 ¼ Sj1 or Sj1 ¼ 0; Sj2 ¼ 0;
Fr ðn; jÞ ¼
.
>
>
>
: S2 =S2
Fa ; for S > S ;
j2
j2
j1
(3)
j1
where the subsample standard deviations Sj1 and Sj2 are calculated in the same way as in Eq. (1). Fa is a threshold value
based on the effective degree of freedom after the correction of
A
Gaoyao station
1.1
Time scales (months)
0.9
128
0.7
0.5
64
0.3
0.1
32
−0.1
−0.5
16
−0.8
−1.1
8
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Time (year)
6
B
4
2
0
−2
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Fig. 2. Contours of the normalized scanning t-test standardized by the ‘‘Table-Look-up’’ critical value t0.05 for the standardized streamflow series at the Gaoyao station. Thick solid
and dashed lines denote abrupt changes significant at >95% confidence level. Solid lines denote positive values and dashed lines negative values (Fig. 2A). Fig. 2B indicates
standardized streamflow, change points and episode average (solid line) from Fig. 2A.
Y.D. Chen et al. / Quaternary International 226 (2010) 44–53
Time scales (months)
256
47
A
Gaoyao station
2.5
2
1.5
128
1
0.5
64
0
−0.5
−1
32
−1.5
−2
16
−2.5
−3
−3.5
8
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Time (year)
6
B
4
2
0
−2
−4
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Fig. 3. Contours of the normalized scanning F-test for the standardized streamflow of the Gaoyao station. Thick solid and dashed lines denote abrupt changes significant at >95%
confidence level. Solid lines denote positive values and dashed lines negative values (Fig. 3A). Fig. 3B indicates standardized streamflow, change points and episode standard
deviation (solid line) from Fig. 3A.
Time scales (months)
256
A
Shijiao station
1.1
0.9
0.7
128
0.5
0.3
64
0.1
−0.1
32
−0.3
−0.5
16
−0.7
−0.9
8
−1.1
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Time (year)
5
B
4
3
2
1
0
−1
−2
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Fig. 4. Contours of the normalized scanning t-test standardized by the ‘‘Table-Look-up’’ critical value t0.05 for the standardized streamflow series at the Shijiao station. Thick solid
and dashed lines denote abrupt changes significant at >95% confidence level. Solid lines denote positive values and dashed lines negative values (Fig. 4A). Fig. 4B indicates
standardized streamflow, change points and episode average (solid line) from Fig. 4A.
48
Y.D. Chen et al. / Quaternary International 226 (2010) 44–53
dependence and in a normalized distribution for the time series.
The effective degree of freedom was estimated as (Hammersley,
1946):
Ef ðnÞ ¼ f ðnÞ k
hX
i1
r 2 ðsÞ
; rðkÞ/0;
(4)
s¼0
where f (n) is the degree of freedom listed in the F table.
A local minimum in Fr (n, j) < 1.0 denotes a significant change
towards a smaller variance, i.e. the record becomes much steadier;
whereas a local maximum in Fr (n, j) > 1.0 indicates a significant
change towards a larger variance, i.e. the record becomes much
unsteadier (Jiang et al., 2007).
3. Results
3.1. Abrupt behavior of monthly streamflow variations
of West River
This study analyzed abrupt changes of first center moment and
second center moment. For the sake of easy understanding, the
contours of scanning t-test and F-test results showing abrupt
behaviors of monthly streamflow variations on different time scales
were mapped. Standardized streamflow series and associated
episode average, standard deviation and significant change points
were mapped. To avoid redundancy, the contours of scanning t- and
F-test with respect to annual minimum and maximum streamflow
series were not mapped. Fig. 2A shows that the monthly streamflow
series of the Gaoyao station is dominated by abrupt decrease interrupted by sporadic intervals characterized by abrupt increase on
time scales less than 32 months. A significant abrupt decrease of
average was identified at 2004. From the perspective of time scales
longer than 32 months, abrupt increase of streamflow was detected
Time scales (months)
256
during 1964–1975, but is not significant at >95% confidence level.
Significant decrease of streamflow can be observed after the early
1980s, and significant increase of streamflow was found in the early
1990s. Fig. 2B demonstrates two periods characterized by decreased
streamflow: 1983–1994 and 2004–2007 and two periods dominated
by increased streamflow: 1956–1982 and 1995–2003. Fig. 2A and B
indicate more frequent increase and decrease of streamflow variations after 1990 when compared to those before 1990. Before the
1980s, no significant abrupt streamflow changes were found. Abrupt
streamflow variations were observed mainly after the early 1980s.
Stability of the streamflow variations of the Gaoyao station
shown by the scanning F-test was illustrated in Fig. 3. More
complicated patterns can be found in Fig. 3A when compared to
the scanning t-test (Fig. 2A). More significant change points of
standard deviation can be detected on different time scales. On
time scales shorter than 64 months, five time intervals were
identified with different stability properties of streamflow variations. The periods of 1956–1965, 1980–1990 and 2003–2007 were
characterized by higher frequency of standard deviation changes;
the remaining periods, i.e. 1965–1980 and 1990–2003 were
dominated by lower variability of standard deviation. On time
scales longer than 64 months, changing patterns of second center
moment were relatively simpler when compared to that on time
scales shorter than 64 months. Higher stability was observed
during 1965–1975 and after 1983, and lower stability during
before 1965 and 1975–1983. The scanning F-test results determined the centers with higher significance level, allowing
mapping of the significant change points and associated episodes
with different stability properties (Fig. 3B). Subseries variances
showed moderate changes. More frequent variations were found
after the 1980s. After the 1980s, the streamflow changes of the
Gaoyao station tend to show variations of larger magnitude and
frequency with lower stability.
A
Shijiao station
128
64
32
16
8
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
3.5
3
2.5
2
1.5
1
0.5
0
−0.5
−1
−1.5
−2
−2.5
−3
−3.5
−5
Time (year)
6
B
B
4
2
0
−2
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Fig. 5. Contours of the normalized scanning F-test for the standardized streamflow of the Shijiao station. Thick solid and dashed lines denote abrupt changes significant at >95%
confidence level. Solid lines denote positive values and dashed lines negative values (Fig. 5A). Fig. 5B indicates standardized streamflow, change points and episode standard
deviation (solid line) from Fig. 5A.
Y.D. Chen et al. / Quaternary International 226 (2010) 44–53
Time scales (months)
256
49
A
Boluo station
1.4
1.2
1
128
0.8
0.6
64
0.4
0.2
32
0
−0.2
16
−0.4
−0.6
8
−0.8
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Time (year)
6
B
4
2
0
−2
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Fig. 6. Contours of the normalized scanning t-test standardized by the ‘‘Table-Look-up’’ critical value t0.05 for the standardized streamflow series at the Boluo station. Thick solid and
dashed lines denote abrupt changes significant at >95% confidence level. Solid lines denote positive values and dashed lines negative values (Fig. 6A). Fig. 6B indicates standardized
streamflow, change points and episode average (solid line) from Fig. 6A.
3.2. Abrupt behavior of monthly streamflow variations
of North River
The scanning t-test results of the streamflow series of the Shijiao
station are shown in Fig. 4. The streamflow series of the Shijiao
station displayed significant abrupt changes in the early 1970s,
mid-1970s, mid-1980s and early 1990s. Frequent abrupt changes
occurred during the 1970s and 1980s, which differ from those of the
hydrological processes of the Gaoyao station, the West River.
Frequent abrupt changes of streamflow variations of the West River
occurred after the 1980s. Generally speaking, time intervals characterized by different hydrological episodes can be observed in the
streamflow series of the Shijiao station. Decreasing streamflow was
observed during 1956–1966, 1976–1989 and after 1998; increasing
streamflow was found during 1967–1975 and 1990–1997. More
complicated changing patterns of decrease and/or increase of
streamflow were detected on shorter time scales, i.e. shorter than
16 months. Fig. 4A indicates that four abrupt changes after 1995 are
not significant statistically. The streamflow of the Shijiao station
after 1995 is characterized by four episodes with different,
changing properties. From a perspective of a longer time scale, e.g.
longer than 32 months, the streamflow at the Shijiao station is
decreasing. Fig. 4B further indicates significant change points and
episodic average streamflow. Increased streamflow occurred
mainly in the early 1970s and decreased after the late 1970s until
the early 1990s. After the 1990s, a slight increase of streamflow can
be detected (Fig. 4B).
Fig. 5 illustrates scanning F-test results in time scale–time space.
More significant change points were identified when compared to
those of the scanning t-test. Visual comparison between Figs. 4A
and 5A indicates that increase of streamflow largely corresponds to
lower stability of streamflow variations. Figs. 4 and 5 also indicate
that the stability of streamflow variations is more sensitive to
climate changes or human activities when compared to changes of
the first center moment. This is also true for the streamflow
variations of the Gaoyao station of the West River. Significant
change points were determined by identifying the center of the
significant regions circled by thick solid/dashed lines (Fig. 5B).
Relatively lower stability of streamflow variations can be observed
during 1960–1965, 1973–1976, and after the early 1990s. The period
of 1970–1985 is characterized by higher frequency of abrupt
changes in terms of the first center moment, and simultaneously
features higher frequency of abrupt changes with respect to the
second center moment (Figs. 4B and 5B). When compared to
streamflow variations of the West River (Gaoyao station), higherfrequency appearance of abrupt changes of the first and the second
center moment was observed within the streamflow series of the
North River (Shijiao River). Therefore, the streamflow variations of
the river basin of smaller drainage area respond in a more sensitive
way to climate changes and/or human activities. Therefore, more
importance should be attached to possible influences of climatic
changes and human activities on hydrological processes within the
river basin of smaller drainage area, e.g. the North River in this
study, and to the impacts of streamflow variations on hydrological
processes of the Pearl River Delta.
3.3. Abrupt behavior of monthly streamflow variations of East River
The scanning t-test analysis for the long streamflow series was
used to define when the change points occurred at Boluo station,
the control hydrological station of the East River (Figs. 1, 5). The
streamflow series from Boluo displayed significant abrupt
50
Y.D. Chen et al. / Quaternary International 226 (2010) 44–53
Time scales (months)
A
Boluo station (A )
256
2.5
2
1.5
128
1
0.5
64
0
−0.5
−1
32
−1.5
−2
16
−2.5
−3
8
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
−3.5
2005
Time (year)
B
6
4
2
0
−2
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Fig. 7. Contours of the normalized scanning F-test for the standardized streamflow of the Boluo station. Thick solid and dashed lines denote abrupt changes significant at >95%
confidence level. Solid lines denote positive values and dashed lines negative values (Fig. 7A). Fig. 7B indicates standardized streamflow, change points and episode standard
deviation (solid line) from Fig. 7A.
decreases in 1975 (on a time scale of 128 months), 1985 (on a time
scale of 128 months), 1993 (on a time scale of 64 months), and 2002
(on a time scale of 32 months). Fig. 6A displays different behaviors
of abrupt changes of streamflow variations on different time scales.
More complicated patterns can be observed on shorter time scales.
On time scales longer than 64 months, the periods of 1954–1967,
1984–1991, 1998–2005 are characterized by decreasing streamflow,
and the time intervals of 1968–1983 and 1992–1997 are dominated
by increasing streamflow. More hydrological episodes characterized by different magnitudes of increase and/or decrease can be
observed on time scales shorter than 64 months. Fig. 6B clearly
shows the time when change points occurred and associated
episode average streamflow of the Boluo station. When compared
3
standardized streamflow
mean streamflow
standard deviation
2
to the scanning t-test results of the streamflow series of the Gaoyao
station and the Shijiao station, the frequency of change points
appeared within the streamflow series seems to be higher than that
of the Gaoyao station, but lower than that of the Shijiao station. Just
Streamflow variations here tend to be more sensitive to climate
changes or human activities. Moderate variations of the streamflow
variations of the East River can be attributed to hydrological
regulations of the water reservoirs (Chen et al., 2009). As for the
scanning F-test results of the streamflow series of the Gaoyao and
Shijiao station, more complex changing patterns of abrupt changes
of the second center moment can be found in Fig. 7. The centers of
the significant areas were checked and the significant change
points were shown in Fig. 7B. Fig. 7B shows that more abrupt
3
standardized streamflow
linear fit
standard deviation
2.5
2
1.5
1
1
0
0.5
0
−1
−0.5
−2
Gaoyao station (annual maximum streamflow)
−3
1960
1970
1980
1990
2000
−1
Gaoyao station (minimum annual streamflow
−1.5
1960
1970
1980
1990
2000
Fig. 8. t- and F-test of the annual maximum and minimum streamflow series of the Gaoyao station. The linear trend in the right panel is not significant. The linear trends of the rest
annual maximum streamflow are also not significant. Thus, we did not analyze the linear trend of those streamflow series. The straight line in the right panel is only for visual
inspection.
Y.D. Chen et al. / Quaternary International 226 (2010) 44–53
2.5
2
51
4
standardized streamflow
standard deviation
standardized streamflow
standard deviation
3
1.5
2
1
0.5
1
0
0
−0.5
−1
−1
−1.5
−2
Shijiao station (annual maximum streamflow)
1960
1970
1980
1990
2000
Shijiao station (annual minimum streamflow)
−2
1960
1970
1980
1990
2000
Fig. 9. t- and F-test of the annual maximum and minimum streamflow series of the Shijiao station.
changes of the second center moment can be found after the 1980s,
when the hydrological processes show larger variability.
3.4. Abrupt behavior of annual maximum/minimum streamflow of
the Pearl River
Owing to hydrological alterations (Chen et al., 2008), there
occurred more frequent abnormally-high water level in flooding
seasons and abnormally-low water levels in dry seasons. Therefore,
it is of great importance to understand the changing properties of
annual maximum and/or minimum streamflow based on monthly
streamflow dataset. Figs. 8, 9 and 10 display annual maximum (AM,
left panel) and minimum (Am, right panel) streamflow variations of
these three control hydrological stations respectively. Fig. 8 indicates that AM streamflow increased after the 1990s with lower
stability. No significant abrupt changes in terms of the first center
moment of Am streamflow can be detected. Scanning F-test indicates higher stability of streamflow variations after the 1980s.
Linear fit line indicates increasing trend of Am streamflow of the
Gaoyao station. Generally, minimum streamflow occurs in winter
(December, January, February) and maximum streamflow in
summer (June, July, August). Changes of streamflow amount of the
West River mean much to the hydrological variations of the Pearl
River Delta in that the streamflow amount of the West River
accounts for more than 70% of the total streamflow amount of the
Pearl River basin. Increasing annual minimum streamflow of the
West River should be beneficial for human mitigation of salinity
intrusion across the Pearl River Delta. Figs. 9 and 10 indicate no
significant abrupt changes of the first center moment. Scanning
F-test results indicate different abrupt changes of the second center
moment. Abrupt changes of standard deviation of the Am
streamflow seem to occur earlier when compared to AM: the
4. Discussion
Hydrological processes are in close relation with climate
changes, particularly precipitation variations in space and time.
Thorough analysis of precipitation variations (Zhang et al., 2009b)
and dryness/wetness variations used the standardized precipitation index (SPI) and aridity index (AI) (Zhang et al., 2009c).
However, the dry/wet tendency is not significant statistically at
>95% confidence level. The wet tendency was observed mainly in
the west parts of the West River basin. The dry tendency was found
mainly in the east parts of the Pearl River basin, specifically the
North and East Rivers. The non-significant wet and dry tendency in
the West River causes the streamflow series of the West River to
show moderate variation. Streamflow variations of the North and
East Rivers are subject to larger magnitude when compared to
those of West River basin, which can be attributed to the relative
450
4
Standardized streamflow
Standardized deviation
3
mean streamflow
standardized streamflow
standard deviation
400
350
300
2
250
1
200
150
0
100
−1
−2
former occurs in the 1980s and even earlier, and the later occurs
after the 1990s. Figs 9 and 10 indicate that AM and Am streamflow
series of the Shijiao and Boluo station come to be lower stability.
However, AM and Am of the Gaoyao station show different properties. AM streamflow of the Gaoyao station tends to be lower
stability after 1990s and Am streamflow comes to be higher
stability. Scanning F-test of AM and Am streamflow series of the
Shijiao and Boluo station indicates larger-magnitude of variations
in terms of AM streamflow changes when compared to those of Am
streamflow variations (Figs. 9 and 10). The Am streamflow variations of the Shijiao and Boluo station have the increasing tendency.
Therefore, the streamflow variations seem to be beneficial for
better mitigation to salinity intrusion within the Pearl River Delta.
Larger-magnitude of streamflow variability will not be helpful for
flood mitigation in the Pearl River Delta.
50
Boluo station (annual maximum streamflow)
1960
1970
1980
1990
2000
0
1950
1960
1970
1980
1990
Fig. 10. t- and F-test of the annual maximum and minimum streamflow series of the Boluo station.
2000
52
Y.D. Chen et al. / Quaternary International 226 (2010) 44–53
drainage areas of the river basins. Study in the Yangtze River basin
(Zhang et al., 2008c) indicated that the impacts of human activity
and climatic changes on the sediment load and runoff changes are
greater in smaller river basins than in larger river basins. In this
study, higher sensitivity of streamflow changes to influences of
climate changes and human activities was represented mainly by
more frequent abrupt changes of the first and second moment
based on the results of scanning t- and F-test technique. The results
of the study on the trends and abrupt changes of precipitation
maximum over the Pearl River basin displayed the time when the
abrupt changes of the precipitation maxima occurred in space
(Zhang et al., 2009b). Generally, the abrupt changes of the precipitation maxima mainly occurred in three time intervals, i.e. early
1970s, early 1980s and early 1990s. Significant abrupt changes of
streamflow series of the Pearl River basin mainly occurred in these
three time intervals, which can be observed in the results by the
scanning t-test technique. This result shows distinctly the
tremendous influences of precipitation changes on the hydrological
processes, though considerable impacts the human activities have
on the hydrological processes (Zhang et al., 2008c). Many studies
tended to corroborate the overwhelmingly larger impacts of
precipitation changes on the streamflow processes when compared
to human activities (e.g. Zhang et al., 2006, 2008c, 2009d). Zhang
et al. (2008) also indicated that the decreasing sediment load of the
Pearl River basin was the result of reservoir construction and
streamflow variations are due to precipitation changes. Therefore,
precipitation changes and human activities have different impacts
on sediment load and streamflow, and streamflow changes are
mainly the result of precipitation variations. As for changes of
annual maximum streamflow, larger magnitude of changes can also
be observed in the North and East Rivers, and moderate variations
in the West River basin, which shows the buffering effect of a larger
river basin on hydrological processes. In river channels close to the
Pearl River Delta, the streamflow variations could be heavily
influenced by topographical changes of river channel due to sand
mining or dredging. However, these changes are mainly observed at
the Makou and Sanshui station. Based on previous studies in the
Pearl River basin, the streamflow changes of the Gaoyao, Shijiao and
Boluo stations are mainly the results of precipitation variations.
Besides, the results of changes of precipitation maxima (Zhang
et al., 2009b) corroborated by the abrupt behaviors of precipitation
maxima are in line with those of streamflow series considered in
this study. For example, the abnormally-high streamflow occurred
in about 1984 was in agreement with the occurrence of abnormally
intense precipitation event in 1984. The hydrological behaviors of
these three hydrological stations, i.e. Gaoyao, Shijiao and Boluo, are
the integrated consequences of human activities and climate
changes. It is hard to say exactly to what degree the human activities and climate changes influence the hydrological variations of
these three control stations representing hydrological processes of
three major tributaries of the Pearl River basin. Even so, precipitation changes should play the key role in the shifts of streamflow
from one statistical condition to another. This result will benefit the
further study on the streamflow changes and also helps to make
sound water resource management policy.
5. Conclusions
Thoroughly analysis was conducted of long streamflow series of
three control hydrological stations of the Pearl River basin: Gaoyao
station of the West River, Shijiao station of the North River and
Boluo station of the East River. Abrupt behaviors of the first and the
second center moment were analyzed with robust statistical
techniques, i.e. the scanning t-test and the scanning F-test. Possible
implications of the changing properties of the hydrological
variations of the Pearl River basin with respect to water resource
management of the Pearl River Delta were considered. The most
important conclusions are:
1) Specific time intervals characterized by increase or decrease of
average and standard deviations of the streamflow series were
identified for the West River, North River and East River
respectively. Analysis results indicated that lower streamflow
stability usually corresponds to higher streamflow average and
vice versa. The first and the second center moment of the
streamflow variations of the river basin of smaller drainage
area are more sensitive to climate changes and/or human
activities. This may be due to buffering functions of more
storage space of the longer river channels, and more complicated and longer runoff yield and concentration processes in
the river basin of larger drainage area.
2) In terms of monthly streamflow variations, after 2005, the
streamflow of the West River and East River decreased in terms
of streamflow average. This is also true for the North River,
however the abrupt changes are not significant at the >95%
confidence level. Annual minimum streamflow of the Pearl
River basin tends to be increasing, and which is greatly helpful
for better human mitigation of the salinity intrusion in dry
seasons across the Pearl River Delta. Larger standard deviation
of annual maximum streamflow when compared to that of the
annual minimum streamflow implies an unfavorable condition
with respect to flood mitigation in the Pearl River Delta.
Extreme water events such as droughts or floods will have
higher probability of occurrence.
3) This study addressed abrupt behaviors of streamflow variations
of the Pearl River basin and discussed possible implications for
the water resource management of the Pearl River Delta. The
results of this paper will be of considerable importance scientifically and practically for water resource management and
sound human mitigation of water hazards across the Pearl
River Delta. Follow-up work will investigate possible correlations between precipitation, human activities such as water
reservoirs and other hydraulic facilities, and streamflow variations of the Pearl River basin. This study also provides a good
case study for the water resource management of other river
deltas in the world under the influences of changing climate
and intensifying human activities.
Acknowledgments
The work described in this paper was fully supported by a grant
from the Research Grants Council of the Hong Kong Special
Administrative Region, China (Project No. CUHK405308), the ‘985
Project’ (Grant No.: 37000-3171315), National Natural Science
Foundation of China (Grant No.: 40701015; 50839005), and by
Program of Introducing Talents of Discipline to Universities – the
111 Project of Hohai University. We are grateful to Prof. Jiang J.M. for
his constructive suggestions of the statistical techniques used in
this study. Last but not least, we would like to thank two anonymous reviewers and also the editor, Norm Catto, for their professional comments which greatly improved the quality of this paper.
References
Birsan, M.-V., Molnar, P., Burlando, P., Pfaundler, M., 2005. Streamflow trends in
Switzerland. Journal of Hydrology 314, 312–329.
Camilloni, I.A., Barros, V.R., 2003. Extreme discharge events in the Paraná River and
their climate forcing. Journal of Hydrology 278, 94–106.
Chen, X.H., Chen, Y.Q., 2002. Hydrologic change and its causes in the river network
of the Pearl River Delta. Acta Geographica Sinica 57 (4), 430–436 (in Chinese).
Y.D. Chen et al. / Quaternary International 226 (2010) 44–53
Chen, Y.D., Zhang, Q., Xu, C.-Y., Yang, T., 2008. Change-point alterations of extreme
water levels and underlying causes in Pearl River Delta, China. River Research
and Application. doi:10.1002/rra.1212.
Chen, Y.D., Yang, T., Xu, C.-Y., Zhang, Q., Chen, X., Hao, Z.C., 2009. Hydrological
alteration along the middle and upper East River (Dongjiang) basin, South
China: a visually enhanced mining on the results of RVA method.
Stochastic Environmental Research Risk Assessment. doi:10.1007/s00477008-0294-7.
Cramer, H., 1946. Mathematical Method of Statistics. Princeton University Press,
Princeton, N.J., USA.
Hammersley, J.M., 1946. Discussion of papers. Journal, Royal Statistical Society 8, 91.
Jiang, J.M., Gu, X.Q., Ju, J.H., 2007. Significant changes in subseries means and
variances in an 8000-year precipitation reconstruction from tree rings in the
southwestern USA. Annales Geophysicae 25, 1–12.
Jiang, J.M., Mendelssohn, R., Schwing, F., Fraedrich, K., 2002. Coherency detection of
multiscale significant changes in historic Nile flood levels. Geophysical Research
Letters 29 (8), 112-1–112-4.
Kahya, E., Kalayci, S., 2004. Trend analysis of streamflow in Turkey. Journal of
Hydrology 289, 128–144.
Loukas, A., Vasiliades, L., Dalezios, N.R., 2002. Potential climate change impacts on
flood producing mechanisms in southern British Columbia, Canada using the
CGCMA1 simulation results. Journal of Hydrology 259, 163–188.
Lund, R., Reeves, J., 2002. Detection of undocumented changepoints: a revision of
the two-phase regression model. Journal of Climate 15, 2547–2554.
Lund, R., Seymour, L.B., Kafadar, K., 2001. Temperature trends in the United States.
Environmetrics 12, 1–18.
Minville, M., Brissette, F., Leconte, R., 2008. Uncertainty of the impact of climate
change on the hydrology of a Nordic watershed. Journal of Hydrology 358,
70–83.
Pearl River Water Resources Committee (PRWRC), 1991. Pearl River Water
Resources Committee (PRWRC). In: The Zhujiang Archive, vol. 1. Guangdong
Science and Technology Press, Guangzhou (in Chinese).
Pekarova, P., Miklanek, P., Pekar, J., 2003. Spatial and temporal runoff oscillation
analysis of the main rivers of the world during the 19th–20th centuries. Journal
of Hydrology 274, 62–79.
Risbey, J.S., Entekhabi, D., 1996. Observed Sacramento Basin streamflow response to
precipitation and temperature changes and its relevance to climate impact
studies. Journal of Hydrology 184, 209–223.
53
Von Storch, H., Zwiers, F., 1999. Statistical Analysis in Climate Research. Cambridge
University Press, Cambridge, p. 116.
World Meteorological Organization (WMO), 1987. Water Resources and Climate
Change. Sensitivity of Water Resources Systems to Climate Change and Variability. WMO/TO.
Xu, C.-Y., 2000. Modeling the effects of climate change on water resources in central
Sweden. Water Resources Management 14, 177–189.
Xu, C.-Y., Singh, V.P., 2004. Review on regional water resources assessment models under
stationary and changing climate. Water Resources Management 18, 591–612.
Zhang, Q., Xu, C.-Y., Becker, S., Jiang, T., 2006. Sediment and runoff changes in the
Yangtze River basin during past 50 years. Journal of Hydrology 331, 511–523.
Zhang, S.R., Lu, X.X., Higgitt, D.L., Chen, C.T., Han, J.T., Sun, H.G., 2008. Recent
changes of water discharge and sediment load in the Zhujiang (Pearl River)
Basin, China. Global and Planetary Change 60, 365–380.
Zhang, Q., Xu, C.-Y., Zhang, Z.X., Chen, Y.D., Liu, C.-L., 2008a. Spatial and temporal
variability of precipitation maxima during 1960–2005 in the Yangtze River
basin and possible association with large-scale circulation. Journal of Hydrology
353, 215–227.
Zhang, Q., Xu, C.-Y., Gemmer, M., Chen, Y.D., Liu, C.-L., 2008b. Changing properties of
precipitation concentration in the Pearl River basin, China. Stochastic Environmental Research Risk Assessment. doi:10.1007/s00477-008-0225-7.
Zhang, Q., Chen, G.Y., Su, B.D., Disse, M., Jiang, T., Xu, C.-Y., 2008c. Periodicity of
sediment load and runoff in the Yangtze River basin and possible impacts of
climatic changes and human activities. Hydrological Sciences-Journal-des
Sciences Hydrologiques 53 (2), 457–465.
Zhang, Q., Xu, C.-Y., Yang, Y., 2009a. Variability of water resource of the Yellow River
basin of past 50 years, China. Water Resources Management. doi:10.1007/
s11269-008-9320-2.
Zhang, Q., Xu, C.-Y., Becker, S., Zhang, Z.X., Chen, Y.D., Coulibaly, M., 2009b. Trends
and abrupt changes of precipitation maxima in the Pearl River basin, China.
Atmospheric Science Letters. doi:10.1002/asl.221.
Zhang, Q., Xu, C.-Y., Zhang, Z.X., 2009c. Observed changes of drought/wetness
episodes in the Pearl River basin, China, using the standardized precipitation
index and aridity index. Theoretical and Applied Climatology. doi:10.1007/
s00704-008-0095-4.
Zhang, Q., Xu, C.-Y., Sing, V.P., Yang, T., 2009d. Multiscale variability of sediment load
and streamflow of the lower Yangtze River basin: possible causes and implications. Journal of Hydrology 368, 96–104.