Water and Energy Conservation of Rainwater Harvesting System in the Loess Plateau of China

Available online at www.sciencedirect.comJournal of Integrative Agriculture2013, 12(8): 1389- 1395心ScienceDirectAugust 2013RESEARCH ARTICLEWater and Energy Conservation of Rainwater Harvesting System in the LoessPlateau of ChinaJIANG Zhi-yun1.2, LI Xiao yanl.2 and MA Yu-jun1.21 State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, Beiing 100875, P.R.China2 College of Resources Science and Technology, Beijing Normal University, Beijing 100875, P.R. ChinaAbstractWater is the source of all the creatures on the earth and energy is the main factor driving the world. With the increasingpopulation and global change, water and energy conservation have become worldwide focal issues, particularly in thewater-stressed and energy-limited regions. Rainwater harvesting, based on the collection and storage of rainfall runoff,has been widely used for domestic use and agricultural production in arid and semiarid regions. It has advantages ofsimple operation, high adaption, low cost and less energy consumption. This study reviewed rainwater harvestingsystems adopted in the Loess Plateau of China and analyzed water use efficiency (WUE) for various rainwater harvestingtechniques. Supplemental irigation using harvested rainwater could increase crop yield by more than 30%, and WUEranged from 0.7 to 5.7 kg m-3 for spring wheat, corn and flax, and 30-40 kg m-3 for vegetables. Moreover, energy consumptionfor rainwater harvesting based on single family was compared with traditional water supply in the city of the Loess Plateauusing the life cycle assessment (LCA) method. Results showed that energy consumption yielded per unit harvestedrainwater was 25.96 MJ m-3 yr-1 which was much less than 62.25 MJ m-3 yr-1 for main water supply in Baoji City, ShanxiProvince, meaning that rainwater harvesting saved energy by 139.8% as compared to the main water supply system. Thisstudy highlights the importance and potential of rainwater harvesting for water and energy conservation in the nearfuture.Key words: rainwater harvesting, water saving, energy conservation, life cycle assessment (LCA)INTRODUCTIONsidering water productivity gains. Energy crisis is alsoserious, and about 1.6 billion people are lacking of en-Water and energy are two basic needs for human toergy for cooking, lighting and heating (Granit 2011). .survive. Unfortunately, water supplies are encounter-Precipitation is the main available water source in theing unprecedented challenge with the increasing demandterrestrial water balance (Oki and Kanae 2006), and itof industry, agriculture and booming urban populations .can be partitioned into two groups: blue water and green(UNESCO 2012). Hundreds of millions of people arewater (Falkenmark 1995). Blue water as the conven-still undergoing water scarcity and waterborne diseasestional water resource consists of surface water and(Gilbert 2012). Rockstrom (2003) reported that an ad-groundwater, and green water is considered to be theditional 5 800 km3 yr! is needed to meet the water de- evapotranspiration flow. Okiand and Kanae (2006) esti-中国煤化工Received 17 October, 2012 Acepted 10 January, 2013CNMHGCorrespondence LI Xiao-yan, Tel: +86- 10-588027 I6, E-mail: xyli@ bnu.cdu.cnMH02013,CAAS.. AII nghs reserved. Publishedby ElsevierLtd.doxi:10.1016/S2095-3119(13)60553-51390 _JIANG Zhi-yun et al.mated that blue water utilized by human beings was aboutergy consumption of an office building. However, it3 800 km3 yrl, only less than 10% of the maximum avail-has also been pointed out that rainwater harvestingable renewable freshwater, which was far lower thanactually had negative impacts on environment, par-the green water estimated to be 22 000 km3 yr'.ticularly in relation to energy consumption and CO2Therefore, green water has a great potential to be usedemission (Parkes et al. 2010). Hence, rainwaterfor solving water stress. Rainwater harvesting, as anharvesting, not to be a simple water saving technique,old and efficient approach to collect rainfall, can de-should be evaluated through taking energycrease unproductive evaporation, which means highlyconsumption, environmental impacts and other aspectsefficient use of green water. It has been widely used into account synthetically. Many previous studies havefor domestic use and supplemental irrigation in China,confirmed the positive effects of rainwater harvestingBrazil, Australia, Germany, India, Japan, New Zealandon energy conservation and environment, but differedand so on (Zaizen et al. 2000; Hills et al.2001; UNEPwith their different conditions, different systems and2002). Previous studies concerming rainwater harvest-different methods (Li and Gong 2002a; Mithraratneing techniques mainly focused on water saving, but theand Vale 2007; Grady and Younos 2008; Cortesi 2009;researches on energy conservation were still scarce.Angrill et al.2011; Ward et al. 2011). Energy conser-In order to build environmentally sustainable economies,vation for rainwater harvesting needs to be furtherit is necessary to integrate the water supply and demand, studied.energy and growing food into consideration. GradyThe history of rainwater harvesting techniques inand Younos (2008) had ever analyzed rainwater har-China may date back to 2700 yr ago extensively ap-vesting of a single family in Virginia, US, and the re-plied in the Loess Plateau (Li and Gong 2002a; Li 2003),sults showed that its energy efficiency was higher thanbut there were seldom systematic studies about rain-that of the groundwater in theory, but in practice, itwater harvesting until the 1980s (Li 1998). Previousdepended on the efficiency of the pump. Actually, rain- studies about rainwater harvesting mainly focused onwater harvesting systems, used concrete rain tanks,its benefits for solving water stress, improving agri-could decrease the life-cycle energy consumption bycultural production (Li 2003), adjusting agricultural3% and reduce the cost by 34% compared with mainstructure and promoting the ecological and environ-water supply in Auckland, New Zealand (Mithraratnemental conservation such as afforestation (Li et al.and Vale 2007). In addition, rainwater harvesting can2002; Cheng et al. 2005). However, few researchesreduce the emission of carbon dioxide compared withabout energy conservation for rainwater harvestingcompact water systems such as main water supplywere conducted in semiarid regions of China. This(Angrill et al. 2011; Ward et al. 2011). Furthermore, itpaper firstly aimed to review the development andhas a significant impact on the management of water-application of rainwater harvesting and analyze itsshed ecosystems, by storing more water in reservoir, water use efficiency in the Loess Plateau, and thenincreasing infiltration and groundwater recharge, recreated a scenario analysis of energy consumption forducing soil erosion, improving food security and eco-rainw ater harvesting by using the life cycle assess-nomic security and so on (Li et al.2002; Cortesi 2009).ment (LCA) method and compared rainwater harvest-In order to have a better understanding of the effectsing with conventional water supply system of the cityof rainwater harvesting on environment, researches arein the Loess Plateau of China.tending to have a quantified and precise evaluation.Rowe (2011) found 0.37 m3 of storage volume per 1 m2RESULTS AND DISCUSSIONof catchment area was the optimum maximum capacity.Ward et al. (201 1) proposed an improved method tobenchmark energy consumption and CO, emission forRainwater harvesting systems and its water userainwater harvesting systems. Results of improvedefficiency in the Loess Plateaumethod suggested that the energy consumption for rain-中国煤化工water harvesting system was only 0.07% of gross en-The brief histo.MYHCN M H Ginwater har-⑥2013, CAAS. Alights reseved. Published by EsevierLtd.Water and Energy Conservation of Rainwater Harvesting System in the Loess Plateau of China1391vesting systems Rainwater harvesting as a technique by Gansu provincial government was to build 100 m2of collecting rainfall runoff for domestic use and agri-concrete catchment in area, 2 rainwater storage tankscultural production (Frasier 1983; Reij et al.1989), has(40 m3) and irigate 1/15 ha of farmland for production.been extended to water-stressed regions around theUntil 2001, this program has achieved great benefit inworld for thousands of yr (Frasier 1980). China alsoeconomy and society. It helped farmers build 2.18 mil-has a long history of rainwater utilization for aboutlion rainwater storage tanks with the reservoir capacity4000 yr. An original rainwater utilization technique of 7.31x107 m', which could meet daily life demand ofnamed“"intertillage" was used to increase infiltration for1.97 million of rural people and irmrigate 2.36x10 ha crop-crop production (Gao and Li 2005). Another very oldland for production in Gansu Province (Gao and Li 2005).but still used flood diversion technique developed sinceWater use efficiency for rainwater harvesting sys-the Spring and Autumn period (about 2700 yr ago) called tem Rainwater harvesting as a technique of collcting“warping", has been widely applied in the Loess Plateaurainwater used to solve household water problems atof China. The underground clay-lined storage tanks ap-rural regions, has been successfully shifted to be apeared in Gansu Province 600 yr ago, the Ming Dynastysupplemental irigation tool for crop production. Pro(Li 2000b). Up to now, many other rainwater harvest-viding supplemental irrigation during water-stresseding techniques such as terraced fields, fish-scale pits andperiod of the crops is important to get a high sustain-mini-dams have appeared to store runoff, improve cropable grain production. Based on the research ofLi et al.production and prevent soil erosion (Li 2003). However,(2000), the relative water satisfaction of winter wheatwith the demand of increasing population and widespreadwas 62% of the whole phenology, but only 35, 40,droughts since the 1980s, people have been aware of the41 % for three important growth phases of jointing,potential of rainwater harvesting to solve water shortagegrain-filling and heading. Therefore, irigating duly isproblem (Li 2002b) and begun to integrate rainwaternecessary. With the limited rainwater and increasingharvesting with moderm agricultural techmiques (Xiao anddemand for water, rainwater efficient utilization is aWang 2003). Owing to simple operation, high adapta-major aspect of rainwater harvesting system to insuretion and low cost, modern rainwater harvesting systemsthe improvement of agricultural production, which canhave been widely built for household use and rainwaterbe assessed by water use efficiency (WUE). Waterharvesting agriculture (RHA) under the government'suse efficiency means the amount of dry matter createdsupport since the 1990s (Li 2000a, 2003). The systemsby per unit water. At present, combining rainwaterconsist of catchment, storage tank and supplemental ir-harvesting with crop supplemental irrigation, orchardrigation means made by modern accessible materials.supplemental inigation and industrialized agriculture (ikeRainwater catchment includes concrete yard, roof, earthygreenhouse) can generate different yard economicaland asphaltic road surface. Water storage tank mademodes. Fig. 1 shows that supplemental irrigation forfrom concrete or red-clay, 20-30 m3 in volumes, is usu-main grain crops of spring wheat, corn, millet, flax canally distributed alongside the yard or in the field approach-increasee yield and water use efficiency by 10.5-88.3%,ing the road. Rainwater harvesting technique combined19.6-88.4%, 20.5%, 44.7-120.6% and 0.7-5.2, 1.5-5.7,with efficient irmigation techniques such as drip irigation,0.9-1.6, 0.9-2.9 kg m-, respectively (Gao et al. 2005).sprinkler irigation has been used for crop, orchard andIt means rainwater harvesting system with supplemen-vegetable production (Gao and Li 2005). At present,tal irrigation has direct effects on crop production andrainwater harvesting systems have been successfully em-economical benefits. Moreover, supplemental iriga-ployed to solve water stress problems not only in thetion system has been also used for high value cropsarid and semiarid Loess Plateau such as Gansu Province,such as vegetables, fruits, flowers to increase farmer' SShanxi Province, Ningxia Autonomous Region and In-income in the semiarid Loess Plateau of China. Fig. 2ner Mongolia Autonomous Region, but also in the semi-shows water use efficiency for greenhouse vegetableshumid and humid areas such as Guizhou Province and of cucumber, tomato, watermelon, sweet melon underGuangxi Autonomous Region (Li 2000a, 2003). Forsupplemental in中国煤化工42.8-47.6, 40,example, the 121 rainwater harvesting program supported 33.3 kg m*', reYHCNMHGateruseefi-⑥2013, CAAS. Alights reseved. Published by EsevierLtd.1392JIANG Zhi-yun et al.ciencyof vegetables is higher than grain crops. It's ment and tank as the two main parts to rainwater har-surveyed that the output value per unit water of veg-vesting system. Details of the inventory analysis areetables was 65-240 CNY m-', which was higher thanshown as below.the output values of com and wheat of 2.9-6.3 CNY m3 LiBased on a survey of 30 sample families, Table shows2003). Naturally, in order to make use of the rainwater that energy consumption per unit water of a commonfor maximum benefits, agricultural structure has beenrainwater harvesting system in its life cycle processadjusted to change land use out of grain production for a rural family use is about 25.96 MJ m-3 yr-1 in theinto cash crops to increase farmers' net returns.semiarid Loess Plateau of China. Energy consumptionper unit water of catchment occupies 65.6% of theEnergy conservation for rainwater harvestingtotal energy consumption every year and the tank issystem in the Loess Plateau of Chinaonly 34.4%, which is corresponding to that the con-crete consumption of catchment is about 4 m' com-Based on the life cycle process of rainwater harvestingpared with the tank of 1.47 m'. Therefore, improvingsystem, an inventory table was obtained by analyzingrunoff efficiency to decrease the catchment area willthe resource consumption of the life cycle of the catch-have a more profound impact on reducing the energyconsumption.Making comparison of energy consumption be-■Yield increase percentage1tween rainwater harvesting system and main water0 Water use eficiency100-supply system in Baoji City, Shanxi Province of Loess80-Plateau (Wang et al. 2006), aims at revealing whetherrainwater harvesting system has positive effects on40energy conservation or not. Wang et al. (2006) also20used the life cycle assessment method to analyze ur-ban main water environment system in Baoji City, which(Spring wheat Com Milletwas divided into five parts of drinking water treat-Crop speciesment system, water distribution system, using system,sewerage system and wastewater treatment system.Fig. 1 Range of yield increase percentage and water use efficiencyFrom the analysis results, there were such consump-of main crops with supplemental irrigation. The yield increasepercentage of millet was 20.5 with no variation range denoted bytions as steels of 149.02 kt, cement of 73.38 kt andhorizontal line in the figure.energy supplies of 113.78 Gwh every year in the lifecycle process. Gross supply of main water was about1.17x108 m3 yr!. Eventually, the energy consump-tion per unit water of main water supply in the BaojiCity was calculated out to compare with rainwaterharvesting system as Fig. 3. Fig. 3 reveals that, in thelife cycle process of rainwater harvesting system,energy consumption per unit of catchment occupies20-17.03 MJ m-3 yr', while the tank is only 8.94 MJ m:3yr'. However, it also shows that energy consump-tion per unit water of main water supply system inBaoji City is about 62.25 MJ m:3 yr, which exceedsthat of the rainwater harvesting system by 139.8%,Cucumber Tomato Water melon Sweet melonand the distribution system occupies 33.75%, whichis higher than those of the other four systems. ItFig.2 Water use efficiency of vegetables with supplementalimplies that rai中国煤化Ihas profoundirrigation.effects on enerHC N M H Gs agreement⑥2013, CAAS. Alights reseved. Published by EsevierLtd.Water and Energy Conservation of Rainwater Harvesting System in the Loess Plateau of China1393Table Inventory analysis of the rainwater harvesting systemStylesLo(yr) CV(m2) MV(m) ECC (MJm) ECM(MJm") EC(MJyr) TEC (MJyr) RW (m) ECY (MJ m3 yr)Catchment203150456063096325.96Tank01.471.16331Lo, longevity; CV, concrete volume; MV, mortar volume; ECC, energy coefficient of concrete; ECM, energy coefficient of mortar; EC, energy consumption; TEC, totalenergy consumption; RW, rainwater; ECY, energy consumption per yr.MATERIALS AND METHODSo-Water use efficiency of the rainwater harvesting三.40-The benefits of rainwater harvesting on economy and ecol-ogy was analyzed by means of collecting the survey and20一statistic data and evaluating the results of previous stud-ies since the 1990s in the semiarid Loess Plateau of China.The collected information included the development, ap-plication mode, crops or vegetables yield, farmer' s incomeATATOTDTDIUsDRWT_TOTbrought by the rainwater harvesting. Furthermore, a se-RWHSMWSSries of basic experiments about rainwater harvesting con-ducted by Li (2000a, b) layed the foundation for quantita-Fig. 3 Comparison of energy consumption between rainwatertively analysising the water saving, production increase,harvesting system and main water supply system in Loess Plateau.economic and ecological effects. WUE as an indicator toRWHS, rainwater harvesting system; CA, catchment; TA, tank;build the relationship between crop production and waterTOT, total; MWSS, main water supply system; DT, drinking waterconsumption (Kramer and Kozlowski 1979) was used totreatment; DI, distribution system; US, using stage; DR, drain system;WT, wastewater treatment.assess water conservation of rainwater harvesting. Calcu-lation of WUE in this paper refered to the work of Li (2000b)as follows:with other researches (Grady and Younos 2008; RoweWUE=ηx,2011; Ward et al.2011).(1)^n+n2Where WUE is the water use efciency (kg m*), Y repre-CONCLUSIONsents the yield under the planting area, W. means the waterconsumption of crops, and n, and n, are the planting areaand catchment area, respectively.Rainwater harvesting was proved to be very helpfulfor water and energy conservation by assessing theCalculation of energy consumption for rainwaterwater use efficiency (WUE) and energy consumptionfor agricultural production in the Loess Plateau.harvestingSupplemental irrigation of rainwater for agriculturaluse will significantly improve the crop yield and in- Energy consumption was calculated via the LCA method.crease farmers' incomes. Furthermore, energy con-Firstly, it is necessary to set up a scenario and analyze itservation has been also confirmed by making the com-with LCA, and then making a comparison with energy con-sumption of main water supply systems in the semiaridparison of energy consumption per unit water for do-mestic use between the rainw ater harvesting systemand main water supply of the city. The results im-Scenario backgroundplied that catchment consumed more energy than thetank in the rainwater harvesting system.After detail field investigation, we set up a case study withConsequently, further studies about energy conserva-tion of rainwater harvesting systems should combinea typical rural family with 4 members in the semiarid Loesswith more systems such as supplemental irrigationPlateau of China Therni"中国煤化工systen con-sists of catchmer= :ollected rain-system and industrialized agriculture system.water transportedYHC N M H Gtilized for do-⑥2013, CAAS. Alights reseved. Published by EsevierLtd.1394JIANG Zhi-yun et al.mestic use. Rainwater catchment and storage rank are madeRainwaterof modern materials such as cement and mortar according tothe technical code (SL267 2001). Based on the technicalcode, it is easy to calculate the total water requirement of36.5 m3 by obtaining the daily water requirement per capitaCatchmentof 25 L for a single family home in semiarid Loess Plateau.MaterialsConsidering the runoff efficiency of 0.75-0.79, the catch-Water tank: Emissionsment area is evaluated to 100 m2 to meet the water demandand the volume of storage tank is 25 m3 (Gao and Li 2005).DisinfectionLCA process of rainwater harvesting systemUsLCA is recognized as a technique for evaluating a productwith its environmental impacts, by accumulating an inven- Fig4 Life cycle boundaries of rainwater harvesting system.tory of all the inputs and outputs of the system, assessingthe potential impacts of those inputs and outputs and ana-lyzing the results of the inventory and the effects on envi-verted into energy consumption by the relative energyronmental aspects (ISO 1997). Moreover, according to thecoefficients (Alcorn and Wood 1998).principles and framework of LCA (ISO 1997), a simple LCAmodel of rainwater harvesting system can be built as Acknowledgementsfollows.The study was supported by the National Natural ScienceGoal and scope definition Goal and scope definition is theFoundation of China (41025001 and 41130640), the Funda-starting point of an LCA studyDefining goal of this studymental Research Funds for Central Universities of China,is to ascertain the energy consumption of the rainwaterand Program for Changjiang Scholars and Innovative Re-harvesting system in the Loess Plateau. Based on the ISOsearch Team in University, China (IRT1108).(1997) documents, the scope should be defined with somemain issues of the function, the functional unit and theproduct system boundaries (Friedrich 2002). 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