Physics and Chemistry of the Earth xxx (2011) xxx–xxx

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Physics and Chemistry of the Earth

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Investigation into the impacts of land-use change on sediment yieldcharacteristics in the upper Huaihe River basin, China

Tao Cai, Qiongfang Li ⇑, Meixiu Yu, Guobin Lu, Lipeng Cheng, Xie WeiState Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, ChinaCollege of Hydrology and Water Resources, Hohai University, Nanjing 210098, China

a r t i c l e i n f o

Article history:Available online xxxx

Keywords:Upper Huaihe RiverSWAT modelLand-use changeSediment yield characteristics

1474-7065/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.pce.2011.08.023

⇑ Corresponding author at: State Key Laboratory ofand Hydraulic Engineering, Hohai University, Nanjing

E-mail address: li_qiongfang@hotmail.com (Q. Li).

Please cite this article in press as: Cai, T., et al.River basin, China. J. Phys. Chem. Earth (2011),

a b s t r a c t

The processes of sediment generation in the upper Huaihe River basin have been altered by the intensi-fied human activities over the past decades, particularly land-use change. To investigate the impacts ofland-use change on the sediment yield characteristics in the upper Huaihe River, the catchment abovethe Xixian hydrological controlling station was selected as the case study site. The Soil and Water Assess-ment Tool (SWAT) model was used to simulate land-use change effects on sediment yield by the use ofthree-phase (1980s, 1990s and 2000s) land-use maps, soil type map (1:200,000) and 1987–2008 dailytime series of rainfall from the upper Huaihe River basin. On the basis of the simulated time series of dailysediment concentration, land-use change effects on spatio-temporal change patterns of soil erosion mod-ulus, rainfall–sediment yield relationship, and the sensitivity of rainfall–sediment yield relationship torainfall for different types of land use were explored. The results revealed that under the same conditionof soil texture and terrain slope the advantage for sediment yield and the sensitivity of rainfall–sedimentyield relationship to rainfall descended by woodland, paddy field and farmland. The outputs of the papercould provide references for soil and water conservation and river health protection in the upper streamof Huaihe River.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Global river-land ecosystems have been intensively altered byhuman activities, particularly land use change. Land use changescould alter substantially the sediment delivery and water dis-charge of a catchment, influence the geomorphological processeswithin the river bed, and sometimes induce non-desirable pro-cesses for river management (Kondolf et al., 2002). Changes in landuse can act as triggers for increases in hillslope soil erosion andcatchment sediment yield (Wicks and Bathurstbt, 1996). Soil ero-sion is a natural and inevitable process that can become a seriousenvironmental and economic problem (López et al., 1998). Hence,it is essential to investigate the effects of land use change on sed-iment yield for soil–water conservation and river health protectionat the catchment scale. During the past two decades, the impacts ofland use change on sediment yield have received increasinglywidespread concern (López et al., 1998; Rodda et al., 2001; Haoet al., 2004; Blavet et al., 2009; Mueller et al., 2009; Ward et al.,2009; Wei et al., 2010, 2007). Hao et al. (2004) used SWAT modelin the Yellow River basin and explored forest will decreasesediment yield and with the increase of land use of agriculture

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Hydrology-Water Resources210098, China.

Investigation into the impactsdoi:10.1016/j.pce.2011.08.023

the sediment yield will increase correspondingly. Mueller et al.(2009) studied the effects of Land use change on sediment yieldfor a meso-scale catchment in the Southern Pyrenees and foundthat land use change have larger impacts on sediment yield thanclimate change. Wei et al. (2010) studied the relationships be-tween soil erosion and sediment yield with vegetation NDVI inthe Yellow River indicated that the vegetation status has a signifi-cant impact on sediment formation and transport. All those studieshave revealed that land use change can affect sediment yield bystudying the total sediment yield of the whole catchment underdifferent land use patterns. However, few researches has been fo-cused on quantifying the effects of land use changes on spatio-tem-poral change patterns of sediment yield characteristics, especiallyin the Huaihe River, China. Soil erosion is highly dependent on spa-tial scale (Xu and Yan, 2005). Investigation the impacts of land usechange on spatio-temporal change of sediment yield can assistwater authorities to identify the most vulnerable erosion-proneareas of a catchment (Tripathi et al., 2005). Therefore quantifyingthe effects of land use change on spatio-temporal change patternsof sediment yield is crucial to development of soil–water resourcesand land use management at a catchment scale.

Developing an approach for simulating and assessing the ef-fects of land use change on sediment yield at the watershed le-vel is essential to land-use planning and river health protection.Owing largely to computer and GIS technology improvements,

of land-use change on sediment yield characteristics in the upper Huaihe

Fig. 1. The location of Xixian catchment.

Table 1Statistics for land use changes in Xixian watershed of 1980s, 1990s, and 2000s.

Land use 1980s(%)

1990s(%)

2000s(%)

1980–1990s (%)

1990–2000s (%)

1980–2000s (%)

Water 0.9 0.78 1.32 �0.12 0.54 0.42Urban 0.63 0.51 0.88 �0.12 0.37 0.25Woodland 38.55 41.03 38.28 2.48 �2.75 �0.27Paddy

field17.42 27.23 17.15 9.81 �10.08 �0.27

Farmland 41.85 30.38 41.81 �11.47 11.43 �0.04Grassland 0.57 0.06 0.54 �0.51 0.48 �0.03

Fig. 2. The soil map of Xixian catchment.

2 T. Cai et al. / Physics and Chemistry of the Earth xxx (2011) xxx–xxx

nowadays, there has been a dramatic increase in the develop-ment and uses of the physically distributed hydrological modelsto investigate the impacts of land use change on sediment yield

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(Hao et al., 2004; Mueller et al., 2009; Ward et al., 2009), WaterErosion Prediction Project (WEPP) and Soil and Water Assess-ment Tool (SWAT) (Nearing et al., 1989; Arnold et al., 1998),for instance. Requiring less parameters and data input comparedwith that of the WEEP Model, the SWAT Model has been widelyused by many experts to simulate the sediment yield under dif-ferent land use patterns. According to Zhang et al. (2003, 2010),Li et al. (2008), Pang et al. (2010) and Wang et al. (2010) it isrecognized that the SWAT model can get a satisfactory accuracyof sediment simulation in China; therefore the SWAT model wasemployed to evaluate the impacts of land use changes on sedi-ment yield in the study.

With rapid economic development and population growth, thesoil–water loss is becoming one serious environmental and ecolog-ical problem in the upper Huaihe River basin. According to the re-port of Soil and water conservation on the upper reach of HuaiheRiver, the average annual soil erosion of the whole catchment is1.58 � 108 ton per year, however, the average annual soil erosionis 1.08 � 108 ton per year in upper stream of Huaihe River basin,accounting for 68.4% of the average annual soil erosion in thewhole basin Therefore, a comprehensive investigation was re-quired on the alterations of sediment yield characteristics resultedfrom the land-use change by long data series with most recentdata.

The objective of this paper is to quantify the effects of land usechange on sediment yield characteristics in the upper Huaihe Riverin China. On the basis of the topographic, land use/cover, soil andhydro-meteorological data, the effects of land use change on spa-tio-temporal change patterns of soil erosion modulus, rainfall–sed-iment yield relationship, and the sensitivity of rainfall–sedimentyield relationship to rainfall for different types of land uses wereinvestigated. The output of the paper could provide referencesfor soil–water conservation and river health protection in theupper stream of Huaihe River basin.

of land-use change on sediment yield characteristics in the upper Huaihe

Fig. 3. Land use of the Xixian catchment in different decades.

T. Cai et al. / Physics and Chemistry of the Earth xxx (2011) xxx–xxx 3

2. Study area

With intensified human activities, the land-use pattern in theHuaihe River basin has been altered to some extent and the soiland water loss in this area is serious (Hu and Zhou, 1998). Thispaper focused on the impacts of land-use change on sedimentyield characteristics in the upper Huaihe River basin. The HuaiheRiver is a major river in China and located about mid-way be-tween the Yellow River and Yangtze River, the two largest riversin China, and like them runs from west to east. The Huaihe Riverhas a drainage area of 174,000 square kilometers, which is situ-ated between latitudes 31� and 35� North and between longi-tudes 112� and 121� East. Originating from the TongbaiMountains of Henan province, it flows 1000 km through fourprovinces (i.e. Henan, Jiangsu, Anhui and Shangdong) before deb-ouching into the Yangtze River. The Huaihe River can be dividedinto the upper, middle and lower streams. This paper selectedthe upper Huaihe River above the Xixian hydrologic station as

Table 2Simulation performance of runoff simulation during 1987–2008.

Decades Application Year Robs (mm) Rsim (mm) Bias (%) Ens

1980s Calibration 1987 714.3 678.9 �4.94 0.7951988 390.2 410.4 4.92 0.725

Validation 1989 457.1 443.5 �7.02 0.7701990s Calibration 1990 300.5 267.9 10.98 0.701

1991 612.3 569.8 6.95 0.7111992 150.4 135.2 10.12 0.6951993 228.0 252.4 �9.66 0.731994 181.8 174.3 4.14 0.7441995 215.7 214.9 0.36 0.776

Validation 1996 523.2 545.6 �4.29 0.7741997 229.6 232.5 �1.28 0.7831998 626.2 601.6 3.92 0.7111999 81.6 90.2 �10.55 0.677

2000s Calibration 2000 580.8 600.1 �3.32 0.7732001 106.3 98.7 7.13 0.7242002 349.7 365.9 �4.63 0.7552003 621.1 601.3 3.19 0.7432004 283.4 301.7 �6.45 0.7142005 610.8 672.5 �10.11 0.7722006 197.3 225.3 �14.22 0.631

Validation 2007 532.4 469.2 8.86 0.7012008 455.0 501.1 �9.12 0.715

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a case study site, The Xixian hydrological controlling stationhas a catchment of 1.019 � 104 km2 (Fig. 1), where the mostsoils are light silt loam and sandy loam, with a small part under-lain by silt clay. The main land use types in the catchment arefarmland, paddy field and woodland and the main land usechanges in the Xixian basin from 1980s to 2000s were analyzedand presented in Table 1. It can be found that from 1980s to1990s, the percentage of paddy field increased by 9.81%, andfarmland decreased by 11.47%, while woodland increased by2.48%. Other changes in land use were insignificant. From1990s to 2000s, the percentage of paddy field decreased by10.08%, while farmland increased by 11.43%, and woodland de-creased by 2.75%. There was no significant land-use change from1980s to 2000s. The Xixian subbasin, with an average annualrainfall of 1145 mm, an average annual runoff of 371 mm, an-nual sediment yield of 1.262 � 108 ton and an average annualevaporation from 800 to 1000 mm, is seated in the transitionzone of northern subtropical region and warm temperate zone,where the rainfall for the flood season is mainly affected bymonsoon and most of the precipitation (�50%) falls betweenJune and September.

3. Methods

3.1. Model selection

To quantify the land-use effects on sediment yield in the upperHuaihe River basin, the SWAT model was selected to simulate dailysediment concentration under three types of land use patterns. Thephysically based SWAT model is considered as one of the mostsuitable models for predicting long-term impacts of land-use onwater, sediment and agricultural chemical yield (nutrient loss) inlarge complex watersheds with varying soils, land-use and man-agement conditions (Arnold and Fohrer, 2005). In the model, a wa-tershed is divided into multiple sub-basins, which are then furthersubdivided into Hydrologic Response Units (HRUs) that consist ofhomogeneous land-use, management, and soil characteristics.Modified Universal Soil Loss Equation (MUSLE) was used to predictdaily sediment concentration in a HRU that would be deliveredinto the channel of the inclusive sub-basin. In the channel network,sediment transport is modeled as a function of two processes,

of land-use change on sediment yield characteristics in the upper Huaihe

Fig. 4. Observed and simulated runoff for Xixian watershed.

Table 3Sediment calibrated parameter values.

Parameters Periods1987–1989 1990–1996 2000–2005

CUSLE Paddy field:0.06 Paddy field:0.06 Paddy field:0.06Woodland:0.01 Woodland:0.01 Woodland:0.01Farmland:0.20 Farmland:0.20 Farmland:0.20

PUSLE Paddy field:0.35 Paddy field:0.35 Paddy field:0.35Woodland:0.19 Woodland:0.19 Woodland:0.19Farmland:0.70 Farmland:0.70 Farmland:0.70

SPCON 0.009 0.007 0.006SPEXP 1.4 1.3 1.2CHEROD 0.5 0.8 0.5CHCOV 0.2 0.3 0.4

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deposition and degradation, operating simultaneously in the reach(Bagnold, 1977). SWAT provides two options to computedeposition and degradation. More detailed description of the SWATmodel can be referred to Arnold et al. (1998).

3.2. Data collection and processing

The topographic, land-use/cover, soil and hydro-meteorologicaldata required by SWAT for this study were collected and/or pro-cessed as follows: (1) the digital elevation model (DEM) data wasdownloaded from the Global Land One kilometer Base Elevationdatabase (http://www.ngdc.noaa.gov/mgg/global.html) with a spa-tial resolution of 30 � 30 s, and the Archydro tool was used to

of land-use change on sediment yield characteristics in the upper Huaihe

Table 4Simulation performance of soil erosion simulation during 1987–2008.

Decades Application Year Sobs (104 t) Ssim (104 t) Bias (%) Ens

1980s Calibration 1987 473.0 564.6 �19.35 0.5511988 72.5 83.0 �14.50 0.503

Validation 1989 414.3 343.1 17.17 0.5231990s Calibration 1990 99.2 83.0 16.35 0.515

1991 254.1 287.2 �13.03 0.5381992 12.3 14.1 �15.00 0.5651993 31.1 25.1 19.23 0.5581994 15.4 14.3 7.41 0.5401995 50.6 60.2 �18.92 0.501

Validation 1996 229.0 187.5 18.13 0.5731997 55.8 63.2 �13.33 0.5261998 283.6 258.9 8.74 0.6231999 4.0 4.8 �20.0 0.517

2000s Calibration 2000 294.5 272.3 7.54 0.5112001 0.9 0.7 21.64 0.4172002 266.5 313.6 �17.66 0.5212003 218.4 191.1 12.49 0.5632004 49.2 57.4 �16.69 0.6152005 322.4 364.5 �13.07 0.5212006 18.7 15.8 15.37 0.501

Validation 2007 178.7 198.5 �11.09 0.5112008 155.6 137.6 11.56 0.522

T. Cai et al. / Physics and Chemistry of the Earth xxx (2011) xxx–xxx 5

generate the river network and catchment boundary; (2) the soildata base of the SWAT model requires the spatial distribution ofsoil types and soil physical characteristics: the soil type map(1:200,000) of Henan province (Fig. 2) was derived from the Chi-nese Soil Database of the Institute of Soil Science and then wasdeveloped the soil map for the study area; Soil physical character-istics data were collected from Henan soil geography (Wei, 1995).Since the classification standard of soil particle used in China wasdifferent from the classification standard of that in the SWAT mod-el, the cubic spline interpolation method was adopted to convertthe data base of soil particle into the data base of that adapted inthe SWAT model. For more details of soil data base for SWAT modelit can be referred to Cai (2009). (3) the national land-use maps ofthree periods (1980s, 1990s and 2000s) were collected from theChinese Academy of Science and used to develop the three-phaseland-use maps for the study area (Fig. 3); (4) the daily time seriesof rainfall at sixty-three rainfall gauges and the daily time series ofdischarge and sediment concentration at the Xixian hydrologygauge during 1987–2008 (missing 1980–1986 observed sedimentdata)were collected from the Xinyang Hydrology Bureau; (5) themeteorological data at eight weather stations in or neighboringthe study area during 1987–2008 were collected from the ChinaMeteorological Administration (CMA), including daily maximumand minimum temperature, solar radiation, humidity, wind speedand direction. The homogeneity and reliability of all data abovehave been checked and firmly controlled by relevant data releaseorganizations.

3.3. Calibration and validation of the SWAT model

Model performance was evaluated by the Nash–Sutcliffeefficiency (Ens) and the relative error (Bias). The Nash–Sutcliffeefficiency and the relative error can be computed by the followingformulas:

Bias ¼Pn

i¼1Pi�Pn

i¼1OiPn

i¼1Oi� 100% ð1Þ

Ens ¼ 1�Pn

i¼1ðOi� PiÞ2Pn

i¼1ðOi� OiÞ2ð2Þ

where Oi and Pi are the observed and predicted values, Oi is themean values of the observed data, and n is the number of data.

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The lower the absolute value of Bias is, the better perform themodel does. Ens is the fraction of the variance in the observationexplained by the model, a high value indicates an accurate model.

3.4. Investigation of the effects of land-use change on sediment yieldcharacteristics

Land-use change may lead to alterations in sediment yieldcharacteristics. Therefore, it is necessary to investigate the effectsof land-use change on sediment yield characteristics. Based on thedaily simulated sediment concentration from different HydrologicResponse Units (HRUs) during 1987–2008, the soil erosionmodulus of each subbasin was computed and their spatial distri-butions were illustrated by using the ArcGIS technology. On thebasis of the three-phase land use maps and spatial distributionsof soil erosion modulus, the effects of land-use change on thespatio-temporal change patterns soil erosion modulus were inves-tigated. The rainfall–sediment yield relationships for differenttypes of land use and their sensitivity to rainfall were comparedand analyzed.

4. Results and discussion

4.1. Runoff calibration and validation

The SWAT model was calibrated and validated by the use of ob-served daily flow according to the maps (land-use, soil and DEM)and data base files (climate, soil properties, etc.). Since the sedi-ment concentration data missed from 1980 to 1986, the calibrationperiods for three phases (1980s, 1990s and 2000s) were dividedinto 1987–1988, 1990–1996 and 2000–2005 respectively, andtheir validation periods were 1989, 1997–1999 and 2006–2008correspondingly. Xixian station was selected for runoff and sedi-ment calibration due to the other hydrological stations being lackof daily sediment concentration time series. The simulation perfor-mance of runoff calibration and validation for the three phases(1980s, 1990s and 2000s) were presented in Table 2. From Table2 it can be seen that the SWAT model can be simulated with satis-factory accuracy. The Ens values both for calibration and validationperiods were more than 0.70 and the Bias values both for calibra-tion and validation periods were generally less than 10% except theyears of 1999 and 2001 due to small annual rainfall.

The observed and computed runoff for the calibration periodswere plotted for visual comparison; some of those plots wereshowed as illustration (see Fig. 4a–c), from the plots it can be foundthat the overall shape of the daily runoff can generally can be sim-ulated well by the SWAT model.

4.2. Sediment calibration and validation

According to Cai (2009), six SWAT parameters, the most sensi-tive to the sediment simulation were determined for model cali-bration (see Table 3), and the simulation performance ofsediment calibration and validation for the three phases were pre-sented in Table 4. From Table 4 it can be seen that sediment yieldcan be simulated accurately by the SWAT model. The Ens values forboth calibration and validation periods were more than 0.50 andthe Bias values for both calibration and validation periods weregenerally less than 20% except the years of 1999 and 2001 due tosmall annual rainfall.

The observed and computed sediment yield for the calibrationperiods were also plotted for visual comparison; some of thoseplots were showed as illustration (see Fig. 5a–c), from the plots itcan be also found that the overall shape of the daily sediment yieldcan be generally simulated well by the SWAT model.

of land-use change on sediment yield characteristics in the upper Huaihe

6 T. Cai et al. / Physics and Chemistry of the Earth xxx (2011) xxx–xxx

It indicated that SWAT model can be used for investigate theimpacts of land use change on sediment yield characteristics inthe upper stream of Huaihe River.

4.3. Effects of land-use change on the soil erosion modulus

Since too many years of simulated results were achieved, onlythree typical years, which have similar annual precipitation(1988, 1993 and 2002 with an annual rainfall of 800.7 mm,803.4 mm and 807.6 mm respectively), were selected to presenttheir subbasin-based spatial distributions of soil erosion modulus(see Fig. 6). From Fig. 6, it can be seen that the soil erosion modulusin the southern area are generally bigger than those in the northernarea. This is mainly due to unevenly spatial distribution of

Fig. 5. Observed and simulated se

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precipitation with higher precipitation occurring in the southernarea and lower precipitation in the northern sub-area.

To assess the effects of land-use on the soil erosion modulus,two subbasins numbered 2# and 45# respectively, in which theland-use changed in different decades, were selected. By use ofthree typical years (i.e. 1988, 1993 and 2002) of simulated results,the corresponding soil erosion modulus were calculated and pre-sented in Table 5. From Table 5 it can be seen the dominantland-use of 2# subbasin was woodland in 1988 while in 1993and in 2002 the dominant land use changed to farmland and paddyfield respectively. Its soil erosion modulus changed to 329.6 in1993 and 229.5 in 2002 respectively from 137.2 in 1988. The dom-inant land-use of 45# subbasin was paddy field in 1988 whilechanged to farmland in 1993 and urban in 2002 respectively. Its

diment for Xixian watershed.

of land-use change on sediment yield characteristics in the upper Huaihe

T. Cai et al. / Physics and Chemistry of the Earth xxx (2011) xxx–xxx 7

soil erosion modulus increased to 617.3 in 1993 and decreased to269.5 in 2002 respectively from 570.5 in 1988. The analysis aboveindicated that under the similar amount of precipitation, the samebasin slope and soil texture conditions the advantages of differenttypes of land use for sediment yield descended by farmland, urban,paddy field and woodland. The result could help relevant stake-holders identify the most vulnerable erosion-prone areas inducedby land-use change and provide references for the sustainable

Fig. 6. Spatial distribution of the annual soil erosion modules for 1988, 19

Table 5Change in land use, soil erosion modulus change in different subbasins.

Number of subbasin Dominant land-use

1980s 1990s

2# Woodland Farmland45# Paddy field Farmland

Fig. 7. The rainfall and sediment yield relationsh

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utilization of land and water resources in the upper Huaihe Riverbasin.

4.4. Effects of land-use change on rainfall–sediment yield relationship

To quantify the effects of land-use change on rainfall–sedimentyield relationship, the scatter diagram between annual rainfall andannual sediment yield for woodland, paddy field and farmland was

93, and 2002. Note. The numbers in red represent different subbasins.

Soil erosion modulus (t/km2 a)

2000s 1988 1993 2002

Paddy field 137.2 329.6 229.5Urban 570.5 617.3 269.5

ip for farmland, woodland and paddy field.

of land-use change on sediment yield characteristics in the upper Huaihe

Table 6Sensitivity of rainfall–soil erosion modulus relationship to rainfall for different types of land use.

Soil erosion modulus K1 (ton/a) K2 (ton/a) S K1 (ton/a) K2 (ton/a) S K1 (ton/a) K2 (ton/a) SLand use P = 1500 (mm) P = 1550 (mm) P = 1000 (mm) P = 1050 (mm) P = 600 (mm) P = 650 (mm)

Farmland 84.7 92.2 2.65 73.8 81.1 1.97 22.8 25.6 1.49Woodland 66.6 71.5 2.21 57.7 62.6 1.69 14.7 16.1 1.17Paddy filed 76.9 83.2 2.44 67.6 73.7 1.81 19.1 21.1 1.28

Note: S = the sensitivity of rainfall–soil erosion modules relationship to rainfall for different types of land use.Ki = the sediment yield responding to the same rainfall for different types of land use.

8 T. Cai et al. / Physics and Chemistry of the Earth xxx (2011) xxx–xxx

plotted (see Fig. 7) respectively by use of the simulated results of1987–2008 from the HRUs with these three types of land use. Itcan be seen from Fig. 7 revealed that the linear trend curve of rain-fall–sediment yield for farmland generally took lowest positionwhile linear trend curve of rainfall–sediment yield for woodlandgenerally took highest position, and that the linear trend curve ofrainfall–sediment yield for paddy field is generally situated be-tween those for farmland and woodland. With the same rainfall,farmland generally produced the most sediment, woodland gener-ally produced the least sediment, and the sediment generated frompaddy field generally fell between those generated respectivelyfrom woodland and farmland. This implied that land use changecould result in alteration in rainfall–sediment yield relationship.The result suggested that more attention should be paid to thefarmland when different land uses were changed in the upper Hua-ihe River basin. It could also provide references for the ungaugedregions during the land resources planning, management anddevelopment.

4.5. Sensitivity of rainfall–sediment yield relationship to rainfall fordifferent land-use

To assess the sensitivity of rainfall–sediment yield relationshipto rainfall for different land-use, on the basis of the computed an-nual rainfall and annual sediment from a typical Hydrologic Re-sponse Unit (HRU) located in No. 44 subbasin, in which land-usechanged among farmland, woodland and paddy field, the sensitiv-ity of rainfall–sediment yield relationship for land use being farm-land, woodland and paddy field was calculated respectively by thefollowing formula:

S ¼ ððK2 � K1Þ=K1Þ=ððP2 � P1Þ=P1Þ ð3Þ

where P1 and P2 are rainfall with difference of 50 mm, and K1, K2 iscorresponding sediment yield to rainfall P1 and P2 respectively.

Table 6 showed that the relative sediment yield changes offarmland responding to the same rainfall difference of 50 mm atdifferent rainfall levels are largest while those of woodland aresmallest. This indicated that the rainfall–sediment yield relation-ship of farmland is the most sensitive to rainfall change with theone of woodland being the least sensitive to rainfall change. Thesensitivity of rainfall–sediment yield relationship to rainfall forpaddy field is higher than that of woodland and lower than thatof farmland. Table 6 also demonstrated that the sensitivity of therainfall–sediment yield to rainfall for different types of land usevaried with rainfall. The sensitivity reduced with rainfall increas-ing. It should be noted that the sensitive degree of rainfall–sedi-ment yield relationship to rainfall may also vary with thelocation and soil type of HRU. The results could provide referencesfor the land-use management and soil–water conservation in theupper of Huaihe River basin.

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5. Conclusions

This paper investigated the effects of land-use change on thesediment yield characteristics in the upper Huaihe River basin.The results can be drawn as follows:

The SWAT model can be used to assess the effects of land usechange on sediment yield characteristics in the upper Huaihe Riverbasin with satisfactory accuracy; under the similar amount of pre-cipitation, the same basin slope and soil texture conditions, theadvantages of different types of land use for sediment yield des-cended by farmland, paddy field and woodland.

Land use change can result in alterations in rainfall–sedimentyield relationship. With the same rainfall, farmland generally pro-duced the most sediment, woodland generally produced the leastsediment, and the sediment generated from paddy field generallyfell between those generated respectively from woodland andfarmland, i.e. the sensitivity of rainfall–sediment yield relationshipto rainfall varied with the types of land use and rainfall, i.e. the sen-sitivity descended by farmland, paddy field, woodland and the sen-sitivity increased when rainfall increased. The sensitivity ofrainfall–sediment yield relationship to rainfall may also vary withthe location and soil type of HRU.

The outputs of the paper could provide references for soil andwater conservation and river health protection in the upper streamof Huaihe River.

Financial support is gratefully acknowledged from a researchproject (200701031) funded by the Ministry of Water Resources,China, a research project (200901045) funded by the Ministry ofWater Resources, China, the Program for Changjiang Scholars andInnovative Research Team in University under Grant No. IRT0717,Ministry of Education, China, and the ‘‘111’’ Project under GrantB08048.

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of land-use change on sediment yield characteristics in the upper Huaihe