Solar energy development in China―A review

RapidurbanizationinChina:ArealchallengetosoilprotectionandfoodsecurityJieChen⁎StateKeyLaboratoryofSoilandSustainableAgriculture,InstituteofSoilScience,ChineseAcademyofSciences,Nanjing210008,ChinaAbstractTofeedits1.3billionpopulationwithapercapitacultivatedlandfarbelowtheworldaverage,Chinaisalreadyfacingagreatchallengeoflandscarcity.Acceleratedurbanizationalongwithexplosiveeconomicgrowthhasfurtherworsenedtheshortageofagriculturallandoverthelasttwodecades.Increasingconcernoverlandisexpressedintermsofsoilavailabilityforgrainproductionandsoilqualitydegradation.Basedonofficialstatisticsanddataderivedfromsatelliteimagery,dynamicsofChina'scultivatedlandoverthepasttwodecadesisoutlinedandthecausesanddestinationsofcultivatedlandlossareanalyzedinthispaper.Particularly,urbanization-relatedland-usechangesandtheirspatialvariationacrossthecountryaredemonstrated.Furthermore,impactsofurbanizationandassociatedwastedisposals,consequentshiftsofsoilutilizationonarealsoilqualityareexpatiated.ItisinitiallyconcludedthatChina'scultivatedlandisshrinkingatarathershockingrate.Althoughconversiontourbanandindustrialusestookupacomparativelysmallshareoftotalcultivatedlandloss,urbanizationshouldstillbeconsideredasagreatthreattofutureagriculturalproductionforseveralreasons.Urbanizationisincreasingtheriskofsoilpollutionthroughwastedisposalandaciddepositionderivedfromurbanairpollution.Facingrapidurbanization,Chinaismakingpositivepolicyresponsestothechallengeofdecreasingavailabilityofcultivatedlandandofferingunremittingeffortstowardsthegoalofnationalfoodsecurity.©2006ElsevierB.V.Allrightsreserved.Keywords:Urbanization;Cultivatedland;Soilresource;Foodsecurity;China1.IntroductionUrbanization,referringtoagrowthintheproportionofapopulationlivinginurbanareas,isoneofthemajorsocialchangessweepingtheglobe.AccordingtothelatestestimateandprojectionreleasedbythePopulationDivision,UnitedNations,theworld'surbanpopulationcontinuestogrowatahigherratethanthetotalpopulationoftheworld,and3billionpeopleorapproximately48%oftheworldpopulationarenowcitydwellers(UnitedNations,2004).Urbanizationisprogressingrapidlyinthelessdevelopedregionsandurbanpopulationisanticipatedtogrowanaverage2.3%peryearinthedevelopingworldbetween2000and2030.Almostalloftheworld'stotalpopulationgrowthinthisperiodisexpectedtobeabsorbedbytheurbanareasofthelessdevelopedregions(Brockherhoff,2000;UnitedNations,2000,2004;UNFPA,2004)(Fig.1).Asthemostpopulousnation,Chinahasthelargesturbanpopulationintheworldbutacomparativelylowurbanizationlevel,approximately10%lowerthantheworldaverageand30%lowerthanmoredevelopedregions(UnitedNations,2004).Ontheotherhand,Chinahasbeenwidelyviewedasacaseofunder-urbanization,andurbanizationhaslaggedratherbehinditsindustrializationasaconsequenceofurban-restrictingpoliciesconcerningmigrationtowardcitiesbeforetheeconomicreform(Chan,1996;ChangandBrada,2002;ZhangandZhao,2003;Liuetal.,2003).Withtheunprecedentedeconomicgrowth,however,thecountryhasbeenwitnessingadramaticgrowthofurbanizationsince1978wheneconomicreformbegan.StatisticsfromtheMinistryofConstructionofChina(abbreviatedasMCC,hereafter)showthat,theurbanizationlevelinChinaincreasedfrom17.9%in1978to40.5%in2003,demonstratingagrowthtwiceasfastastheworldaverageCatena69(2007)1–15⁎Tel.:[phone];fax:[phone].E-mailaddress:[e-mail].0341-8162/$-seefrontmatter©2006ElsevierB.V.Allrightsreserved.doi:10.1016/j.catena.2006.04.019ofthesameperiod(MCC,2002–2004)1(Fig.2).Recogniz-ingurbanization'scentralroleinfurthereconomicgrowthandsocialdevelopment,Chinawillcontinuetogivehighprioritytourbanizationinthecomingdecades.China'surbanizationlevelisprojectedtorangebetween48%and50%by2020andtheproportionofurbanpopulationisexpectedtoexceed60%by2030.Despitenumerousbenefitsoriginatingfromurbanization,arapidlyurbanizingworldincludingChinafacesintensifiedresourcescarcityandenvironmentaldegradation.Itisknownthaturbanizationisdependentonasteadysupplyofnaturalresourcesincludingfreshwater,fuel,land,foodandalltherawmaterials(WRI,1998;UNFPA,1999;Hardoyetal.,2001;Hinrichsenetal.,2001).Alongwithrapidurbanizationandcitysprawl,theredefinitelyaredrasticincreasesbothinnaturalresourcedemandsandintheareafromwhichtheseresourcesaredrawn(O'Meara,1999).Urbanizationalsoleadstosignificantalterationsofphysicalenvironmentfarbeyondcitylimits,resultinginhabitatloss,climaticchanges,andaccumulationandspreadofwastesintheEarth'satmosphere,hydrosphereandpedosphere.Asthefoundationofterrestrialecosystems,soilnotonlyfunctionsasanindispensablephysicalbasetoprovidehumankindamajorityoffood,livestockfeed,fibreandbioticfuel,butservesasbothasourceandasinkforgreenhousegasesandanintegratedpartofbiogeochemicalcycles(Yaalon,2000;BunningandJiménez,2003).Withuniquepedogeneticcharacteristicsformedbythecombinedeffectsofenvironmentalandbiologicalfactorsovergeologicalperiods,soilcouldbeconsideredasanon-renewableresourceinahumantimeperspective(Amund-sonandJenny,1997;Amundsonetal.,2003).Urbaniza-tionleadstoconversionofanaturallandscapetoanurbanareaandin