Water and Energy Consumption by Agriculture in the Minqin Oasis Region

Journal of Integrative Agriculture2013, 12(8): 1330-1340 August 2013

© 2013, CAAS. All rights reserved. Published by Elsevier Ltd.

doi:10.1016/S2095-3119(13)60542-0

RESEARCH ARTICLE

Water and Energy Consumption by Agriculture in the Minqin Oasis Region

LI Cheng, WANG Yue and QIU Guo-yu

Key Laboratory for Urban Habitat Environmental Science and Technology, School of Environment and Energy, Peking University,

Shenzhen 518055, P.R.China

Abstract

Water used in agriculture consumes much energy, mainly due to pumping water for irrigation, but the water-energy nexus

is always neglected in arid and semi-arid areas. Based on hydrological observation data, irrigation data and socio-

economic data over the past 50 yr, this study has derived a detailed estimate of greenhouse gas (GHG) emissions from

agricultural water use in the Minqin Oasis. Results show that the decreasing water supply and increasing demand for

agriculture has caused severe water deficits over the past 50 yr in this region. The groundwater energy use rate rose by

76% between 1961 and 2009 because of the serious decline in groundwater levels. An increase in pump lift by an average

1 m would cause GHG emission rates to rise by around 2%. Over the past 10 yr, the GHG emissions from groundwater

accounted for 65-88% of the total emissions from agricultural water. GHG emissions for diverted water varied from 0.047

to 0.074 Mt CO2e as the water input increased. Long distance conveyance and high pump lifts need more electricity input

than groundwater abstraction does. Government policies have had a favorable effect on total emissions by reducing

water abstraction. But groundwater depletion, exacerbated by a growing population and an expansion in arable land,

remains the principal energy-water nexus challenge in the region. In response to the increasing water-energy crisis,

energy-saving irrigation technology, matching to cost efficiencies, and better coordination between different infrastructural

agencies could be feasible ways of rendering the water and energy sectors more sustainable over the long term.

Key words: water, energy, irrigation, emissions, Minqin Oasis

INTRODUCTION

Water and energy, two of the most important resourcesneeded for human development, are inextricably inter-linked (Gupta 2002). Climate change, rapid urbanization,and carbon economy, among other factors, have el-evated the energy-water nexus from an operational toolto a new joint-resource management and policy para-digm (Vlek et al. 2004). In recent years, there hasbeen an ever increasing body of research that aims tointegrate the traditionally separate issues of water and

energy use across the spectrum of policy, planning,design and operation (Pimentel et al. 1973; Schroll 1994;Gupta 2002; Lofman et al. 2002; Erdal et al. 2007;Mukherji 2007; Kahrl and Roland-Holst 2008;Mohammadi et al. 2008; Khan et al. 2009; Jackson et al.2010; Moreno et al. 2010; Dale et al. 2011). As grow-ing populations demand more energy, water resourcesand food supplies, understanding the agricultural wa-ter-energy nexus has become increasingly important(Khan 2009a, b). According to the IPCC’s special re-port on emission scenarios, around one fifth of theworldwide annual anthropogenic greenhouse gas (GHG)

Received 17 October, 2012 Accepted 10 January, 2013

Correspondence QIU Guo-yu, Tel: +86-755-26033309, E-mail: [email protected]

Water and Energy Consumption by Agriculture in the Minqin Oasis Region 1331


emissions came from the agricultural sector (excludingforest conversion). Wang et al. (2012) showed thatthe agricultural sector was responsible for roughly 17-20% of the total annual GHG emissions in China.

In arid and semi-arid regions, agricultural produc-tion fundamentally depends on available water resourcesbecause of the extensive use of irrigation (Hu et al.2009; Topak et al. 2010). But multiple drivers are gen-erating immense pressure on water resources. Therelated increase in energy consumption, mainly causedby pumping water for irrigation (Lal 2004; Moreno et al.2010), also faces challenges. Minqin Oasis, in the aridinland of Northwest China, is one of four areas thatproduce sandstorms and is the most severely desertifiedregion in China (Zhang et al. 2005). As the most im-portant economic sector in Minqin County, agriculturalproduction accounts for 80% of the gross domesticproduct (Feng et al. 2011) and 76% of its population isengaged in agricultural production (Statistical Bureauof Minqin County 2009). Water resources in this areaare not only essential for the ecological and environ-mental wellbeing of the region, but are also a criticalfactor in maintaining agricultural and economicsustainability (Ji et al. 2006). In order to alleviate thewater crisis in the region, the government has imple-mented the policies of “conversion of cropland to for-est and grassland” and “closing motor-well and reduc-ing cultivated land” since 2002 and 2004, respectively(Forestry Bureau of Minqin 2003). The Jingdian waterdiversion project was completed in 2000 and put intooperation in 2001. Water is diverted and lifted from theYellow River through a large number of steps that use33 pumping stations. The natural river course ofShiyang River is used as the main transfer channel andHongyashan reservoir is used for storage (Minqin Wa-ter Conservancy Bureau 2003). Water planners andpolicy makers have often been concerned with watershortages, supply augmentation and management, buthave rarely been concerned with the related energyissues. There has been a growing need to explore theenergy implications in order to meet the challenges andopportunities for reducing both energy and water use.

Over-exploitation and severe water-resourcewastage, together with the induced degeneration of theecological environment in this region, have attractedmuch research attention (Wang and Cheng 1999a, b; Wang

et al. 2002; Kang et al. 2004; Li et al. 2005, 2007; Zhuet al. 2007; Sun et al. 2007, 2009; Zhang et al. 2008; Huet al. 2009; Huang et al. 2011). However, there has beenlittle research into the energy needed for increased waterexploitation, and there has been no detailed attempt to quan-tify the related energy consumption from agriculture overtime. With particular emphasis on the water-energy nexusfor agriculture, the specific objectives of this paper were to:(a) characterize surface water and groundwater resourcesand track their development over time in the Minqin Oasisarea; (b) present a systematic and quantitative evaluation ofenergy use rate and GHG emissions from water used forirrigation; (c) discuss the effectiveness of government poli-cies and the water diversion project on energy consump-tion and the responses of farmers who are facing acutewater problems; and (d) analyze the results to derive fea-sible options for the sustainable use and management ofenergy and water for agriculture in the Minqin Oasis area.

RESULTS

Water supply and withdrawals

The agricultural sector consumes 83-96% of the totalwater resources in the Minqin Oasis area (Table 1).This includes surface water, groundwater and waterdiverted from the Yellow River. The inflow into theHongyashan reservoir, the only surface water sourcein the region, decreased by 71% from 4.49×108 m3 yr-1

in 1956 to 1.87×108 m3 yr-1 in 2009 (Fig. 1). The mini-mum volume of water flowing into the Minqin Oasiswas only 0.62×108 m3 in 2002. This change has mainlycome about because of overuse and surface waterwastage in the upper and middle reaches of the ShiyangRiver basin. As a component of total surface watersupply, the Jingdian water diversion project has deliv-ered a total of 4.26×108 m3 water to the Minqin Oasisarea, with the annual volume increasing from 0.41×108

m3 in 2001 to 0.65×108 m3 in 2009 (Minqin Water Con-servancy Bureau 2010). Although the project adds sig-nificantly to the available water supply for agriculturein the region, it is far from enough to completely miti-gate water scarcity. Furthermore, the high construc-tion and maintenance costs, totaling more than 0.3 bil-lion CNY (Minqin Water Conservancy Bureau 2003),

1332 LI Cheng et al.


and the immense pressure on water resources in theYellow River basin, can result in an inadequate watersupply for the project.

The decreased surface water inflow has directlyshifted the ever-growing water demand to groundwater,which has become the primary water source forirrigation. The contribution made by groundwater tothe total amount of water available to agricultural was59.4% in 2009, despite its diminishing trend over time.The annual groundwater exploitation in the Minqin Oa-sis area was less than 1.0×108 m3 before 1960 and reachedthe maximum (6.65×108 m3) in 2003. The average incre-ment rate has been 0.2×108 m3 yr-1. The amount ofgroundwater in use has gradually decreased by 68%from 6.85×108 m3 yr-1 in 2002 to 2.22×108 m3 yr-1 in2009 because of the implementation of the nationalpolicy: “closing motor-well and reducing cultivatedland” (Table 1). The over-exploitation of groundwa-

ter caused serious groundwater level declines and aqui-fer overdraft (Ma et al. 2007; Feng et al. 2011). Ingeneral, the decreasing water supply and increasingdemand for agriculture has caused severe water defi-cits over the past 50 yr at the Minqin Oasis area.

Energy consumption from agricultural water

Energy use rates, GHG emission rates, emissions fromthe different water resource sectors for agriculture overthe past 50 yr in the Minqin Oasis area, and details ofgroundwater levels and pump lifts are shown in Table 2.The energy use rate for groundwater increased by 76%from 1961 to 2009 due to increased use of electric anddiesel pumps, even though there has been a move to-wards replacing diesel pumps with electric pumps. Asshown in Table 2, electric pumps have a much lowerenergy use rate than diesel pumps because they aremore efficient. Similarly, the GHG emission rate fromgroundwater increased from 0.38 kg CO

2e m-3 in 1961

to 0.68 kg CO2e m-3 in 2009, which has coincided with a

serious decline in groundwater levels. The averagegroundwater level has dropped from 2.29 to 22.35 mover the past 50 yr, and pump lift has correspondinglyincreased (Table 2). The average groundwater level inQuanshan, Huqu and Baqu declined at a rate of 0.80,0.56, 0.51 m yr-1, respectively (Fig. 2). Quanshan, withsubstantial population density and lush plantationagriculture, showed a greater reduction trend than theother two areas. Deteriorating water quality has limitedabstraction in Huqu, the most important agricultural zone,

Table 1 Water supply and withdrawals for agriculture in Minqin since the 1960s (×108 m3 yr-1)

YearWater supply Agricultural water use

Surfacewater Groundwater Diverted water1) Total Surface water Groundwater Total

1960s 4.49 <1 <5.49

1970s 3.17 3.50 6.67

1980s 2.28 5.73 8.01

1990s 1.51 5.92 7.43

2000 1.14 6.57 7.71 0.65 5.89 6.53

2001 1.14 6.77 0.41 7.91 0.99 6.26 7.25

2002 0.62 6.97 0.49 7.59 0.61 6.85 7.46

2003 1.17 6.65 0.40 7.82 1.17 5.50 6.67

2004 0.65 5.91 0.45 6.56 0.64 5.90 6.54

2005 0.90 5.84 0.45 6.74 0.88 5.76 6.64

2006 1.30 5.41 0.46 6.71 0.89 4.94 5.83

2007 1.53 4.92 0.45 6.45 1.01 4.19 5.20

2008 1.78 3.97 0.49 5.75 1.30 3.43 4.73

2009 1.87 2.78 0.65 4.65 1.52 2.22 3.74

1) Diverted water is a part of surface water. Surface water is the inflow into Hongyashan reservoir.

Fig. 1 The variation of annual inflow into the Hongyashan reservoirsince 1956.



so there was only a small drop in ground water levels inthis region (Huo et al. 2007; Sun et al. 2009). Theresults from this study were in close agreement with theestimates for North China (Wang et al. 2012) and sug-gested that an average 1 m increase in pump lift wouldincrease the GHG emission rate by around 2%. Theresults also showed that energy consumption in theMinqin Oasis area (0.64 kg CO

2e m-3) was significantly

higher than that in Gansu province (0.57 kg CO2e m-3 in

2006) and North China (0.38 kg CO2e m-3 in 2006) (Wang

et al. 2012).The Minqin Oasis area has depended primarily on

Table 2 Total GHG emissions from groundwater and diverted water for agriculture in Minqin Oasis over the past 50 years

YearGroundwater level Pumplift Energy use rate1) (kWh m-3) GHG emission rate (kg CO2e m-3) Emissions from groundwater Emissions from diverted water

(m) (m) Diesel Electric Groundwater2) Diverted water3) (Mt CO2e) (Mt CO2e)

1961 2.29 23.82 0.43 0.26 0.38

1962 2.47 23.98 0.44 0.26 0.39

1963 2.71 24.21 0.44 0.26 0.39

1964 2.86 24.34 0.44 0.27 0.39

1965 3.00 24.47 0.44 0.27 0.39

1966 3.29 24.73 0.45 0.27 0.40

1967 3.43 24.86 0.45 0.27 0.40

1977 5.43 26.67 0.48 0.29 0.43

1979 5.71 26.93 0.49 0.29 0.43

1980 6.00 27.19 0.49 0.30 0.44

1981 6.06 27.24 0.49 0.30 0.44

1982 6.32 27.47 0.50 0.30 0.44

1983 6.58 27.71 0.50 0.30 0.45

1984 7.22 28.29 0.51 0.31 0.46

1985 7.32 28.38 0.52 0.31 0.46

1986 7.78 28.80 0.52 0.31 0.46

1987 8.42 29.38 0.53 0.32 0.47

1988 8.97 29.88 0.54 0.33 0.48

1989 9.65 30.50 0.55 0.33 0.49

1990 9.72 30.55 0.55 0.33 0.49

1991 10.83 31.56 0.57 0.34 0.51

1992 11.48 32.15 0.58 0.35 0.52

1993 11.87 32.51 0.59 0.35 0.52

1994 12.76 33.31 0.60 0.36 0.54

1995 12.74 33.29 0.60 0.36 0.54

1996 13.58 34.05 0.62 0.37 0.55

1997 14.47 34.86 0.63 0.38 0.56

1998 14.96 35.30 0.64 0.38 0.57

1999 15.82 36.08 0.65 0.39 0.58

2000 15.83 36.10 0.66 0.39 0.58 0.32

2001 16.41 36.62 0.66 0.40 0.59 1.14 0.38 0.047

2002 16.87 37.03 0.67 0.40 0.60 1.14 0.34 0.056

2003 17.66 37.75 0.69 0.41 0.61 1.14 0.31 0.045

2004 19.37 39.30 0.71 0.43 0.63 1.14 0.33 0.051

2005 19.16 39.11 0.71 0.43 0.63 1.14 0.34 0.051

2006 19.50 39.42 0.72 0.43 0.64 1.14 0.29 0.052

2007 20.55 40.37 0.73 0.44 0.65 1.14 0.25 0.051

2008 21.07 40.84 0.74 0.44 0.65 1.14 0.21 0.056

2009 22.35 42.00 0.76 0.46 0.68 1.14 0.14 0.074

1) The pump efficiency for diesel is 15% and that for electricity 40% while T&D loss is 15%.2) The distribution of electric and diesel pumps are set to 76 and 24% from 2000 to 2009 (Chai et al. 2010; Wang et al. 2012).3) The water transfer project has operated since 2001.

Fig. 2 The average groundwater levels between 1981 and 2009 infarming zones.



groundwater for irrigation since the 1980s. Popula-tion growth has intensified water use and energy in-puts and has enlarged the environmental footprint. AsFig. 3 indicates, the population and amount of arableland rapidly increased and peaked in 2008 (3.15×105)and 2002 (6.4×104 ha), respectively. The expansionof arable land required more water and, in many cases,more energy for abstraction, transportation and appli-cation to crops (Sauer et al. 2010). In addition, theexpansion of tube wells across the Minqin Oasis areahas been phenomenal since the 1970s, rising to al-most 10 000 in 2000 (Fig. 4). The number of aban-doned wells and their replacements has also grownsharply. Due to the absence of widespread publicprovisioning of irrigation and the failure of institutions,over 90% of the wells were drilled before a permitwas obtained (Wang et al. 2009). Digging tube wellsfor pumping groundwater, the most obvious responseby farmers to water scarcity, greatly increased en-ergy consumption. After implementing “conversionof cropland to forest and grassland” policies in 2002and “closing motor-well and reducing cultivated land”in 2004, the area under arable cultivation and the num-ber of tube wells showed obvious decreases (Figs. 3and 4). Over the last ten years, GHG emissions fromgroundwater have accounted for 65-88% of the totalemissions from agricultural water. As shown inTable 2, the total GHG emissions rose to 0.38 Mt CO

2e

in 2001, and then progressively declined from 2002 to2009 as the volume of groundwater being useddecreased. This change reveals that government poli-cies have had a favorable effect on total emissions byreducing water abstraction. However, energy use ef-ficiency has not been taken into account.

The GHG emissions from the Jingdian water diver-sion project varied from 0.047 to 0.074 Mt CO

2e as

the water input increased (Table 2). According to theMinqin Water Conservancy Bureau, 1.2 kWh of elec-trical energy is required to transfer one cubic meterof water for the project. The energy use rate fromdiverted water is 1.14 kg CO

2e m-3, which is signifi-

cantly more energy compared to groundwaterabstraction. It also shows a higher energy use ratethan in California (1.09 kg CO

2e m-3) for imported wa-

ter (Stokes and Horvath 2009). Long distance convey-ance (260 km) and a high pump lift (470 m), which are

the most energy intensive (per unit volume) processesinvolved in water diversion (Siddiqi and Anadon 2011),leading to enhanced energy use. The high constructioncosts and operational investment required for the project,accompanied by the rise in the water price, have had aninevitable negative impact on farmer income. Com-pared with the economic cost, the long-term energyuse challenge has always been neglected bypolicymakers. High energy consumption and the lowefficiency of water transfer facilities make itunsustainable. Outcomes will, however, depend onmany factors and a training program combining practi-cal experience in energy use and water-saving mea-sures would help guide practitioners and regulators.

DISCUSSION

On a global scale, about 70% fresh water is withdrawnfor irrigation, and the top abstractors are India, China

Fig. 3 Variations in population and arable land area from 1980 to2008.

Fig. 4 The variation in the number of tube wells in Minqin Oasisfrom 1981 to 2009.



and the US (Rothausen and Conway 2011). In mostregions of India, almost half of all energy produced isused for irrigation. Emissions from groundwater pump-ing for irrigated rice in India were 58.7 Mt CO

2e in

2000 (Shah 2009). With more than 40% energy con-sumed for extracting groundwater in Gujarat state, thishas had a serious impact on the energy balance (Gupta2002). Examples from Asia show that the energy con-sumed in irrigated rice production can be twice as highas in rain-fed rice, and groundwater irrigation can be25% more energy intensive than surface water irriga-tion (Mushtaq et al. 2009). In Saudi Arabia, 5% ormore of total electricity consumption can be attributedto water pumping (or alternatively, 10% of the totalfuel consumption in the country) (Siddiqi and Anadon2011). The US agricultural sector was estimated toaccount for 0.055 of national GHG emissions in 2007(National Farmers Federation 2007). Another study inCalifornia indicated that energy consumed in pumpinggroundwater for irrigation accounted for 90% of allelectricity used on farms in 2004 (Rothausen andConway 2011). Most studies show conclusions simi-lar to ours. Pumping water for irrigation in the regionswith greater dependence on groundwater, as one of theprimary energy consumers on farms, is energy-intensive. Direct energy consumption is primarily dueto operating pumps and farm machinery (Lal 2004;Topak et al. 2010). Improvements in energy use effi-ciency for pumping through better lifting devices, bet-ter maintenance or improved technical knowledge areimportant if the negative externalities in tube-well basedsystems are to be addressed (Chaitra and Chandrakanth2005). Greater efficiency in using either energy orwater will also help stretch the finite supplies of both,as well as reduce costs to water and power consumers.In the Minqin Oasis area, flood and/or furrow irrigationare the dominant irrigation methods. However, theyare inefficient and can accelerate soil salinization (Huanget al. 2011). The emission estimates for different irri-gation methods by Lal (2004) implied that flood irriga-tion is the most wasteful irrigation system. The failureto modernize water-sector technology to improve wa-ter and energy efficiency is evident in the region. Dripirrigation, low pressure pipeline irrigation and sprinklerirrigation are promising new methods. Some studiesfrom Australia (Jackson et al. 2010) and America (Lal

2004) indicated that the emission rate for drip irrigationwas far less than furrow irrigation (216 and 395 kg CEha-1, respectively). The application of pressurized sys-tems in groundwater irrigation and trickle systems couldreduce energy consumption by 12-44% and 27%,respectively. However, further research into the capitalinvestments and external energy requirements for inno-vative water-saving irrigation techniques in the MinqinOasis area is still required. With a stronger focus onenergy consumption by agricultural water use, there aremany challenges to generating standardized comparableestimates. There was a lack in standardized conversionfactors for different units (for example, kg CO

2e m-3,

kWh ha-1 or MJ mm-1) between different countries andregions. Assumptions about the efficiencies, powersources and distribution further complicate comparison.So, an annual survey about the distribution of electricand diesel pumps in the Minqin Oasis area is needed inorder to obtain more accurate data.

In response to increasing water shortages, farmershave changed cropping patterns by expanding the areasown with cash crops or higher-value-added crops.Econometric results have indicated that it is only whenirrigation managers and farmers are offered effectiveincentives do they systematically begin to reduce waterand energy use (Wang et al. 2005). Regardless of theeconomic benefits for the farmer, policies promulgatedto control the right to drill tube wells and extract ground-water have been difficult to implement in the region.Policy makers, therefore, need to use incentives to re-duce the adverse effects of water scarcity and encour-age energy saving. While economic incentives canchange use, public initiatives that address agriculturalwater regulation and balance short-term economic ef-ficiency with long-term energy sustainability are alsourgently needed (Mukherji 2007). However, organiza-tional barriers and poor institutional communicationmake policy development and implementationcomplicated. There are many overlaps among differ-ent ministries and agencies, particularly in irrigationsupply, groundwater management and the reservoiroperation of. Principal to one of them is the need toreform the institutional system so that collaborationamong multiple parties can be improved (Scott andPasqualetti 2010). Further, there is a need to advancethe understanding of water-energy relationships in or-



der to develop tools and mechanisms that will help real-ize energy savings as well as reductions in the signifi-cant risks associated with capturing savings.

CONCLUSION

Based on multiple data sources, water resource devel-opment over time and a systematic and quantitativeenergy consumption evaluation of agricultural water inthe Minqin Oasis region were presented. The resultsshow that groundwater energy use for agriculture hasgradually increased over the past 50 yr in the MinqinOasis area. Analysis of the available energy data revealedthat GHG emissions from groundwater accounted for65-88% of the total emissions from agricultural wateruse over the past 10 yr. The continual decline in ground-water levels has led to a substantial increase in energyconsumption. Groundwater depletion, exacerbated bya growing population and an expansion in arable land,remains the principal energy-water nexus challenge inthe Minqin Oasis area. Although diverted water addssignificantly to the available water supply, long distanceconveyance and a high pump lift mean it needs moreenergy inputs than groundwater abstraction. This re-gion has entered a circle of continual water-energy-water crises. Analysis of the factors affecting energyuse highlighted the importance of energy efficiency.The potential for energy-saving irrigation technologies,matching with cost savings, may be considerable. Theresponses and effectiveness of policies suggest thatbetter coordination among different infrastructuralagencies, economic incentives for farmers and publicinitiatives can make the water and energy sectors moresustainable over the long term.

MATERIALS AND METHODS

Study area

The Minqin Oasis region, with an estimated area of 2 868km2, is located in the lower reaches of the Shiyang RiverBasin, Gansu Province, north west China (102°54 -́103°49´E,38°27 -́39°07´N) (Fig. 5). Elevation ranges from 1 309 to1 459 m, sloping generally downwards from the southwestto the northeast. Surrounded by the Badanjilin Desert andthe Tenggeli Desert, it has a typical arid continental cli-

mate characterized by low rainfall, high evaporation, andprolonged drought periods. The average annual tempera-ture is 7.8°C. The mean annual precipitation is 110 mm, halfof which occurs in the summer season months of July toAugust, and the potential evapotranspiration is 2 664 mm.Soil types in the area include gray desert soil, gray-browndesert soil and aeolian sandy soil (Huo et al. 2007). Nativevegetation is mainly drought-resistant shrub, salt-resis-tant shrub and perennial sand-loving herbaceous plants,such as Elaeagnus angustifolia, Populus euphratica, andSalix purpurea (Kang et al. 2004).

The area was divided into five farming zones based ontheir agricultural development history and biophysical andsocio-economic characteristics (Fig. 5). Huqu is located ina lacustrine depression in the northern part of the oasisarea. Huanhe and Changning are in the upper part of theoasis area, Quanshan is located in the lower part and Baqu,the seat of local government, is located in the middle. Thereare 20 communities in the above zones, which occupy 16.6%of the region’s total area. The final zone, Muqu, with itsthree small communities, lies in a desert area and it focusessolely on animal husbandry. The oasis and agriculture arethe economic backbone of Minqin County, and plantationagriculture and stock husbandry account for 97% of thetotal agriculture income (77 and 20%, respectively) (Fenget al. 2011). The main crops are wheat, potato, oil crops,beets, and melons.

Data collection

Hydrological observation data, including annual rainwaterrunoff (1956-2009) and annual diverted water (2002-2009),groundwater exploitation (1960s-2009), average ground-water levels (1981-2009) and the number of tube wells (1970-2009) were provided by the Minqin Water ConservancyBureau. The groundwater levels of typical individual wellsin three farming zones (Baqu, Huqu and Quanshan) from1981 to 2009 were also archived by the Minqin Water Con-servancy Bureau. Specifically, the experiment sites in Baquinclude Jiahe, Sanlei, Xinhe, Shajingzi, and Xuebai with atotal 16 wells. The sites in Huqu include Dongzhen,Zhongqu and Xiqu with 15 wells. The sites in Quanshaninclude Quanshan, Datan, Hongshaliang and Shuangcike,totaling 12 wells. Irrigation data, including irrigation area,irrigation schedules and available water for irrigation (2000-2009), were collected from the Gansu Water ResourcesReport. Socio-economic data and other supplementarydata, population (1980-2008) and arable land (1980-2008),were supplied from the Statistical Bureau of Minqin County.

Energy use rate

In arid areas, energy consumption from water for irrigationis made up of two components: energy for pumping the



water, either from groundwater or from a surface source,and energy for distribution (Jackson et al. 2010; Topak et al.2010). The required energy per cubic meter of water variesdepending on the depth of the water being pumped, thetype of irrigation system (whether it is a gravity fed or apressurized irrigation system), and the water requirements(Lal 2004). The irrigation system for surface water in thestudy area was gravity-fed, so this study focused on en-ergy consumption from groundwater and diverted wateronly. The energy-use rate for pumping water for irrigationis determined using eq. (1), which calculated the energyrequired to lift 1 m3 of water (with a density 1 000 kg m-3 up toa height of 1 m at 100% efficiency, as being 0.0027 kWh(Rothausen and Conway 2011).

(1)

In order to obtain a more precise calculation, detailedknowledge of the pumping system, the transmissionmethod and the distribution losses of the power supplysystem are required. The pump lift was extrapolated usingthe relationship (eq. (2)) defined by the linear regression ofgroundwater levels (x) and the average pump lift (y) takenfrom 366 surveyed villages in North China (Wang et al.2012). With coefficient of determination R2=0.62, the equa-tion is valid, and the pump lift was closely related to ground-water level.

y=0.906x+21.75 R2=0.62 (2)Average groundwater levels were calculated using all

the individual wells distributed within the Minqin Oasisarea (Li and Xiao 2005; Sun et al. 2007, 2009; Minqin WaterConservancy Bureau 2010; Feng et al. 2011). The averagegroundwater level for each farming zone was also calcu-lated in the same way in order to demonstrate spatialvariations (Fig. 2). Pump efficiency varies dependingon the power source used, which are mainly electricityand diesel in the Minqin Oasis area. The overall effi-ciency of using electricity to power pumps is reducedby inefficiencies in the transmission and distributionnetwork for electricity (Wang et al. 2012). Because de-tailed efficiency data for the individual pumps wereunavailable, this study used efficiency data recorded inprevious studies in north China and India (Xia 2003;Sun 2006; Li et al. 2007; Shah 2009). The values of 15,40 and 15% have been adopted for diesel and electricitypump e f f i c i enc ies and T&D ( t r ansmiss ion anddistribution) losses, respectively.

Greenhouse gas emission rates

Energy use data for agriculture from numerous previousstudies were quoted in a large number of different units,such as volume (gallons or liters) of diesel; calories (kcal,Mcal); joules (MJ, GJ) and electricity (kWh). This made it

Fig. 5 The location of study area.



extremely difficult to compare the GHG emissions from dif-ferent farm practices (Lal 2004). Therefore, in the presentstudy, emissions data were converted into kilograms ofcarbon dioxide equivalent (kg CO

2e). The United Kingdom

Department of Environment, Food and Rural Affairs/De-partment of Energy and Climate Change GHG conversionfactors for diesel and electricity produced in China are

0.32021 kg CO2e kWh-1 and 0.94773 kg CO

2e kWh-1,

respectively. This study used these figures to derive theaverage GHG emission rates (kg CO

2e m-3) based on the

combination of power sources for pumps in the MinqinOasis area. Eq. (3), which is an expansion of Wang’s equa-tion (Wang et al. 2012), was used to calculate the GHGemission rates:

GHG emission rate =Energy use rateElectric

×0.94773 +Energy use rateDiesal

×0.32021 (3)

There has been a shift from diesel to electricity as theprincipal fuel for pumps in the Minqin Oasis area. Dieselengines for pumping were introduced into the region in thelate 1960s. The proportion of total energy supplied bydiesel increased steadily until the 1980s when a rapid shiftto electricity began, which continued up to 2010 (MinqinWater Conservancy Bureau 2010). The steep increase indiesel price over the last few years has also accelerated theprocess. Wang et al. (2012) suggested that three-quartersof the electrical pumps were, at the time, distributed innorth China. Chai et al. (2010) indicated that electricity hasbeen the dominant power for pumping irrigation water inthe Minqin Oasis area since 2000. As annual data on themix of power supplies being used to pump water was diffi-cult to obtain, this study assumed that the distribution ofelectric and diesel pumps was 76 and 24%, respectively,between 2000 and 2009, according to Wang et al. (2012)and Chai et al. (2010). It was not possible to identify themix prior to 2000, and therefore the emissions from ground-water before 2000 could not be estimated. When the se-lected figures were put into the equations for the energyuse rate by electricity and diesel from groundwater overthe past 50 yr, the GHG emissions from groundwater from2000 to 2009 could be obtained. As reported by the MinqinWater Conservancy Bureau, the energy consumption fromdiverted water was 1.2 kWh m-3. This allowed a calculationof GHG emissions from water diversion to be made usingeq. 3. The diesel component has not been taken into ac-count because the pump sets ran only on electricity.

AcknowledgementsThis research is partially supported by the Special Fundfor Forestry Research in the Public Interest, China(201304305), the National 973 Program of China(2009CB825103), the Shenzhen Science and TechnologyProject, China (ZYC201006170373A). We acknowledge,with gratitude, all reviewers and editors for their valuablecomments and suggestions.

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Water and Energy Consumption by Agriculture in the Minqin Oasis Region