effects of the three gorges reservoir on the hydrological droughts at the downstream yichang station...

HYDROLOGICAL PROCESSESHydrol. Process. (2012)Published online in Wiley Online Library(wileyonlinelibrary.com) DOI: 10.1002/hyp.9541

Effects of the Three Gorges Reservoir on the hydrologicaldroughts at the downstream Yichang station during 2003–2011

Shuai Li,1 Lihua Xiong,1* Leihua Dong1 and Jun Zhang21 State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China

2 Department of Hydro-meteorological Forecasting, Bureau of Hydrology, Yangtze River Water Resources Commission, Wuhan 430010, China

*CResWuE-m

Co

Abstract:

Since the Three Gorges Reservoir (TGR) was put into operation in June 2003, the effects of the TGR on downstream hydrology andwater resources have become the focus of public attention. This article examines the effects of the TGR on the hydrological droughts atthe downstream Yichang hydrological station during 2003–2011. The two-parameter monthly water balance model was used togenerate themonthly discharges at theYichang station for the period of 2003–2011 to represent the unregulatedflow regime and thus toprovide a comparison benchmark for the observed flow series at the Yichang station after the operation of the TGR. To provide areference series for the observed monthly discharge series of the entire study period of 1951–2011, we constructed the naturalizedmonthly discharge series at the Yichang station by joining the observed monthly discharge at the Yichang station for the periodof 1951–2002 and the two-parameter monthly water balance simulated monthly runoff at the Yichang station for the period of2003–2011. For both the observed and naturalizedmonthly discharge series of 1951–2011, the hydrological drought index series werecalculated using the standardized streamflow index method. By comparing the drought indices of these two monthly discharge series,we investigated the effects of the TGR on the hydrological droughts at the downstreamYichang station during 2003–2011. The resultsshow that the hydrological droughts at the downstream Yichang station are slightly aggravated by the TGR’s initial operation from2003 to 2011. The river flow reduction at the Yichang station after impoundment of the TGR might account for the downstreamdrought aggravation. Copyright © 2012 John Wiley & Sons, Ltd.

KEY WORDS Three Gorges Reservoir; hydrological droughts; downstream effects; naturalized discharges; standardizedstreamflow index

Received 17 February 2012; Accepted 30 August 2012

INTRODUCTION

The Three Gorges Dam (TGD) across the Yangtze Riveris the world’s largest hydroelectric dam (Wu et al., 2003).The Three Gorges Reservoir (TGR) formed by theconstruction of the TGD is a key infrastructure for variouswater supplies and hydropower supply in east and centralChina. The TGR has been in operation since June 2003,and its initial operations show that it has significantsocioeconomic benefits, including mitigating an energycrisis in China to a great extent (Gleick, 2009). However,the construction of the TGR and its subsequent operationsalso pose great challenges to the hydrological regime andecosystem of the entire Yangtze River basin (Shen andXie, 2004). With the emergence of scientific interest in theTGRmanagement practices and its effects (Wu et al., 2006;Zhu and Chang, 2008; Zhang et al., 2009; Fu et al., 2010;Mcmanus et al., 2010; Zhang et al., 2010), most studieshave focused on the TGR area and the upstream inundatedarea, and little attention has been paid to the downstreamarea. In recent years, with the frequent occurrence ofextreme drought events in the middle and lower reachesof the Yangtze River, and especially with the sharp

orrespondence to: Lihua Xiong, State Key Laboratory of Wateources and Hydropower Engineering Science, Wuhan Universityhan 430072, China.ail: [email protected]

pyright © 2012 John Wiley & Sons, Ltd.

r,

decreases in water areas and water levels of the downstreamDongting Lake and Poyang Lake (Du et al., 2011; Guoet al., 2011), the relation between the TGR and its operationsand the downstream droughts has become an importantsocial–environmental issue (Dai et al., 2008; 2010a; Luet al., 2011). Hence, it is necessary to investigate the linkbetween the TGR and the downstream droughts.Droughts are phenomena that commonly start with

shortage of precipitation, resulting in soil water deficitdue to evapotranspiration, and river flow reduction,damaging normal plant growth and human activities.Droughts can be categorized into four types: meteoro-logical drought, agricultural drought, hydrological droughtand socioeconomic drought (Wilhite and Glantz, 1985;AmericanMeteorological Society, 2004). Among differenttypes of droughts, hydrological drought is the mostimportant because of the high dependence of manyactivities (industrial, agricultural, urban supply andhydropower generation) on surface water resources(López-Moreno et al., 2009, Vasiliades, et al., 2011). Upto now, the best and most widely used approach forcharacterizing droughts is to establish various droughtindices for the objective quantification of different droughtcharacteristics in terms of intensity, magnitude, durationand spatial extent (Heim, 2002; Keyantash and Dracup,2002; Mishra and Singh, 2010). They include the Palmerdrought severity index (Palmer, 1965), the crop moisture

S. LI ET AL.

index (Palmer, 1968), the surface water supply index(Shafer and Dezman, 1982), the standardized precipita-tion index (SPI) (McKee et al., 1993, 1995) and thestandardized precipitation evapotranspiration index(Vicente-Serrano et al., 2010). Among these droughtindices, because of the low data requirements and simplicity,SPI has become themost accepted index that not only can becalculated at varying time scales (Hayes et al., 2011) but alsois comparable both in time and space (Lana et al., 2001;Livada and Assimakopoulos, 2007; Patel et al., 2007; Wu etal., 2007; López-Moreno and Vicente-Serrano, 2008). Inprevious studies, however, the SPI has been applied mostlyto precipitation records in different regions and seldom toflow data (López-Moreno et al., 2009). For this reason,several discharge-based drought indices based on the sameconcept of the SPI have been proposed to assesshydrological droughts, for example, the standardized runoffindex (Shukla and Wood, 2008), the streamflow droughtindex (Nalbantis and Tsakiris, 2009), the standardized flowindex (Wen et al., 2011) and the standardized streamflowindex (SSI) (Vicente-Serrano et al., 2012).Past studies on hydrological droughts have mostly been

devoted to hydrological drought characteristics under naturalconditions (i.e. without considering the effects of anthropo-genic activities on the hydrological process). However, theexploitation and utilization of water resources (e.g. damconstruction, reservoir operation, etc.) have substantialeffects on the natural flow regime. River regulations byreservoirs alter the temporal and spatial distribution ofnatural flow and thus change hydrological drought char-acteristics. López-Moreno et al. (2009) examined the effectsof a large dam on hydrological droughts in a transboundarybasin using the SPI method. In another study, Wen et al.(2011) applied the SPI at the 12-month time scale in defininga standardized flow index based on the river gauge records toassess the effects of river regulation and water diversion on

Figure 1. Map of the upper Yangtze River basin. (QCT represents the obsermonthly runoff generated from the Cuntan–Yichang intervening basin by u

monthly discharge at the Yichang station without

Copyright © 2012 John Wiley & Sons, Ltd.

hydrological drought characteristics in the Lower Murrum-bidgee River, Australia. Both of these studies concluded thatthe use of reservoirs is responsible for the aggravation ofdownstream hydrological droughts.This article has two major objectives: (i) to reconstruct

the continuous time series of naturalized (i.e. unregulated)monthly discharge at Yichang hydrological station, whichis just downstream of the TGR, for the postdam period of2003–2011; and (ii) to quantitatively assess the effects ofthe TGR on the hydrological droughts at the Yichang stationduring 2003–2011. The article is organized as follows.First, the study area is introduced. Second, two differentmonthly discharge series at theYichang station are prepared:the observed series under the influence of the TGR and thenaturalized series without the TGR. Third, the methods usedin this research for the monthly discharge simulation,drought index calculation and drought impact analysis aredescribed. Fourth, the results are presented and discussed.Finally, conclusions are made with regard to the effects ofthe TGRon the hydrological droughts at theYichang station.

STUDY AREA

The Yangtze River is the longest river in China and is thethird longest river in the world. It flows eastward 6300 kmfrom the Qinhai-Tibet Plateau across southwest, central andeastern China, reaching the East China Sea at Shanghai. Theriver is divided into three sections: the upper reachesflowingfrom the source of the Yangtze River to Yichang, themiddlereaches fromYichang toHukou, and the lower reaches fromHukou to the Yangtze River mouth (Yang, et al., 2006). TheThree Gorges Project, as shown in Figure 1, is a vitallyimportant project in the mid–upper reaches of the YangtzeRiver and has played a key role in the development of theYangtze River in China. The upstream area of the Yangtze

ved monthly discharge at Cuntan station; QsimCT-YC represents the simulated

sing the TPMWB model; and QCTPMWB represents the TPMWB simulated

the consideration of the influence of the TGR)

Hydrol. Process. (2012)DOI: 10.1002/hyp

EFFECTS OF THREE GORGES RESERVOIR ON THE DOWNSTREAM DROUGHTS

River, with a length of main course of approximately4.5� 103 km and a drainage area of 1� 106 km2, is nowintercepted by the TGD.The Yichang hydrological station, located at the junction

of the upper Yangtze River and the middle Yangtze River,approximately 44 km downstream from the TGD site, is animportant monitoring station for outflow from the TGR(see Figure 1). The reach between the TGD and the Yichangstation has no large tributaries; thus, the streamflow recordsat the Yichang station can reasonably be assumed to reflectthe immediate downstream hydrological regime under theinfluence of the TGR’s operation. As shown in Figure 1, theinflow at the Yichang station consists of two components.One is the upstream inflow from the area above the Cuntanhydrological station, and the other is the runoff generatedfrom the intervening basin between the Cuntan and theYichang stations (including the Wujiang River basin andthe Three Gorges intervening basin, collectively calledthe Cuntan–Yichang intervening basin hereafter). Theintervening basin has a main river course of approximately660 kmand a catchment area of 138 942 km2, accounting forapproximately 13.9% of the upstream Yangtze River basinarea above Yichang.The TGR impounded water and generated hydropower

for the first time in June 2003. Until September 2006, thewater level of the TGR was controlled at 135m in the floodseason and at 139m in the dry season. After the flood seasonof 2006, the second storage phase of the TGR commencedwith the water level increased from 135 to 156m. For thefirst time on 26 October 2010, the TGR had reached itsdesign maximum water level of 175m, indicating that theThree Gorges Project already meets the requirements of itsprimary designed functions and targets, which include floodcontrol, hydropower generation, river transportation andwater supply.

DATA

Observed monthly discharge data at the Yichang stationfor the period of 1951–2011

Monthly discharge records at the Yichang station for theperiod from 1951 to 2011, which are denoted as observeddischarge series S0 in this article, were collected from theBureau of Hydrology of the Yangtze RiverWater ResourcesCommission (called BHYWC hereafter). To systemicallyexplore the effects of the TGR’s operation on thehydrological droughts at the downstream Yichang station,the observed discharge series S0 was divided into two partsby year 2003when the TGR started to impoundwater, one isthe monthly discharge records for the period of 1951–2002,which was denoted as data series A, and the other is themonthly discharge records for the period of 2003–2011,which was denoted as data series B.

Generation of naturalized monthly discharge data at theYichang station for the postdam period of 2003–2011

The flow regime of the mid-lower reaches of the YangtzeRiver has been altered by the construction of the TGR since


2003. To reflect the flow regime that was unregulated bythe TGR and thus to provide a comparison to data series B,we reconstructed the naturalized (i.e. unregulated) monthlydischarge data at the Yichang station for the postdamperiod of 2003–2011, denoted as data series C. In fact, a setof naturalized discharge data at the Yichang station afterimpoundment of the TGR has been calculated by BHYWC.The main idea of the naturalization procedure adopted byBHYWC is to have the observed (i.e. regulated) flow at theYichang station (QO) naturalized to the unregulated flowQC

BHYWC

� �by adding the variation of water stored in the

TGR (ΔVR) within a specified time step (Δt). The sign ofΔVR is positive (negative) when water storage of the TGRincreases (decreases). The procedure generally follows asimple water balance method, which is defined by

QCBHYWC ¼ QO þ ΔVR=Δt (1)

In this article, another method is used to reconstruct thenaturalized monthly discharge at the Yichang station, whichis derived as a sum of the monthly runoff simulated by thetwo-parameter monthly water balance (TPMWB) model(Xiong andGuo, 1999) for the Cuntan–Yichang interveningbasin, denoted by Qsim

CT-YC , and the observed monthlydischarge at Cuntan station (QCT). The naturalizeddischarges at the Yichang station obtained through theTPMWB model is denoted as QC

TPMWB, and its calculationformula is expressed as

QCTPMWB ¼ Qsim

CT-YC þ QCT (2)

By using Equation 2, the flow routing and the flow lossbetween the Cuntan and the Yichang stations is reasonablydisregarded on the monthly scale (see Figure 1). Theobserved monthly discharge records at Cuntan station QCT

for the period of 1951–2011 were also obtained fromthe BHYWC.The quality-controlled daily precipitation and temperature

data (including maximum, minimum and mean values)covering the upper Yangtze River basin at 62 meteorologicalstations (see Figure 1) for the period of 1951–2011 wereobtained from theChinaMeteorologicalData SharingServiceSystem (CMDSSS, 2012). Monthly precipitation data at 62meteorological stations for the period of 1951–2011 werecalculated as the sum of corresponding daily precipitationdata. Monthly precipitation and daily temperature data at 16meteorological stations covering the intervening basin werethen used as inputs to the TPMWB model.

Construction of naturalized monthly discharge series at theYichang station for the period of 1951–2011

With the aim of providing a reference series for S0,the naturalized monthly discharge series for the period of1951–2011 at the downstream Yichang station, denoted byS1, was constructed to consist of the data series A for theperiod of 1951–2002 and the data series C for the period of


S. LI ET AL.

2003–2011. Therefore, both the observed discharge seriesS0 and the naturalized discharge series S1 were obtained forthe analysis of the effects of the TGR on the hydrologicaldroughts at the downstream Yichang station.

METHODS

TPMWB model

The TPMWB model (Xiong and Guo, 1999) is simpleand has a clear physical basis. The model had been used tosimulate runoff of 70 subcatchments in the south of China,with satisfactory simulation results. Figure 2 represents thestructure of TPMWB model (Li et al., 2011). A detailedintroduction to the TPMWBmodel can be found in the studyof Xiong and Guo (1999).The use of the TPMWBmodel for simulating themonthly

runoff generated from the Cuntan–Yichang interveningbasin for the period of 2003–2011 is as follows. Theclimate inputs to the TPMWB model are the monthly arealprecipitation P(t) and the monthly areal potential evapo-transpiration PET(t). P(t) and PET(t) were calculated bythe Thiessen polygon method using the monthly precipita-tion and the monthly potential evapotranspiration forall meteorological stations covering the study area,respectively. The monthly potential evapotranspiration ofeach meteorological station was calculated as the sum ofcorresponding daily potential evapotranspiration, whichwas calculated by the Hargreaves method (Hargreaves andSamani, 1985) using the daily maximum, minimum andmean temperature data. Because the Hargreaves method hasthe advantage of only requiring temperature data whileobtaining results similar to those of the complex methods(Beyazgül et al., 2000; Xu and Singh, 2001), it has beenrecommended for estimating the potential evapotranspir-ation when sufficient or reliable climate data are notavailable (Droogers and Allen, 2002; Hargreaves andAllen, 2003). Finally, the observed monthly discharges ofthe Cuntan–Yichang intervening basin area for the period of1951–2002, which were approximately calculated as thedifference between the observed monthly discharge at the

E

S

Q

P

E = f (PET, P, c)

SC

Figure 2. Schematic representation of the TPMWB model (P, E, S, Q andPET represent precipitation, actual evapotranspiration, soil water content,discharge and potential evapotranspiration, respectively. c and SC are twononnegative parameters, representing coefficient and field capacity of

catchments, respectively)


Yichang station and that at the Cuntan station for the periodof 1951–2002, was used to calibrate and validate theparameters of the TPMWB model.To fully test the applicability of the TPMWBmodel in the

study area, the whole period of 1951–2011 was split intothree subperiods, that is, calibration period (1951–1992),validation period (1993–2002) and forecasting period(2003–2011). The calibration period was used to findthe optimized values of the model parameters using thefirst part of the data set, and the validation period was usedto justify the persistence of the model performance withthe optimized parameter values obtained in the calibrationperiod. Only when the performance of the model issatisfactory in both the calibration and the validation periodscan the model be used with confidence in the forecastingperiod (Xiong and Guo, 1999). The Particle SwarmOptimization algorithm (Kennedy and Eberhart, 1995)was chosen for the parameter optimization as it canefficiently determine parameter values.Twomajor criteria were used to assess the performance of

the TPMWBmodel. Themain criterion was the widely usedNash–Sutcliffe efficiency (NSE) coefficient (Nash andSutcliffe, 1970). The second was the relative error (RE) ofthe volumetric fit between the observed runoff series and thesimulated series (Xiong and Guo, 1999). The NSE and theRE are defined as follows:

NSE ¼ 1�

Xnt¼1

Qobs;t � Qsim;t

� �2Xnt¼1

Qobs;t � Qobs� Þ2

� (3)

RE ¼

Xnt¼1

Qobs;t � Qsim;t

� �

Xnt¼1

Qobs;t

(4)

where Qsim,t is the simulated streamflow at time t, Qobs,t isthe observed streamflow at time t, Qobs

� is the mean ofobserved streamflow and n is the number of time steps.According to the hydrological forecasting regulations

specified by the Ministry of Water Resources (2000) ofChina, only if the forecast accuracies in both the calibrationand the validation periods achieve grade B, that is, theNash–Sutcliffe efficiency coefficient NSE in both thecalibration and the validation periods are 70% or greater,can the model be used to predict the runoff.

Calculation of drought index

In the present study, the SPI method based on monthlydischarge series was used to characterize the hydrologicaldroughts at the downstream Yichang station. Consideringthat SPI is commonly used to analyze meteorologicaldroughts based on monthly precipitation, we refer to thisindex as SSI when it is calculated using streamflow data(Vicente-Serrano et al., 2012). As discharge series arehighly biased and rarely follow a normal distribution, it is


1

2

3

-1

-2

-31999 2000 2001 2002 2003

0SSI

D1 D2 D3

M1 M2 M3

Figure 3. Diagrammatic sketch of the smoothing procedure for SSI seriesand the calculation of drought magnitude and duration (M1 and D1;M2 andD2; and M3 and D3 represent magnitude and duration of different drought

events, respectively)


necessary to standardize the probability distribution of thedischarge series. Vicente-Serrano et al. (2012) tested sixthree-parameter distributions by using amonthly streamflowdata set to select the most suitable distribution for theEbro Basin in Spain. The results show that, because oflarge variability in the statistical properties, using a uniqueprobability distribution for each gauging station does noobtain a reliable index. The findings reported by Vicente-Serrano et al. (2012) also indicate that in most cases (>95%for each monthly streamflow series), the Pearson IIIdistribution fit the streamflow series well. In China,numerous studies have also investigated the optimalprobability distribution to fit river discharge series, and ithas been suggested that the Pearson III distribution is thebest one for fitting the discharge series, especially in theSouth China Basin (Zhan and Ye, 2000; Xiong and Guo,2004). Therefore, the Pearson III distribution was selectedfor calculating the hydrological drought index. The detailedprocedure for parameters estimation for the Pearson IIIdistribution and calculation of SSI is described inthe appendix.

Drought event identification

After calculating a drought index for the streamflowdata series, it is important to adopt some criteria to identifythe drought events. To identify drought events successfully,special attention should be paid to the occurrence of minordroughts and mutually dependent droughts (Fleig et al.,2006; López-Moreno et al., 2009). Minor droughts areevents characterized by both short duration and lowmagnitude, are of little hydrological importance and maydisturb the integral analysis of all drought events. Mutuallydependent drought events refer to the phenomena thatdischarge occasionally exceeds the threshold level in ashort period, dividing a long period of low discharge intoseveral droughts events. These phenomena do not mean thetermination of droughts but the temporary interruption ormitigation of droughts. These smaller drought events cannotbe considered mutually independent; therefore, it is wiseto combine them into a single large event to capture thetrue severity of the drought. Tallaksen et al. (1997) proposedvarious procedures for combining mutually dependentdroughts. In this study, we chose the 5-month movingaverage method to smooth the original drought index series.The diagrammatic sketch of the SSI series after beingsmoothed is shown in Figure 3. Figure 3 illustrates that thesmoothing procedure can not only accurately combinemutually dependent droughts into a single drought event butalso clearly represents the drought characteristics of allmajor drought events.Severity, magnitude and duration are three important

drought characteristics. These parameters are interrelated,and any two of them are sufficient to completely define asingle drought event (Sadeghipour and Dracup, 1985). Inthe present study, two main drought characteristics chosenfor analysis of drought events were drought magnitude,which is defined as the sum of negative SSI anomaliesbelonging to the same drought event and denoted as M


(represented by shaded areas in Figure 3), and droughtduration, which is the number of months below a certainthreshold and denoted as D (Tarhule and Wo, 1997;López-Moreno et al., 2009).

Drought impact indices

Three drought impact indices are defined in this article.The first proposed index is called the drought index ratio(DIR) of upstream to downstream. The rationale for DIR isexplained as follows. Preliminary data analysis has shownthat the observed discharge at Cuntan station accountsfor approximately 86.1% of the observed discharge at theYichang station, and excellent correlation (r= 0.98) betweenthe observed monthly discharge series at the two stations forthe period of 1951–2011 suggests that the hydrologicaldrought situation at Cuntan station might provide a clue tothe hydrological drought situation at the Yichang stationeven if the information of runoff generated from theintervening basin between the Cuntan and the Yichangstations is not available. To roughly describe the degree ofinfluence of the hydrological droughts at the upstreamCuntan station on those at the downstream Yichang station,the DIR of upstream to downstream is defined by

DIR ¼ DI-CT�

DI-S0� ¼

1n CT

Xn CT

SSI-CT tð Þ<0;t¼1

SSI-CT tð Þ

1n S0

Xn S0

SSI-S0 tð Þ<0;t¼1

SSI-S0 tð Þ(5)

where SSI_CT(t) represents the SSI values for theobserved discharge series at Cuntan station and SSI_S0(t) represents the SSI values for the observed dischargeseries S0 at the Yichang station. DI-CT� and DI-S0�

represent the multiyear mean drought intensity at theCuntan and Yichang stations, respectively, which arecalculated as the mean value of all negative SSI values inthe corresponding series; n_CT is the number of negativevalues in the SSI_CT(t) time series; and n_S0 is thenumber of negative values in the SSI_S0(t) time series.Per the above definition, if DIR> 1, the multiyear meandrought intensity at upstream is greater than that atdownstream; if 0<DIR< 1, the opposite relation is


S. LI ET AL.

implied. Furthermore, the closer the DIR to 1, the greaterthe effect of hydrological droughts at upstream on thoseat downstream.To understand the effects of the TGR on the downstream

flow regimes and to distinguish the influence of non-reservoir-related changes (mainly precipitation changes) onthe hydrological droughts at the downstream Yichangstation from the influence of the TGR, we also calculatedtwo more indices: the drought impact index, denoted asΔSSI, and the relative drought impact index, denoted as CR.These indices are calculated as follows:

ΔSSI ¼ SSI�S0 � SSI�S1 (6)

CR ¼ ΔSSISSI�S0

(7)

where SSI_S1 represents the time series of SSI for thenaturalized discharge series S1, ΔSSI represents the effectsof the TGR on the hydrological droughts at the downstreamYichang station and CR represents the contribution ratio ofthe TGR to the hydrological droughts at the downstreamYichang station. Accordingly, ΔSSI> 0 indicates themitigation effects of the TGR on the hydrological droughtsat the downstream Yichang station; the larger the value, themore significant the mitigation effects. Similarly, ΔSSI< 0indicates the aggravation effects; the smaller the value, themore significant the aggravation effects. Finally, ΔSSI = 0indicates no effects; the closer the value to zero, the lesssignificant the effects.

RESULTS AND DISCUSSION

Simulation of unregulated monthly discharge at theYichang station for the postdam period of 2003–2011

Before the simulation of the monthly discharge generatedfrom the intervening basin between the Cuntan and theYichang stations using the TPMWB model, a preliminarynumerical experiment was conducted using the observeddata from 1951 to 1956 to establish relatively reasonableantecedent soil moisture content. Soil moisture content atthe end of the test run was then adopted and specified as theinitial condition for long-term simulation run for the periodof 1951–2011. Simulation results in different periods, suchas values of the Nash–Sutcliffe efficiency coefficient NSE

Precipitation Obs

Dis

char

ge (

m3 /s

)

0

5000

25000

20000

15000

10000

t (y1951 1956 191976197119661961

NSE = 71.04%RE = -0.14%

Calibration Period

Figure 4. The observed monthly discharge for the Cuntan–Yichang intervenifor the Cuntan–Yichang intervening


and the RE, are presented in Figure 4. As seen in Figure 4,the value of NSE in the calibration and validation periods is71.04% and 75.92%, respectively, both of which are greaterthan 70%; the value of RE is �0.14% and 7.41%,respectively, both of which do not exceed �10%. As allforecast accuracies reach grade B, the criteria specified bythe Ministry of Water Resources (2000) of China, theTPMWB model is suitable for simulating the discharge ofthe Cuntan–Yichang intervening basin for the postdamperiod of 2003–2011. Figure 4 represents the simulatedmonthly discharges of the intervening basin for the period of1951–2011.The simulated monthly discharges QC

TPMWB at theYichang station under natural conditions for the period of2003–2011 were calculated using Equation 2. To ensureQC

TPMWB at the Yichang station for the postdam period of2003–2011 were as reliable as possible, the naturalizedmonthly discharges QC

BHYWC were also obtained using theBHYWC’s method, that is, Equation 1. As shown inFigure 5, the determination coefficient R2 between theTPMWB-simulated QC

TPMWB and the BHYWC-naturalizedQC

BHYWC for the postdam period of 2003–2011 was 0.99,indicating an excellent match. Thus,QC

TPMWB could be usedas the data seriesC in reconstructing the naturalizedmonthlydischarge series at the Yichang station for the period of1951–2011.

Effects of the hydrological droughts at the upstreamCuntan station on those at the downstream Yichang station

Table I shows the multiyear mean drought indices at theCuntan andYichang stations for pre- and post-2003 periods.Droughts at Yichang and Cuntan stations during thepost-2003 period were both aggravated when comparedwith the pre-2003 period, although the change at theYichang station was greater than that at the Cuntan station.The DIR decreased from 1.19 for the pre-2003 period to0.73 for the post-2003 period, suggesting weakenedupstream effects after 2003, and other factors, such as theconstruction and operation of the TGR, might have playedan important role since 2003. Therefore, to quantitativelyassess the effects of the TGR on the hydrological droughtsat the Yichang station, the drought indices (SSI) of theobserved discharge series S0 and the naturalized dischargeseries S1 were analyzed and compared.

erved Simulated

Prec

ipita

tion

(mm

)

300

0

600

900

1200

ear)200119961991198681 2006 2011

Validation PeriodForecasting

Period

NSE = 75.92%RE = -7.41%

ng basin for the period of 1951–2002, and the simulated monthly dischargebasin for the period of 1951–2011


0

10000

20000

30000

40000

0 10000 20000 30000 40000

1:1 line

(a)

R2=0.99

QT

PM

WB

(m3 /s

)C

QBHYWC (m3/s)C

0

10000

20000

30000

40000

50000

2003 2004 2005 2006 2007 2008 2009 2010 2011

0

300

600

900

1200

t (year)

Dis

char

ge(m

3 /s)

Prec

ipita

tion

(mm

)

(b)

Precipitation TPMWBBHYWC

Figure 5. (a) Scatter plot between the naturalized monthly discharge seriesobtained by using the BHYWC’s method and the simulated monthlydischarge series obtained by using the TPMWB model at the Yichangstation for the period of 2003–2011. (b) The BHYWC naturalized andTPMWB simulated monthly discharge series at the Yichang station for the

period of 2003–2011

Table I. Multiyear mean drought intensity for the observeddischarge series at Cuntan station ( �DI-CT) as well as at theYichang station ( �DI-S0 ) and the DIR during the pre-2003period (1951–2002) and the post-2003 period (2003–2011)

DI�

DIRDI-CT� DI-S0�

Pre-2003 period (1951–2002) �0.58 �0.49 1.19Post-2003 period (2003–2011) �0.63 �0.87 0.73


Hydrological drought variation for the period of 1951–2011

The time series of SSI for the observed discharge seriesS0 is plotted in Figure 6a. At the Yichang station, thehydrological droughts were mainly recorded in the 1970s,the 1990s and the early years of the 21st century, whereasthe wettest years were the 1950s and 1960s, with the1980s showing an average behaviour (Figure 6a). Themost severe drought, which started from September 2006and reached its maximum value in January 2007,occurred after the construction of the TGR (Figure 6a).The extreme drought event in 2006 was further validated

through the inspection of SSI at Cuntan station (Figure 6c).The well-matched SSI at the Cuntan and Yichang stations(correlation coefficient r=0.92) suggests that the hydro-logical droughts might be caused by the governing climaticconditions (Figure 6d).

Comparison of hydrological droughts for the naturalizeddischarge series before and after 2003

The time series of SSI for the naturalized discharge seriesS1 is plotted in Figure 6b. A comparison of the SSI series of


S0 and S1 (Figures 6a and b) suggests that they are rathersimilar with only slight differences in the magnitude andduration of droughts. The correlation coefficients of the SSIseries of both S0 and S1 with the SPI series of the arealmonthly precipitation over the whole upper Yantze Riverbasin are r=0.80 and 0.79, respectively, indicating that thehydrological droughts at the downstream Yichang stationare natural phenomena mainly related to precipitationvariations over the upstream region. The downstreamhydrological droughts at Yichang would still have occurredeven without the construction of the TGR.Chen (2010) pointed out that droughts occurred

frequently in the middle and lower reaches of the YangtzeRiver before the construction of the TGR. Table II showsthe number of months and occurrence probabilities ofdroughts within different SSI value ranges for thenaturalized discharge series S1 during the pre-2003 period(1951–2002) and during the post-2003 period (2003–2011).Compared with the pre-2003 period, the occurrenceprobability of moderate droughts (�1.49≤SSI≤�1.0)during the post-2003 period decreased slightly, whereasmild droughts (�0.99≤ SSI≤ 0.0), severe droughts(�1.99≤SSI≤�1.5) and especially extreme droughts(SSI≤�2.0) increased significantly. The breakdowncomparisons further demonstrated that the occurrence andseverity of hydrological droughts at Yichang are morerelated to climatic conditions during 2003–2011.

Comparison of hydrological droughts for the observeddischarge series and naturalized discharge series after 2003

By comparing the statistical characteristics of thehydrological drought index (SSI) for the observed dischargeseries S0 and the naturalized discharge series S1 for thepostdam period of 2003–2011, the effects of the TGR on thehydrological droughts at the downstream Yichang stationcould be quantified. Compared with S1 (naturalizeddischarge series), the number of months of mild droughts(�0.99≤SSI≤ 0.0), moderate droughts (�1.49≤SSI≤�1.0), severe droughts (�1.99≤SSI≤�1.5) and extremedroughts (SSI≤�2.0) for S0 (observed discharge series)increased by between 4.5% and 57.1% (Table III). Figure 7shows the time series of SSI for the observed dischargeseries S0 and the naturalized discharge series S1 after 2003.In Figure 7, the SSI values of S0 were less than those of S1despite their extreme similarity on the general variationtrend after the initial impounding time of the TGR. There aretwo obvious drought events after the TGR construction—one is in the period of June 2003 to August 2005 andthe other spans the period of May 2006 to October 2011.For both events, the drought magnitude and duration of S0increased when compared with S1. For the first droughtevent, the drought magnitude and duration increased by6.9 and 7.0months, respectively, whereas for the seconddrought event, the drought magnitude and durationincreased by 17.6 and 8.0months, respectively. Theseresults indicate that the hydrological droughts at thedownstream Yichang station are slightly aggravated by theTGR’s initial operation from 2003 to 2011.


-4

-3

-2

-1

0

1

2

3

4

1950 1960 1970 1980 1990 2000 2010t (year)

SSI_

S0

TGR operation starting year

2006

(a) Observed Discharge Series S0

(d) Precipitation Series

(c) Observed Discharge Series at Cuntan

(b) Naturalized Discharge Series S1

-4

-3

-2

-10

1

2

3

4

1950 1960 1970 1980 1990 2000 2010

t (year)

SSI_

S1


2006

-4

-3

-2

-10

1

2

3

4

1950 1960 1970 1980 1990 2000 2010

t (year)

SSI_

CT


2006

-4

-3

-2

-10

1

2

3

4

1950 1960 1970 1980 1990 2000 2010

t (year)

SPI_

P


2006

Figure 6. Time series of SSI for (a) the observed monthly discharge series S0, (b) the naturalized monthly discharge series S1 and (c) the observedmonthly discharge series at Cuntan station. (d) Time series of SPI for the areal monthly precipitation over the whole upper Yangtze River basin

Table II. Number of months and occurrence probability of droughts falling within different SSI value ranges for the naturalizeddischarge series S1 during the pre-2003 period (1951–2002) and during the post-2003 period (2003–2011)

SSI Value Range

Pre-2003 Period (1951–2002) Post-2003 Period (2003–2011)

No. Months Probability (%) No. Months Probability (%)

�0.99≤SSI≤ 0.0 223 36.5 67 63.2�1.49≤SSI≤�1.0 43 7.0 7 6.6�1.99≤SSI≤�1.5 5 0.8 3 2.8SSI≤�2.0 0 0.0 8 7.5

S. LI ET AL.

To understand the possible reason why the hydrologic-al droughts at the downstream Yichang station wereaggravated by the TGR’s operation, the differences inwater discharge (ΔW) between the observed discharge


series S0 and the naturalized discharge series S1 at theYichang station for the period of 2003–2011 werecalculated. As shown in Figure 8, most of the naturalizeddischarges were greater than the observed discharges at


Table III. Number of months for droughts falling within different SSI value ranges for the observed discharge series S0 and thenaturalized discharge series S1 during the postdam period (2003–2011)

SSI Value Range

Postdam Period (2003–2011)

Observed Discharge Series S0 Naturalized Discharge Series S1 Change (%)

�0.99≤ SSI≤ 0.0 70 67 4.5�1.49≤ SSI≤�1.0 11 7 57.1�1.99≤ SSI≤�1.5 4 3 33.3SSI≤�2.0 10 8 25.0

-4

-3

-2

-1

0

1

2003 2004 2005 2006 2007 2008 2009 2010 2011

t (year)

SSI

Initial impoundingtime of the TGR

Observed Discharge Series S0

Naturalized Discharge Series S1

M1 = 6.9

M2=17.6

D2 = 8.0 monthsD1 = 7.0 monthsΔ

Δ

Δ

Δ

Figure 7. Time series of SSI for the observed discharge series S0 and the naturalized discharge series S1 after 2003

-200

-150

-100

-50

0

50

100

150

2003 2004 2005 2006 2007 2008 2009 2010 2011

t (year)

W(1

08 m3 /m

onth

)

October, 2008 October, 2010October, 2006

June, 2003

Figure 8. Differences in water discharge (ΔW) between the observed discharge series S0 and the naturalized discharge series S1 at the Yichang station forthe period of 2003–2011


the Yichang station. Moreover, apart from the initialimpoundment in June 2003, the flow reduction mainlyoccurred between July and December, with the reductionpeaking in October. To understand the link between flowreduction at the Yichang station and the impoundment

Table IV. The historical water levels with

Date Impoundment Period (d

1 June 2003–10 June 2003 1020 September 2006–27 October 2006 3728 September 2008–5 November 2008 3826 October 2010 —


of the TGR, listed in Table IV are the historical waterlevel with storage changes in the TGR after 2003. FromTable IV, three large-scale impoundment processes hadbeen carried out for the TGR before it reached its finaltarget water level of 175m for the first time at the end of

storage changes in the TGR after 2003

Water Level (m)

ay) Start End Change Storage Change (108m3)

66.0 135.0 69.0 100.0135.0 156.0 21.0 111.0145.0 172.3 27.3 195.0175.0 — —


S. LI ET AL.

October in 2010. Figure 8 and Table IV indicate that theflow reduction peaks at the Yichang station coincidedwith the three large-scale impoundments, which signifi-cantly reduced the downstream runoff and thus increasedthe downstream hydrological drought index as shown inFigure 7. These findings suggest that the TGR-inducedaggravation of the hydrological droughts at the Yichangstation could be explained by the river flow reductioncaused by impoundment of the TGR during 2003–2011.

Drought events analysis at the downstream Yichang stationafter 2003

The above analysis shows that the occurrencesof hydrological droughts at the Yichang station for theperiod of 2003 to 2011 were mainly governed by naturalclimatic conditions but aggravated by the presence of theTGR. To investigate how the operation of the TGR effectshydrological droughts at the downstream Yichang station,we chose two drought events, one from June 2003 toAugust2005 and the other from May 2006 to October 2011, for amore detailed study.Figure 9a shows the average monthly water storage in the

TGR and average monthly inflow and outflow of the TGR

0

200

400

600

800

May Jun Jul Aug Sep Oct

(a)

Infl

ows

&O

utfl

ows

(108 m

3 /mon

th)

t (mon

Wate

-4

-3

-2

-1

0

1

2

Jun-03 Nov-03 Apr-04

SSI

&SS

I

t (mmm

(b)

-4

-3

-2

-1

0

1

2

May-06 Feb-07 Nov-07 Aug-08 M

SSI

&SS

I

(c)

t (mmm

Figure 9. (a) Mean monthly inflow, outflow and storage volume in the TGR;for the drought event from June 2003 to August 2005; (c) variations of SSI_

from May 2006 to


for the period of 2003 to 2011. The TGR’s operation followsthe guiding principle of ‘storing clear water and releasingmuddywater’ (CWRC, 1997). From the previousDecemberto the next May, the outflow is controlled to be larger thanthe inflow to lower the reservoir water level to the floodlimited water level. During the flood season from June toSeptember, the reservoir is generally operated at this lowlevel, with inflow equal to outflow. In October andNovember, inflow exceeds outflow, and the reservoir waterlevel is raised gradually to the normal pool level. Within theperiod from December to April in the following year,although the reservoir should be kept as high level aspossible to allow operation of the power station forregulating the peak load of the electrical grid, outflow stillexceeds inflow due to the electricity demand, industrial andirrigation water uses, navigation and urban supply; thus, thereservoir water level is lowered further. Even so, thereservoir water level has to be kept above the dry controlwater level to satisfy upstream navigation conditions.The water amount stored in the TGRwas relatively stable

throughout the first drought event, which occurred fromJune 2003 to August 2005 (Figure 9b). However,ΔSSI hada decreasing trend before February 2004. Before impound-ment of the TGR in June 2003, the downstream experienced

Nov Dec Jan Feb Mar Apr0

100

200

300

400

Wat

erst

ored

(108 m

3 /mon

th)

th)

r stored Inflows Outflows

Sep-04 Feb-05 Jul-050

100

200

300

400

500

-yy)

Wat

erst

ore d

(108 m

3 /mon

th)Water stored SSI_S0 SSI

ay-09 Feb-10 Nov-10 Aug-110

100

200

300

400

500

Wat

erst

ored

(108 m

3 /mon

th)

-yy)

Water stored SSI_S0 SSI

(b) variations of SSI_S0 and ΔSSI in relation to water storage in the TGRS0 and ΔSSI in relation to water storage in the TGR for the drought eventOctober 2011



moderate droughts. Because of the dramatic rise of waterlevel in the TGR, a large amount of upstream water wasstored in the TGR (Huang et al., 2011), and consequentlythe hydrological droughts at the downstream Yichangstation were significantly aggravated. Since February 2004,ΔSSI increased slightly, and it became stable from thestarting time of the next operation (May 2004) to thetermination of the first drought event (August 2005;Figure 10b).The comparison of the variations of SSI_S0 and ΔSSI

showed an opposite trend from June 2003 to February 2004(Figure 9b), meaning that the effect of the TGR’s operation(ΔSSI) on the hydrological droughts at the downstreamYichang station kept growing, whereas the natural hydro-logical droughts (SSI_S0 as proxy) at the Yichang stationwere mitigated gradually. Following February 2004, ΔSSIwas basically unchanged while SSI_S0 finally increased tozero, which means that the effects of precipitation changeson the hydrological droughts at the Yichang stationstrengthened gradually and finally overwhelmed thenegative effects of the TGR operation.For the second drought event from May 2006 to October

2011, the effects of the TGR’s operation on the hydrologicaldroughts at the downstream Yichang station were not verystrong but long-lasting, for ΔSSI always fell within therange of �0.5 to 0.0 (Figure 9c). In contrast, the fluctuationof SSI_S0 was more remarkable. The downstream Yichangstation experienced an extreme hydrological drought event(SSI_S0≤�2.0) for the period fromSeptember 2006 to July2007, lasting nearly one year. At the same time, thecontribution ratio CR of the TGR on the hydrologicaldroughts at the downstream Yichang station ranged from0.15 to 0.18—always less than 0.5. It can thus be reasonablyinferred that the non-reservoir-related factors (mainlyprecipitation changes) played a more important role inthe occurrence of this extreme hydrological drought event.As previously discussed, the whole upper Yangtze Riverbasin experienced the extreme weather conditions with lowprecipitation in 2006 (Figure 6d), and the measuredprecipitations in 2006 at some stations were even 30%lower than those in normal years (Dai et al., 2010b).

CONCLUSIONS

After the construction of the TGR, there have beenconsiderable debates on the effects of the TGR ondownstream hydrology and water resources. The mainpurpose of this study was to analyze the role of the TGR’sinitial operation on the magnitude and duration of thehydrological droughts at the downstream Yichang stationduring 2003–2011.On the basis of the proposed DIR of upstream to

downstream, the hydrological droughts at Cuntan stationwere found to largely contribute to the occurrence ofdroughts at the Yichang station for the period of 1951–2011.By analyzing the SSI results of twomonthly discharge seriesS0 and S1 and the SPI results of the precipitation series overthe whole upper Yangtze River basin, it is found that the


hydrological drought variation at the downstream Yichangstation was mainly governed by the precipitation changesover the upstream region rather than by the TGR, which isfurther demonstrated by the comparison of the occurrenceprobabilities of droughts within different SSI value rangesbefore and after 2003 on the basis of the naturalizeddischarge series S1.By comparing the statistical characteristics of the

hydrological drought index (SSI) between the observeddischarge series S0 and the naturalized discharge series S1for the postdam period of 2003–2011, the degree to whichthe TGR has altered the hydrological drought situation atthe downstream Yichang station was quantified. Resultsshow that the hydrological droughts at the downstreamYichang station were aggravated slightly by the TGR’sinitial operation from 2003 to 2011. On the basis of thedifferences between the observed and the naturalizedmonthly discharge series at the Yichang station for theperiod of 2003–2011, it was demonstrated that the riverflowreduction caused by the impoundment of the TGR couldaccount for the TGR-induced aggravation of the hydro-logical droughts at the Yichang station. Two drought eventsafter the construction of the TGRwere chosen to investigatein detail how the TGR’s operation influenced the hydro-logical droughts at the downstream Yichang station during2003–2011. With all these analysis and findings, the overallconclusion was that the impoundment of the TGR duringthe postdam period of 2003–2011 indeed made a slightcontribution to aggravation of the hydrological droughtsat the Yichang station; however, the overall trend ofhydrological droughts at the Yichang station was mainlydetermined by natural climatic conditions closely relatedto precipitation changes.This study aimed to enhance our understanding of the

influence of the TGR on the hydrological droughts at thedownstream Yichang station. Results from this work mighthelp decision makers improve reservoir operation rulesfor the TGR. It must be noted that the Yichang station isimmediately downstream of the TGR, without influencefrom large tributaries in the middle and lower reaches ofthe Yangtze River. Thus, the effects of the TGR on thehydrological droughts further downstream from Yichangshould be investigated with greater consideration of theinfluence of downstream tributaries. Meanwhile, consider-ing the TGR is currently in its initial operation phase,an assessment of the long-term effects of the TGR on thedownstream hydrological droughts can only be made aftermore observed data are available.

ACKNOWLEDGEMENTS

This research was financially supported by NationalNatural Science Foundation of China (grant nos.51190094 and 51079098). The authors thank Dr SergioM. Vicente-Serrano at the Spanish National ResearchCouncil and two anonymous reviewers for their highlyconstructive suggestions and comments. They also thankDr David E. Rheinheimer and Ms Samantha Tress forimproving the English of this manuscript.


S. LI ET AL.

REFERENCES

Abramowitz M, Stegun IA. 1965. Handbook of Mathematical Functions.Dover Publications: New York.

AmericanMeteorological Society (AMS). 2004. Statement onmeteorologicaldrought. Bulletin of the American Meteorological Society 85: 771–773.

Beyazgül M, Kayam Y, Engelsman F. 2000. Estimation methods for cropwater requirements in the Gediz Basin of western Turkey. Journal ofHydrology 229: 19–26.

Chen J. 2010. Approach on drought defying operation of Three GorgesReservoir. Journal of Yangtze River Scientific Research Institute 27(5):19-23 (in Chinese with English abstract).

CMDSSS (China Meteorological Data Sharing Service System). 2012.Available online at http://new-cdc.cma.gov.cn:8081/home.do

CWRC (Changjiang Water Resources Commission). 1997. ComprehensiveUtilization and Reservoir Operation of Three Gorges Project. HubeiScience and Technology Press: Wuhan, China (in Chinese).

Dai Z, Du J, Li J, Li W, Chen J. 2008. Runoff characteristics of theChangjiang River during 2006: effect of extreme drought and theimpounding of the Three Gorges Dam. Geophysical Research Letters35: L07406, DOI: 10.1029/2008GL033456

Dai Z, Du J, Chu A, Li J, Chen J, Zhang X. 2010a. Groundwater discharge tothe Changjiang River, China, during the drought season of 2006: effects ofthe extreme drought and theThreeGorgesDam.Hydrogeology Journal 18:359–369.

Dai Z, Chu A, Du J, Stive M, Hong Y. 2010b. Assessment of extremedrought and human interference on baseflow of Yangtze River.Hydrological Processes 24: 749–757.

Droogers P, Allen RG. 2002. Estimating reference evapotranspiration underinaccurate data conditions. Irrigation and Drainage Systems 16: 33–45.

Du Y, Xue H, Wu S, Ling F, Xiao F, Wei X. 2011. Lake area changes inthe middle Yangtze region of China over the 20th century. Journal ofEnvironmental Management 92: 1248–1255.

Fleig AK, Tallaksen M, Hisdal H, Demuth H. 2006. A global evaluationof streamflow drought characteristics. Hydrology and Earth SystemSciences 10: 532–552.

Fu B, Wu B, Lü Y, Xu Z, Cao J, Niu D, Yang G, Zhou Y. 2010. ThreeGorges Project: efforts and challenges for the environment. Progress inPhysical Geography 34: 741–754.

Gleick PH. 2009. Three Gorges Dam Project, Yangtze River, China. In: PGleick, ed., The world’s water 2008–2009: the biennial report onfreshwater resources. Washington DC: Island Press: 139–150.

Guo H, Hu Q, Zhang Q, Feng S. 2011. Effects of the Three Gorges Damon Yangtze River flow and river interaction with Poyang Lake, China:2003–2008, Journal of Hydrology 416–417: 19–27.

Hargreaves GH, Allen RG. 2003. History and evaluation of Hargreavesevapotranspiration equation. Journal of Irrigation and DrainageEngineering 129(1): 53–63.

Hargreaves GH, Samani ZA. 1985. Reference crop evapotranspirationfrom temperature. Applied Engineering in Agriculture 1(2): 96–99.

Hayes M, Svoboda M, Wall N, Widhalm M. 2011. The Lincolndeclaration on drought indices: Universal meteorological drought indexrecommended. Bulletin of the American Meteorological Society 92:485–488.

Heim RR. 2002. A review of twentieth-century drought indices used inthe United States. Bulletin of the American Meteorological Society 83:1149–1165.

Hosking JRM. 1990. L-moments: Analysis and estimation of distributionsusing linear combinations of order statistics. Journal of Royal StatisticalSociety B 52(1): 105–124.

Huang H, Song D, Yun H, Lee DH, Cho JM. 2011. Water level changecaused from Three Gorges Dam construction in Yangtze River basin.Journal of Coastal Research SI64: 1672–1675.

Kennedy J, Eberhart R. 1995. Particle Swarm Optimization. Proceedingsof IEEE International Conference on Neural Networks. IV:1942–1948.

Keyantash J, Dracup J. 2002. The quantification of drought: An evaluationof drought indices. Bulletin of the American Meteorological Society 83:1167–1180.

Lana X, Serra C, Burgueno A. 2001. Patterns of monthly rainfall shortageand excess in terms of the standardized precipitation index for Catalonia(NE Spain). International Journal of Climatology 21: 1669–1691.

Li S, Xiong L, Wan M. 2011. Comparison of monthly water balancemodels. Journal of China Hydrology 31(5): 35–41 (in Chinese withEnglish abstract).

Livada I, Assimakopoulos VD. 2007. Spatial and temporal analysis ofdrought in Greece using the standardized precipitation index (SPI).Theoretical and Applied Climatology 89: 143–153.


López-Moreno JI, Vicente-Serrano SM. 2008. Positive and negativephases of the wintertime North Atlantic Oscillation and droughtoccurrence over Europe: A multi-temporal-scale approach. Journal ofClimate 21: 1220–1243.

López-Moreno JI, Vicente-Serrano SM, Beguería S, García-Ruiz JM,Portela MM, Almeida AB. 2009. Dam effects on droughts magnitudeand duration in a transboundary basin: The Lower River Tagus, Spainand Portugal. Water Resources Research 45: W02405, DOI: 10.1029/2008WR007198

Lu X, Yang X, Li S. 2011. Dam not sole cause of Chinese drought. Nature475: 174, DOI: 10.1038/475174c

McKee TB, Doesken NJ, Kleist J. 1993. The Relationship of DroughtFrequency and Duration to Time Scales, Paper Presented at 8thConference on Applied Climatology. American Meteorological Society:Anaheim, CA.

McKee TB, Doesken NJ, Kleist J. 1995. Drought Monitoring withMultiple Time Scales, Paper Presented at 9th Conference on AppliedClimatology. American Meteorological Society: Dallas, Texas.

Mcmanus DP, Gray DJ, Li Y, Feng Z, Williams GM, Stewart D,Rey-Ladino J, Ross AG. 2010. Schistosomiasis in the People’sRepublic of China: the era of the Three Gorges Dam. ClinicalMicrobiology Reviews 23(2): 442–466.

Mishra AK, Singh VP. 2010. A review of drought concepts. Journal ofHydrology 391: 202–216.

MWR (Ministry of Water Resources). 2000. Standard for HydrologicalInformation and Hydrological Forecasting (SL250-2000) (in Chinese).18–20.

Nalbantis I, Tsakiris G. 2009. Assessment of hydrological droughtrevisited. Water Resources Management 23: 881–897.

Nash JE, Sutcliffe JV. 1970. River flow forecasting through conceptualmodels. Journal of Hydrology 10: 282–290.

Palmer WC. 1965. Meteorologic Drought. US Department of Commerce,Weather Bureau, Research Paper No. 45, 58.

Palmer WC. 1968. Keeping track of crop moisture conditions, nationwide:the new crop moisture index. Weatherwise 21: 156–161.

Patel NR, Chopra P, Dadhwal VK. 2007. Analyzing spatial patterns ofmeteorological drought using standardized precipitation index. Me-teorological Applications 14: 329–336.

Sadeghipour J, Dracup JA. 1985. Regional frequency analysis ofhydrologic multiyear droughts. Water resources bulletin 21(3):481–487.

Shafer BA, Dezman LE. 1982. Development of a Surface Water SupplyIndex (SWSI) to Assess the Severity of Drought Conditions inSnowpack Runoff Areas. In: Preprints, Western SnowConf., Reno,NV, Colorado State University, 164–175.

Shen G, Xie Z. 2004. Three Gorges Project: chance and challenge. Science304: 681.

Shukla S, Wood AW. 2008. Use of a standardized runoff index forcharacterizing hydrologic drought. Geophysical Research Letters 35:L02405, DOI: 10.1029/2007GL032487

Tallaksen LM, Madsen H, Clausen B. 1997. On the definition andmodelling of streamflow drought duration and deficit volume.Hydrological Sciences Journal 42: 15–33.

Tarhule A, Wo M. 1997. Towards an interpretation of historical droughtsin northern Nigeria. Climatic Change 37: 601–616.

Vasiliades L, Loukas A, Liberis N. 2011. A water balance derived droughtindex for Pinios River Basin, Greece. Water Resources Management25: 1087–1101.

Vicente-Serrano SM, Beguería S, López-Moreno JI. 2010. A multiscalardrought index sensitive to global warming: The standardized precipitationevapotranspiration index. Journal of Climate 23: 1696–1718.

Vicente-Serrano SM, López-Moreno JI, Beguería S, Lorenzo-Lacruz J,Azorin-Molina C, Morán-Tejeda E. 2012. Accurate computation of astreamflow drought index. Journal of Hydrologic Engineering 17: 318–332.

Wen L, Rogers K, Ling J, Saintilan N. 2011. The impacts of riverregulation and water diversion on the hydrological droughts character-istics in the Lower Murrumbidgee River, Australia. Journal ofHydrology 405: 382–391.

Wilhite DA, Glantz MH. 1985. Understanding the drought phenomenon:the role of definitions. Water International 10: 111–120.

Wu J, Huang J, Han X, Xie Z, Gao X. 2003. Three-GorgesDam—experiment in habitat fragmentation? Science 300: 1239–1240.

Wu L, Zhang Q, Jiang Z. 2006. Three Gorges Dam affects regionalprecipitation. Geophysical Research Letters 33: L13806, DOI: 10.1029/2006GL026780

Wu H, Svoboda MD, Hayes MJ, Wilhite DA, Wen F. 2007. Appropriateapplication of the standardized precipitation index in arid locations anddry seasons. International Journal of Climatology 27: 65–79.


http://new-cdc.cma.gov.cn:8081/home.do


Xiong L, Guo S. 1999. A two-parameter monthly water balance modeland its application. Journal of Hydrology 216: 111–123.

Xiong L, Guo S. 2004. Trend test and change-point detection for theannual discharge series of the Yangtze River at Yichang hydrologicalstation. Hydrological Sciences Journal 49(1): 99–112.

Xu C, Singh VP. 2001. Evaluation and generalization of temperature-based methods for calculating evaporation. Hydrological Processes 15:305–319.

Yang Z, Wang H, Saito Y, Milliman JD, Xu K, Qiao S, Shi G. 2006. Damimpacts on the Changjiang (Yangtze) River sediment discharge to thesea: The past 55 years and after the Three Gorges Dam. WaterResources Research 42: W04407, DOI: 10.1029/2005WR003970

APPENDIX

Parameters estimation for the Pearson III distribution

The probability density function of a Pearson III distributedvariable is written as

f xð Þ ¼ 1baΓ að Þ x� gð Þa�1e� x�gð Þ=b (A1)

where a, b and g are shape, scale and location parameters,respectively, for discharge values x> 0. Γ(a) is the Gammafunction of a. The parameters were estimated using theL-moment method (Hosking, 1990), described as follows.The L-moment ratios t3 and t4 are calculated as

t3 ¼ l3l2

t4 ¼ l4l2

(A2)

where l2, l3 and l4 are the L-moments of the riverstreamflow series. These were obtained from probability-weighted moments by using the formulae

l1 ¼ o0; l2 ¼ o0 � 2o1;

l3 ¼ o0 � 6o1 þ 6o2;

l4 ¼ o0 � 12o1 þ 30o2 � 20o3

(A3)

The probability-weighted moments of order s werecalculated as

os ¼ 1N

XNi¼1

1� Fið Þsxi (A4)

where xi is the data from a given streamflow series and Fi

is a frequency estimator calculated by using the approachof Hosking (1990):

Fi ¼ i� 0:35N

(A5)

where i is the rank of observations arranged in risingorder, and N is the number of data points.When L-moment ratios have been calculated, the

parameters of the Pearson III distribution can be thenobtained as follows (Hosking, 1990).If t3≥ 1/3, then tm = 1� t3 and a can be obtained

using the formula:


Zhan D, Ye S. 2000. Engineering Hydrology. Chinese Water Power Press:Beijing, China (in Chinese).

Zhang H, Wei Q, Du H, Shen L, Li Y, Zhao Y. 2009. Is there evidencethat the Chinese paddlefish (Psephurus gladius) still survives in theupper Yangtze River? Concerns inferred from hydroacoustic andcapture surveys, 2006–2008. Journal of Applied Ichthyology 25: 95–99.

Zhang M, Shao M, Xu Y, Cai Q. 2010. Effect of hydrological regime onthe macroinvertebrate community in Three-Gorges Reservoir, China.Quaternary International 226: 129–135.

Zhu D, Chang J. 2008. Annual variations of biotic integrity in the upperYangtze River using an adapted index integrity (IBI). EcologicalIndicators 8: 564–572.

a ¼ 0:36067tm � 0:59567t2m þ 0:25361t3m� �1� 2:78861tm þ 2:56096t2m � 0:77045t3m� � (A6)

If t3< 1/3, then tm ¼ 3pt23 and a can be obtained usingthe following expression:

a ¼ 1þ 0:2906tmð Þtm þ 0:1882t2m þ 0:0442t3m� � (A7)

b ¼ ffiffiffip

pl2

Γ að ÞΓ aþ 1=2ð Þ (A8)

g ¼ l1 � ab (A9)

Calculation of SSI

After the parameters of the Pearson III distribution wereestimated using the L-moment method (Hosking, 1990),the cumulative probability distribution function of aPearson III distributed variable is thus written as

F xð Þ ¼ 1baΓ að Þ

Z x

gx� gð Þa�1e� x�gð Þ=bdx (A10)

Following the approach formulated by Abramowitzand Stegun (1965), the SSI is finally obtained as

SSI ¼ W � C0 þ C1W þ C2W2

1þ d1W þ d2W2 þ d3W3(A11)

W ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi�2 ln Pð Þ

p;P≤0:5 (A12)

where P is the probability of exceeding a determinedvalue, P = 1�F(x). If P> 0.5, P is replaced by 1� P, andthe sign of the resultant SSI is switched. The constants areas follows:C0 = 2.515517, C1 = 0.802853, C2 = 0.010328,d1 = 1.432788, d2 = 0.189269 and d3 = 0.001308. Themean of hydrological drought index is zero, and thestandard deviation is one.


effects of the three gorges reservoir on the hydrological droughts at the downstream yichang station...

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