Theor Appl Climatol (2010) 101:53–65
DOI 10.1007/s00704-009-0203-0
ORIGINAL PAPER
Precipitation extremes in a karst region: a case study
in the Guizhou province, southwest China
Qiang Zhang & Chong-Yu Xu & Zengxin Zhang &
Xi Chen & Zhaoqing Han
Received: 16 January 2009 / Accepted: 17 August 2009 / Published online: 2 September 2009
# Springer-Verlag 2009
Abstract We analyzed the changing properties of precipitation extremes in the Guizhou province, a region of
typical karst geomorphology in China. Precipitation
extremes were defined by the largest 1- and 5-day
precipitation total. Trends of precipitation extremes were
detected by using Mann–Kendall trend test technique.
Besides, we also investigated moisture flux variations
based on the National Centers for Environmental Prediction
and the National Center for Atmospheric Research reanalysis dataset with the aim to further explore the possible
causes behind the changes in precipitation extremes. The
results of this study indicated that: (1) Although the
changes in precipitation extremes at most of the stations
Q. Zhang (*)
Department of Water Resources and Environment,
Sun Yat-sen University,
Guangzhou 510275, China
e-mail: zhangqnj@gmail.com
were not significant, enhanced precipitation extremes were
still detected after the early 1990s mainly in the middle and
west parts of the Guizhou province; (2) In winter, east and
south parts of the Guizhou province were characterized by
increasing precipitation extremes; In summer, enhanced
precipitation extremes were observed mainly in the middle
and east parts of the Guizhou province; (3) A significant
increase of moisture flux was observed after the 1990s
when compared to that before the 1990s. Cumulative
departure analysis results of moisture flux and precipitation
extremes confirmed the influences of moisture flux on the
variations of precipitation extremes in the study region.
This study clarified the changes of weather extremes and
their linkages with large-scale atmospheric circulation in
the karst region of China, which will definitely enhance
human mitigation to natural hazards in the fragile ecological environment under the influences of changing climate.
1 Introduction
C.-Y. Xu
Department of Geosciences, University of Oslo,
Sem Saelands vei 1,
Blindern 0316 Oslo, Norway
Z. Zhang
Jiangsu Key Laboratory of Forestry Ecological Engineering,
Nanjing Forestry University,
Nanjing 210037, China
X. Chen
State Key Laboratory of Hydrology-Water Resources
and Hydraulics Engineering, Hohai University,
Nanjing 210098, China
Z. Han
Center for Chinese Historical Geography Studies,
Fudan University,
Shanghai 200433, China
Global warming, characterized by increasing temperature,
has the potential to cause higher evaporation rates and
transport larger amounts of water vapor into the atmosphere, probably having accelerated the global hydrological
cycle (Semenov and Bengtsson 2002; Labat et al. 2004; Xu
et al. 2006). One of the most significant consequences of
global warming would be an increase in the magnitude and
frequency of precipitation maxima brought about by
increased atmospheric moisture levels and/or large-scale
storm activities (Shouraseni and Robert 2004). Significantly
decreasing number of rainy days and significantly increasing precipitation intensity were identified in many places of
the world, such as China (Ren et al. 2000; Gong and Ho
2002; Zhai et al. 2005; Zhang et al. 2008a, b), USA (Karl et
54
al. 1996), and India (Goswami et al. 2006). Recently,
Goswami et al. (2006) reported significantly increasing
frequency and magnitude of extreme rain events, rainstorms, over central India during the monsoon season in a
warming environment. Global warming might give rise to
increase and intensification of extreme events, such as
precipitation extremes defined by various indices (WMO
2003). Due to the tremendous influences of climatic
extremes, public awareness has risen sharply in recent
years and as a result, catastrophic floods, droughts, storms,
and heat waves or cold spells have been receiving
tremendous attention (e.g., Beniston and Stephenson
2004; Zhang et al. 2006a, b, 2008c). Suppiah and Hennessy
(1998) have pointed out that heavy precipitation events in
most parts of Australia have increased. Groisman et al.
(1999) indicated that the probability of daily precipitation
exceeding 50.8 mm in midlatitude countries (the USA,
Mexico, China, and Australia) have increased by about
20% in the later 20th century.
As mentioned above, increasing precipitation extremes
can be observed in some regions of China. Changing
properties of precipitation events are different from region
to region due to the inhomogeneous distribution of
precipitation variations over China (e.g., Zhang et al.
2008d). Zhai et al. (1999) have indicated increased
intensive precipitation events in west China since 1950.
Wang and Zhou (2005) investigated the spatial distribution
of extreme precipitation during 1961–2001 and found that
the annual mean precipitation increased significantly in
southwest, northwest, and east China, and significantly
decreased annual mean precipitation was observed in
central, north, and northeast China. The increasing trends
were observed mainly in summer in east China, while in
both spring and autumn, the decreasing trends were
identified mainly in central, north, and northeast China.
Besides, increasing precipitation maxima can also be
identified in the southeast China (e.g., Zhang et al.
2008a). Located in the east parts of the Yunnan–Guizhou
Plateau, China, the Guizhou province is characterized by
typical karst geomorphology termed as “karst rocky
desertification” and by the extremely fragile ecological
environment (Song et al. 1983; Wang et al. 2004). The karst
topography in the Guizhou province gives rise to large
slopes in mountainous areas with thin soil thickness,
leading to frequent landslides and serious soil erosion. In
this case, occurrence of precipitation maxima has great
potential to trigger appearances of natural hazards, such as
flash floods, serious soil erosion, landslides, and so on. Luo
et al. (2006) indicated that precipitation in flooding season
accounted for about 75% of the annual total precipitation.
Besides, they also found abrupt increase of rainstorm days
after 1991. Wu and Wang (2006) analyzed relations
between summer precipitation and wind field in the
Q. Zhang et al.
Guizhou province, indirectly addressing significant influences of moisture flux on the summer precipitation
changes. Therefore, changes of precipitation maxima and
possible underlying causes in the Guizhou province have
drawn considerable concerns. However, so far, studies of
precipitation changes were mainly found in Chinese
literatures. Besides, studies focusing on the seasonal
changes of precipitation maxima and associated linkages
with atmospheric circulation, particularly the moisture flux,
were not found. Now that the currently well-evidenced
global warming is expected to accelerate the hydrological
cycle and would cause more climatic extremes, and the
results of studies illustrated increasing frequencies of
precipitation extremes in east and south China (e.g., Zhai
et al. 1999; Zhang et al. 2008a, b). Thus, it is natural to ask
the question as to whether extreme weather and climate
events are truly increasing under the changing climate in
the Guizhou province, a typical karst area, and what could
be the circulation patterns behind the changes in extreme
climate events, if any, in the study region. This constituted
the major motivation for this study.
Thereby, the objectives of this study were: (1) to detect
changing properties of precipitation extremes defined by
various indices and (2) to study large-scale atmospheric
circulation patterns behind the changes in precipitation
extremes with the aim to understand possible physical
mechanisms causing changing properties of precipitation
extremes in the karst region of China. The results of this
study would be of practical significance in the local
ecological environment conservation and the natural hazard
management in the karst region of China.
2 Study region
Located in the southwest China, the Guizhou province
(Fig. 1) is dominated by a typical karst geomorphology.
The karst area covers 17,600 km2, being one of the largest
karst regions of the world with a population of 32.4 million.
The karst area covers about 73% of the Guizhou province
and is characterized by soluble carbonate rocks (Zeng
1994). The mountainous area occupies 92.5%, and the
mountain ridges account for only 7.5% of the total area of
the Guizhou province (Wu et al. 2003). Typical cone and
cockpit karst geomorphology gives rise to sharp relief and
steep slopes with an average slope of 17.8°. Large terrain
slopes, thin soil thickness, and vegetation degradation due
to human activities result in fragile ecological environment.
Frequent natural hazards, such as floods, droughts, landslides, debris flow, and so on, have caused significant loss
of economy and human life in the study region. Specifically, in 1954, serious floods occurred in the Guizhou
province, about 0.16 million hm2 fields were affected, and
Precipitation extremes in a karst region
55
Fig. 1 Location of the study
region and the meteorological
stations. The solid dots in the
right panel show the locations
of the meteorological stations
Altitude (m)
2508.7-2798
2219.3-2508.7
1930-2219.3
1640.7-1930
1351.3-1640.7
1062-1351.3
772.7-1062
483.3-772.7
194-483.3
29 N
#
#
#
#
#
#
#
#
27 N
#
#
#
#
#
#
# Stations
more than 180 people died (Yang and Xu 1999). In 1998,
the economic losses due to rainstorm-induced floods
reached more than 0.16 billion US dollars (Liu et al.
1999). With respect to climate, the study area is characterized by subtropical monsoon climate with the mean
summer temperature of 20–25°C and the mean winter
temperature of 4–9°C. The annual mean precipitation is
1,100–1,300 mm. Precipitation mainly occurs in summer
with a large variability. This kind of climate and topographical properties easily trigger natural hazards such as
flash floods or droughts.
Table 1 Locations of rain gauging stations; precipitation
mean, maximum, and IQR
(interquantile range) at each
station for 19 rain stations
25 N
#
Rivers
103 E
#
#
#
Guizhou Province
400 km
0
105 E
107 E
109 E
3 Data and methodology
Daily precipitation data for 1960–2005 were collected from 19
national standard rain stations in the Guizhou province (Fig. 1;
Table 1). There are missing data in the daily precipitation
dataset. The missing precipitation data at a station were filled
in by the average value of its neighboring days (Zhang et al.
2008a). We consider the gap filling method will have no
influence on the long-term temporal trend (Zhang et al.
2008b). The consistency of the data was checked by the
double-mass method, and the results revealed that all the
Station name
Longitude
Latitude
Altitude (m)
Mean (mm)
Maximum (mm)
IQR (mm)
Weining
Panxian
Tongzi
Xishui
Bijie
Zunyi
26°52'N
25°43'N
28°08'N
28°20'N
27°18'N
27°42'N
104°17'E
104°28'E
106°50'E
106°13'E
105°17'E
106°53'E
2237.5
1800
972
1180.2
1510.6
843.9
899.17
1395.54
1036.68
1117.27
892.13
1084.90
1263.45
2106.03
1335.67
1461.06
1285.44
1452.73
196.9
260.37
186.95
211.36
119.88
154.54
Meitan
Sinan
Tongren
Qianxi
Anshun
Guiyang
Kaili
Sansui
Xingren
Wangmo
Luodian
Dushan
Rongjiang
27°46'N
27°57'N
27°43'N
27°02'N
26°15'N
26°35'N
26°36'N
26°58'N
25°26'N
25°11'N
25°26'N
25°50'N
25°58'N
107°28'E
108°15'E
109°11'E
106°01'E
105°54'E
106°44'E
107°59'E
108°40'E
105°11'E
106°05'E
106°46'E
107°33'E
108°32'E
792.2
416.3
279.7
1231.4
1431.1
1223.8
720.3
626.9
1378.5
566.8
440.3
1013.3
285.7
1140.85
1139.30
1267.90
979.01
1349.17
1118.07
1213.34
1116.15
1337.39
1233.49
1140.12
1319.49
1196.65
1428.72
1673.43
1608.68
1415.05
1898.72
1441.71
1641.68
1548.39
1888.23
1743.45
1624.07
1730.42
1580.04
230.44
271.02
244.69
160.38
272.36
193.92
281.96
225.26
320.24
202.43
318.45
213.79
329.39
56
Q. Zhang et al.
Table 2 Definitions of the indices of precipitation extremes
Indices of
precipitation
extremes
Descriptions
Precipitation days
Frequency of days with at least 2 mm of
precipitation
Total precipitation of the rain days with at
least 2 mm of precipitation
The maximum daily precipitation in 1 year,
in summer, or in winter
Greatest precipitation sum for 5-day interval
Precipitation total
Largest 1-day precipitation
Largest 5-day total
precipitation series used in the study were consistent. Various
extreme precipitation variables were defined by using
different indices (Table 2). The definitions of these precipitation indices are based on the previous studies (e.g., Tebaldi
et al. 2006; Zhang et al. 2008b; Fatichi and Caporali 2009).
In this study, rainy days were defined as those days with
precipitation of greater than or equal to 2 mm. The threshold
of 2-mm rainfall in the definition of “rainy days” was used to
avoid artificial trends, which can arise from a tendency of
some observers failing to report small rainfall amounts
(Lavery et al. 1992). To understand possible physical
mechanisms behind the changing properties of precipitation
extremes, we analyzed moisture flux by using the National
Center for Atmospheric Research and the National Centers
for Environmental Prediction (NCAR/NCEP) reanalysis dataset. In the actual atmosphere, the moisture is very low over
Fig. 2 Spatial distribution of
annual trends of a largest 1-day
precipitation, b largest 5-day
total, c rain days (greater than or
equal to 2 mm), and d precipitation intensity. Precipitation intensity is defined as the average
precipitation of rain days with
precipitation greater than or
equal to 2 mm. Filled triangle
denotes significant increase,
inverted filled triangle denotes
significant decrease, inverted
unfilled triangle denotes not
significant decrease, and unfilled
triangle denotes not significant
increase. The same symbols in
the following figures denote the
same meanings
300 hPa. Thus, the moisture content and related transport
features, also the moisture flux in the following text, of the
whole Ps layer (surface pressure) −300 hPa were studied with
the NCAR/NCEP reanalysis data covering 1960 to 2005
(Miao et al. 2005; Zhang et al. 2008e).
There are many statistical techniques available to detect
trends within the time series, including moving average,
linear regression, Mann–Kendall trend test, filtering technology, etc. Each method has its own strengths and weaknesses
in trend detection. However, nonparametric trend detection
methods are less sensitive to outliers than are parametric
statistics, such as Pearson's correlation coefficient. Moreover,
the rank-based nonparametric Mann–Kendall test (Kendall
1975; Mann 1945) can test trends in a time series without
requiring normality or linearity (Wang et al. 2008) and is,
therefore, highly recommended for general use by the World
Meteorological Organization (Mitchell et al. 1966). It was
widely used in detection of trends in hydrological series (e.
g., Gao et al. 2007; Zhang et al. 2008a). This paper also used
the Mann–Kendall test method to detect trends within the
precipitation series.
4 Results
4.1 Annual variations in precipitation extremes
In terms of the largest 1-day precipitation, 11 out of 19
stations showed increasing trends in the largest 1-day
a
b
c
d
Precipitation extremes in a karst region
57
precipitation (Fig. 2a), and these stations are located mainly
in the middle and east parts of the Guizhou province. With
respect to changes in the largest 5-day total, 12 out of 19
stations indicated decreasing trends, although the increases
were not significant at the 95% confidence level. Thus,
Fig. 2a, b indicated no significant trends in the largest 1and 5-day precipitation total. It was observed that all the
stations studied in the study region showed decreasing rainy
days, and only three stations showed significant decreasing
rainy days (Fig. 2c). The precipitation intensity at most of
the stations in the study region was increasing (Fig. 2d),
specifically, 16 out of 19 stations, accounting for 84.2% of
the total stations, showed increasing precipitation intensity.
stations considered in the study and were found mainly in
the east, south, and north parts of the Guizhou province
(Fig. 4a). Most of the stations showed increasing largest 5day precipitation total (Fig. 4b), and these changes were not
yet significant at the 95% confidence level. Figure 4b also
indicated that the stations showing increasing largest 5-day
total were observed mainly in the east, south, and north
parts of the Guizhou province. It can be identified in Fig. 4c
that the increasing number of rainy days can be observed at
all the stations. Increasing precipitation intensity can also
be identified at most of the stations. Figure 4d demonstrated
that 18 out of 19 stations showed increasing precipitation
intensity, and only one station showed significantly increasing precipitation intensity.
4.2 Seasonal variations of precipitation extremes
4.3 Cumulative departure changes of precipitation extremes
Generally, heavy precipitation events in the Guizhou province
occur mainly in summer. Therefore, the changes in the largest
1-day precipitation and the largest 5-day total should be the
same as annual variations. Thus, we did not analyze the
changing properties of these precipitation variables. Figure 3a
indicated that the majority of stations showed increasing
number of rain days. Fourteen out of 19 stations showed
increasing rainy days, accounting for 73.7% of the total
stations, and these stations were found mainly in the middle
and east parts of the Guizhou province. With respect to the
precipitation intensity in summer (Fig. 3b), most of the
stations displayed increasing trends. It should be noted here
that only three stations showed significantly increasing rainy
days or precipitation intensity in summer.
As for the precipitation changes in winter, we analyzed
the largest 1-day precipitation, the largest 5-day total, rain
days (greater than or equal to 2 mm precipitation), and
precipitation intensity (greater than or equal to 2 mm
precipitation). Figure 4 showed the spatial distribution of
trends in the changes of the largest 1- and 5-day
precipitation total, rainy days, and precipitation intensity.
In winter, the largest 1-day precipitation at 14 stations was
increasing, but was not significant at the 95% confidence
level; these stations accounted for 73.7% of the total
Fig. 3 Spatial distribution of
trends of a rain days (greater
than or equal to 2 mm) and b
precipitation intensity in summer. The precipitation intensity
in summer is defined as the
average precipitation of the rain
days with precipitation greater
than or equal to 2 mm
a
The areal average rainy days in the Guizhou province
were increasing before the mid-1980s and were decreasing thereafter (Fig. 5a). Increasing rainy days were
observed during 1990–2000, and decreasing rainy days
were identified after 2000. Changes in rainfall amount
(greater than or equal to 2 mm precipitation) displayed
similar properties when compared to those of rainy days
(Fig. 2). Rainfall intensity (greater than or equal to 2 mm
precipitation) was in slight increase during 1960–1980,
decrease during 1980–1990, and increase again after 1990.
Figure 5b displayed cumulative departure variations of
precipitation variables defined by the 2-mm precipitation
threshold. Decreasing (decreasing) rainy days with precipitation of greater than or equal to 2 mm precipitation
were detected during 1960–1990 (after 1990). Similar
changing characteristics can also be identified for the
rainfall intensity (greater than or equal to 2 mm precipitation). Figure 5c indicated that the number of rainy days
in winter was decreasing during 1960–1980 and was
increasing during 1980–2005. However, consistently increasing rainy days were observed after 1990. The
precipitation intensity in winter was decreasing during
1960–1990 and was increasing during 1990–2005.
b
58
Q. Zhang et al.
4.4 Moisture flux and possible correlations with changes
in precipitation extremes
The results of analysis indicated that a trend in daily rainfall
variance was related to a trend in large-scale moisture
availability (Goswami et al. 2006). Zhang et al. (2008b)
also found relationships between moisture budget and
precipitation variations in the Yangtze River basin. Our
analysis indicated that changes in precipitation extremes
indicated enhanced precipitation extremes after 1990. To
further understand the possible causes behind the changing
properties of precipitation extremes, we analyzed the trends
in the moisture flux in the longitudinal and latitudinal
directions and also the difference between moisture flux
before and after 1990. Figure 6 displayed trends in the
annual variations in moisture flux in the latitudinal and
longitudinal directions before and after 1990. Gray areas
indicated the areas covered by significant trends. Figure 6
indicated that the moisture flux in the latitudinal direction
(the range of the study region can be referred to Fig. 1) was
increasing before 1990, but was not significant (Fig. 6a). The
moisture flux in the latitudinal direction was in significant
increasing trend (Fig. 6b). Similar phenomena were identified in terms of moisture flux changes in the longitudinal
direction (Fig. 6c, d). The moisture flux in the longitudinal
direction was increasing (Fig. 6c), but the increase was
significant after 1990 (Fig. 6d). Figure 7 displayed cumulative departure variations in the areal average moisture flux,
which showed that, after the 1980s, the areal average
moisture flux was increasing.
Figure 8a, b displayed changes in the moisture flux in
summer in the longitudinal and the latitudinal direction,
respectively. Comparison between Fig. 8a and b indicated
that the moisture flux before 1990 was increasing, but was
not significant; the moisture flux after 1990 was in
significantly increasing trend. Different results can be
obtained for the changes of moisture flux in the longitudinal
direction. The moisture flux in the longitudinal direction was
decreasing both before and after 1990. Figure 8d indicated
that part of the study region was dominated by significantly
increasing moisture flux. The cumulative departure of the
areal average moisture flux is displayed in Fig. 9 which
indicated that areal average moisture flux was decreasing
before the end of the 1970s and was increasing thereafter.
Figure 10 illustrated changes in the moisture flux before
and after 1990 in the latitudinal and longitudinal directions,
respectively. It can be seen from Fig. 10a that the moisture
flux in the study region was decreasing before 1990 and
a
b
c
d
Fig. 4 Spatial distribution of trends of a largest 1-day precipitation, b largest 5-day total, c rain days (greater than or equal to 2 mm), and d
precipitation intensity (greater than or equal to 2 mm) in winter
Precipitation extremes in a karst region
59
turned into a significant increasing trend thereafter
(Fig. 10b). The decrease can be identified in the moisture
flux variations in the longitudinal direction (Fig. 10c, d). The
cumulative departure (Fig. 11) indicated an increasing trend
in the areal average moisture flux in winter after the mid1980. Moreover, we also analyzed the difference between
moisture flux before and after 1990, and the results are
demonstrated in Fig. 12. In terms of annual variations and
changes in summer, decreasing northward moisture flux
transport can be observed (Fig. 12a, b). The study region
was also characterized by a positive difference of moisture
flux before and after 1990, indicating an increase in the
moisture flux after 1990. In winter, however, the direction of
moisture transport was not distinctly altered. Slightly
increased moisture flux can still be identified.
Fig. 5 Cumulative departure of
a the precipitation variables defined by the precipitation
threshold as 2 mm, b precipitation variables defined as precipitation threshold as 2 mm in
summer, and c rain days and
precipitation intensity in winter
5 Discussions and conclusions
The Guizhou province, the study region of this study, is
characterized by typical karst geomorphology. The unique
geographical and topographical characteristics of the study
region, such as large terrain slopes, thin soil thickness, poor
vegetation coverage, etc., leaded to fragile ecological
environment, which is highly sensitive to weather extremes
and precipitation extremes in particular. Frequent natural
hazards, such as flash floods, landslides, debris flow,
droughts, and so forth, have caused tremendous loss of
human life and economy. Changing properties of precipitation extremes and precipitation intensity will exert
considerable influences on hydrological processes, spatial,
and temporal distribution of geologic hazards such as
100
Rainy days (>=2mm)
50
0
–50
1960
1970
1980
1990
2000
200
1000
500
–200
0
–400
–600
–500
1960
1960
1970
1980
1990
Rainy days (>=2mm)
0
Rainfall amount (>=2mm)
1970
1980
1990
2000
2000
10
2
Rainfall intensity (>=2mm)
Rainfall intensity (>=2mm)
0
0
–2
–10
–4
–6
1960
–20
1970
1980
1990
2000
(A)
1960
1970
1980
1990
2000
5
Rainy days (>=2mm)
0
–5
–10
–15
–20
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
2
Rainfall intensity (>=2mm)
0
–2
–4
–6
–8
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
(C)
(B)
60
Q. Zhang et al.
(A)
(B)
(C)
landslides and debris flow. We analyzed changing characteristics of precipitation extremes and underlying causes by
analyzing moisture flux with NCAR/NCEP reanalysis
dataset. We think it is the important step toward good
understanding of changes of weather extremes under the
influences of global warming in the typical karst region of
China.
The following important conclusions were obtained and
discussed: (1) Analysis of precipitation extremes indicated
enhanced extreme precipitation in the Guizhou province,
particularly in the middle and east parts. The enhanced
precipitation extremes are mainly reflected by decreasing
rainy days and increasing precipitation intensity. In summer
1991–2005, c trends of moisture flux in longitudinal direction during
1960–1990, and d trends of moisture flux in longitudinal direction
during 1991–2005
80
Moisture flux (kg/m.s)
Fig. 6 Spatial distribution of the annual trends of moisture flux (unit:
kg/m·s). a Trends of moisture flux in latitudinal direction during
1960–1990, b trends of moisture flux in latitudinal direction during
(D)
60
40
20
0
1960
1970
1980
1990
Time (years)
2000
Fig. 7 Cumulative departure of areal annual variations of moisture
flux (unit: kg/m·s)
Precipitation extremes in a karst region
61
(A)
(B)
(C)
and winter, rainy days were increasing and so were the
variations in precipitation intensity. From the viewpoint of
annual variations, rainy days were decreasing. Therefore,
we can conclude that precipitation extremes in the Guizhou
province were increasing with a shift of more precipitation
to summer and winter. In summer, enhanced precipitation
extremes were observed mainly in the middle and east parts
of the Guizhou province; in winter, however, enhanced
precipitation extremes were identified mainly in the west
and south parts of the Guizhou province. It should be noted
here that more high lands were found in the west parts than
in the east parts of the Guizhou province. In this case,
enhanced precipitation extremes in winter may cause more
serious soil erosion in the west. Enhanced extreme
c trends of moisture flux in longitudinal direction during 1960–1990, and
d trends of moisture flux in longitudinal direction during 1991–2005
30
Moisture flux (unit: kg/m.s)
Fig. 8 Spatial distribution of the trends of summer moisture flux (unit:
kg/m·s). a Trends of moisture flux in latitudinal direction during 1960–
1990, b trends of moisture flux in latitudinal direction during 1991–2005,
(D)
20
10
0
–
–
10
20
1960
1970
1980
1990
Time (years)
2000
Fig. 9 Cumulative departure of areal average moisture flux in
summer (unit: kg/m·s)
62
Q. Zhang et al.
(A)
(B)
(C)
(D)
Fig. 10 Spatial distribution of the trends of winter moisture flux (unit:
kg/m·s). a Trends of moisture flux in latitudinal direction during 1960–
1990, b trends of moisture flux in latitudinal direction during 1991–
Moisture flux (kg/m.s)
30
20
10
0
–10
–20
1960
1970
1980
1990
Time (years)
2000
Fig. 11 Cumulative departure of areal variations of moisture flux in
winter (unit: kg/m·s)
2005, c trends of moisture flux in longitudinal direction during 1960–
1990, and d trends of moisture flux in longitudinal direction during
1991–2005
precipitation was identified mainly after early 1990s, which
could be attributed to influences of global warming; and (2)
Studies show increasing extreme precipitation, particularly
over land areas in middle and high latitudes of the Northern
Hemisphere, and a decrease in rainy days in the latitudinal belt
around 40°N during summer (Khon et al. 2007). Changes in
precipitation intensity would be attributed to relative
contributions of precipitation originating from convective
mechanisms (Gregory and Mitchell 1995). Under the
increasing CO2 scenarios, some global climate models
demonstrate enhanced midlatitude precipitation intensity
(e.g., Osborn et al. 2000). Furthermore, altered atmospheric
moisture, temperature fields, and shifts in the strength of
Asian monsoon could have driven across the board changes
Precipitation extremes in a karst region
(A)
63
(B)
(C)
Fig. 12 Spatial distribution of the moisture flux anomalies between 1991–2005 and 1961–1990 (unit: kg/m·s). a Annual, b in summer, and c in
winter
in precipitation intensity, with no shift in the importance of
various mechanisms (Osborn et al. 2000). The trend analysis
of moisture flux in the longitudinal and latitudinal directions,
respectively, indicated significantly increasing moisture flux
after the 1990s. The moisture flux was increasing before
1990s, but the increase is not significant at the 95%
confidence level. The difference between the moisture flux
before and after the 1990s indicated more moisture flux after
the 1990s and decreasing northward transport of moisture
flux. Changes of moisture were in good line with those of
precipitation extremes, corroborating considerable influences
of moisture flux on precipitation extremes. It should be
64
pointed out here that the results of this study indicated
enhanced precipitation extremes. More significant increase
of moisture flux after the 1990s may be the major driving
factor triggering enhanced precipitation extremes after
1990s. The results of this study will be of practical
significance in mitigation of the detrimental effects of
variations of weather extremes, particularly in the Guizhou
province characterized by the fragile ecological environment.
Acknowledgments The research was financially supported by the
National Basic Research Program (“973 Program”, grant number
2006CB403200), National Natural Science Foundation of China
(grant number: 40701015; 40771199), and by the “985 Project”
(Grant No.: 37000-3171315). Thanks should be extended to the
National Climate Center and China Meteorological Administration,
China for kindly providing the meteorological data. The last but not
the least, we are also indebted to two anonymous reviewers and the
managing editor, Dr. Hartmut Grassl, for their invaluable comments
which greatly improved the quality of this paper.
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