Water Resources in China.docx

Water Resources in China.docx

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WaterResourcesinChina

WaterResourcesinChina—2004.08.02

I.PHYSICALBACKGROUND

ChinaissituatedatthesoutheasternpartofEurasiaontheNorthernHemisphere,closedtothePacificOceanonthesoutheasternside,stretchingintothehinterlandsofAsia,borderedbythesubcontinentofsouthernAsia.Thetotallandareais9.60millionkm2,orequivalenttoabout1/5oftheworldtotal,rankingthirdamongallcountriesintheworld.Chinabordersmorethantencountrieswiththetotallengthoflandboundariesbeingmorethan2000km.Chinahasaseaareaofabout3millionkm2,andmorethan5400islandsofvarioussizes,inwhichTaiwanisthelargest.Thetotallengthofcoastallinesofthemainlandandislandsis32000km,inwhichthecoastallineofthemainlandoccupies18000km.

1.Topography

ThetopographyofChinaischaracterizedbyhighwestpartandloweastpart,graduallydescendinginelevationfromthewesttowardstheeasttoformthreesteps.ThehigheststepistheQinghai-TibentanPlateauwiththeelevationbeinggenerallymorethan4000mabovesealevel,henceknownas"theroofoftheworld".TotheeastoftheQinghai-TibetanPlateauisthesecondstepwithmuchlowerelevations,rangingbetween1000mand2000mandalternatingwithhugebasins.ThethirdstepstretchesfromthelineinthewestcomposedofMountsDaxing'an,Taihang,WuandtheeasternrimoftheYunnan-GuizhouPlateautothecoastintheeast,andembracesalternatinghillsandplains,andtherearelargeareasoflowmountainsandhillsatelevationsoflessthan500mabovesealevelwithonlyafewpeaksbeingat2000m,andtheelevationofplainsisalllessthan200m.Theplainsaredistributedinthenorthtosouthdirection,includingNortheastPlain,NorthChinaPlain,MiddletoLowerYangtzePlainandPearlRiverDeltaPlain,beingimportantindustrialandagriculturalbasesandeconomiccentersofChina.

Classifiedaccordingtotypesoftopography,mountainsaccountfor33.3%ofthenationallandarea,plateaus26.0%,basins18.8%,hills9.9%andplains12.0%.Mountains,hillsandruggedplateaus,whicharecustomarilycalledmountainousareas,totallyaccountfor2/3ofthenationallandarea.

2.Climate

Asaffectedbythevastareaandcomplextopography,China'sclimateisendowedwithafeatureofcomplextypes.Chinaissubjecttostrongmonsoonclimateandmostoftheareasareundertheimpactsofthesoutheasternandsouthwesternmonsoons,thusmakingthesoutheasternChinawetandthenorthwesternChinadry.Theprecipitationvariesgreatlyfromyeartoyearandfromseasontoseason.Asaffectedbymonsoonandtopography,Chinabecomesoneofthecountrieswithmostfrequentdrought,floodandwaterlogginghazardsintheworld.

TheaverageannualprecipitationinChinais648mm,or19%lessthantheworldaverage800mmonland,andthevolumeofaverageannualprecipitationis6190billionm3.Theregionaldistributionofprecipitationisveryuneven,showingageneraltrendofgraduallydescendinginmagnitudefromthesoutheasterncoastlinetothenorthwesternhinterlands.Theannualprecipitationinthesoutheasterncoastalareasandpartsofthesouthwesternareasismorethan2000mm,butthatinthenorthwesternChinaisusuallylessthan200mm,and50mmintheTarimandTurpanbasinsinXinjiangandChaidamuBasininQinghai,etc,evenlessthan25mmatcentersofthosebasins.

Asaffectedbythemonsoonclimate,theprecipitationshowsnotonlyabiginter-yearvariation,butalsowetspansanddryspans,andinter-yearvariationisbiggerinareasorforseasonswithlessprecipitation.TheratioofmaximumannualprecipitationtominimumatobservationstationhasthebiggestvalueinthenorthwesternChina,possiblyexceeding8,butonlyhasvaluesranging2-3orlessthan2inthesouthernandsouthwesternChina.Exceptinafewsmallspecialareas,precipitationisusuallyconcentratedinsummerandmainlyoccursinrainstorms.Inmostoftheareas,theratioofaveragemaximumprecipitationoffourconsecutivemonthstoaverageannualtotalranges60-80%fromthesouthtothenorth.

Theaverageannualevaporationfromwatersurfacealsovariesgreatlyoverregions,withthelowestvaluebeingonly400mm,andthehighestupto2600mm.Thelowvaluesmainlyoccurinmountainousareasandthehighonesonplainsandplateaus.Theaverageannuallandevaporationalsoshowsatrendsimilartoprecipitation,descendinginmagnitudefromthesoutheasttothenorthwest.Ithasavalueof700-800mmintheeasternareasandusuallylessthan300mminthewesternareas.

3.RiversandRiverBasins

Chinahasalargenumberofriverswithatotallengthof420000km.Therearemorethan50000riverseachwithadrainageareaofmorethan100km2andmorethan1500eachwithadrainageareaofmorethan1000km2.Asaffectedbythetopographyandclimate,theriversaredistributedveryunevenlyoverregions.Mostoftheriversaresituatedintheweteasternmonsoonclimaticzone,directlyflowingintothesea,withthemajoronesincludingtheYangtze,Yellow,Heilong,Pearl,Liaohe,Huaihe,Haihe,etc.ThenorthwesternChinaisdrywithslightprecipitation,andhasonlyasmallnumberofrivers,mostofwhichareinlandoneswithoutconnectiontosea,andtherearealsolargenone-runoffareas.

Thewholecountrymaybedividedintoninemajorriverbasins,includingYangtze,Yellow,Haihe,Huaihe,Songhua-Liaohe,Pearl,SoutheastRivers,SouthwestRiversandInlandRivers,bycombiningalargeriverwithnearbysmallerriversflowingdirectlytotheseaoroutoftheregionorbycombininganumberofneighboringriversinaregion.TheSonghua-Liaohe,Haihe,Yellow,HuaiheandInlandRiversarepracticallysituatedinthenorthernareasofChinaandtheYangtze,Pearl,SoutheastRivers,SouthwestRiversinthesouthernareas（seeattachedfigureinAnnex）.

II.WATERRESOURCES

WaterResourcesarereferredtothefreshwatersthatarerenewable,closelyrelatedwithusesbyhumansocietiesandecosystems,includingbothsurfacewaterandgroundwaterwithprecipitationbeingthemainsourceofrecharge.

1.SurfaceWaterResources

Thevolumeofsurfacewaterresourcesisreferredtothedynamicvolumeofwaterinrivers,lakes,glaciers,etcandgenerallyexpressedinvolumeofnaturalriverrunoff.Thevolumeofannualriverrunoffinthecountryis2711.5billionm3,equivalenttoadepthof284mmoverthewholelandarea.Thedirectrechargebyprecipitationaccountsforabout71%ofthisvolume,andindirectrechargebyprecipitationviaaquifer27%andrechargebyglacierandsnowmelt2%.

Thedepthofnaturalriverrunoff,whichdependsonprecipitationandconditionsofwatersheds,graduallydescendsinmagnitudefromthesoutheasttowardsthenorthwest,havingvaluesofmorethan1000mminsomesoutheasternareasandvaluesoflessthan10mminsomewesternareas.Thetotalvolumeofriverrunoffinthefivenorthernriverbasinsaccountforlessthan20%ofthenationaltotal,butthefoursouthernriverbasinsaccountformorethan80%ofthenationaltotal.

Theriverrunoffshowsinter-yearvariationsimilartoprecipitation,buttoabiggerextentwiththeimpactsofwatershed.Theratioofmaximumannualrunofftominimumusuallyhasavalueoflessthan5inthesouthernareas,butmayexceed10inthenorthernareas.Theintra-yearvariationofriverrunoffisalsobigasaffectedbythesizeofriverbasinaswellasintra-yearvariationofprecipitation.Theriversinthenorthernareasshowabiggerintra-yearrunoffvariationwiththemaximumrunoffofconsecutivefourmonthsaccountingformorethan80%oftheannualtotalinsomeareas,andthisratiohasavalueofabout60%forriversinthesouthernareas.

Table1Averageannualriverrunoffbyriverbasin

2.GroundwaterResources

Thevolumeofgroundwaterresourcesisreferredtothedynamicvolumeofwaterinaquiferthatisdirectlyrelatedwithprecipitationandsurfacewaterviarechargeand/ordischarge.Mostofrunoffformedbyprecipitationflowsintorivers,butthereisapartofrunoffthatpercolatesintoundergroundtoformgroundwater.Thevolumeofgroundwaterresourcesisusuallyexpressedintermsofvolumeofgroundwaterrecharge.Asactivitiesofhumanbeingsaffectgroundwaterrechargetosomeextent,thevolumeofgroundwaterresourcesisdefinedunderspecificconditionsofdevelopmentandutilizationofwaterresources.

TheannualvolumeofgroundwaterresourcesinChinais828.8billionm3,inwhichgroundwaterinmountainousareasoccupies676.2billionm3andthatinplainareas187.4billionm3with34.8billionm3ofoverlappingvolumebetweenthem.Mostofgroundwaterinmountainousareasflowsoutasbaseflowofrivers,thusoverlappingwithsurfacewaterresourcesandbeingmainlyexploitedassurfacewater.Thegroundwaterresourcesinplainareasaremainlyinthenorthernareasandthefivenorthernriverbasinsoccupy78.8%ofnationalgroundwaterresourcesinplainareas.Table2showsgroundwaterresourcesbyriverbasin.

3.TotalWaterResources

Totalwaterresourcesinaregionarereferredtothetotalyieldofsurfacewaterandgroundwaterformedbylocalprecipitation.Surfacewaterinteractswithgroundwaterwiththeriverbaseflowformedbygroundwaterandpartofgroundwaterrechargecomingfrompercolationofsurfacewater.Incalculatingtotalwaterresourcestheoverlappingvolumebetweenthemshouldbededucted.

With2711.5billionm3ofannualriverrunoff,828.8billionm3ofannualgroundwaterresourcesand727.9billionm3ofoverlappingvolumebetweenthem,thevolumeoftotalwaterresourcesinChinais2812.4billionm3.Thefivenorthernriverbasinstotallyhave535.8billionm3ofannualtotal