1427 3 012 15,16 more 3 a,b,c Therefore, the significance 17 2012 Society of Chemical Industry per ton (50.98% green water, per ton (61.90% green water, c 3 3 and Xi-Ning Zhao The emphasis has been given to blue water 14 b,c – green water, while it consumed 7.84 Gm 12 3 Correspondenceto: Pu-TeWu,InstituteofSoilandWaterConservation,ChineseAcademy of Sciences and Ministry of Water Resources,[email protected] Yangling, China. E-mail: Institute of Soil andMinistry Water of Water Conservation, Resources, Chinese Yangling, Academy China of Sciences and Institute of Water Saving Agriculture inUniversity, Arid regions Yangling, of China China, Northwest A & F National Engineering Research Center for Water SavingYangling, Irrigation China at Yangling, Graduate University of Chinese Academy of Sciences, Beijing, China ∗ c a d b In addition, green waterand generally smaller has environmental a impact. lower opportunity cost (rainwater consumed during theblue water (surface crop or ground water production consumed in process) crop production) in and crop VWC. of green water for agriculture and ecosystem has triggered in conventional waterHowever, resources the planning usehigh opportunity and of cost blue management. andMeanwhile, large water this influence becomes is on thedevelopment the restricted limiting in environment. factor by water-scarce to areas. itsthe socio-economic terrestrial Green scarcity, ecosystem water and rain-fed has agriculture sustained worldwide. 11 www.soci.org Yu-Bao Wang Virtual 1,2 Therefore, 4 a,b,c∗ Meanwhile, other 2,6,7 Hitherto, most studies of virtual Pu-Te Wu, per ton (76.27% green water, 23.73% blue water) and 1294 m 10 3 – 4,5,8 Countries or regions with scarce water 3 a,b,c,d 93: 1427–1437 2013; virtual water content; green water; blue water; virtual water flows; water saving; China 2,5

2012 Society of Chemical Industry Since the 1990s, several researchers have estimated the virtual c water flow representsin the traded volume commodities. of water that is embedded blue water than with a no-grain transfer scenario in 2009. CONCLUSION: In order to guarantee foodwater security content in of China, the crops) government duringland-water should the resources improve grain availability, water production China productivity should process. (reduce guarantee virtual Meanwhile,green the under water grain-sown resources the area and preconditions in to southern of alleviate regions economic the for feasibility pressure taking on and full water advantage resources. of Keywords: At the same time, few studies focus on distinguishing green water J Sci Food Agric INTRODUCTION The amount of waterproduct consumed is in defined the production as process its of virtual a water content (VWC). (59.91% green water, 40.09% blue water). Meanwhile, China saved 11.47 Gm Abstract BACKGROUND: The disproportionate distribution of arable landfood and water resources security has become in a bottleneck China.resources for management guaranteeing Virtual in agriculture water and alleviate andand water blue crises virtual virtual in water water-scarce water content regions. of The tradeof wheat, present maize virtual theory study and water evaluates rice flows have at the related the green to provided regional the scale transfer a in of China. the potential It three thenRESULTS: solution crops assesses between The the to regions. water-saving national benefits improve average water virtual water content of wheat, maize and rice were 1071 m in China Shi-Kun Sun, and virtual water flows between regions (wileyonlinelibrary.com) DOI 10.1002/jsfa.5911 The virtual water content of major grain crops Research Article Received: 14 April 2012 Revised: 22 August 2012 Accepted article published: 11 September 2012 Published online in Wiley Online Library: 22 November 2 49.02% blue water ), 830 m water and virtual water trade haveglobal generally or been carried national out scale, at thus a of concealing countries the that regional consist differences of a wide range of agro-climatic areas. resources could import water-intensive productspressure to decrease on the theirwater own trade could water save water resources. globallyis if Meanwhile, a traded water-intensive the product from virtual productivity a to a region region with where lower water it productivity. is produced with high water 38.10% blue water), respectively. With the regional transfer of wheat, maize and rice, virtual water flows reached 30.08 Gm water flows embedded in thetural products importing between countries or or regions. exporting of agricul- the virtual water flow process may proveglobal significant water for use improving efficiency and alleviatingresources. pressure on local water studies have stressed that thelocal virtual water water scarcity trade and couldimporting improve alleviate high global water-intensive watera use commodities efficiency country (like by grains) orabundant from region water resources. that has a low VWC for commodities or (1) (4) (2) (3) the the and et al. n 2 R U ) ), a 1 including e − C), is the crop ◦ 27 C 28 − ◦ s 93: 1427–1437 the saturation e ( per ton) of crop, as follows: s Shi-Kun Sun e 3 2 × the psychrometric Y )and ), 2013; 2 γ 1 1 U − ), − ) 1 2 is the reference crop c × − ha ) d 0 ET ); evapotranspiration over 3 27,30 0 2 1 p 1 273 − − = 0.34U ET 900 + Y d
log 2 China Statistical Yearbook T ( ha 23,29 + × CWR × 3 c 1 × J Sci Food Agric ( K = 10 γ γ = ). 1 = the actual vapor pressure (kPa). + c + 26,27 − a ) VWC ET e G the average air temperature ( CWR − T n ), R ( 1 − C ◦ is the crop coefficient; ET 0.408 c is the slope of the vapor pressure curve (kPa = K 0 ) over the crop-growing period: ET c. The green and blue VWC for a crop is calculated as the green and The CWR is calculated from the accumulated evapotranspiration Chinese agricultural statistics data. net radiation at the crop surface (MJ m wind speed measured at 2 m height (m s vapor pressure (kPa) and blue water in crop waterunitarea.ThevaluesforgreenandbluewaterinCWUarecalculated use (CWU) divided by the crop yield per (ET CWR is the crop water requirement (m Climate data Climate data were taken from the CLIMWAT database, Methods The components of crop VWC are the typein of water the resources used crop growthor process, groundwater) including and blue green water watera (effective (surface rain-fed precipitation). water scenario, Under green watercrop. The is VWC of equal primary to crops can themethodology be calculated developed total according by to VWC Hoekstra the of and Hung the monthly averageminimum maximum temperature, relative humidity, temperature,hours wind and precipitation. speed, monthly sunshine average Agricultural data The agriculturalagricultural data, inputs (fertilizers, including pesticides,etc.) crop agricultural (Table 1), machinery, were yield, taken from the sown area and where VWC denotes the virtual water content (m yield per unit area (tons ha where FAO Cropwat8.0 model CROPWAT is aand decision Water support DevelopmentOrganization tool Division of developed (FAO). the byagronomists Food It the and and Land can irrigation Agriculture crop engineering help water personnel requirements agricultural to andsoil, climate calculate irrigation meteorologists, and crop requirements data. based on evapotranspiration (mm) and is calculatedPenman–Monteith according equation to as the follows: FAO the crop-growing period (mm) is calculated as follows: where the factor 10 is intendedwater to volume convert per water land depth surface (m (mm) into where constant (kPa 25 The 21 www.soci.org ha, which 6 2012 Society of Chemical Industry 10 c × In order to achieve this Matters of food security in 17 20 In this context, determining 19 – The present paper first provides a 23 15,17 This shift will have a significant effect on By virtue of favorable climatic conditions 23 22 24 Agriculture, as the primary consumer of water around the In order to explore the foregoing problems, the present paper accounts for about 60%water of resources total in arable northern regions landof is of only China. China, 19% while of In totalaccounts the for contrast, quantity 40% of the total arable cultivated landresources of in China; land however, southern the in water regionsresources make southern in up regions over China. 81% of total water purpose, it is important to quantifyblue the and amount green and water proportion in of crop production. world, is increasingly squeezed by the demands fromand other sectors threatened by climatic change. the redistribution of arable land and watertransfer resources in of China. grain The fromdiversion north from northern to to south southern regions. will Thisup diversion cause brings several water resources issuesdifferences that of green and need blue VWC to for the majoramount be grain of crops; virtual (2) considered: the water flows (1) related toand the the (3) grain any transfer regional water process; saving benefits related toregions. grain transfer between and water resources,been the overwhelmingly southern superiorsouthern in regions regions food have used production;Since traditionally to the hence be 1990s, the the however,the this major influence of situation economic, grain social has and ’export’ other changed. factors,and the Owing regions. grain arable to land production of southernover regions the last have 20 been years, decreasing the and the grain southern ’importer’. regions have turned into Data The model and data used in the study include the following: wileyonlinelibrary.com/jsfa (Fig. 1). DATA AND METHODS Study area The study region contains 31 provinces,municipalitiesinmainlandChina.Theyaredividedintotwoprimary autonomous regions and regions and eight sub-regions according to geographicalclimatic location, conditionsThe and northern agricultural regionsHuang-huai-hai include Region production Northregions and conditions. China, contain Northwest Northeast Southeastof China. China, China, the The the Yangtze southern Middle–Lower River, Reaches South China and Southwest China concerns among scholars. China have attracted much attention aroundthe the world. uneven However, distribution ofbecome arable a land bottleneck and waterArable for resources guaranteeing land has food iswater security resources mainly in are located concentrated China. in in the southern the regions. northern regions, while total arable land in northern regions was 73.03 takes wheat, maize andmajor grain rice crops in as China the andtotal account research national for grain more objects than output. which 86% of are the how to reduce blue water consumption inand agricultural divert production the blue waterof to other countries sectors has and become regions the target worldwide. more detailed analysis of the green andand blue rice VWC at of the wheat, regional maize scalewater in China. flows It and then evaluates volume theof of virtual the water three crops savings between related regions. to the transfer

1428 1429 (7) (8) ) 3 7 6 m . .1 .3 . 5 9 51.3 58.6 21.5 77.2 32 73 46 applied (10 Irrigation kW) 3 ) ) eff P eff 3 966 9 118 3 426 5 228 7 655 61 663 12 375 26 753 P − , Power of c c agricultural wileyonlinelibrary.com/jsfa ET ( machinery (10 0, ET ( min = max Agricultural inputs tons) = 3 green Pesticide (10 blue ET ET 27,31 tons) 3 is the effective rainfall over the crop-growing period www.soci.org fertilizer Chemical (10 eff P By using the CROPWAT model combined with CLIMWAT (mm). database, the crop water requirement (CWR), effectiveirrigation rainfall requirements and of wheat, maizefor and each rice sub-region. were Subsequently, calculated accordingthree to crops in the the yield producing ofwheat, region, maize the and the rice green were and calculated. blue In order VWC to of further analyze where CROPWAT model: tons) 3 (5) (6) blue Yield (10 2012 Society of Chemical Industry and CWU c green Y green blue Y ET ET × ha) × 3 are green and blue water 10 10 = blue = per ton), CWU 3 because of limited data availability the study did not include Hong Kong, Macao and Taiwan. blue green Y Y and ET are the green and blue components, 5 651 4 376 7 2 777 22 547 4 948 195 Sown area (10 Note: 869 1685 17 3 382 8 551 109 1 429 32 CWU CWU blue 2 green Wheat Maize Rice Wheat Maize Rice during the crop-growing period can = = blue 93: 1427–1437 blue green and VWC ), and ET 1 VWC 2013; − VWC green ha Sown area, yield of the three crops and agricultural inputs of each region and ET 3 Study area partition. green ET Because of limited data availability theM&L, study Middle–Lower did not Reaches. include Hong Kong, Macao and Taiwan. Sub-regions North China Table 1. Huang-huai-hai Region 13 548 9240 3 036 74 750 52 312 19 926 16 978 2 050 Northeast China 707 10741 3 806 2 502 65 047 26 731 6 274 175 Northwest China 3 088 2511 281 11 722 13 260 1 943 4 391 70 Southeast ChinaM&L of Yangtze RiverSouth China 3 098 103 1126 67 11 399 13 325 1 907 5 640 409 76 957 268 10 249 12 585 442 2 260 131 Southwest China 2 200 3844 4 419 6 367 18 060 31 096 5 863 139 J Sci Food Agric are green and blueperiod (m water consumption over the crop-growing by computing the accumulation ofthe daily crop evapotranspiration growing over period: Figure 1. Virtual water content of major grain crops in China be estimated using the Food and Agriculture Organization’s evapotranspiration over the crop growing period (mm). respectively, of VWC for a crop (m where VWC et al. blue — — VWC 93: 1427–1437 Shi-Kun Sun green 2013; the precipitation in northern per ton) in the eastern part of 21 , VWC VWC 1131 627 504 1293 855 438 3 J Sci Food Agric blue — 1190 — — 1321 — VWC per ton. 3 per ton) 3 green China Water Resources Bulletin The national average green water proportion of VWC for wheat, regions only accounted forwhole 31.51% country. of total Inaccountedfor68.49%oftotalprecipitationinChina. precipitation contrast, of the precipitation Consequently, the green in water proportion of crop southern VWC in southernbe regions regions would higher than that in northern regions. maize and ricewas showed in that maize VWC the (76.27%),(50.98%). followed highest by This share rice (61.90%) suggests of and thaton wheat green the green water growth water ofranked last. in Such maize variability was China. mainly mainly caused relies by Riceseasonal the distribution non-uniform of precipitation. took Precipitation is concentrated secondmostly place in and summer wheat coincides and with autumn the (from growingChina. May Thus period the to of green water maize October), proportion inOn in and maize the VWC most it was contrary, regions higher. due of period to for the wheat (particularly limited forproportion rainfall winter of during wheat), wheat the the VWC green growing (Fig. was water 3). much smaller than that of maize The green and blue VWC of wheat,The maize and analysis rice of greenshowed and that the blue green VWCgradually water for proportion from wheat, in northern maize each toproportion crop and of southern increased rice green regions. water Forwhile in example, it wheat was VWC the more was thanThe 18.62% 80% regional in variability in Beijing, of most green of wateraccordance southern with proportions the regions in distribution VWC (Fig. of was precipitation 3). in in The China (Fig. 3a). regions withproportion abundant of green precipitation water inregions usually crop is VWC. have Precipitation far in greater a southern thanthe that high in northern regions. According to resources than wheat andas maize, extensive the sown as area thatrelatively of of low rice (less wheat was than and not 1200 maize. m The VWC of rice was Northeast China, Middle–Lower Reaches of thethe Yangtze eastern River and part of Southwestof China. VWC In for contrast, rice thesouth were high of values located Xinjiang Uygur in Autonomous Region the (Fig.more west 2c), than which of 1600 were m Inner Mongolia and VWC VWC 3 3 3 www.soci.org blue — 844 — — 801 — 2012 Society of Chemical Industry VWC c per ton). These 3 green Wheat Maize Rice per ton. The high values of 3 VWC VWC 975 — 214.150.17 284.03 0.42 447.84 131.58 0.80 174.70 0.15 192.36 0.25 99.07 252.08 1.22 245.37 0.07 0.35 0.41 1184 968 16 919 900 19 1472 1085 387 13621538 340 5311103 1022 1060 1007 819 43 883 599 605 1050 220 988 278 1390 62 1285 521 527 1336 869 974 758 362 1450 827 623 762 758 4 1408 327 1081 1007 446 561 1373 351 1022 1071 546 525 830 633 197 1294 801 493 per ton). The CV of maize (0.15) took 3 per ton) and rice (1294 m per ton) was approximately 1.60 times that 3 3 per ton. The VWC of maize was between 583 3 per ton, and the spatial distribution was slightly 3 The green and blue virtual water content (VWC) of each crop in sub-regions (m 2,13 Figure 2(a) shows that the regional differences of VWC for SD CV Hoekstra and Hung (2002) 690 — National average Liu (2007) Southwest China SD, standard deviation; CV, coefficient of variation; M&L, Middle–Lower Reaches. South China North China Northeast China Huang-huai-hai RegionNorthwest China Southeast China 960M&L of Yangtze River 512 1025 839 448 759 186 656 665 659 103 1311 6 805 506 Sub-region Table 2. results are approximately consistentstudies. with the results of former second place, followed by VWC of riceVWC (0.07). The of national wheat, average maize and rice were as follows: wheat (1071 m of the lowest value (960 m wileyonlinelibrary.com/jsfa per ton, and these values were mainlythe located in western Northwest part China, of InnerChina Mongolia (Fig. and 2b). most As parts of rice Southeast production needs more water and heat per ton, wereHuang-huai-hai located region, in the theReaches western eastern of part part the of Yangtze ofthe the River Northeast high and Middle–Lower values China, Southwest of China. VWC In contrast, for maize reached more than 1000 m per ton), maize (830 m RESULTS VWC of wheat, maize and rice Table 2 shows the greenin and each blue VWC region. of Owingcrop wheat, yields maize to and and crop the rice management differences betweendifferences of regions, in VWC the for regional climatic wheat, maize condition, coefficient and rice of were variation significant. The (CV) ofhighest value wheat (1538 VWC m reached 0.17, and the the regional differences of VWC for the three crops,and meteorological yield dataprovinces were from used to morerice. calculate than Kriging the VWC interpolation 100 ofthe technology wheat, sites spatial was maize distribution used in and maprespectively. for the of generating VWC producing for wheat, maize and rice VWC for wheat werewest mainly of distributed Inner in Mongolia, Northwest theof China, south the the of Yangtze the River and Middle–Lower themore south Reaches than of 1800 Southwest m China, and were different from that of wheat. The low values, less than 800 m wheat were significant. Thethe VWC eastern of part of wheat Northeast was China,of Huang-huai-hai relatively the region, low Middle–Lower parts in Reachesprovince of being the less Yangtze River than and 1000 Sichuan m and 1341 m

1430 1431 the regions where wheat wileyonlinelibrary.com/jsfa 32 the region where the sown area was less Note: www.soci.org southern regions since 1990, suchChina. as South Since China and the Southeast grain beginning production regions of were located in the Northeast China,huan-hai Huang- current region century, and the the Middle–LowerRiver. major According Reaches to of information the providedGrain Yangtze by and the Oil China National Information Center, per ton): (a) wheat; (b) maize; (c) rice. 3 2012 Society of Chemical Industry c (c) (b) (a) 93: 1427–1437 2013; ha and is deemed ’no planting’. 3 Spatial distribution of VWC of wheat, maize and rice (m ×10 than 10 J Sci Food Agric Virtual water flows related to grain transfer betweenThe regions imbalance between graingrain supply transfer between and regions. demand Asproduction can will be in lead seen northern from to regions Fig.the has 4, grain past increased 60 substantially years, over hai such as region, in whereas Northeast there China and has Huang-huan- been an obvious downtrend in Figure 2. Virtual water content of major grain crops in China et al. 93: 1427–1437 Shi-Kun Sun 2013; J Sci Food Agric www.soci.org 2012 Society of Chemical Industry c (d) (c) (b) (a) Distribution of precipitation and green/blue water components of VWC: (a) precipitation distribution; (b) wheat; (c) maize; (d) rice. Figure 3. wileyonlinelibrary.com/jsfa

1432 1433 wileyonlinelibrary.com/jsfa www.soci.org Demand and supply analysis of wheat, maize and rice in China Therefore, the transfer of grain fromwould northern to have southern a regions significant impactin on northern the regions. water resources situation Water savings related to grain transferin between China regions Through ’importing’ virtual water embodiedregion in could grain, a save nation the or water required to produce those grains Figure 5. (megatons) (2009). ,ofwhich 3 2012 Society of Chemical Industry c Agriculture is a high water-consuming 21 93: 1427–1437 , which occupied 11.47% of total water supply 3 , and the Middle–Lower Reaches of the Yangtze 3 2013; . The Huang-huai-hai region was the primary wheat- 3 Grain production of China in different periods (megatons). The above results showed that with the regional transfer of As can be seen from Table 3, northern regions were the major ’exporting’ region (Fig.maize-exporting region. The 6a). volume of virtual Northeastto water flows maize related China ’export’ from was Northeast China the was 13.30 Gm major 68.57% was green water (Fig.southern 6b). Rice regions, was so mainly it plantednorthern was in regions. usually the During this transferred process, from the amountflows southern of was to 1.2 virtual Gm water River was the major ’exporting’ region (Fig. 6c). wheat, maize and rice inreached 2009, 30.08 Gm the volume of virtual water flows J Sci Food Agric output exceeds demandhai were region, mainly Northwest locatedoversupply regions and in were Huang-huai- Southwest distributedChina, China; in Huang-huai-hai North region, For Northwest China,China. maize, For China Northeast rice, and the the surplus Southwest China, regions Middle–Lower were Reaches distributed of the in Yangtze River Northeast China and Southwest (Fig. 5). Based onmaize the and calculation rice results above, of virtual VWC watercan for flows be obtained related wheat, (Table to 3). grain transfer grain-’exporting’ regions in China.flows The related to volume the of9.98 transfer virtual Gm of water wheat from north to south was Figure 4. Virtual water content of major grain crops in China in northern regions. sector; the production of grain would consumewater large and quantities of put pressure on water resources of northern regions. ) 1 c − et al. blue −8.03 −6.82 −0.53 −5.30 −0.02 −12.06 VWC 93: 1427–1437 −8.86 −0.72 −5.97 −2.64 green −11.61 −18.02 Shi-Kun Sun compared with a 2013; in Northwest China. 3 1 − . Green water generally 30.08 18.02 12.06 −1.25 −2.66 VWC VWC −19.64 −15.68 −11.27 −30.08 9,18,36 blue J Sci Food Agric water, it resulted in a considerable 3 −7.11 −5.95 −0.41 VWC green 35 −4.93 −0.79 −11.61 .04 .24 2.97.27 4 11.29 5.13 6.16 .20.79 0 0.41 .80.96 1 2.84 .20 0.79 0.41 .34 7.50 3.84 19.78 12.98 6.80 .56 .01.31 3 1.70 19.42 11.66 7.74 −1.20 VWC VWC −12 −17 Crop water consumption mainly depends on the local blue .96 11 .48 .39 5 .82 2 Although the virtual water trade for the three crops between According to the virtual water theory, the VWC of a crop −4.18 −0.26 1 −3.37 4 −7.82 1 −0.02 — — — ) VWC Therefore, regional differencesmainly in VWC by for theamong wheat diversities regions. were of caused climate condition and cropregions in yields China saved 3.63 Gm water and virtual waterto trade improve theory global water provide use a efficiencyand for feasible to agricultural solution production alleviate the pressurecountries or on regions. water resources in water-scarce in Huang-huai-hai region and 3795.98 kg ha agro-meteorological condition and irrigation system. On the other hand, crop yield per unit was influenced notmeteorological only condition by the but local agro- also bylevel, the such as agricultural agricultural inputs. production The crop evapotranspiration (ET has a lower opportunity costThus and we smaller are environmental impact. committedwater to in increasing crop thethe VWC national proportion and level, of reducing however, green regions blue the to transfer water of southern consumption. grainblue regions At from water. will northern As increaseabundant the mentioned green consumption above, water of resources,water the in and crop southern the VWC regions is proportionin much have of northern higher in green regions. southernnorth regions Thus will than the reduce that blue transfer waterprecondition of consumption. of Therefore, grain economic under from the feasibilityavailability, and south China land–water to southern should resources regions to guarantee take full advantageMeanwhile, the of green the water grain-sown green resources. VWCsoil area of characteristics, conservation in a practices cropcrop and is crop and also species. soil The influenced properties by have the a significant influence on surface no-grain diversion scenario inregion would 2009. not The be concerned ’importing’ withproduced country whether by the or using grain green has or been or blue region, water but in nevertheless the thisa exporting has country global significant implications or from national perspective depends on the crop waterwater) consumption over (blue the water crop-growing and periodarea. green and the crop yield per unit net national blue water loss of 7.84 Gm of wheat in thewas Huang-huai-hai 583.82 region was mm 529.67 inintense mm, evaporation. For Northwest while the yield China it of wheat, due it was to 5517.42 kg sparse ha rainfall and 3 .48 7 green of The −9.12 −1.69 −2.68 −2.64 3 −13.48 Virtual 16 of blue www.soci.org 3 of water .08 7.60 3 3 33,34 2012 Society of Chemical Industry −1.95 −6.05 −2.66 ; although it VWC VWC of water (1.33 −13.30 3 −21.30 c 3 more blue water more blue water. 3 3 blue .42 .89 — — — 7 .96 .65 .99.17 4 3.21 0 .66 8.70 5.31 3 .65 21.30 13 water by ’importing’ −6 −4 3 VWC water in China. From the 3 .48 0 .16 1 .28 1 .05 2 .33 4 green per ton, of which 44.56% was Wheat Maize Rice Total −7.97 −5.33 3 blue water). per ton, of which 33.87% was blue 3 3 .90 0 more blue water was consumed than 4.05 2 0 4.27 2 5.71 3 3 −9.98 VWC VWC −14.93 of green water, it used 7.26 Gm 3 Virtual water flows related to grain transfer between regions (Gm of green water, while consuming 7.84 Gm green water and 0.84 Gm 3 3 Based on the principle mentioned above, an analysis was In summary, the virtual water trade for wheat, maize and rice Northeast China ’—’denotes no virtual water flows; ’−’ denotes virtual water output; M&L, Middle–Lower Reaches. North China Sub-region Table 3. Huang-huai-hai Region Northwest China — — — Total of Northern Region Southeast China M&L of Yangtze River — — — 11 South China Southwest China — — — Total of Southern Region 9.98 5 water was savedblue at water the only, national 1.42 Gm scale. However, if we look at loss per ton at theblue national water, scale. transfer However, of if rice from the theYangtze focus River Middle–Lower is region to Reaches only Southwest of China on the would save 66 m The transfer of rice between regions saved 2.17 Gm blue water. In thethe Middle–Lower VWC for Reaches rice of was1293 the m Yangtze River, water. Southwest China could save 1131 m wileyonlinelibrary.com/jsfa DISCUSSION The dominantmanagement for challenge comingto for generations meet is food agricultural how demands to of water the secure rapidly water resources expanding world. in their ownin country Southwest or China region. was 1131 For m instance, the VWC of rice water per ton of rice at the national scale. conducted to determine whetherbenefits there of were virtual any water waterregions flows savings from related the to national grainTable perspective. transfer 4. between The Through results wheat are transfer shown in between regions, 3.01 Gm saved 5.71 Gm growth of population andwater climate requirements for change grain may production in further the increase future. 1 ton of rice from the Middle–Lowerregion. At Reaches the of national the Yangtze scale, River from however, the when rice Middle–Lower was transferred ReachesSouthwest of China, the there Yangtze wererice River production no region in the water to Middle–Lower saving Reaches ofregion benefits the Yangtze needed because River morediversion water of than rice from that theRiver in Middle–Lower region Southwest Reaches to China. of Southwest the China The Yangtze would lead to 162 m than with a no-grain transfer scenario. Gm perspective of proportions of green and blueGm water, it saved 11.47 between regions had saved 3.63 Gm with a no-grainflows transfer embedded scenario. in For maizea maize, transfer considerable between the net regions virtual national resulted water water in loss of 1.55 Gm

1434 1435 wileyonlinelibrary.com/jsfa www.soci.org 38 Currently, most of the studies related to virtual water focus on fresh water availability. However, inresources, countries reclaimed with limited water water may contribute considerably to the water use efficiency by maximizingas plant the transpiration productive and minimizing flow non-productive water of flows, including water soil evaporation, runoff and percolation beyond thezone. root ): (a) wheat; (b) maize; (c) rice. 3 2012 Society of Chemical Industry c Therefore, better green water 37 (c) (b) (a) 93: 1427–1437 2013; Virtual water flows related to grain transfer between regions (Gm – in some cases up to 40%. J Sci Food Agric runoff, transpiration, evaporationrecharge. Good and husbandry of potential soil,management) would water groundwater increase and groundwater crops recharge (greenbase and flow. water stream Several studies showed that,onerosion,mulchingisabletoreducesoilevaporationsignificantly besides the positive effect Figure 6. Virtual water content of major grain crops in China management would contribute to the improvement of green , Ecol Glob et al. blue −0.96 −3.04 −0.06 −0.52 VWC 30:1413–1430 93: 1427–1437 −5.29−0.67 3.11 3.41 −0.02 −6.95 5.90 green Virtual Water Trade: Shi-Kun Sun −11.47 7.84 2013; World Dev −0.30−2.18 0.66 −0.54 −0.02 0.04 −1.05 −2.28 0.76 −3.63 VWC VWC . Value of water research report Proceedings of the International blue J Sci Food Agric −0.95 −0.07 −0.84 −0.62 VWC 49:203–209 (2004). green 15:45–56 (2005). −1.04 0.66 −1.03 0.14 −1.33 68:1454–1464 (2009). VWC VWC −0.38 −0.89 −0.30.65 0 −0.02.05 0 −2.17 −0.58.04 0 ) 3 Virtual water trade to Japan and inProceedingsoftheInternationalExpertMeetingonVirtualWaterTrade the World, in 12–13 December 2002, ed. by221–235 Hoekstra AY. (2003). UNESCO-IHE, Delft, pp. for southern Mediterranean(2002). countries. Expert Meeting on Virtual Water Trade series no. 12,(2003). UNESCO-IHE, Institute for Water Education,Spanish Delft grain tradeEcon consistent with relative water scarcity? Water Sci Technol Eastern economies? OccasionalAfrican paper Studies (SOAS), 3, University of School London (1997). of Oriental and virtual water flows between nations in relationtrade. to international Value crop of Water ResearchDelft (2002). Report Series No. 11, UNESCO-IHE, international virtual waterEnviron Chang flows in relation to crop trade. blue .64 .41 — — — 2.74 .20 .26 8 Oki T, Sato M, Kawamura A, Miyake M, Kanae S and Musiake K, 5 Yang H and Zehnder AJB, Water scarcity and food import: a case study 6 Hoekstra AY, Virtual water trade, in 7 Novo P, Garrido A and Varela-Ortega C, Are virtual water ’flows’ in 4 Oki T and Kanae S, Virtual water trade and world water resources. 1 Allan T, ’Virtual water’: a long term solution2 for water Hoekstra short AY Middle and Hung PQ, Virtual water trade: a quantification3 of Hoekstra AY and Hung PQ, Globalization of water resources: VWC ACKNOWLEDGEMENTS ThisworkisjointlysupportedbytheSpecialFoundationofNationalScience and Technology SupportingProject Plan (No. (2011BAD29B09), B12007) 111 and and basic the operational SupportingUniversity. cost Plan of of Young research Elites from Northwest A & F REFERENCES in agricultural water resources management. Grain diversionnorthern from regions to southern regions wasdistribution disproportionate to of the water resourcesguarantee food in security in China, China. the government Therefore, shouldwater use improve efficiency in (reduce VWC of order crops) during to grain production through the applicationand of better management water-saving ofis irrigating all necessary agricultural techniques inputs. to Meanwhile,through alleviate it stabilizing the grain-sown pressure areasthe on precondition in of economic southern blue feasibility and land–water regions water resources availability. under resources 43 green For The −1.81−0.67 0 3 −3.22 3 −5.71 7 China 45 39 www.soci.org 46 40,41 .74 2012 Society of Chemical Industry VWC VWC −1.17 −0.02 c blue −0.51 — — — — — — −2.42 — — — VWC found evidence that long- −’ means with grain transfer between regions, this will save water at the national scale. green 44 Wheat Maize Rice Total −2.43 1.80 −0.02 −2.71 2.57 −4.43 1.42 1.55 VWC VWC −0.63 −0.54 −0.14 −3.01 −1.70.72 0 While the inefficient treatment and recycling 42 The volume of water savings related to grain transfer between regions (Gm in China. 3 In addition, the virtual water metaphor is not sufficiently broad Southeast China Northeast China Northwest ChinaM&L of Yangtze RiverSouth — China — — — — — — 2 — — Huang-huai-hai Region — —Southwest ChinaTotal — — — — — — — — — — — — — — — — ’—’denotes there is no grain transfer; ’ North China Sub-region Table 4. term irrigation of aridaccumulation of loess salts soil and surfactants with inin the wastewater soil soil, may causing properties changes resultneeds and in to toxicity be to properlyirrigation. plants. Meanwhile, treated Therefore, how before wastewater wastewater is reusewater involved content for and in virtual water crop the flows needs virtual to purposes be studied of in future. in scope toadvantage. In be particular, virtual considered water discussions and thedo calculations same not consider conceptto opportunity as determine costs, comparative the which optimal must allocation be considered of scarce resources. wileyonlinelibrary.com/jsfa CONCLUSION Food security has significant implicationswater for resources China, become especially increasingly as scarce.to The be issues concerned we with need aredemand for whether grain production the and whether water the resources distribution ofplanting meet grain is reasonable. the Thus to determine theof green and crops blue and VWC the virtual waterfor flows providing between references regions is for important decision making for the government The study conducted by Gross water budget and alleviate stress on fresh water resources. use of wastewater forwidely irrigation used. is It one is of particularly important the in methods arid currently regions. is one offor the which countries providingchallenging that issue. sufficient The annual suffer discharge water of domestic a wastewater41.4 for is Gm serious different water sectors shortage, is a example,thepresentpaperfocusessolelyonthephysicalefficiency of water use in differentaccount regions the in regional China differences and oflimitation does of economic not the efficiency; take present this into study is andmake a further reasonable research decisions is about needed. the To only use the of water technical resources, efficiency not ofvalue water of water use, in but different also regions, should the be economic considered. of wastewater resultaggravation of in water crisis, the there is pollutionthrough a great improving of water-saving potential domestic water wastewaterrate areas centralized and and treatment reclaimed the irrigation water with treated utilizationof wastewater rate natural can water in mitigate resources,problems. China. the One it particular Although utilization may concern alsoissue is result (e.g. the the long-term in sustainability increase environmental of salinity and sodium content in soil).

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