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Inter-catchment comparison of flow regime betweenthe Hailiutu and Huangfuchuan rivers in the semi-aridErdos Plateau, Northwest ChinaYangxiao Zhoua, Zhi Yangac, Danrong Zhangb, Xiaomei Jinc & Jun Zhangd

a UNSCO-IHE Institute for Water Education, 2601 DA Delft, the Netherlandsb Hohai University, Nanjing 210098, Chinac China University of Geosciences, Beijing 100083, Chinad Free University of Amsterdam, 1081 HV Amsterdam, the NetherlandsAccepted author version posted online: 14 Feb 2014.Published online: 11 Mar 2015.

To cite this article: Yangxiao Zhou, Zhi Yang, Danrong Zhang, Xiaomei Jin & Jun Zhang (2015) Inter-catchment comparisonof flow regime between the Hailiutu and Huangfuchuan rivers in the semi-arid Erdos Plateau, Northwest China, HydrologicalSciences Journal, 60:4, 688-705, DOI: 10.1080/02626667.2014.892208

To link to this article: http://dx.doi.org/10.1080/02626667.2014.892208

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Inter-catchment comparison of flow regime between the Hailiutu andHuangfuchuan rivers in the semi-arid Erdos Plateau, Northwest China

Yangxiao Zhou1, Zhi Yang1,3, Danrong Zhang2, Xiaomei Jin3 and Jun Zhang4

1UNSCO-IHE Institute for Water Education, 2601 DA Delft, the Netherlandsy.zhou@unesco-ihe.org2Hohai University, Nanjing 210098, China3China University of Geosciences, Beijing 100083, China4Free University of Amsterdam, 1081 HV Amsterdam, the Netherlands

Received 29 July 2013; accepted 15 January 2014

Editor Z.W. Kundzewicz; Associate editor Y. Gyasi-Agyei

Abstract Two river catchments, the Huangfuchuan and the Hailiutu, located in the same climate zone in theErdos Plateau, China, have distinctly different flow regimes. This study systematically compared differencesbetween the flow regimes of these two catchments using several statistical methods, and analysed the possiblecauses. The variations in yearly, monthly and daily mean discharges were found to be much greater in theHuangfuchuan catchment than in the Hailiutu catchment. Preliminary analysis indicated that these differences arenot caused by changes in climate, but are instead attributable to differences in geology, geomorphology,hydrological processes and human interventions. In the Hailiutu catchment, the dominant groundwater contribu-tion maintains stationary daily and monthly river discharges, while shifts in yearly mean discharges were closelyassociated with the expansion or reduction of crop area. In the Huangfuchuan catchment, the dominant directrainfall–runoff process generates flashier daily and monthly river discharges, while the decrease of yearly meandischarges is caused mainly by the construction of check dams. These findings have significant implications forwater resource management and the implementation of proper soil and water conservation measures in the middlereach of the Yellow River Basin of China.

Key words flow regime differences; climatic factors; geology and geomorphology; land use; hydrological process; semi-aridarea; Erdos Plateau; China

Comparaison des régimes d'écoulement des bassins des rivières Hailiutu et Huangfuchuan dans leplateau semi-aride d’Erdos du Nord-Ouest de la ChineRésumé Les bassins versants deux rivières, la Huangfuchuan et la Hailiutu, situés dans la même zoneclimatique du plateau d’Erdos, dans le Nord-Ouest de la Chine, ont des régimes d’écoulement nettementdifférents. Cette étude compare les différences entre les régimes d’écoulement de ces deux bassins enutilisant plusieurs méthodes statistiques et en analyse les causes possibles. Les variations des débits moyensannuels, mensuels et journaliers sont plus importantes dans le bassin versant de Huangfuchuan que danscelui de Hailiutu. Une analyse préliminaire montre que ces différences ne sont pas causées par les change-ments climatiques, mais sont plutôt attribuables à des différences de la géologie, de la géomorphologie, desprocessus hydrologiques et des interventions humaines. Dans le bassin de Hailiutu, la contribution dominantedes eaux souterraines maintient des débits journaliers et mensuels stationnaires, tandis que les modificationsdes débits moyens annuels sont étroitement associées à l’expansion ou à la réduction de la superficiecultivée. Dans le bassin de Huangfuchuan, le processus dominant d’écoulement direct génère des débitsquotidiens et mensuels rapides, tandis que la baisse des débits moyens annuels est causée principalement parla construction de barrages de retenue. Ces résultats ont des implications importantes pour la gestion desressources en eau et la mise en œuvre de mesures de conservation des eaux et des sols dans le bief moyen dufleuve Jaune en Chine.

Mots clefs différences de régimes d’écoulement ; facteurs climatiques ; géologie et géomorphologie ; utilisation des terres ;processus hydrologiques ; zone semi-aride ; Plateau Erdos ; Chine

688 Hydrological Sciences Journal – Journal des Sciences Hydrologiques, 60 (4) 2015http://dx.doi.org/10.1080/02626667.2014.892208

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1 INTRODUCTION

River flow regimes have been altered worldwide byhuman activities and climate change (Matheussenet al. 2000, Bergström 2001, Yang et al. 2004,Gibson et al. 2005, Hu et al. 2005, Thodsen 2007,Bejarano et al. 2010, Lavers et al. 2010, Doll andSchmeid 2012). The Yellow River of China is promi-nent among altered rivers. Due to climate change andhuman activity in recent decades, the Yellow Riverdischarge has fallen to zero many times since 1960,with devastating impacts on downstream water use andecosystems (Liang et al. 2010). Several tributaries jointhe Yellow River where it flows around the ErdosPlateau, increasing not only the flow discharge butalso sediment concentrations. The Erdos Plateau con-sists of two distinct geomorphic regions: the MaowusuDesert in the northwest and the Loess Plateau in thesoutheast. The Loess Plateau is one of the most severelyeroded areas in the world, due to its loose loess soils,steep slopes, high rainfall intensity and poor vegetation(Rustomji et al. 2008, Feng et al. 2010). In the desertand semi-desert region, however, erosion is not a majorconcern; instead, desertification and dust storms havebeen identified as the most severe problems (Wanget al. 2010). Thus, semi-desert regions require differentmeasures for soil, water and ecosystem conservationthan do loess hill ravines.

To combat soil erosion and desertification in thearea, China has implemented soil conservation anddesertification prevention measures since the 1950s.The soil erosion control measures comprise convertinggentle sloping farmland to terraces, returning steep farm-land to nature, and constructing check dams (also calledsediment trapping dams) in gullies. The desert preven-tion measures comprise vegetating sand dunes, returningfarmland to forest and grassland, and keeping cattle andsheep in stalls. The landscape in the Erdos Plateau islargely modified. Regional-scale landscape modifica-tions have had profound effects on river discharge andsediment yields. Statistical analyses of long-term riversediment concentrations have identified a significanttrend of decreasing river sediment loads in the coarsesandy, hilly areas of the Loess Plateau since the late1970s (Xu 2004, 2010, Rustomji et al. 2008). Similardecreasing trends in river discharge have also beendetected (Huang and Zhang 2004, McVicar et al. 2007,Mu et al. 2007, Zhang et al. 2008, Yang et al. 2012). Soiland water conservation measures have reduced bothriver discharges and sediment concentrations.

However, there are few inter-catchment compari-sons that explore the influences of geological and

geomorphologic characteristics on river flow regimechanges under the impacts of climate variability andhuman activities. Huang et al. (1999) compared thehydrological behaviours of forest and grassland water-sheds in the Loess Plateau and found that the forestwatershed had less discharge than the grasslandwatershed. Qian et al. (2004) found that the baseflowindex of the loess hill ravine region was less than that oftheMaowusu semi-desert area. Chang and Zhang (2008)indicated that the Kuyehe River discharge in the loesshill ravine region is influenced mainly by precipitationand responds rapidly to rainfall events. They also foundthat discharge from rivers originating in blown-sandgrasslands are mainly fed by groundwater dischargeand have smaller fluctuations. The factors that controlthe differences in river flow regimes between semi-desertand loess hill ravine regions have not been thoroughlyinvestigated, and their different hydrological responsesto climate change and human activities have not beencompared. Understanding how flow regime changescorrespond to geological and morphological conditionsfacilitates the implementation of appropriate and effec-tive soil and water conservation measures in river basins.This study compared the flow regimes of two rivers fromthe Erdos Plateau: one from the Loess Plateau(Huangfuchuan River) and another from the Maowususemi-desert (Hailiutu River). We used statistical methodsto analyse various hydrological responses to climatefactors and human activities. Geological and geomor-phologic factors controlling these differences wereexplored. The results show that these two catchmentsare located in the same climate zone, but have distinctlydifferent flow regimes. The findings have significantimplications for water resource management and theimplementation of proper soil and water conservationmeasures in the middle reach of the Yellow RiverBasin of China.

2 MATERIALS AND METHODS

2.1 Study area

Two medium-size river catchments were investigated inthis study: the Hailiutu and the Huangfuchuan (Fig. 1).These two catchments are located in the same climatezone, but in different geological and geomorphologicenvironments. The Hailiutu River catchment (38°02′–38°50′N, 108°37′–109°19′E) lies in the Maowususemi-desert, while the Huangfuchuan River catchment(39°12′–39°54′N; and 110°8′–111°59′E) is located in theloess hill ravine region. The catchment areas of theHailiutu and Huangfuchuan are 2645 and 3240 km2,

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respectively. Significant differences in topography canbe observed between the two catchments (Fig. 1). Thegeomorphology of the Hailiutu catchment is character-ized by undulating sand dunes, low hills at the northernand western water divide, and one primary river valley inthe downstream area. The area is relatively flat, andthe stream network is limited to one main river and onebranch in the Hailiutu catchment. Meanwhile, the geo-morphology of the Huangfuchuan catchmentis characterized by high hills, deep valleys, and steepslopes. The stream networks are well developed, with upto third-order branch rivers in the Huangfuchuancatchment.

The geology of the two catchments is also verydifferent (Fig. 2). The geology of the Hailiutu catchmentis uniform, with Cretaceous sandstones covered by aeo-lian sand dunes in the entire catchment. In contrast, there

are three distinct geological areas in the Huangfuchuancatchment: aeolian sand dunes underlain by loess in theupper catchment, Jurassic sandstone and mudstone over-lain by loess in the middle catchment, and a loess plateauin the lower catchment.

The two catchments belong to the same conti-nental semi-arid climate zone. The summer (June–August) is hot, with average daily temperaturesabove 20°C. The winter (November–March) is cold,with average daily temperatures below zero. Thelong-term average annual precipitation is approxi-mately 350–400 mm/year. Total rainfall in the rainyseason (June–September) accounts for approximately80% of the annual rainfall. The long-term averageannual pan evaporation is 2400 and 2000 mm/yearin the Hailiutu and Huangfuchuan catchments,respectively.

Fig. 1 Catchment map of the Hailiutu and Huangfuchuan rivers.

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2.2 Data

There are three meteorological stations around theHuangfuchuan catchment, and three stations aroundand one inside the Hailiutu catchment (Fig. 1). For allof these stations, daily rainfall, daily average tem-perature and daily pan evaporation data are availablefrom 1959 to 2005. Daily mean discharge measure-ments from 1957 to 2007 were available atthe Hanjiamao gauging station in the Hailiutu catch-ment and at the Huangfu gauging station in theHuangfuchuan catchment (Fig. 1). In the Hanjiamaostation, daily rainfall measurements were also avail-able from 1959 to 2007. All these data were kindlyprovided by the Yellow River Conservancy

Commission. A digital elevation model (DEM) at90 m resolution was derived from 1:50 000-scaletopographic maps for both catchments. The DEMdata were used to compute the topographic para-meters, such as surface slope and drainage density.The Landsat-5 TM (thematic mapper) image of 10July 2010, at 30-m resolution, was obtained from ashared dataset provided by the InternationalScientific Data Service Platform, ComputerNetwork Information Centre, Chinese Academy ofSciences (http://datamirror.csdb.cn/). Normalized dif-ference vegetation index (NDVI) values were derivedfrom the image and converted to a land cover map(Lv et al. 2013).

Fig. 2 Geomorphological map of the Erdos Plateau (from the Xi’an Geological Survey Centre).

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2.3 Methods

Differences in river discharge between the Hailiutuand Huangfuchuan catchments were analysed forannual, monthly and daily mean discharge.

Most studies have used the Pettitt test to detect aregime shift (or a change point) in river flows (Zhanget al. 2008, Love et al. 2010). However, the Pettitttest can only detect a single change point in a timeseries and is not applicable for time series composedof multiple change points. In this study, two regimeshift detectors were applied to detect multiple regimeshifts in annual mean discharge in the Hailiutu andHuangfuchuan catchments: the cumulative sum(CUSUM) chart with a bootstrap analysis(Taylor 2000a) and the regime shift index (RSI;Rodionov 2004). The CUSUM chart plots the cumu-lative sum of deviations of successive sample valuesfrom the mean. A sudden change in the direction ofthe CUSUM chart indicates a sudden shift in themean. Change-Point Analyzer Software is availableto detect change points, together with both confi-dence levels and confidence intervals for each change(Taylor 2000b). The RSI is a sequential algorithm toestimate the regime shift by statistically testing themeans of the previous subsets and subsequent data-sets. The regime shift point is identified when themeans are significantly different. This point is con-sidered to be the possible starting point of the newregime. A piece of add-in software for MicrosoftExcel (RSI) is available to perform regime shiftdetection (http://www.beringclimate.noaa.gov/regimes/). Yang et al. (2012) detected multiple shiftsin annual mean discharges in the Hailiutu catchmentusing CUSUM and RSI.

The periodic characteristics of monthly meandischarge were analysed using a harmonic series(Zhou 1996). The periodicity, magnitude and phaseshift of the harmonic components were investigatedto contrast the differences between monthly dischargeseries in the Hailiutu and Huangfuchuan catchments.

The differences in daily mean discharges wereanalysed by constructing flow duration curves (FDC).Flow duration curves have been widely used to analysechanges of daily flow characteristics (Zhanget al. 2008) or differences in daily flow characteristicsbetween catchments (McMahon et al. 2008).

To explore whether climate factors are plausiblecauses of flow regime differences between the twocatchments, a number of statistical methods wereused. First, the regime shift detectors (CUSUM andRSI) were applied to test whether annual

precipitation, annual pan evaporation and annualaverage daily temperature also present similar trends.Second, statistical descriptors (mean, variance, skew-ness, coefficient of variation) of climate factors werecomputed and compared. Third, the Student t-test forthe difference in means and the F-test for the differ-ence in variances of climate factors between the twocatchments were performed. Fourth, correlation coef-ficients of climate factors between the two catch-ments were evaluated.

To diagnose the effects of catchment character-istics on flow regime differences, differences in landcover were evaluated by converting NDVI values tovegetation types for each catchment (Lv et al. 2013).The differences in topographic controls of flowregime were analysed by computing topographicindices with high resolution DEM data (Merz andBlöschl 2009, Tetzlaff et al. 2009, Capellet al. 2012). In this study, drainage density wascalculated, and the surface slopes were classifiedand compared between two catchments.

Although differences in geology can indicatethat groundwater may be contributing to flow regimedifferences, streamflow recession and baseflowseparation can provide quantitative assessment(Chapman 1999, Wittenberg and Sivapalan 1999,Kirchner 2009). In this study, the automated hydro-graph separation tool HYSEP (Sloto andCrouse 1996) was used to separate baseflow fromdaily average river discharge using three baseflowseparation methods: fixed interval, sliding intervaland local minimum. The ratio of baseflow to totaldischarge is defined as the baseflow index (BFI). Theannual average baseflow indices of the two catch-ments were computed and compared.

Finally, a multiple regression analysis was usedto ascertain the relative effects of climate variablesand human activities on annual flow regimes in bothcatchments.

3 ANALYSIS OF DIFFERENCES IN FLOWREGIMES

3.1 Differences in annual mean discharges

Regime shift detectors (CUSUM and RSI) were usedto detect multiple change points in the annual meanriver discharge of the Hailiutu and Huangfuchuancatchments. Four flow regime shift points weredetected in 1968, 1986, 1992 and 2001 in theHailiutu River discharges (Fig. 3(a)). These flowregime shifts were caused largely by land-use policy

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changes (Yang et al. 2012). Two flow regime shiftpoints were detected at 1968 and 1999 in theHuangfuchuan River discharges (Fig. 3(b)).However, Zhang et al. (2008) detected only onechange point there, in 1982, using the Pettitt test. Itseems likely that the Pettitt test was not able to detectmultiple change points and instead indicated a com-promise change point between two real changepoints. The first change point in 1968 correspondedto a point in the Hailiutu catchment. However, thecause of this change point in the Huangfuchuan

catchment was most likely terrace construction.Though flow has increased since 2001 in theHailiutu catchment, the annual mean discharge hasdecreased since 1999 in the Huangfuchuan catch-ment. This latter flow regime shift was caused mainlyby the construction of check dams for soil conserva-tion (Wang et al. 2012). Furthermore, the inter-annual variation in annual mean discharge(deviations from the step trends) in theHuangfuchuan River is much larger than those ofthe Hailiutu River (Fig. 3(c)). The standard deviation

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Fig. 3 Flow regime shifts of annual mean discharges of (a) the Hailiutu River (four flow regime change points in 1968,1986, 1992 and 2001); (b) the Huangfuchuan River (two flow regime change points in 1968 and 1999); and (c) departuresof annual mean discharges from their step trends.

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of the variations in annual mean discharges in theHuangfuchuan River is 2.44 m3/s, while it is only0.28 m3/s for the Hailiutu River. The F statistical testfor the difference in variances confirms that the var-iance of annual mean discharges in HuangfuchuanRiver is significantly greater than the variance in theHailiutu River, at a 99% confidence.

3.2 Differences in monthly mean discharge

Differences in monthly mean discharge were com-pared with discharge measurements under naturalsituations in the period 1959–1967. The responses ofmonthly runoff depth to monthly precipitation areclearly different between the two catchments in thescatter plot (Fig. 4). When the monthly precipitation isless than around 50 mm/m, the monthly runoff depthin the Hailiutu catchment is stationary around 3 mm/m, while the monthly runoff depth in theHuangfuchuan catchment varies greatly with the mini-mum zero depth. When monthly precipitationincreases beyond 50 mm/m, monthly runoff depth in

the Huangfuchuan catchment increases much fasterthan in the Hailiutu catchment. This means that agreater percentage of heavy rainfall is converted todirect runoff in the Huangfuchuan catchment than inthe Hailiutu catchment.

Statistical characteristics of monthly mean dis-charges from 1959 to 1967 were calculated for thetwo catchments (Table 1). The coefficient of varia-tion in the Huangfuchuan River was more than sixtimes greater than that in the Hailiutu River. TheSpearman correlation coefficient between themonthly mean discharge and monthly precipitationwas only 0.20 for the Hailiutu River, but as high as0.74 for the Huangfuchuan River. Statistical testsfor differences in the means (t-test) and variance(F-test) indicate that both the monthly mean dis-charge and the variance in the HuangfuchuanRiver are significantly larger than those in theHailiutu River, at a 99% level of confidence. It isclear that the variation in monthly mean discharge inthe Huangfuchuan River is greater than that in theHailiutu River.

Huangfuchuany = 0.0011x2 + 0.0272x + 1.4171

R2 = 0.89

Hailiutuy = 0.0002x2 –0.0088x + 3.3836

R2 = 0.46

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Fig. 4 Scatter plot of monthly mean discharge (runoff depth in mm) vs monthly precipitation in the Huangfuchuan andHailiutu catchments.

Table 1 Statistical characteristics of river discharges.

Statistics Monthly mean discharges 1959–1967 Daily mean discharges in 1967

Hailiutu Huangfuchuan Hailiutu Huangfuchuan

Mean (m3/s) 3.62 6.57 3.36 12.18Standard deviation (m3/s) 1.20 13.70 2.26 44.10Coefficient of variation 0.33 2.09 0.67 3.62Coefficient of skewness 3.68 4.04 4.48 6.16Range (m3/s) 9.61 83.87 21.12 407.00Minimum (m3/s) 2.01 0.00 1.48 0.00Maximum (m3/s) 11.62 83.87 22.60 407.00No. of days of zero discharge – – 0 78Spearman correlation coeff. with rainfall 0.20 0.74 0.33 0.46

(p = 0.038) (p < 0.001) (p < 0.001) (p < 0.001)

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The harmonic analysis identified dominant sea-sonal fluctuations in the two rivers. TheHuangfuchuan River had larger seasonal fluctuationsthan those of the Hailiutu River (Fig. 5). The ampli-tude of the annual periodic fluctuation in theHuangfuchuan River is 15 times larger than that inthe Hailiutu River. The monthly mean discharges inthe Hailiutu River had smaller peaks in March and inSeptember. In the Huangfuchuan River, a small

discharge peak occurred in March and a much largerpeak occurred in September (Fig. 5).

3.3 Differences in daily mean discharge

To visualize the differences of the daily mean dis-charge in responses to daily rainfall in the twocatchments, daily mean discharge values for 1967were plotted against rainfall (Fig. 6) and statistical

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Fig. 6 Variation of daily mean discharge in relation to rainfall in 1967 in (a) the Hailiutu and (b) the Huangfuchuan rivers.

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descriptors were computed (Table 1). The dailymean discharge of the Hailiutu River in 1967 wasstationary during no-rain days, and responded toheavy rain events with a moderate increase in dis-charge (Fig. 6(a)). The river was never dry. TheHuangfuchuan River was dry on most days inJanuary, February and December 1967, andresponded to heavy rain events with flash floods(Fig. 6(b)). The Spearman correlation coefficientbetween the daily mean discharge and daily pre-cipitation was 0.33 in the Hailiutu River, and 0.46in the Huangfuchuan River. The variation in dailydischarge in the Huangfuchuan River is extremelylarge compared with the coefficient of variation inthe Hailiutu River (Table 1).

The flow duration curves of the mean dailydischarge were constructed to compare differencesbetween natural (1959–1967) and recent flowbetween the two rivers (Fig. 7). TheHuangfuchuan River has much steeper flow dura-tion curves, implying a flashier runoff hydrograph.The Hailiutu River, on the other hand, has very flatflow duration curves indicating stationary dailydischarges. Furthermore, in the HuangfuchuanRiver, the flow duration curve of the recent flows(1999–2007) is shifted largely to the left comparedto the natural flows (1959–1967). This indicates alarge reduction in daily flows since 1999, asdetected in the annual mean discharges(Fig. 3(b)). In the Hailiutu River, the flow durationcurve of the recent flows (2001–2007) is onlyslightly lower than that of the natural flows.Therefore, the overall impacts on flow regimes(the difference between recent and natural flows)were greater in the Huangfuchuan River than in theHailiutu River.

4 ANALYSIS OF CAUSES OF DIFFERENCESIN FLOW REGIMES

4.1 Climate effects

The regime shift detectors did not find any significanttrend in the changes in annual precipitation in theHailiutu (Hanjiamao) and Huangfuchuan (Jungar)catchments (Fig. 8(a)). The Pearson correlation coef-ficient of annual precipitation between the two sta-tions was 0.65. The long-term mean annualprecipitation at Hanjiamao station (352 mm/year)was not significantly smaller than that (397 mm/year) at Jungar station, according to the Student tstatistical test at a 99% level of confidence.Furthermore, there was no significant difference inthe variance of annual precipitation between the twostations according to the F statistical test at a 99%level of confidence. The coefficient of variation ofannual precipitation was similar at the two stations(Table 2). The monthly precipitation variations werealso very similar. The correlation coefficients ofmonthly precipitation between the two stations wasas high as 0.79 (p < 0.001). Therefore, rainfall is notlikely the cause of the differences in flow regimeshifts between the two rivers.

Air temperature changes were also not signifi-cantly different in the two catchments. A significantincrease in temperature was detected since 1997 inboth catchments (Fig. 8(b)). The Pearson correlationcoefficient of annual mean temperatures between thetwo catchments was as high as 0.92 (p < 0.001),which indicates similar variation in annual meantemperature in the two catchments. The Student ttest indicates that the mean temperature in Yulin(Hailiutu catchment) was higher than that in Jungar(Huangfuchuan catchment) at a 99% confidence.

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However, the F test indicates there was no significantdifference in the variance of annual mean tempera-tures between the two catchments at a 99% confi-dence. The correlation coefficient of monthly meantemperatures between two catchments was nearlyequal to one, indicating similar seasonal temperaturevariations. Therefore, temperature is also not thecause of the differences in flow regimes betweenthe two rivers.

Finally, annual pan evaporation measurementsshowed significant differences between the Hailiutu(Wushenqi station) and Huangfuchuan (Jungarstation) catchments (Fig. 8(c)). A significant

decreasing trend in annual pan evaporation wasdetected beginning in 1988 at the Wushenqi stationand beginning in 1982 at the Jungar station. Bothmean evaporation and standard deviation atWushenqi station were statistically greater thanthose at Jungar station (Table 2) at a 99% level ofconfidence. The correlation coefficient of annual eva-poration between the two stations was 0.76. Thecorrelation coefficient of monthly evaporationbetween two stations was as high as 0.97.Therefore, the larger variation of annual evaporationin the Hailiutu catchment and smaller variation in theHuangfuchuan catchment cannot explain the lower

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Fig. 8 Comparison between (a) annual precipitation, (b) annual mean temperature, and (c) annual pan evaporation in theHailiutu and Huangfuchuan catchments.

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variability of discharge in the Hailiutu catchmentand the higher variability in the Huangfuchuancatchment.

4.2 Topographic effects

The DEM data were used to compute drainagedensity and surface slopes. Land surface slopeswere classified into three categories for both catch-ments (Fig. 9). The upper limit for classes was 15degrees because steep farmland with a slope over15° must be returned to trees or grasses accordingto a governmental policy issued in 1999 (Caoet al. 2009). It can be clearly observed that theHailiutu catchment is flat; 95% of the area has asurface slope less than 5° (Table 3). Furthermore,the land surface is covered by permeable Aeoliansand; therefore, the stream network is limited toonly one main river and one branch in the Hailiutucatchment (see Fig. 1). The drainage density wascalculated only as 0.18 km/km2. In contrast, almost70% of the areas of the Huangfuchuan catchmenthave surface slopes greater than 5° (Table 3). Onlyin valley bottoms is the surface slope less than 5°(Fig. 9). Moreover, large areas are covered byresponsive loess soil. As a result, the stream net-works are well developed into third-order branchstreams (Fig. 1). The drainage density was calcu-lated as 0.40 km/km2, more than double that of theHailiutu. In conclusion, the flat land surface cov-ered by permeable sand with very low drainagedensity in the Hailiutu catchment resulted in astationary streamflow hydrograph (Fig. 6(a)),while the steep land surface covered largely byimpermeable loess with relatively high drainagedensity generated a flashy streamflow hydrographthere (Fig. 6(b)).

4.3 Groundwater effects

HYSEP was used to separate baseflow from dailymean discharge for the period 1957–2005. The BFIwas computed every day, and the annual averagevalues are plotted in Fig. 10. It is evident that theBFI in the Hailiutu catchment is much larger thanthat in the Huangfuchuan catchment. In theHailiutu catchment, the dominant hydrologicalcycle is precipitation infiltration through sanddunes to sandstone aquifers, followed by dischargeto rivers. The direct surface runoff is limited. Theannual mean discharge in the Hailiutu River con-sists of approximately 88% groundwater discharge,on average, which explains why the annual,monthly and daily mean discharges are relativelystable. In the Huangfuchuan catchment, however,the dominant hydrological cycle is direct surfacerunoff. Groundwater discharge contributes only15% of the annual mean discharge, on average.Therefore, the variation in yearly, monthly anddaily mean discharges are much larger in theHuangfuchuan River.

4.4 Land cover effects

Landsat-5 TM-derived NDVI data were used to ana-lyse the distribution patterns of vegetation. Imagesfrom 10 July 2010, with 30-m resolution, were pro-cessed for the Hailiutu and Huangfuchuan catchments.The NDVI values were converted to five land coverclasses (Fig. 11). Both catchments are mainly coveredby low-density (NDVI < 0.15) and high-density(0.15 < NDVI < 0.30) shrublands. Meadows(0.30 < NDVI < 0.40) and farmlands (NDVI > 0.40)are limited (Fig. 12). The main difference in land coverbetween the catchments is that the Huangfuchuan hasslightly more high-density shrublands, while Hailiutu

Table 2 Statistical characteristics of annual precipitation and pan evaporation.

Statistics Annual precipitation (1959–2005) Annual pan evaporation (1959–2005)

Jungar Hanjiamao Jungar Wushenqi

Mean (mm/year) 396.5 351.8 1994.9 2400.0Standard deviation (mm/year) 111.6 107.8 171.9 307.7Coefficient of variation 0.28 0.30 0.09 0.13Coefficient of skewness 0.22 0.93 0.25 0.45Range (mm/year) 493.5 605.4 818.5 1619.4Minimum (mm/year) 145.9 143.5 1617.7 1655.5Maximum (mm/year) 639.4 748.9 2436.2 3274.9Pearson correlation coefficient 0.65 (p < 0.001) 0.76 (p < 0.001)

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has more farmland. However, the crop types are nota-bly different: because there is no groundwater forirrigation and the annual rainfall is above 400 mm/year, the crops in the Huangfuchuan catchment are

rainfed. Drought-resistant crops, such as barley andmillet, are planted there. Since 1999, the steep slopesin Huangfuchuan have been terraced and planted withtrees. The increase in high-density vegetationincreases the total evaporation, as trees evaporatemore water than drought-resistant crops (Yanget al. 2003, McVicar et al. 2007, Feng et al. 2012).The main crops in the Hailiutu catchment are maizeand potatoes, which are irrigated with groundwater inthe upland and with river water in the valley. Thesedifferences in land cover partly explain why the annualmean discharges have increased in the Hailiutu catch-ment but decreased in the Huangfuchuan catchmentsince 1999.

Fig. 9 Differences in slopes in the Hailiutu and Huangfuchuan catchments.

Table 3 Differences in slope in the two catchments.

Slope(degree)

Hailiutu catchment Huangfuchuan catchment

km2 % km2 %

0–5 2511.6 95.0 976.7 30.25–15 131.8 5.0 1399.5 43.3>15 1.6 0.1 856.8 26.5Total 2645 100.0 3233 100.0

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4.5 Regression analysis

Multiple correlation and regression analyses havebeen widely used to explore the relative effects ofclimate factors and human activities on stream flow

changes (Zhang et al. 2008, Merz and Blöschl 2009).In this study, annual precipitation and annual meandaily temperature were used to represent climatevariables since annual pan evaporation was not

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Fig. 10 Differences in baseflow index between the Hailiutu and Huangfuchuan rivers.

Fig. 11 Distribution of NDVI in the Hailiutu and Huangfuchuan catchments, 10 July 2010.

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significantly correlated to annual mean discharge at a95% confidence (Table 4). Because crops were irri-gated in the Hailiutu catchment, the effects of reser-voirs and river diversions for irrigation can beindirectly represented by the crop area. Check damshad drastic impacts on the decrease of river dischargein the Huangfuchuan catchment. The data on checkdams (number, dam height, storage capacity anddrainage area) from 1962 to 2005 were collectedfrom Erdos municipality. Correlation analysis foundthat the cumulative check dam storage was correlatedto the annual mean discharge significantly (Table 4).Therefore, the cumulative check dam storage wasused in regression analysis in the Huangfuchuancatchment.

There is a strongly negative correlationbetween the annual mean discharge of theHailiutu River and crop area, and there are lowercorrelations with annual precipitation and tempera-ture (Table 4). Because the crops are irrigated, theincrease in crop areas results in a decrease in riverdischarge. Therefore, the return of farmland todesert shrubland decreases evaporation, thusincreasing the river discharge (Yang et al. 2012).The multiple regression between the annual runoffdepth and its influencing factors (precipitation,crop area and temperature) in the period

1968–2006 was significant, with a coefficient ofdetermination of 0.64 (Fig. 13(a)).

In the Huangfuchuan catchment, the annualmean discharge is highly correlated with precipitation(Table 4). Furthermore, discharge is negatively corre-lated with the cumulative check dam storage andtemperature. The increase of check dam storageresulted in the decrease of river discharge. The multi-ple regression between the annual runoff depth andinfluencing factors (precipitation, cumulative checkdam storage and temperature) in the period 1962–2005 is significant, with a coefficient of determina-tion of 0.75 (Fig. 13(b)).

5 IMPLICATIONS FOR SOIL AND WATERCONSERVATION

Soil and water conservation measures for the MiddleYellow River basin were initiated in the mid-1950s.However, these measures did not have significanteffects until the end of the 1960s. Numerous mea-sures were implemented in the 1970s, including theconstruction of check dams, bench terraces, fish scalepits and reservoirs, and planting of trees and grass(Xu and Cao 2002, Li et al. 2009). Since 1999,projects designated to return farmland to forest and

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Fig. 12 Comparison of NDVI index between the Hailiutu and Huangfuchuan catchments, 10 July 2010.

Table 4 Correlation between annual mean river discharge and causative factors.

Pearson correlationcoefficient

Hailiutu River discharge (mm/year)(1968–2006)

Huangfuchuan River discharge (mm/year)(1962–2005)

Precipitation (mm/year) 0.42 (p = 0.008) 0.65 (p < 0.001)Temperature (°C) −0.33 (p = 0.040) −0.45 (p = 0.002)Evaporation (mm/year) −0.27 (p = 0.149) −0.18 (p = 0.242)Crop area (km2) −0.71 (p < 0.001) –Check dam (106 m3) – −0.47 (p = 0.001)

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grassland have been implemented (Cao et al. 2009).The vegetation recovery and soil conservation pro-jects have proved effective in reducing the sedimentyields in the region (Xu and Cao 2002, Rustomijet al. 2008, Feng et al. 2010). However, the effectson the river discharges are clearly different anddepend on the characteristics of the catchments(McVicar et al. 2007, Bi et al. 2009, Fenget al. 2012).

The Huangfuchuan River is one of the mainsources of sediment in the Middle Yellow Riverarea (Wang et al. 2002). In 1983, the catchmentwas designated as one of the eight key areas forcombating soil and water erosion in China. Eversince, it has become an experimental site for soiland water conservation and ecosystem restoration inthe Loess Plateau (Zhu et al. 2003, Yu et al. 2008,Wang et al. 2012). Two methods of soil and water

erosion control have been widely practiced. To con-trol surface erosion, farmlands with slopes greaterthan 15° have been converted to forest, while gentlysloping farmlands have been terraced. Check damshave been constructed in gullies to control gullyerosion. In 2003, the Ministry of Water Resource ofChina started a new campaign to speed up the con-struction of check dams. As many as 163 000 checkdams are planned for the Loess Plateau by 2020(Jin 2012). A large number of check dams havealready been constructed in the Huangfuchuan catch-ment. The main objective of check dams is to reducethe sediment pouring into the Yellow River. Checkdams have also created new farmlands (Xiang-zhouet al. 2004). However, check dams are also expectedto reduce the river discharge (Jin 2012). The decreasein the annual mean discharge in the HuangfuchuanRiver since 1999 is largely due to the construction of

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Fig. 13 Scatter plot of measured annual mean runoff depth against that predicted by regressions for (a) the Hailiutu and(b) the Huangfuchuan.

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check dams. It is necessary to modify the check damdesign to trap sediments while releasing sufficientclean water discharge to maintain the minimumflow of the Yellow River. To control soil erosion onsteeper slopes, native bushes should be promotedinstead of trees, which transpire more water and areless effective in the conservation of soil.

The main challenge in the Hailiutu River catch-ment is different from that of the Huangfuchuancatchment. Control of desertification is the toppriority in the Hailiutu catchment. The area suffersfrom frequent sandstorms, and farmland is threa-tened by moving sand dunes. At the beginning ofthe 1980s, the Chinese government started a foresta-tion project known as ‘Three North ForestShelterbelts’ (Wang et al. 2009, 2010). Since 2000,projects returning farmland to forest and grasslandhave also been implemented (Wang et al. 2009).Human activities have greatly shifted the flowregimes. The construction of reservoirs and riverdiversion dikes and the extraction of groundwaterfor irrigation are the main causes of the multipleflow regime shifts (Yang et al. 2012). The returnof farmland to desert shrubland has increased theriver discharge since 2001. Water and ecosystemmanagement strategies must satisfy both environ-mental water use by vegetation and water use forsocioeconomic development. In the future, theHailiutu River catchment must manage the ground-water recharge for water resource conservation andthe maintenance of healthy vegetation.

6 CONCLUSIONS

Distinct differences in flow regimes were identifiedbetween the Hailiutu and Huangfuchuan riverslocated in the same climate zone in the ErdosPlateau. The variations in yearly, monthly, and dailymean discharge are much greater in theHuangfuchuan River than in the Hailiutu River.Climate factors were not found to be the causes ofthe differences in flow regimes between the twocatchments. Instead, the differences in flow regimesare mainly attributed to geology and geomorphology.In the Hailiutu catchment, the homogeneous sand-stone serves as a good aquifer for groundwater sto-rage. The aquifer is covered by permeable undulatingsand dunes, which allow substantial precipitationinfiltration. The dominant hydrological cycle is pre-cipitation infiltration through sand dunes to sandstoneaquifers followed by discharge to rivers. A largepercentage of the groundwater baseflow maintains a

stationary river flow regime. In the Huangfuchuancatchment, the interbedded sandstone and mudstoneare less permeable. Furthermore, the aquifer is cov-ered by impermeable loess. The steep slopes of theland surface are favourable for surface runoff.Therefore, the dominant hydrological cycle is directsurface runoff. The groundwater baseflow is limited;therefore, the river flow varies widely.

The influences of human activities are also dif-ferent in the two catchments. At the Hailiutu catch-ment, river discharge is closely related to crop areachanges. Because most crops are irrigated, the returnof farmland to desert shrubs reduced evaporation andtherefore increased river discharge. Conversely, theconstruction of a large number of check dams in theHuangfuchuan catchment reduced both the sedimentyield and the river discharge.

These findings have important implications forsoil and water conservation and ecosystem manage-ment in the catchments. The water and ecosystemmanagement priority in the Hailiutu catchmentshould be to increase groundwater recharge by redu-cing evaporation loss. Plant species with less eva-poration should be selected to vegetate sand dunes.Crops with lower irrigation demands should be pro-moted to reduce water abstraction. In theHuangfuchuan catchment, river discharge and vege-tation depend directly on rainfall. The extent of rain-fed crops should be expanded, and bushes instead oftrees should be used for soil and water conservationin steep slopes. Modification of the check damdesign is also necessary to allow cleaner water dis-charge and maintain the minimum flow of theYellow River.

Acknowledgements The critical review and con-structive comments from the associate editor, DrYeboah Gyasi-Agyei, and an anonymous reviewerhelped improve the manuscript.

Disclosure statement No potential conflict of inter-est was reported by the author(s).

Funding This research was financed by theUNESCO-IHE DUPC research fund, the Dutch gov-ernment’s Asian Facility for China project‘Partnership for education and research in water andecosystems interaction’, and the Honor PowerFoundation.

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