Analysis of the current world biofuel production under a water–food–energy nexus perspective

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ContentslistsavailableatScienceDirect

Advances

in

Water

Resources

journalhomepage:www.elsevier.com/locate/advwatres

Analysis

of

the

current

world

biofuel

production

under

a

water–food–energy

nexus

perspective

Emanuele Moioli

a

_{, Federico Salvati}

a

_{, Marco Chiesa}

a

_{, Roza T. Siecha}

a

_{, Flavio Manenti}

b

_,

Francesco Laio

c

_{, Maria Cristina Rulli}

d,∗

a Alta Scuola Politecnica, Piazza Leonardo da Vinci 32, 20133 Milano, Italy

b Politecnico di Milano, Dipartimento di Chimica, Materiali ed Ingegneria Chimica ‘G. Natta’, Piazza Leonardo da Vinci 32, 20133 Milano, Italy c Politecnico di Torino, Dipartimento di Ingegneria dell’Ambiente, del Territorio e delle Infrastrutture, Corso Duca degli Abruzzi, 24, 10129, Torino, Italy d Politecnico di Milano, Dipartimento di Ingegneria Civile ed Ambientale, Piazza Leonardo da Vinci 32, 20133 Milano, Italy

a

r

t

i

c

l

e

i

n

f

o

Keywords: Food–energy–water nexus Bioenergy 1st generation biofuels Energy eﬃciency

a

b

s

t

r

a

c

t

Thispaperassessesthesustainabilityofbioenergyproductionunderanexusperspectivethroughanew effi-ciencytypeindex.Theindexdescribes1stgenerationbiofuelproductionundertheperspectiveoftheimplied consumptionofnaturalresources.Weconsiderthesustainabilityofenergyproductionasasequenceofsteps, eachcharacterisedbyitsefficiency,andproposeanindexwhichreturnsanoverallefficiencyvaluedescribing theadequacyorinadequacyoftheconsideredprocessesunderanexusperspective.Thedirectapplicationof thenexusindexentailsanindicationofthepossibleimprovementsneededtomoveproductiontowardsmost sustainableprocessesorplaces.Moreover,itallowsevaluatingtheefficiencyofthemaincropscurrentlyusedin biofuelproductionwithrespecttothewater–food–energynexus.Theresultsdepictcountriespresentlycapable ofperformingsustainableproductionof1stgenerationbiofuelfromparticularcrops.Furthermore,theanalysis ofthesinglecomponentsofthenexusindexallowsunderstandingtheeffectsofpossibleimprovements(e.g.soil andwatermanagement,newgenerationbiofuels)ontheoverallproductionefficiencyunderanexusperspective.

1. Introduction

Someofthemostdebatedtopicsforscienceinthe21stcenturyare relatedtoenergyavailabilityandproduction(IEA,2014; Johansson, 2013).Theneedformoreenergy,duetopopulationincreaseandglobal economicgrowth,isconﬂicting withtherequestof lowerCO₂ emis-sionsanddecreaseourrelianceonfossilfuels(Edenhoferetal.,2011) Theconcernforfoodsecurity,waterscarcityandlandconsumptionare becomingdaybydaymoreimportantandtheseaspectsarefarfrom be-ingindependentfromenergyproductionanduse.Thestrictlinkamong energy,foodandwaterisgenerallyreferredtoasthewater–food–energy nexus(Sanders,2015).

Itisimpossibletoboundtheanalysisofenergyproductiontoasingle limitedsectorbecauseactionsaimedtolocallyoptimisetheeﬃciency can,attheend,causethesettlingoftheglobalsystemtoacondition worsethantheinitialone(Dubreuiletal.,2013).

Inthiscontext,theproductionofbiofuelsisapointofgreatdebate amongstscholars.Recently,decisionmakershavegivenmany incen-tivestotheproductionofenergyfromrenewableresources,ﬁndingin biofuelsagoodopportunitytodecreaseCO₂emissions(EUparliament, 2009;EUcommission,2010;USCongress,2005; USCongress, 2007;

∗_{Corresponding}_author.

E-mail addresses: emanuele.moioli@fau.de(E.Moioli),cristina.rulli@polimi.it(M.C.Rulli).

IEA,2012).Infact,biofuelscandecreaseCO₂emissionsinenergy pro-ductionwithrespecttofossilfuelssincetheyproduceenergyfroma feedstockwithlowerlifecycletime(BentsenandFelby,2012;DaCosta etal.,2010;Campbelletal.,2008;Dornburgetal.,2010)Atthesame time,theycanincreasethequoteofself-producedenergyformany coun-tries(AminehandCrijns-Graus,2014;Thöneetal.,2009;Faveroand Pettenella,2014).Nevertheless,theuseofediblecropsasfeedstockfor energyconversionisindirectcompetitionwithfoodproduction(Harvey andPilgrim,2011),aﬀectingwaterandlandmanagement.Thisisdue tothehigherrequestofcropscausedbythesimultaneousdemandfor foodandfeedstockforenergyproduction(Gude,2015).Moreover,the cropyieldisoftenincreasedbymassiveirrigation,givingahigherfood production, butaccompaniedbyalow eﬃciencyintheuseofwater resources.

Thedesignofenergyproductionsystems,carriedouttakinginto ac-countalltheseaspects,isachallengingduty.Aspecificdesignmethodis farfrombeingcompletelydefined(Howells,2013).Thecurrentenergy, foodandfreshwatersupplysystemsareoptimisedtogivethemaximum possibleoutputintermsofthecommodityor/andsourcetheyare de-signedtoproduceordeliver(CosgroveandLouck,2015;Hejazietal., 2015),Thisleadstothecreationofsystemswhichareefficientintheir ownscope,butwhicharefarawayfromtheabsoluteoptimalpointin

https://doi.org/10.1016/j.advwatres.2018.07.007

Received5May2017;Receivedinrevisedform31May2018;Accepted15July2018 Availableonline26July2018

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termsofsustainableuseofwaterandenergyresourcesundera food-energy-water(hereafter,FEW)nexusperspective.

Manyauthorshaveanalysed thesinglesubcomponentsof water– food–energynexusandmanyindicators existtoanalyse theeffectof 1stgenerationbiofuel(asadefinition,1stgenerationbiofuelsareliquid fuelsproduceddirectlyfromcropsotherwiseusedforfoodproduction. Thisdistinguishestheseproductsfromthefuelsobtainedfrom conver-sionofwaste(2ndgeneration)ornon-foodcrops)productionintermsof wateruseanddepletion,competitionwithfoodandlandconsumption. Forexample,indicatorsofwaterandlanduseforbiofuelproduction alreadyassesstheimpactofbioenergyproductionofanysinglenatural resourcetheyaredealingwith(Rullietal.,2016).However,justfew attemptsofanalysingtheinterlinksbetweenfood,energyandwaterin biofuelproductionhavebeen done(D’ Odoricoetal., 2018).andat ourknowledgenoindicatordoesexisttotakeinbioenergyproduction underFEWnexusperspective.Historically,twodifferentworkssetthe basistodefineandanalysetheconceptofwater–food–energynexus.In ‘Thelimitstogrowth’(Meadowsetal.,1972)importantinsightsinthe problemweregiven,butthesehintsdidnotformasingletoolsuitable forpolicymakers.Thisstudyplacedthefirstmilestoneforthe sustain-abilityassessment,butitdidnotaddresstheWEFnexusasawhole. Fewyearslater,themethodWELMM (GrenonandLapillonne,1976) wasdeveloped, directly focusingonfiveconnectedresources:water, energy,land,materialsandmanpower.Thismethodologyprovidedthe firstexampleofdatasetusedforsustainabilityassessment,butitdidnot involveanintegratedanalysisusefulunderaWEFperspective. Nowa-days,thewayisstillopenforthedevelopmentofintegratedassessment models(Tol,2006).ThisstudyproposesanewmethodologyfortheFEW description,consideringalltheaspectsofthisconceptandsummarising theminasinglesimpleindicator.Mostoftheexistingmodelsconsider thesinglerelationshipsenergy-land andenergy-wateruse.However, mostoftheavailabletoolsdonotaddresstheproblemasawhole.The commonlyusedmethodsforenergysystemanalysisincludeMESSAGE (MessnerandStrubegger,1995),MARKAL(Zonoozetal.,2009),LEAP (Heaps,2012)models;ontheotherside,theWEAP(Stockholm envi-ronmentinstitute,2011)modelisoftenusedforwatersystemplanning. Thesemodels,whileprovidingusefulinformationintheirapplication field,lackthedataandmethodologicalcomponentsrequiredtoconduct anintegratedpolicyassessment(Bazilian,2011).Atool,whichshould besimpleenoughtobeusefulforpolicymakers,butpreciseenoughto welldescribethecurrentenergyproductionunderanexusperspective, isstillmissing.

Herewe proposea newindex, which resumesin onesingle out-puttheeffectof1stgenerationbiofuelenergyproductionon sustain-abilityunderaFEWnexusperspective.Theindexisaimedtoanalyse theinterrelationshipamongwater,foodandenergyin1stgeneration biofuel productionat the globalscale andto assess the sustainabil-ityofbiofuelproductionfromaspecificcropinasinglecountry.For thispurpose,thevariouscomponentsoftheFEWNexusarestudiedin detailforbiofuelproductionfromany specificcrop,and,inorderto defineanefficiencytypeindex,theuse oftheresources (water,food andland)iscomparedtoareferencevalue(i.e.theleastimpactinguse ofthespecificresource).Thisnewindexdoesnotsubstitutethe exist-ingtoolsusedfortheanalysisofthesingleaspectsoftheFEWnexus, butitintegratesandcomplementsthemgivinga preliminary assess-mentofthecomplexinterrelationsbetweenthecomponentsoftheFEW nexus.

2. Methodologicalframework

ThedesignofanindexassessingtheFEWnexusshouldfollowthe deepunderstandingofthepunctualindicatorscharacterisingthesingle aspectsofthenexusitself.Forthisreason,werecallheresomeliterature resourcesusefultoaddressthesinglefacetsoftheproblem.

2.1. Water

Sincethispaperisfocusedonbiofuelproduction,itisnecessaryto havetoolsforanalysingthewaterrequiredtoproduceareference quan-tityofenergyfrombiofuels.Waterisnotonlyusedinenergyconversion, butitisvirtuallycontainedincropsusedasfeedstock,becausethey re-quirelargeamountsofwatertogrow(FinleyandSeiber,2014).A con-ceptofprincipalimportanceinthisfieldisvirtualwater(Antonelliand Sartori,2015).Virtualwaterisanindicatorusedtodescribethequantity ofwaterrequiredtoproduceaspecificindustrialoutput(Allan,1993). Thisindicatoriswidelyusedtodescribetheembeddedwaterintraded goods,asshownintheexampleofvirtualwatertrade(Antonelliand Sar-tori,2015).However,thevirtualwaterconceptisdesignedtoassessthe waterembeddedonlyinphysicalgoods.Whenacommodityisusedto produceothergoods(derivedgoods)infurtherprocesses,thevirtual wa-terconceptresultsnotsufficient(AntonelliandSartori,2015).Toextend theconcepttoderivedgoods,thewaterfootprintindicatorwas devel-oped.Waterfootprintchangestheperspectivewithreferencetovirtual water:Theformerindicatorallowsthedeterminationofthequantityof waterusedinproductionofgoodsandservices,whilethelatterallows thequantificationoftheamountofwaterusedduringtheprocessof consumingthesamegoodsandservices(ChapagainandHoeksrtaetal. 2003).

Waterfootprintisafundamentalconcept,sinceitallowsdefiningin aprecisewaytheamountofwaterrequiredtoproducebioenergy.Many studiesaredevotedtothistopic(Grebens-Leenesetal.,2009;Velazquez etal.,2011)Theresultsofthesestudieswillbeusedasastartingpointin definingour“water-efficiency” index(seeSection3),buttheydescribe onlyasingleaspectofacomplexproblem.Theyallowdeterminingthe quantityofwaterneededthroughouttheproductionchainofbiofuels, buttheyallowneithertounderstandtherenewabilityofthewaterused, nortorelateittotheresourceseffectivelyusedduringproduction.

Thesustainabilityofthewaterusehasbeenrelatedtoasortof hier-archyinthetypologyofwatersources,withsomesourcesmorevaluable thanothers,alsofromaneconomicpointofview(Chapagainand Hoek-stra,2004).Toaddressthisproblem, theconceptsof greenandblue waterweredeﬁned.Blue waterreferstotheliquidwaterabove and belowtheground(rivers,lakes,andgroundwater).Greenwateristhe soilwaterintheunsaturatedzonederivedfromprecipitations( Gerbens-Leenesetal.,2009).Onlygreenwaterisusuallyconsideredarenewable resourceinthestrictsense(MekonnenandHoekstra,2010).Bothgreen andbluewaterareintensivelyusedinagriculture,butbluewaterisused indirectcompetitionwithotherhumanuses(e.g.industries, municipal-ities…)(RulliandD’Odorico,2013).Wedonotconsidergreywaterin thisanalysisbecauseofthescarceaccuracyandspatialhomogeneityof theavailablegrey-waterfootprintestimators(Novoetal.,2009; Falken-mark,1986;Mancosuetal.,2015).

Theseparationofblueandgreenwateristhereforeusefulto under-standtheoverallsustainabilityoftheprocessunderawaterperspective, inparticularbecauseanalysingthebluewaterfootprintallowsoneto quantifytheimpactofbiofuelproductiononrenewableresources.The shareof renewableresourcesusedforbiofuelproductionistherefore usedasthemaincomponentofour“water-quality” indicator.

Alsoconsideringtheseparationbetweentheblueandgreenwater footprint,oneisleftwithawatereﬃciencyindicatorwhichlacks in-formationabouttheabundance(orscarcity)ofwaterintheproduction place.WateravailabilityisaccountedforbyconsideringtheWorlddata bankWaterWithdrawalIndexasafurtherdeterminantoftheindex(see Section3).

2.2. Food

Thesecondelementtobediscussedinawater–food–energynexus analysis is the possible interaction of biofuel production with food production, includingbothcommoditiesused forhumanandanimal nutrition. We do not aim toconsider, separately for each crop, the

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amountoffoodwhichissubtractedtohumanconsumptionbybiofuel production,becausethiskindofanalysiswouldinvolvedietaryand nu-tritionalfacetswhicharebeyondthescope ofthepaper. Incontrast, wewanttoincludeinourindexthesimpleconceptthat,atthe coun-tryscale,humancropconsumptionshouldbefavouredwithrespectto thecrop usefor energy-productionwhenmalnutritionaffects a non-negligibleportionofthecountry’spopulation.Thereferenceconceptin thisfieldisthusfoodsecurity.Foodsecurityisdefinedas‘asituation thatexistswhenallpeople,atalltimes,havephysical,socialandeconomic accesstosufficient,safeandnutritiousfoodthatmeetstheirdietaryneeds andfoodpreferencesforanactiveandhealthylife’(FAO,2003).While thisdefinitionisrathersimple,itisdifficulttoturnthisexpressioninto aquantitativeindex,whichstatestheeffectsoffoodinsecurity world-wide.Wethereforerefer,inthedefinitionofour“foodefficiency” index inSection3,toaverysimpleandwellagreedconcepttoatleastroughly characterisefoodsecurityinacountry:theprevalenceofmalnutrition, asdefinedbyFAOineachcountry.

2.3. Land

Thethirdelementtobeinvestigatedintheanalysisisland.Landis thebasicresourceneededinagricultureandthequantificationofland requiredtoproduceadefinedamountofcropisapointofcapital im-portance.Modelsarerequiredtohaveagoodunderstandingofthe effi-ciencyinexploitingthisresourceforanypurpose.

Thekeyparameterinagricultureiscropyield,deﬁnedasthe quan-tity of crop producedfor ha of land used (Gebbers andAdamchuk, 2010).Cropsyielddependsoncroptype,climate,cultivar,soiland ter-rainconditions,levelofinputs(waterandfertilizers)andmanagement. Yielddatasuﬀersimilarproblemsasdataoffoodsecuritybecause theyaremainlytheresultsofstatisticalmeasurements.Onlypunctual dataareprecise,buttherecoveryofsuchdataishardandtheyarenot alwayssuitableforfurtherstudies.Theuseofaverageorcountry-based datagiveslesspreciseindicationsonlandyield,butinmanycases,these aretheonlydataavailableorusable(Barretetal.,2002).

Anotherimportantfeaturetobeconsideredin asustainability as-sessmentoflanduseisthequantityoflandavailableandsuitablefor agriculture.Togetherwithagriculturalintensiﬁcationandincreased ap-plicationoffertilisersandpesticides,theexpansionincultivatedareais thekeyfactorfortheincreaseinfoodproductionobservedoverthelast 50years(KhanandHanjra,2008).Thetotalglobalagriculturalareahas expandedby11%to5billionha,andthearablelandareahasexpanded from1.27to1.4billionha(FAOSTAT,2014).Morelandhasbeen con-vertedtocroppingin the30 yearsafter1960thanin the150years between1700and1850(FAOSTAT,2014).Thesedataarefundamental tounderstandthepossiblefurtherincreaseinagriculturalproduction andiftheuseoflandiscompatibletoasustainabledevelopmentand changingclimateregimes.

3. Materialsandmethods

Inordertoassesstheeﬀectsofbiofuelproductiononglobal sustain-abilityunderawater–food–energynexusperspectivethecurrent pro-ductionofbiofuelsisevaluated bymeansof anewindex,which we callthenexusindex(NI).Wecalculatethenexusindexforthemost im-portantcropsusedinbiofuelproduction.Thelistofconsideredcropsis reportedinTable1.Theindexisdesignedtoevaluatetheresources re-quired,intermsofwater,foodandland,toproduceoneunitofenergy (Fig.1).

Theformulaofthenexusindexis:

𝑁𝐼= 𝜂_{𝑤𝑎𝑡𝑒𝑟}∗ 𝜂_{𝑓𝑜𝑜𝑑}∗𝜂_{𝑙𝑎𝑛𝑑} (1)

whichisthemathematicaldescriptionofasystemsimilar totheone shown in Fig.1, wherethe use of three resources (water,foodand land)isnecessarytogetthefinaloutput(energy).NIistheNexus In-dex,𝜂wateristheefficiencyinwateruse,𝜂foodtheefficiencywithrespect

Table1

Listofcropsconsideredduringanalysis.

Crops considered for analysis Bioethanol Biodiesel

Maize Oil palm

Rice Soybean

Rye Sorghum Sugar beet Wheat

Fig.1.Water–food–energynexusunderanenergyperspective.

tofoodproductionand𝜂landis theeﬃciencyin theuse ofland.The

ﬁrstterm(𝜂water)islinkedtothewaterusedforcropproduction,

stat-inganeﬃciencywithrespecttothelowestquantity ofwaterthatis possibletouseinaspeciﬁcprocess.Thesecondterm(𝜂food)is

country-relatedanddescribestheeﬀectsofthecompetitionbetweenbiofueland foodproduction.Thethirdterm(𝜂land)takesintoaccountthequantity

oflandrequiredtoproduceoneunitofproduct,againreferringtothe best attainableperformance.This methodallowscomparingdifferent systems,providingaresultintherangebetween0and1.Inordertoget agoodscore,aprocessmustworkwiththebestavailabletechnology, preventingtheresourcesfrombeingdepletedandguaranteethewater andfoodsecurityandarigoroususeofland.Thethreepartshavethe sameweightintheindex,sothattheinefficiencyinasinglestepis di-rectlytranslatedintotheresult.Themultiplicationof3differentfactors ischoseninordertoincreasetheinfluencetheinefficiencyofanysingle aspectoftheindex.Infact,thankstothetheoryoflimitingeffects,if onlyonefactorisnotefficientlymanaged,thevalueoftheindexresults stronglypenalised.Thisformispreferredtootherpossible mathemat-icalformulations(e.g.:additiveform)toavoidtheneedofweighting factors,whichwouldincludemorearbitrarychoicesintheindex defi-nition.Thenumberoffactorsislimitedtothreetohaveacompromise betweencomplexityinthedataminingphaseandprecisionoftheindex. Thethreefactorsdeterminetheinfluenceofbiofuelproductiononthe threemostimportantelementsthataffectsthewater–food–energynexus (wateruse,landconsumptionandfoodavailability),givingasimplebut preciseindicatorofefficiency.

InthefollowingeachcomponentoftheNexusIndexisdescribedin detail.

3.1. Watereﬃciency

Thewatereﬃciencyindexisintroducedforassessingtheuseof wa-terrelatedtobiofuelproduction.Tothisaimthisindexconsidersboth theamountofwaterandthesourceofwaterusedforcropproduction (i.e.soilmoistureduetoprecipitation,thatisthesocalledgreen wa-terorirrigationwater,thesocalledbluewater)requiredtoproducea pre-deﬁnedamountofenergyviabiofuels.

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Thewatereﬃciencyishereexpressedastheproductoftwoterms:

𝜂𝑤𝑎𝑡𝑒𝑟= 𝜂𝑤𝑎𝑡𝑒𝑟.𝑞𝑢𝑎𝑛𝑡.∗ 𝜂𝑤𝑎𝑡𝑒𝑟.𝑠𝑜𝑢𝑟𝑐𝑒 (2)

Thetwotermsareequallyimportantanddeterminetheeﬃciencyof wateruseinbiofuelproductionbothforthequantityofwaterusedand forthequalityofthiswater.

Thefirstpartofthisindexreferstothequantityofwaterusedinthe stepsrequiredtoproducethecropadoptedforenergeticpurposesand toconvertitintoliquidfuel.Inordertoassessthisquantity,thewater footprintofenergyfromaselectedcrophasbeencalculatedfollowing theapproachintroducedbyGerben-Lenensetal.(2009).Wethendivide thebioenergywaterfootprint(inm3 /MJ)bythelowestglobalvalue ofthebioenergywaterfootprint,whichcorrespondstothehighest ef-ficiency.Thereverseofthisratioisanefficiency,lyinginthedesired rangeofvalues,[0,1].Theresultingformulais:

𝜂𝑤𝑎𝑡𝑒𝑟.𝑞𝑢𝑎𝑛𝑡.= (_𝑊_𝐹 𝑚𝑖𝑛 𝑊𝐹𝑖 ) (3) where𝜂water. quant. isthequantitativepartofwatereﬃciency,WFiisthe

waterfootprintofbioenergy(fromselectedcrop)ofthecountryi,WFmin

istheminimumwaterfootprintofbioenergy(fortheselectedcrop)at theglobalscale.Thehyperbolicformischosenafterasensitivity anal-ysis,whichshowedthatthisformprovidesthemostrealisticresults. Otherfunctionalforms(e.g.exponential)wouldmaketheindexmore complicated,withanincreasedcomputationalcomplexitynot compen-satedbyahigheraccuracy.

Thispartoftheindexneedsbeingcomplementedwithsome addi-tionalinformationonthewaterused.Forthispurpose,itisimportant toconsidertheeffectofwaterfootprintaccordingtotheavailabilityof freshwaterresourcesinaregion.Moreover,thereisagreatdifferenceif thewaterusedinbiofuelproductioncomesfromirrigation(bluewater footprint)orfromsoilwater(greenwaterfootprint).Toquantifythese aspectsaspecificindexisdefined.

Thestartingpointtocalculatethiseﬀectistheratiobetweengreen waterfootprintofbiofuelproductionaccordingto(Gerben-Lenensetal., 2009)andthetotalwaterfootprint.Themaximumvalue(equalto1)is reachedifonlygreenwater(i.e.onlyarenewableresource)isusedto producebiofuel.Topenalisecountrieswherewaterislessabundant,we considerthefollowingdeﬁnition

𝜂𝑤𝑎𝑡𝑒𝑟.𝑠𝑜𝑢𝑟𝑐𝑒= (_𝑊_𝐹 𝑔𝑟𝑒𝑒𝑛 𝑊𝐹𝑡𝑜𝑡 )𝑊𝑊𝐼 (4) where𝜂water.sourceisthesource-relatedpartofwatereﬃciency,WFgreenis

thegreenwaterfootprintofbiofuelproduction,WFtotisthetotalwater

footprintofbiofuelproductionandWWIisthecalculatedwater with-drawalsindex.Thisexponentiscalculatedaccordingtodataonwater withdrawalscomingfromtheWorldBankdata(Worldbank,2014).This indexassumesincreasingvaluesaccordingtothewaterwithdrawalrate ofaspeciﬁccountry.Thewaterwithdrawalindexusedhereisdeﬁned as:

𝑊𝑊𝐼=𝑤𝑎𝑡𝑒𝑟𝑤𝑖𝑡ℎ𝑑𝑟𝑎𝑤𝑎𝑙𝑠[%] (5)

3.2. Foodeﬃciency

Thefoodeﬃciencycomponentofthenexusindexaimstoaccount forthepotentialcompetitionforﬂexiblecrops(cropsusablebothfor nutritionandenergypurposes)betweenfoodandbiofuelsectorsinfood insecurecountries.

ThedatafromFAOSTATdescribingtheprevalenceof undernourish-ment(FAOSTAT,2014)areusedtoassessfoodefficiency.Thisindicator (M.I)assumesvaluesbetween0and1andexpressesthepercentageof populationwithinacountrythatdoesnotconsumeasufficientamount offood.Thisvalueisthenadjustedwithanexponent(𝛼)thataimsat penalisingthecountriesmoreaffectedbythisphenomenon.This param-eter(𝛼)issetat5,avaluechosenafterasensitivityanalysisshowing

Table2

Listofcountriesavailableforeachcropandlocation ofthemaximuminnexusindex.

Item No. of countries Maximum country

Wheat 110 Belgium

Maize 140 Belgium

Rice 100 China

Rye 58 Denmark

Sorghum 32 Algeria

Sugar beet 57 Mexico

Soybean 100 Algeria

Oil palm 50 Peru

thatlarger𝛼 valuesproducemoresensibleresults,andforvaluesof𝛼 greaterthen5𝜂foodisstable.Theresultingformulais:

𝜂𝑓𝑜𝑜𝑑=(1−𝑀.𝐼)𝛼 (6)

where𝜂foodisthefoodeﬃciencyandM.Iistheprevalenceof

malnutri-tionaccordingtoFAOSTAT(2014).Foodeﬃciencyasdeﬁnedhereis notcropbased,butitconsidersthefoodsecurityconditionofacountry, becausewedonotaimtoconsidertheenergy-foodcompetitionforeach crop,buttheoverallnutritionalpictureforeachcountry.

3.3. Landeﬃciency

Themainaimofthelandefficiencyindexistheevaluationofthe impactof biofuelproductionontheavailabilityof cultivablelandin aspecificcountry.Todoso,similarlytothecaseofwaterefficiency, itisnecessarytoconsiderboththeuseoftheresource(land)andits availability.Theefficiencyinusinglandforgrowingacertaincropis definedasthecropyieldregisteredinthespecificcountrydividedby themaximumvalueofthecropyieldreachablewiththecurrent technol-ogy(i.e.,themaximumyieldregisteredworldwide)(FAOSTAT,2014). ThesedataareprovidedbyFAO(FAOSTAT).

Inordertoaccountforthecountryavailablelandsuitablefor agri-culture(notalreadyused),acountryspeciﬁclandusedindex(LU)is developed. Thisindexis theratiobetween thelandalreadyusedfor agriculture(the arablelandinFAOSTAT) andthetotalareasuitable foragricultureinaspeciﬁccountry.Weselectedtheextentofvery suit-able,suitableormoderatelysuitablelandformixedinputunderrainfed and/orirrigationconditionsforallcropsasreportedbyGAEZ(2014). Finally,thelandcomponentoftheNIis:

𝜂𝑙𝑎𝑛𝑑= ( _{𝑦𝑖𝑒𝑙}_𝑑 𝑖 𝑦𝑖𝑒𝑙𝑑𝑚𝑎𝑥 )𝐿𝑈 (7) where𝜂landisthelandeﬃciency,yieldi istheyieldfortheconsidered

cropinthecountryi,yieldmaxisthemaximumpossibleyieldforthe

spe-ciﬁccropandLUisthelandusedindex.Similarlytothecaseofsource watereﬃciency,thehyperbolicformischosentohavearightbalance betweenthetwocontributions(useandavailabilityoftheresource).

4. Resultsanddiscussion

Forapplyingtheproposedmethodology,thenexusindexforvarious cropsusedin1stgenerationbiofuelproductionwascalculated.Inorder tohaveahomogeneousandcompleteframework,avoidingtheproblems duetothedifferencesintheuseddatabases,thecalculationwaslimited to191countries(eliminatingincongruentdatacomingfromcountries withincompleteorunreliablestatisticaldata).Thenumberofavailable countriesdependsonthedistributionofthecropintheworld.The to-talnumberofcountrieswithacalculatednexusindexforeachcropis showninTable2.Thestudyisperformedwiththedatareferredtoyear 2014.Largelydiffusedcropslikemaize,rice,wheatandsoybeanhavea largequantityofavailabledata,becausetheyarecultivatedandusedas feedstockforbiofuelsinmostpartoftheconsideredcountries.Onthe otherhand,forlessdiffusedcultivations,likeSorghumandOilPalm,the

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Fig.2. MaximumNexusIndexvaluesfortheconsideredcrops.

numberofcountriesinwhichtheNexusIndexcanbecalculatedisquite low.Table2 alsoreportsthelocalisationofthehighestscoreforeach consideredcrop.Thisdependsontheareawheretheclimateismost suit-ableforcultivation,butalsoontheefficiencyofcultivationtechniques. Themaximumvaluesattainablehaveagreatvariability(Fig.2),with cropscharacterisedbyhighmaximumefficiency(especiallyWheat)and cropswithlowmaximumefficiency(e.g.sorghum).Themethodis de-signedtogiveexcellentresultswhenonecountryishighlyefficientin allof thestepscomposingNexusIndex.Thismeansthatcrops culti-vatedwithminimumwaterrequirement,maximumagriculturalyield andwithoutcompetingwithfoodproductionwillgivehighscores; mis-managementofonlyoneofthesestepsstronglydecreasestheoverall performance.

Themostproducedcropshaveingeneralthehighestmaximal eﬃ-ciency.Thisisanaturalconsequenceoftheintensiveresearchperformed

inthepasttoimproveagriculturalyieldforthesespecies(Fisheretal., 2002).Ontheotherhand,somecropswithlow diﬀusion(e.g.,Palm Oil)alsoscoregoodresults.Thisismainlyduetothehigh specialisa-tioninthesecultivationsthatsomecountrieswereabletoestablishin somecasesduetothehighproﬁtabilityofsuchcashcrops.Themaxima areonlyrepresentativeoftheglobalcapabilitytoreachgoodscoresin thenexusindex;tohaveacompleteunderstandingoftheworld per-formanceitisnecessarytodiscusstheresultsindetailfortheselected crop.Asanexample,resultsformaizearediscussedinthefollowing section.Theresultsfortheothercrops(limitedtothecaseswithmore than50 countriesavailable) arereported asmapsin the supplemen-tarymaterial.Theresultsofthesingleelementsoftheproposedindex can becomparedwiththeindicatorsrepresentingthecomponentsof theFEWnexusavailableinliteraturetoverifytheconsistencyofthe results.

4.1. Nexusindexformaize

Maizeisoneofthemostproducedcommoditiesintheworldandit iswidelyusedasafeedstockforbiofuelproduction(Rullietal.,2016). Thismakesmaizeaninterestingcroptobeanalysed.Asmentioned,the maximumvalueforthenexusindexformaizeis0.611anditisreached inBelgium.Themaximumvalueisnothigh,statingtheexistenceof in-efficienciesinbioethanolproduction.Thegeneralanalysisofthenexus indexisdisplayedinFig.3asamapandthevaluesfortop10countries arereportedinTable3.Thenumberofcountrieswithscoresclosetothe highestvaluesisnotlarge.Thismeansthat,despitethelargediffusionof Maizeattheglobalscale,inefficienciesarewidelypresentand,inmany cases, thecurrent bioethanol production does not fulfil the require-mentsofsustainabilityunderaWFEnexusperspective.The geographi-caldistributionofscoresdoesnotshowspecificareaswherebioethanol production is particularly favourable or penalised. Inall continents, therearecountrieswithNexusIndexvaluesclosetothemaximum.In

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Table3

Thetop10countriesinnexusindexformaize.

Nexus index Quantitative water eff Source water eff Food efficiency Land efficiency

Belgium 0,611 1,000 0,999 1,000 0,611 Luxembourg 0,565 0,625 1,000 1,000 0,905 Netherlands 0,475 0,858 0,995 1,000 0,557 New Zealand 0,445 0,503 0,992 1,000 0,892 Switzerland 0,366 0,700 1,000 1,000 0,523 Austria 0,362 0,749 1,000 1,000 0,483 Germany 0,353 0,699 0,999 1,000 0,505 Slovenia 0,351 0,503 1,000 1,000 0,699 Greece 0,310 0,558 0,913 1,000 0,608 Canada 0,307 0,622 1,000 1,000 0,494

Fig.4. Quantitativewatereﬃciencyformaize.

general,thelargestvaluesarefoundinindustrialisedcountries.Mostof thecountrieswithlowscoresareinthesub-SaharanAfrica;other inef-ﬁcientcountriesareplacedintheareacomprisedbetweentheMiddle EastandtheIndiansubcontinent.Thediscussionofthesingle compo-nentsofthenexusindexwilldisentangletheproblemsthatmakesome countriesnoteﬃcient.

4.1.1. Watereﬃciency

Quantitativewaterefficiencystronglyinfluencestheindexbecause itdirectlystatesthequantityofwaterneededtoproducebioethanolin aspecificcountry.ResultsareshowninFig.4.Maizeissuitabletobe growninmanyclimates,sothatitscultivationisdiffusedinmany ar-easoftheworld.Thecultivationtechniqueshavebeenrefinedinallthe industrialisedcountriessincelongtimeago.Forthisreason,inthese

placesitisnotpossibletodetermineareaswherethecultivationis par-ticularefficient.Thisrelativehomogeneityoftheresultsisbecausethe quantityofwaterrequiredforgrowingmaizeisquitesimilar.Inalmost all theindustrialisedcountries,specificcountrywater andsoil man-agementdoesnotsignificantlychangethecropwaterfootprint. Con-versely,othercountries(suchasmostofthesub-SaharanAfricanand southeastAsiancountries)arepenalisedinthisindex,becauseofthe largequantityofwaterrequiredtocultivatemaize,bothintermofcrop waterrequirementandascropwaterfootprint.Thislargeneedof wa-tercanderivebothfromclimateconditionsthatdeterminehighercrop waterrequirementandfromproductioninefficiency(lowyieldthat re-sults inlow production perunit of waterused). Wewilldistinguish betweenthetwophenomena,whilediscussingthequality-basedwater efficiency.

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Fig.5. Sourcewatereﬃciencyformaize.

Thesourcewater(greenvs.bluewater)efficiencycompletesthe in-formationonsustainableuseofwaterinbiofuelproduction.The situa-tiondescribedbythesourcewaterefficiencyislargelydifferentfromthe previouspartoftheindex(Fig.5).Wenoticethatthescaleoftheresults isextremelynarrow:thelowestvalueis0.77.Thismeansthatmaizeis producedinthegreatmajorityofcountriesusingmainlygreenwater resources.Interestingly,someofthecountrieswithhighlevelofsource waterefficiencyhave,atthesametime,alowscoreinquantitativewater efficiency.ThisisthecaseofBrazil,ofmanysub-SaharanAfrican coun-triesandofsomecountriesoftheAsianSoutheast.Thisisaclearclueof thehighcropwaterrequirementofmaizeinthesecountries.Other coun-trieshavehighquantitativewaterefficiencyandrelativelylowsource waterefficiency.These countries(e.g.,theUSA,Western Europeand China)producemaizeusinglowquantitiesofwater(green+blue),but withaconsiderablecontributioncomingfromirrigation.

4.1.2. Foodeﬃciency

Thesecondcomponentofthenexusindexisfoodefficiency.This in-dexis,bydefinition,independentofthebiomassconsidered.Theresults aredisplayedinFig.6.Mostoftheworld’scountrieshavethemaximum score;butinAfrica,SouthAmericaandSoutheasternAsiasome coun-triesarenotefficientinprovidingfoodtotheirpopulation.

4.1.3. Landeﬃciency

Landuseeﬃciencycharacterisesthelastpartofwater–food–energy nexus,assessingtheappropriateuseoflandincropproduction.The re-sultsformaizearedisplayedinFig.7.Thisindexislinkedtoquantitative watereﬃciency,butwithsomeexceptions.Infact,agriculturalyield, cropwaterrequirementsandirrigationarestrictlyconnected.Usually, largeuseofirrigationcanguaranteehighagriculturalyield,butthisis

notnecessarilythecase.Furthermore,agriculturalyieldispartofthe definitionofwaterfootprint,sothatahighyieldcandecreasethewater footprint.Thesecomplexrelationshipshighlighttheneedofapunctual analysisof thesituationforeverysinglecrop.Inthespecificcaseof maize,wecannoticethatthedistributionofscoresforlandefficiency issensiblydifferentfromthequantitativewaterefficiency.

Mostof theindustrialisedcountrieshave lowvalues of land effi-ciency,oppositetothehighvaluesofwaterefficiency.Thisisdueto thefocusintherationalisationofuseofwaterincultivation.Theuseof waterisadjustedtotheoptimalpoint,butthisdoesnotcorrespondtothe highestlevelofcropyield.Furthermore,inthesecountriesmostofthe suitable landis alreadydedicatedtointensivecultivation,preventing thepossibilityofincreasingtheproduction.Acaseofparticularinterest isBelgium,leadingcountryinnexusindexranking.InBelgium,water andfoodefficiencyhavethemaximumvalue,whilelandefficiency re-sultsthebottleneckofthebiofuelproductionprocess.Inthiscountry, landsuitabletobecroppeddoesexist,buttheratiobetweenthemaize cropyieldinBelgiumandthemaximumyieldintheworldislow(0.5). Someothernationsarecharacterisedbylowscoresinwaterefficiency, butalsobyhighcrop yield.This isthecaseof somesmallcountries (e.g.,Israel)wherethelittlelandavailableforcultivationisexploited inahighlyefficientway.Theanalysisofsub-Saharancountriesgives someotherinterestinghints:mostofthecountriespenalisedin quanti-tativewaterefficiencyhavehighlandefficiencyscores.Thisisdueto thelargequantityoflandavailableforcultivation.Inthesecountries, maizeproductioncanbeincreasedwithoutdecreasingthenexusindex. Measurestomakethesecountriesmoreefficientshouldfirstfocuson thereductionof thewaterfootprint.Thegoodmanagementofwater isingeneralakeypointtogenerateasustainablebiofuelproduction system.

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Fig.6. Foodeﬃciency.

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5. Conclusions

Thesustainabilityof1stgenerationbiofuelproductionattheglobal scaleisassessedthroughthedefinitionofanewindex,calledtheNexus Index.Theoutputofthemethodisascore,whichdefinestheefficiency oftheproductionofbiofuels.Theindexistheproductofthree interme-diateindexesthatquantifyallthekeyparametersinbiofuelproduction. TheNexusIndexdeterminesifacountryisefficientlymanagingbiofuel productionfromaspecificcrop,definingthelowestattainable consump-tionofresourcesinthisprocess.

Theresultsoftheanalysisprovidethestartingpointfor considera-tionsconcerninggeographicdiﬀerencesinbiofuelproduction.Evenif weacknowledgethesubcountryspatialvariabilityofresources avail-abilityanddemand,thecountryscaleofanalysisischoseninorderto havehomogenousandreliableresultsbecause,often,onlyatcountry levelalltherequiredinformation(forwater,foodandland)is avail-able.

EfficiencyinProductionofbiofuelsfromthesamecropcanbevery differentfromonecountrytoanother.Thisisduetodifferencesin agri-culturalyield,butalsotodifferencesin resourcesdeploymentdueto farming.Inthecaseofmaize,whosecultivationisoptimisedinmost partof theworld,theeffectoffarmingtechniqueson globalprocess sustainabilityisparticularlyevident.Somecountriescouldbe ableto increaseyieldtooptimalvalues,butonlywhileincreasingbluewater consumption.Ontheotherhand,alsolandissometimesmismanaged. Nevertheless,inmanysituations,watermanagementisthekey param-etertodesignasustainableenergeticsystem.

Theanalysisofthenexusindexmakesitevidentwhatthebest cul-tivablecropsinthecountryare,givingtodecisionmakersaninstrument tounderstandhowtodefineanenergypolicyinbiofuelproductionto exploitinthebestwaythecountry’sresources.Furthermore,the inef-ficienciespresentinthecountrybecomeevidentthankstotheNexus Index,allowingonetodesignthebestsolutionstoincreaseefficiency.

OneofthemainpotentialityoftheNexusIndexisthepossibilityto analyseinasimpleanddirectwaytheeffectsof correctivemeasures usedtoimproveprocessefficiencyanddecreasetheimpactofbiofuel production.Todoso,theNexusIndexcanbeusedinadynamicway, consideringthevariabilityofthesameovertime,andcomparingthe expectedeffectsofnewtechnologiesontheresultsofpastchanges.In thisway,itispossiblealsotoanalysetheeffectsofclimatechangeon theWEFnexus.

Inadditiontothis,thenexusindexiscapabletodeterminethe pos-sible impactin termsof increasedordecreased waterandland con-sumptionofimportantinnovationsinthefieldofbioenergyproduction, likeaswitchto2ndgenerationbiofuels.Thisispossible,becausethese changesareonlymodifyingsomeparametersusedtogeneratethenexus index,butnotthegeneralassumptionsthemethodisrelyingon. More-over,itisimportanttohighlightthattheNexusindexreturnsthe sustain-abilityof1stgenerationbiofuelinthecurrentscenariosofsoilandwater technologymanagement,climateandsoiluseandatcountryscale. Fu-tureimprovementstranslatingbothincrop’syieldincreaseand/orin moreefficientwaterusecanbetakenintoaccountbytheNexusindex, sodescribingtheeffectsofagricultureintensificationon1stgeneration biofuelproduction.

Acknowledgements

Thisresearchhasbeenconductedwithinthemasterdegreeprogram ‘AltaScuolaPolitecnica’ﬁnancedbyPolitecnicodiMilanoand Politec-nicodiTorino.FLacknowledgesﬁnancialsupportfromtheERCproject CWASI,grantno.647473.

Supplementarymaterials

Supplementarymaterialassociatedwiththisarticlecanbefound,in theonlineversion,atdoi:10.1016/j.advwatres.2018.07.007.

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