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IJW.2017.081107

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Int. J. Water, Vol. 11, No. 1, 2017
1
Hydrological drought assessment in Aksu River basin
Jun Hou
Kunming University of Science and Technology,
Kunming, 650000, China
and
State Key Laboratory of Simulation and
Regulation of Water Cycle in River Basin,
Institute of Water Resources and Hydropower Research,
1-A Fuxing Road, Haidian District,
Beijing 100038, China
Email: 819072298@qq.com
Baisha Weng
State Key Laboratory of Simulation and
Regulation of Water Cycle in River Basin,
Institute of Water Resources and Hydropower Research,
1-A Fuxing Road, Haidian District,
Beijing 100038, China
Email: 278423141@qq.com
Xiaogang Liu
Kunming University of Science and Technology,
Kunming, 650000, China
Email: 455313853@qq.com
Jun Yin, Zhiyong Yang and Denghua Yan*
State Key Laboratory of Simulation and
Regulation of Water Cycle in River Basin,
Institute of Water Resources and Hydropower Research,
1-A Fuxing Road, Haidian District,
Beijing 100038, China
Email: 281162594@qq.com
Email: 14434773@qq.com
Email: denghuay@gmail.com
*Corresponding author
Copyright © 2017 Inderscience Enterprises Ltd.
2
J. Hou et al.
Abstract: Based on the monthly stream flow date of three representative
hydrological stations, in the Aksu River basin during the period of 1957–2010,
i.e., ShaliGuilanke station, XieHela station and XiDaqiao station, this paper
calculates river inflow anomaly index and stream flow drought index (SDI).
The simulation results of these two indexes were compared and the results
showed that the SDI could reflect the drought situation better. Runs theory was
used to analyse the SDI, getting the drought duration and droughts intensity in
Aksu River basin. The results indicate that drought in Aksu River basin occurs
mainly in spring (March–May). During 1957–2010, drought occurred 50 times,
approximately once per year, with an average interval time of eight to nine
months. After the 1990s, drought duration became shorter and intensity
decreased in ShaliGuilanke station and Xi Daqiao station, but drought risk
frequency and drought intensity became larger. Drought situation is
increasingly grim in XiDaqiao station of China.
Keywords: river inflow anomaly index; stream flow drought index; SDI; runs
theory; Aksu River basin.
Reference to this paper should be made as follows: Hou, J., Weng, B., Liu, X.,
Yin, J., Yang, Z. and Yan, D. (2017) ‘Hydrological drought assessment in Aksu
River basin’, Int. J. Water, Vol. 11, No. 1, pp.1–13.
Biographical notes: Jun Hou is a student and his major is Water Resource.
Baisha Weng is an Engineer in Water Resource.
Xiaogang Liu is a Professor in Water Saving Irrigation.
Jun Yin is a student and her major is Water Resource.
Zhiyong Yang is a Professor in Water Resource.
Denghua Yan is a Professor is Water Resource.
1
Introduction
Stream runoff is an important basis for comprehensive utilisation and management of
water resources, whose changes are driven by both climate change and human activities
(Wang et al., 2011). With the deepening impacts of climate change, extent and frequency
of drought events are becoming larger (Yan et al., 2014). One of the distinct results of
climate change is regional water cycle change and the corresponding change in runoff
coefficient (Xu, 2000). Evaluating the drought in the study region can strengthen its
drought prevention and management, promoting the rational distribution of water
resources.
Hydrological drought assessment in Aksu River basin
3
A series of achievements of hydrological drought research has been made all around
the world. Nalbantis and Tsakiris (2009) adopted the same method of standardised
precipitation index (SPI) to calculate multiple time scale of stream flow drought index
(SDI) in hydrological year. Zhou et al. (2011) used the runoff as hydrological drought
index to identify hydrological drought variable feature via two methods of river inflow
anomaly index and runoff cumulative frequency; the curve fitting method was utilised to
determine the distribution of individual drought variables, then a copula function was
used to build a joint distribution of drought duration and drought intensity based on this.
Yin
et al. (2009) used truncation level to get hydrological drought events, and applied Markov
chain and first-order autoregressive model to simulate the stochastic compound runoff,
discussing drought strength, drought intensity, drought duration and risk probability
statistics.
Studies on drought index showed that if drought indicators were established
objectively and reasonably, the drought process could be reflected accurately. Otherwise,
some drought processes will be missed and some non-dry processes could unnecessarily
be added (Wang et al., 2007). This paper took Aksu River basin as the case study, and
evaluated the Aksu River basin hydrological drought by combining long sequences of
hydrological data.
2
Case study
Aksu River basin is located between 75° 35’E~80° 59’E, 40°17’N~42°27’N, covering an
area of 52,000 square kilometres, of which 33,000 square kilometres are in China, rest of
them in Kyrgyzstan. In general, the northwest area is higher than the southeast area with
huge difference in landform. Located in the deep Eurasian continent, it has high
evaporation and low precipitation, resulting a dry climate. Sunshine hours are long, thus
having rich heat resources. Climate in this area changes sharply with cold winter and hot
summer. Temperature range between day and night is large while average wind speed is
small. The average precipitation is 64 mm per year. Average evaporation is 1,890 mm
and average temperature range 9.2°C~12°C.
Aksu River is one of the three major international rivers in Xinjiang, originated from
Cork Hill in Kyrgyzstan, which is located between 75°35’E~82°00’E, 40°00’N~42°27’N.
Kun Ma Li Ke River and Tuoshigan River are two main tributaries of the Aksu River.
The main supply water of north branch Kun Ma Li Ke River is glacier melt, whose
catchment area is 12,816 km2. The full-length from headwaters to the confluence of the
two rivers is 293 km, with annual runoff of 460 billion m3. The main supply water in
west branch Tuoshigan River is rain and snow, whose catchment area is 12,816 km2. The
full length from source to confluence is 457 km, with annual runoff of 2.576 billion m3.
4
J. Hou et al.
Figure 1
3
The location of Aksu River basin
Methodology
3.1 River inflow anomaly index
River inflow anomaly index (Wang et al., 2007) is an index to express the increment and
decrement of runoff in a certain period compared with normal years. It can reflect the
drought caused by runoff abnormalities directly. It can be expressed as follows:
I = ( R − R ) / R × 100%
where
I
represents the river inflow anomaly index
R
represents the current river flow
R
represents average flow of many years in the same period.
River inflow anomaly indexes according to the classification of precipitation anomaly in
classification meteorological drought (GB/T 20481-2006, 2006), for various drought
levels are shown in Table 1.
Hydrological drought assessment in Aksu River basin
Table 1
5
Drought level of river inflow anomaly index
Drought level
Light drought
Medium drought
Serious drought
Severe drought
Anomaly
percentage (%)
–10~–30
–31~–50
–51~–80
< –80
3.2 Stream flow drought index
SDI (Weng, 2013) used Γ distribution to describe the change of runoff, standardising
runoff skewed distribution normality. Finally, normalised runoff cumulative frequency
distribution was used to divide the drought level. Assuming a time-scale runoff is x, then
probability density function f(x) which meets Γ distribution is as follows:
f ( x) =
1
β α Γ(α )
xα −1e− x / β ( x > 0, α > 0, β > 0)
Normalise Γ distribution get SDI:
SDI = S
t − ( c2 t + c1 ) t + c0
[( d3t + d 2 ) t + d1 ] + 1
where t = 2 ln( P ), c0 = 0.802853, c1 = 0.0100328, c2 = 0.010328, d1 = 1.432788,
d2 = 0.189269, d3 = 0.001308. When F > 0.5, S = 1; when F < 0.5, S = –1.
SDI was divided according to the classification of precipitation drought index in
Classification Meteorological Drought (GB/T 20481-2006, 2006), drought level was
shown in Table 2:
Table 2
Drought level of SDI
Drought level
SDI
Light drought
Medium drought
Serious drought
Severe drought
–1~–0.5
–1.5––1
–2~–1.5
< –2
3.3 Runs theory
Drought duration and drought intensity are two indicators describing drought
phenomenon. Drought duration refers to the period of drought events from the beginning
to the end. Drought intensity could be obtained by dividing drought severity by drought
duration (Mishra and Singh, 2010, 2011). When the index is smaller or equal to R0,
drought occurs. For drought events who has only one period, only when the index is
smaller than R1, could it be defined as a drought events. Otherwise, it will be neglected
since it is only a small drought event. In two drought events, when only one drought
indicator periods is larger than R0 but smaller than R2, we assume that these two droughts
are subordinate droughts, which can be combined into one (Fleig et al., 2006). After the
combination, drought duration is D = d1 + d2 + 1, and drought intensity is S = s1 + s2.
J. Hou et al.
6
Figure 2
4
Identification of drought duration and drought (see online version for colours)
Results and discussion
4.1 The simulation effect of two drought index in Aksu River basin
Based on the monthly runoff data of three representative hydrological stations between
1957–2010 in Aksu River basin, the three rivers’ inflow anomaly index and SDI were
calculated. Statistical results show that drought in Aksu River basin occurs mainly in
spring (March–May). The results are shown in Figure 3 and Figure 4.
According to the historical drought conditions in Aksu River basin, the simulation
results of river inflow anomaly index and SDI in Shali Guilanke station, Xie He La
station and Xi Da Qiao station were compared with each other. It is found that SDI can
reflect the drought situation in Aksu River basin better. Between 1957–2012, there were
25 droughts events in Aksu River basin, which are listed in Table 3. Most of them
occurred in spring. From the inter-annual point of view, river inflow anomaly index
corresponds with the actual drought for only ten years, and SDI corresponds with the
actual drought 16 times. They are shown in Figure 5. From the monthly-scale data
respect, the SDI can reflect Aksu River basin drought conditions better, which are in
Figure 4 and Figure 5.
SDI used Γ distribution to describe the change of runoff, and standardised
runoff skewed distribution normality. Finally normalised runoff cumulative frequency
distribution was used to divide the drought level. SDI indicators make droughts which
occurred in the same area but different times comparable. At the same time, droughts
occurred in different parts but the same period become comparable.
Hydrological drought assessment in Aksu River basin
Figure 3
Main river of river inflow anomaly index in Aksu River basin, (a) Shali Guilanke
station (b) Xi Da Qiao station (c) Xie He La station
(a)
(b)
(c)
7
8
Figure 4
J. Hou et al.
Main river of SDI in Aksu River basin, (a) Shali Guilanke station (b) Xi Da Qiao station
(c) Xie He La station
(a)
(b)
(c)
Hydrological drought assessment in Aksu River basin
Table 3
9
The drought conditions in Aksu River basin
Age
Drought conditions
Age
1957
1959
1961
1962
1965
1968
1974
1979
1980
1981
1985
1991
A Wa Ti
A Wa Ti
Ku Che
Ku Che
Ku Che
A Wa Ti
Wu Shi
A Wa Ti, Aksu
Ke Ping, Ku Cheetc
Ke Ping
Aksu
Aksu
1993
1998
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Drought conditions
Ku Che, BaiCheng, WuQia
Aksu
Aksu
Ku Che, ShaYa, Xin He
Aksu
Aksu
Aksu
Ku Che
Aksu
Aksu
Ku Che, A Wa Ti
Aksu
Wen Su, ShaYa
Source: Tan et al. (2013)
Figure 5
Comparison of river inflow anomaly index and SDI, (a) Shali Guilanke station
(b) Xi Da Qiao station (c) Xie He La station
(a)
(b)
10
Figure 5
J. Hou et al.
Comparison of river inflow anomaly index and SDI, (a) Shali Guilanke station
(b) Xi Da Qiao station (c) Xie He La station (continued)
(c)
4.2 Temporal evolution of hydrological droughts in Aksu River basin
Combined with monthly sequence data of SDI between 1957–2010 in Shali Guilanke
station, Xie He La station and Xi Da Qiao station, threshold levels R0 = –0.5, R1 = –1,
R2 = –2 were selected to extract drought time. There were 45 drought events during
1957–2010 in Shali Guilanke station, and average drought duration was 5.75 months. The
average drought intensity was 4.93, and drought duration maximum was 19 months
which occurred in 1960-October to 1962-April, corresponding to the historical drought
intensity maximum value 18.56, and average drought interval is 8.4 months. Xi Da Qiao
station showed 50 drought events, whose average drought duration was 3.78 months and
average drought intensity was 3.90. Maximum drought duration was 12 months from in
2009-December to 2010-December, corresponding to the historical drought intensity
maximum value 30.80, and average drought interval was 9.12 months. There were
50 drought events during 1957–2010 in Xie He La station, and average drought duration
was 4.62 months. The average drought intensity was 3.78, and drought duration
maximum was 14 months which occurred in 1963-July to 1964-August, corresponding to
the historical drought intensity maximum value 8.26, and average drought interval is
8.26 months. Detailed statistics are shown in Table 4.
Table 4
Drought events statistics of hydrological stations in Aksu River
Drought
times
Drought
duration
mean
Drought
intensity
mean
Drought
duration
maximum
Drought
intensity
maximum
Drought
duration
mean
Shali Guilanke
45
5.75
4.93
19
18.56
8.4
Xi Da Qiao
50
3.78
3.90
13
30.8
9.12
Xie He La
50
4.62
3.78
14
11.88
8.26
Station
In the 1950s, 1960s, 1970s, 1980s, 1990s, and 2000s, drought events for each age
changes in hydrological stations statistical results are shown in Table 5. For Shali
Guilanke station, the frequency of drought was the highest in the 1980s, and the drought
Hydrological drought assessment in Aksu River basin
11
intensity was largest in the 1950s. Drought times minimum and drought intensity
minimum were in the 2000s. To Xi Da Qiao station, drought times maximum was in the
1970s and 1990s, drought intensity minimum was in the 1970s, and drought intensity
maximum in the 2000s. To Xie Hela station, drought times maximum was in the 1970s,
drought times minimum but drought intensity maximum were in the 1950s, drought
intensity minimum was in the 1990s.
By comprehensive analysis of drought characteristics of each hydrological station, we
found that for Shali Guilanke station, drought occurred frequently before the 1980s.
Besides, the duration was longer and intensity was greater. Drought intensity became
smaller and drought events became fewer after the 1990s. For Xie Hela station, the
duration of drought became longer and intensity became greater before the 1980s;
entering the humid period after the 1990s, the characteristic of drought became shorter
and intensity became lower. The reason is that in the past ten years, as temperatures rose,
runoff of Kun Ma Li Ke River and Tuoshigan River, which was supplied mainly with
glacier melt water, increased significantly (Wang et al., 2008). After the 1990s, drought
happened frequently, drought intensity became larger and drought situation became
increasingly grim in Xi Daqiao station.
Table 5
Ages
1950s
1960s
1970s
1980s
1990s
2000s
Drought events age change of Hydrological station in Aksu River basin
Drought Drought
duration intensity
maximum maximum
Drought
duration
mean
Drought
times
Drought
duration
mean
Drought
intensity
mean
Shali Guilanke
4
12
–11.44
19
–18.56
4
Xi Da Qiao
5
4.4
–4.55
9
–9.35
9.4
Xie He La
4
6.25
–5.87
10
–11.88
6.75
Shali Guilanke
7
4.85
–3.78
9
–8.67
9.85
Xi Da Qiao
8
3.75
–3.9
11
–11.54
8.75
Xie He La
10
5.1
–4.275
14
–10.86
6.1
Shali Guilanke
8
7.4
–5.71
18
–13.5
7.375
Xi Da Qiao
10
3.3
–2.58
6
–4.33
8.6
Xie He La
11
5.27
–4.02
11
–7.86
6.18
Shali Guilanke
12
5.75
–5.62
12
–16.78
3.83
Xi Da Qiao
8
2.875
–2.84
6
–6.64
14
Xie He La
10
4.4
–3.237
10
–7.26
7
Shali Guilanke
9
2.45
–2.02
11
–4.82
15
Xi Da Qiao
10
3.7
–3.285
7
–5.73
7.6
Xie He La
7
3
–2.66
7
–8.23
12.25
Shali Guilanke
3
2.67
–2.17
10
–3.42
7.33
Xi Da Qiao
9
4.89
–6.6
13
–30.8
7.22
Xie He La
5
2.28
–2.37
4
–5.2
12
Station
12
J. Hou et al.
5
Conclusions
1
The calculated results of river inflow anomaly index and SDI indicated that drought
in Aksu River basin occurs mainly in spring (March–May).
2
According to the recording of the historical drought conditions in Aksu River basin,
the simulation results of two indexes were compared and we found that SDI can
reflect the drought situation better.
3
Runs theory was used to analyse SDI, getting the drought duration and droughts
intensity in Aksu River basin. The result indicates that between 1957–2010, there
were 50 drought events in Aksu River Basin, once a year on average and the average
drought duration was eight to nine months.
4
After entering the 1990s, drought duration became shorter and intensity decreased in
Shali Guilanke station and Xi Da Qiao station, but drought risk became frequent,
drought intensity became larger and drought situation became increasingly grim in
Xi Da Qiao station.
Acknowledgments
This research was partially sponsored by the National Science and Technology Support
Program Project (2013BAC10B01), Twelve-Five Science and Technology Support
Program (2012BAC19B03), NSFC (51309129).
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