C h apter 8

In1pacts of Global Change on W ater

R esources in Dryland East Asia

Ge S un, X iaoming Feng, Jingfeng Xiao, Alex Shiklomnnov, Shcngping Wang, Zhiqiang Zhang, Nan Lv, Shua-i Wang, Liding Chen, fl ojie Fu, Yaning Chen, and Jiquan Chen

Summary: T he vast Dryland East Asia (DEA) a rea coHsisLs of several large geographic regions including the Qinghai-T ibet P la teau, Loess Pla teau, and Mongolia Pla teau. T he region is of greaL impor tance to the functioning of the ear th system under a changing climate. In lhe past three decades, due to the unprecedented land usc/ la nd cover change, urbanizat ion, ind tts tr ializa tion and cl imate change, wa ter stress in 111any areas in DEA have rcnclted a dangerous

level that t hrea tened the susta inabili ty of lhr region. ln adcliLion to reviewing li tera t ure for the causes of the water crisi::; observed in Lhc region, m; cn.sc st.nrlics. we examined water ba lances at a bas in and regional scale using mull iple lllOdel­ing techniques, inc:luding a remote seHsing-basecl EC-MOD model, n wa tershed water balance model (vVBMPlus), alJCl an evapotranspirat ion model calibrated for the Loess P latcEt u region. Our synthesis s tudy suggests Lhal la nd usc changr and human water wiLhtlr<:l\val acc011 11t for tuosL of l he observt'd w;\ t.c r resourn· declines in t he s tudy region. However, climate change will hnxc profound im­pacts on areas where local water s upply and ecosystem services rely on melt iltg glaciers. The current large-sca le soil conscn·a t ion practices a nd n 'gcLation-ba.5ecl ecological restoration act ivit ies such as rcfon •, talioll should he cotn prchcn~ivcl~·

evalua.t.ed to assess their b road impacts on water resources such RS grounrl wn­

ter recharge and water yield downstream. I'vluc!J uncer taimy remains Lv predict. ful'tt re water availabi li ty in DEA cl ue Lo t.lte uncertainty i11 pred icting climate

cba nge patLcm s. Pacing t he larg(' unccn<~ in ty of clinwl <' chang!' aud sociocco­tlomic changes in DEA, dccision-maki11g proccs,;cs and insl.ill tl i n11~ must adopt a robust and adaptive framework to achicYe long-term su~t ai n;~ hil it.y.

154 - G<' Stt ll , l'l al.

8.1 Introduction

G lobally, about 20% of t he human p opulat ion li ve in drylands, which cover

approxinw tcly 50% of the Ear t h 's surface. Depending on local moisture a nd

!teat conditions, a var iety of ecosystems wilh high biodiversity is found in dry­

land,; . prima r ily inclwl in~ woodlands. savanna:;, irrigated croplands. and d..:~erl~

(e.g., J ohn t'l <ll., 21!0<:>). Dryland Ea,t Asia (DEA) cons ists of s•·\·cral large

geographic rc·gion,; includiug the Qinghai-Tibet Plalca.u, Loess Plall'<ltl. and

.\longolia l'lnl.< 'illl , which arc or g real impor lnncc l o the fu nctioning of the l'a rlh

systc 111 (Fig. 8 . .1 ) (Groisma n et a l. , 2007, 2009; Qi et al., 2012).

D Loess Plutcau - Major Rivers

Lakes Precipitation (mm yr-1)

II igh: I ,588

N

+ 0

km 1,000

F ig . 8.1 i\·l<tjor river syslc llls tuld precipitatiou regime in D ry lnnd East Asia.

l n Ch in<~, <~hu1 1 1 :3:1% of Lhc l<liHl i ~ iu arid Lo sem i-ar id regions and about

27%. of Lhc land is considen'd LU be sii:-cl'PLihlc Lo deser t ification. Desert ifica­

tion is currenlly ex pa nd ing al a rale o f 2,4GO km2 per year, resulting in serious

CJwironmcnt.al p rohl<•rn,; s uch as soi l erosio n a nd sandstorms (Kurosaki eL a l..

2011). The t.otal DEA an'a (Fig . 8 .1 ) in the Xinjiang liygur Antonomous Ht' ­

gion (X.J ), wc:;Lcm Gansu Province(G S) . weslem Qinghai Provincc(QH) , ami

western l nucr !vlongolia Autonomous R egion (1:11) is a pproxim ately 2.16 million

km2 . The t11a1 1agemenl of Lhe area is important for combat i11g dcscrLificat. ion and

bandstorms. T he m ajor envi ronmental LlueaL of t he a rea is lhe lack of water n'­

sourceb. Snndstonm; occur freque ntly a11d some oases have already dclcrioralt'd

or disappeared. The Hexi corridor in GS is one of the seve rest dcser lificatintt

areas in C hin a. The Qil ia n !.lountains, located between CS ;wd Q l l. is a 111ajor

ecological conser\'at.ion Ul'l'a. fo r uatural g rassla nds, forests and ~ou rccs of ri vers.

The DBA rl'~ion i~ dolll iHated by summ er and winter monsoon climate sy~­

t.c ms . b11l in llih'I IC'('d by lnud sur face coudiLions of the 111assive E urasian COil-

~ lllljJ .I• .,rt : •i.! c·L.Il'' Ill \\lii.(• S•"'\J if't :-:iu) 1 ut nd l·:~t't .\sia - I~.j

tinent . The re14ion contains t.ltc headwaters of many important ri ver systems (i .c., Yellow Ri ver) l it <LL (.lrO\'iue crilic<-~.1 wi lcllife lmbi L<~ls H.lld sustain stream flow for downs tream wat.cr usc. Dry la ud eco~ysLcms and socioeconomic vitality arc mainly constrni ned by water availability. The DEA region in China produces n ~i.~n i ficant par l of the country ·,.: tot.al produdion of gTi1in r· "·· \'. int< r v·lH':ol .

. d i ... '. \ ,.., l.! hlc:-. h'l lit ····in· rrrvht r h" • )lllol;. l) i ":.' 11.· ietll\l 111<111\' of til L' :\ort ll•'rt l C! , <T •. !.•11•~ irri.J,at•·d ("u•hert ! 'l a1 '.!1 •1(,' aud 1\'<t­

ter wi Lhdrawab an· Ill ('Xcess of ::ill:-it.linahl<• water use. A gl .. ba l ".\·nt h<•sis on

gronndwater reclta rgc iu DBA suggests t. ltnt. recharge rates vary fn:.. tu JO Lo 48G 111111 per year, representing only 1 o/o-25% of irrigation plus precipitation, resulting

iu long-term grouudwaLcr mining in grouud watcr- fed irrigated are<t s (Sen.nlon el a.l.. 2006) .

T he drastic chflngcs in land use and land CO\'er (i.e., increase in irrigated crop­lands and urbani~aLion) . industrialization and climate warming have resul ted in dramatic degrada tion of wa ter quant ity and quali ty in the ar iel region , as evi­denced by many of the regional severe water resource problems, s uch as shortages for drinking waler, water poll ution , loss of wetlands, lakes and rivers, soil sani li­zn.tion, and dust s torms . Other drivers of environmental changes include woody plo:mt extraction, overgrazing, modificat ion of fire regimes, and mba n expan­sion . cont ribut ing lo t he current ecological crisis . La nd degrada tion, soil erosion (both wind- and water-induced ), woody plant encroachment and clominntion by im·asiYe species, and water shor tages a re t he common phenomena (Wilcox et al. , 200G) . For example, 1najor ri\·ers in Nortl1 China, including t·h<' might .\· Yellow Hin'r, he:n-e rtlll dry d m in)!; part of tit{' yea r (t·.g., Yang cl a!., 200·1; Li11 a nd Xia, 2004 ) and grou ndwater levels in t lw Norl.lt Chin<~ Plain arc dropping rapid ly (Liu and Yu. 2001 ). \·Va ter s l rcss in B, ijinp; a nd t hl' surrCJlll ldi n ~-?; rP!!.,i nn:-; ltas r!'achcd a dnngerous leYvl. ' ]() all•·'.·iat.,, tltc• sit 111 1ion, ;1 llliljor Suurh to :\"nh \\.atcr Di­

version project is en tTl •ttl 1.' · under cons I ruvl ir111 ( \'f'lll ra I ;wd CilSI• 'I'll rr >111 (',;) and in planning (wP:-.t.em rout e) lO clivut "-'-].-, km:l yr 1 ("-J O<J. uf Chi na 's smfare water rc~omces) from thf' Yangtze l3a.-;in to the Yellow Hi\'l'r and l\urth China Plain (CIJ,•ng ct al., 2ll09). Jn inb·J. nd riq·r l l<tS i n~ in l\ort.IHwst Chinn. exccs~i vc

wat cr u~c is kadiug lo deserti fica tio tt a nd severe challenges for food prod uct ion (e.g., 1\:ang eL al. , 2008). Irrigation i11 norLhent and \·\."estern Chinn rel ics, in pan, on rtlllufr frnnt hi l!,lt l:' if'\'nt imts, incl ttding the T ilwt-Qi ng-ltni J> bttr ·ntl. fur "significant fn1ct i<lll of it.f' :-;, 1 lillalo!. irrigali•lll water. 11 du:--t.rial \\·at r•r nse in

i\urlbew Clt im1 is expc<"led LO inct v;r :-.L' by > 50',{ and clolllcstic water demand Ly rv80% by 2050 (JBlC, 2004). Ecological restora tion LhaL a int::; at reducing soil erosion and la nd degradation has been challenging in DEA in large part due to the delicate relationship between water and human innneuccs on t he vege­t.a l ion·s consuJnpt i'·" water usc (Sun('[ al.. 2006: Cao, 2008; C'ao el al., 2011 ). H eccut. Clll phasis on l>iocacrgy prod uct io tt <1 11d biological ce~ rbon scqtiCSLratiou

crtuses fur ther conccrm; about t heir wat er illl pnct::; and prolllotes tTnewc·cl scicn-

15fi - Gc Sun, eL al.

lific debaLe on the efl'ecls of vegetation on water and other ecosystem services (.Jackso11 eL a l. , 2005; E llison e l. a l. , 2011) .

Climate change and variability have direct impacts ou water resources in DEA ([PCC, 2007) . Small changes in precipitation would result in large changes in runofl'. The rising air Len1peraturc is es'pecially of coucern to watersheds where s lream flow is generated from snow mel t. The cryosphere (snow aud ice) of the

Qinghai-Tibet PlaLeaH is a major wa ter source area for intensively developi ng DEA. Tho Qinghai-Tibet Plateau has warmed rv0.25°C per decade over 40 years whi le precipitation has declined 5- 10 mm per decade (Yang et al., 2003). :ti'Ja ny glaciers m e found on the Qinghai-T ibet P lateau. For example, there arc 15,953

glaciers in the whole Tiansha.n l\1foun tains range with a total area of 15,416 km2

a nd an icc volulllc of 1,048 km3 , supplying the majority of the river flows in

.X.J. lloweYer, like other glaciers in the Himalaya-T ibet Plateau, which drains lo SouLh Asia (Bagla, 2009; Ba rnett et al., 2009; Yang et al., 2003; Xu eL al., 2009), the glaciers in XJ have been retreating rapidly in the past few decades.

For example, Lhe Tianshan glaciers retreated as much as 3 km fTom the l 860s to 2003 (Aizcn el a!. , 2007) . During the past 60 years, the total a rea of the T ia11slmn glaciers reduced by 14..2% dne to au increase in summer a ir tempera­Lu re~;, especially since the 1970s (Aizen et al. , 2007) . The Qinghai-Tibet Plateau permafrost is thawing and this may be contributing to the reduced water vol­ume and deteriorating ceo-environments in the source region of major rivers in

the Qll region of the Qinghai-Tibet P lateau (Cheng and Wu, 2007). A recent national st udy on Chiim's lakes concludes that, overall, hydrological functions (i.e., flooding miLigation) and water quality (i.e., eu ~roph icaLion) arc degrading. Lake wa l,er levels in a rid nor thern an d Nor thwestern China have dropped sig­nifi ca ntly and sa linity has i11crcascd dramatically while lake water resources in

the Q inghai-Tibet Platea u show la rge a nnua l variabil ity. Ecosystem functions in D I~ A arc cxtren1ely responsive to soil moisture dy na mics that are directly

linked Lo climatic variability. For example, the remote sensing monitoring dala show !.hal. vegetation evolutions a re pa rticularly sens i ~ ive to changes in a ir Lcm­pcmwrc and precipitalion iu a rid aud semi-arid regions in China (Cao et al., 20 12) .

This s tudy focuses on drylamls in Northern China . vVe use published li Leratme a nd regiona l water balaucc, P recipitation minus Evapotranspiration modeling Lo auswcr the following qucstious:

\VItaL are the key walcr resource issues <:md driving factors? llow has land usejlnml cover change afl'ccted water quantity and water quality?

flow lias climate change impacted the chronic water shortage in DEA? What are tllC potential options to mitigate negative impacts of climate cha.11ge a nd to adapt Lo future cnviromnental condi tions with higher water stress?

8 l111p ... ·ts of C: lubal Ch:-mgc on \\'a t<'r Hr·somc• ,, in D1y laud Ea't .\ sia - ].')7

Integrat ed watershed management, practices that focus on ba lancing waLershed services and hea lthy socioeconomic developmen t, could provide Lhe best solutions Lo water problems and enviromnental susLain ::~bility for Lhe DEA region.

8 .2 Key V\Tater R esource Challeng~s

Due to lo\\' precipiLa Lion ( <400 nun per year, in n1osL places) a11d large differ­ences in air temperature between Lhe growing season and non-growing season, Lhe DEA region is dominated by grasslands a nd desert.s thaL a rc sensiti ve to both nalural climate var ia tion (Cao eL a l. , 20:1 2) and human dis turbances. T he

DEA regiou has severa l impor tam river sysl.<'ll iS, notably t.he Yellow Jliwr and several inla nd r ivers such as the Tarim River (Fig. 8.1). Sources of' water supply include glaciers (Sorg eL al. , 2012) and :-;I, rca m flow general ed l'ro111 mou nlfl in­ous upland areas thaL receive relatively higher precipitaLion Lhan t.he lowlands. Deep groundwater is another importan t, W<LLer source LhaL supporLs productive agriculture in a dry environment. Sim il a r to other arid regions in the wor ld ,

DBA is considered one of the most waLcr-stressed regions where wal.er supply has increasingly fallen beh ind water demand due to human popul 11t.iou growth , exhaus tion of groundwater resources, a nd clima te changes. For example, the 1.321 km Tarim River, C hina's largest, inla nd river tha t. supports eight mil lion people living iu oases clustered along its banks and in an a lluvia l ph1.in down­stream , has been seriously impacted (Citt'' ' and X u. 2005) and major :l!'SO<'ia.t.cd lakes ltavc been dryi1tg up for decades dllt' to ex<'cssivc water usc for irrigation aud random land rccla1nation upstrca lll.

8.2.1 Dis triuution of \ iVate r Balauccs nc1·oss DEA a nd Histor ical C h a nges

We usc t.he a nnual \\'aLer ba lance equm iun (Wa.t.er Yield = Precipitation- Evap­otra.llspiratiou) to examine the spatial va riaLion of water yield . P recipitation data were deri ved from t.he Modern Era Hd .rospcctive-Analysis for Rest'a rch alltl Applications ( l\1 ERR A) reanalysis data set. 1\ lER RA make.~ usc of uhscrvatious

from ::.lASA's l~anl1 Observing S.YsLcw sat.elli les and reduct.>s t. hc uncertainty in precipitaLiou and i11 t.cmnnua l variabili L.\' by i111 proving the repr<'sculaLion of the wat.er cycle (Ri<'tHX:kPr d al., 2011 ) . 1 he l\lEI iHA dat.a ( I / 2 dl'p;n•cs Ia t.itude x 2/ 3 degrees l!ing it.uch•) were obt.a iu··d fro11 1 liH• C:lobn I :Vlodcli 11 g a 11d ;\ ssi1 nila­t.ion Office (Gf\ IJ\ 0 ) . \\'e calculatPtl II Jt•a.n ~tlll l llal precipita tion owr ll tr period of 2001- 20) 0. We C'xl. rn.cted evap ol n tlt:-, piration (ET) estima l r:-, i'vr t.lw DEA

L58 - Gc Sun, et a!.

region from a global fl ux da taset (Jingfeng Xiao, unpublished) prod uced by the EC-NIOD model. The EC-JVlOD da taset consists of gridclcd estima tes of carbon fluxes and ET with 0.05 degree spatial resolution and eight-day time step over the period from 2000 to 20 I 0. This dataset was developed from FLUXN ET observations and MODIS data streams using a data-driven approach (Xiao cL al.. 2008). The i'viOD IS land cO\·er map (i\ICDJ2Ql) with the "Cnivers ity of ~ lary laud ((jl\lD) classification scheme (Pried] et al. , 2002) was used to estimn.te ET uy land-co\'er type. Obtr1i uecl from the NASA's Warehouse Im·entory Search Tool, l bc land cover map was developed from various MODIS data streams using a regrcstiion tree approach. \Vc aggregated the vegetation types of the map to !.he following five broad vegetation types: forests, shrublauds, savaunas, grasslands and croplands.

Vegetation cover , land usc, hydrologic fl uxes (ET, mean water yield defined as precipitation minus ET) and human settlement in the DEA region are largely controlled by surface and groundwater availability (Fig. 8.2) . P recipitation varies greatly across lhc DEA region with a steep gradient, resulting in la rge spatia l and temporr1 l variability in ET ra tes and water yield. In Ll tis st udy, ET rates for areas classiried as uon-vegeta ted barren lands (Fig. 8.2 a) arc not mapped (Fig. 8.2c:)

0 125 250

(c)

375

0 250

500 -500 - 250

500 (b)

I I

0

(d)

750 1,000

250 500

F ig. 8 .2 Disl ribulion of land cover (a), an nual mean precipitation (1mn yr- 1) (b), cvapol r<Jnspi rH~iou (mm yr- 1

) (c), and water yield (nu n y r- 1) (d) in DE A during t.he

period of 2001- 2010. Som <:c: .Jingfcng Xiao, unpublished data.

8 llllpacts ol C lobal Change on '..Vni t•r i{csourl't'" II Dryland r a, t As ia - 159

and are p resumably similar to precipitation, which is rather low ( < ] 00 mm

yr - 1) (Fig . 8.2b). The areas mapped with high precipitation rates (>~750 m m

yr - 1) show high water yield , representing the source areas for local river systems (Fig. 8.2d). Large areas show negative values, indicating that local precipi tation

does not meet ET demands . This migh t be especia lly true for the crorlnnd

areas l':her<' irri:.;atin n i ~• t!:·'< 'd ( Lin et ;.!., 2012) . These Hre:t~ me id~:111i l icd in norLhwf',.;t 1'\ X. <·<·nt '<tl L\ 1 <~ 1td nort lt,,.f'~t X .J (ri!.:,. ti.2 d ), w here• gJ"t,;s i<Htd,; have

been converted t o IIighly productive croplands. Ground\,·ater: 0\'Cru:;e is a ma jor

water crisis for lltese aren~ . as it is in o l11cr ag riculture-dominated regions in

Nor thern China. Because ET is es timated independently from precipi taLion , t he

negative values of water y ield can be par tially caused by data or modeling errors.

Howe1·er, the general patterns suggest Lhal the major renew:1ble sources of wa ter

supply in the region arc concentrated in sou t;hcm GS (Qili~tll i'vlonntain Ra nge),

central XJ (Ti<msh an Mouutain nangc) and nor thern Mongolia, which arc h ig h­elevation mountainous areas wit h rcla t. ivcly high p recipitation and glaciers.

Analysis of historic changes in the runofF over 2001- 2010 versus 1979- 2000

across Northem Clt ina a ud IJv1 was made using meteorological data from t he

NASA's MEIU1A (Rienecker et al., 2011 ) a nd a water balance model ('WBMPlus)

(Wisser et a l. , 2008) (Fig. 8 .3). RunofF in most of t he DEA region showed an

upw·ard trend except for a few wet areas. Northeastern China, Lhe Northern

China Plain, and northern Mongolia showed a decline in water availability during

the past decade. Alt hough the MERRA-driven runoff simulation had better

agreement with nmoff observations in E urasia than other reanalysis prod ucts

- 150 - I 00 -50 0 50 I 00 ! 50 200 250 300

F ig . 8 .3 Simnla t.cd clcviat.ion of average aiJIIUal n utoll' dnring t he 200 .1 - 2010 period l'rom the mean owr the 1979 21100 time 1w riod (\Visser et a l. , 2008).

160 - Gc Suu, ct nl.

(Shiklomanov et al. , 2013), t he regional modeling results showed large variability and uncertainty in predicting mean annual runoff.

8.2.2 La nd Use/ Land Cover C ha nge

In DBA, laud usc clJangc is driven by several forces such as agricult ura l devcl­oprneut (i .e., la nd conversion from forests or grasslands to croplands), intensive grazing, m banization, and soil conservation practices. Previous global studies show that water balances in DEA can be greatly infiuenced by land use/ land cover change (Zhang et al. , 2001; Andreassian, 2004; Brown et al. , 2005; Foley et a l. , 2005; J ackson et a!. , 2005; Scanlon et al., 2006) . For example, defor­estation generally increased river flow because of reduced total ET . Similarly, conversion of native vegetation to cropland in semi-arid regions can increase the recharge inLo uuderlying aqui fers and lead to secondary impacts, such as water­table rise and salinization (Allison et al. , 1990; Leduc et al., 2001; Scanlon et a l. , 2006) , alld changes from natural grasslands and slll'ublands to dry land (ra in­fed) agricult,ure-altercd systems from discharge (ET) to recharge in the southwest US. Iu Niger, t he impacL of land use change was much greater than Lhat of eli­maLe variabili ty, where replacement of savanna by crops increased groundwa ter recharge by about an order of magni tude even during severe droughts (Scanlon et a l. , 2006). A theoretical analysis on hydrologic data from Northern China suggests t hat, anmw l vegetation cover dynamics aA:'ect regional wat er balances in the llOll-.ilumid region (Yang et al. , 2009 ).

Land 11se and land cover change dir ectly a lter the hydrologic processes includ­ing ET (Zhaug eL al. , 2001; Huang et al. , 2003a, 2003b; Sw1 et al., 2011; Yang et a l. , 2009; Wang;, Y. et a l., 2011; 'Wang S. et a !. , 2011), soil infiltration and groundwat,er recharge (Gates et al. , 2008), and soil moisture dyn amics (Lu et a l. , 2011) . Divert ing surface water or mining groundwater for cropland irrigation (Liu and Yu, 2001) are major causes of wctla.Jld losses in DEA. Land use changes may also 111ocli (y land surface energy and wa ter balances (Zhang et al. , 2012) and thus a.lLer regional climate pat terns t hrough land surface-climate feedback mechanisms (Liu et, a l. , 2008) .

T he effects of laud use change, land management , and climatic variability on water balances have been studied across DEA in China such as the Loess Plateau and Mongolia Plat,ea u that span a complex physiographic gradient. Techniques used iucl ude stable isotope tracers (Ga tes et a l. , 2008), weighing lysirneter (Ohte et a!. , 2003; \V01 ng, X. et a l. , 2004), eddy-covariance flux measurement (Miao et al. , 2009; Chen et al. , 2009; Wilske eL al. , 2009) , plot or sma ll watershed vegetation tua.nipulaLions (\Vang, Y. et a.l. , 2008; Zhang, et al. , 2008a, 2008b; ' iVang, S. et, a!. , 2008), remote sensing techniques (John et al., 2009; Cao et al.,

8 I '"pacb of C:lol,al Change on \ Vat,, ,. Ht;sources in Dry !and Ea, ; :\ ~m - I 0 I

2012), a nd watershed ecosystem modeling (Zhang et al., 2008) . Lu e l al. (20] 1) found that,, compared Lo Lhe und is turbed grasslands, t he mean

ET /P ratios of croplands a nd grazed grasslands were s ignifi canlly lower . The observed lower surface soil moisture content in the grn.zed a nd fallowed croplands was part of the r<:8son for t he mcasun•d lower ET/P. The widely planted and hst-gmwin:.' poplar l. rcc;; it• Nuri.lt crn Chi t!;!, a llwit. in l.l r,• ir ear ly gruwi11;2 !' I ag< s, : t~t ·d tnore \'. ;ll <'r (a lt iglwr 1· 1'/P) t lt<lll t ht· liJ tdi~lurbcd sltl'llb.J all<i . prr<' tt tt tilbly

becaHse of iLs ability to <1ccess groundwater by drop roots. Lu et al. (20 11) coucludcd that ccos.rstelll ET was maitrly l'Oirtrolled lJy soil moisture iu Lhc semi­arid region unless groundwater >vas avail ~~blc and acccssibl<~ . T lris s lucly indicat.es that land cover and land usc can have different sources of water for ET clue to

a ltered soil phys ical properties a nd root d istr ibut ions. \i\iat cr hala nr.c s f Hdies in t.he Tenggcr Desert (IJ\1 ) by \Vang eL al. (200,J) showed t.haL re-vegclnt. i11g

shifting d unes used a ll available soil water . Sim ilar fi ndings were reported tha l plant ing t rees iu some dr:y arens (precipitation < 400 mm per year ) on the Loess

P lateau can result in soil mois ture desiccation and increase compaction (Chen et a l. , 2010; J in et al., 2011), t hus causing a decrease in infilt rat ion, promoting overlan d flow and reducing groundwater recharge. Studies wit h stable isotope t racers also suggest that mature t rees and shrub plantations can prevent deep

drainage in t he Loess P la teau. Wang, Y. et. a l. (2008, 2011) exami ned how t he soil erosion cont rol mea­

sures, such as reforestat ion , t he affected water y ield at t he watershed scale in t he semi-arid Loess P lateau region in ::.J"o rthwestcrn China. JvJ ult i-year w<1ter bala nces were coJrsLructccl Lo estimate Lbc rc·spectivc long-term mean annua l l::T and runof[ for t.l rc forestla nds a.nd nmr- fore::;t.lan cls of 57 basins. T hey reported

thal the overall annua l runofi' a nd corresponding runofl/ prccipitaLion ratio \\' ('f'C

low, with a mcall of 33 mm (7%) rangi np; from 10 mm (2%) lo !)(j !IIlii (J:j'/{. ). The average of annual precipita tion w:1s '163 mm for a ll basins. T ht' corrC'spond­ing averages of am rual ET and runofl" were 44 7 and J (j mm for forc:;d ands and 424 and 39 mm for non-forcsLlands, res pectively. Altltough tltc absolu te dil~

fercnce in the gra nd a\·cmge of a nnutt l run ofi' was only 23 mnr , iL represent s n.

la rge di fference in relatiYe t.erms, representing 58% of annual runof[ fro1u non­forestla nds. S im il~r findings were report.cd in a synthesis st ncly Lhat a imed a t detecting fores ls' roles in infl uencing at rnnal water yield across Nor thern China (\Vang, S. et al. , 2011). T he authors concl uclccl t hat. s t reaw flow <tmount a nd

nurofl/precipiLnt ion ratios for \n \tershcd:; on t he Loess Pln.Lcau were Hegat.i\·l'ly COITI'Iat,cd t o the percentage o[ forest covers . Howewr, t: hc relaLionships bel.wc<'ll forest cover percent age <=l!ld stren.m fl ow were not as obvious ::1ncl consis lent. in

two ot.her rela t in ' ly wetter regions in ltortlrwcs tcnl (XJ / GS) and Nort ltcasLern C hinn (Fig. 8.Li). Air tem perature regin1c. snu\v/glaci••r distri bn lion, ami forP~t. cover types mighL luwe masked tire Lr uc io res t-waLcr relatiousltips (Wang, S et al., 20 11) fo und in the sen ti-arid LocHs P lateau region or otlrN regions in tire

162 - GC' Sun, et al.

Northeast ~ 400

..t.. RunofT/P --- Poly.(RunofTIP) • 0.51 • RunoiT - Poly.(Runofl) ..t.. 350

RunofTIP = I E-05 Forest2"'-0.0026 Forest"'-0.12 _...t;~ 300

0.4 /12=0.60 / 250 '!>..

~ 0. 2 g .3 200 g ~ ~

~'<: 0.2 - 150 g c::

- - 100 0. I f==:=== •

Runoff=O.O 164 Forcst2+0.7054 Foresl+70.5 50 R•=0.58

0 0 0 20 40 60 80 I 00

Forest Percentage(%)

Northwest 1.2 500

RunoflYP --- Poly.(RunofTIP) 450

1.0 1 :. - t1 • RunofT - Poly.(Runoft) • 400

0.8 350 ....._

~ 300 !;.. 0 -~ s § 0.6 ----- 250 E ~'<: RunoiT=-0.0 152 Forest2+3.96 Forcst+ l98 !;;

R2=0 l3 200 o . ~

M I~ ~ tF 100

0.

2J. e I I I I r~Q 0 20 40 GO 80 100

Forest Percentage(%)

Loess Plateau

O. l S c l ..t.. RunoiTiP --- Poly.(Runoft'P) n I OO 0.16 I • RunofT - Poly.(Runofl) H 0. 14 80

0.12 Kunon=u.uu 17 l'orest~-0.3!1 Forest 1-36 ~ ~ 0.1 0 2=0 0 60 ·~ o e § 0.08 _§. ~ 40 ~

0.06 • ~ ~ w 0.02 "f-e,_.'------~t------'==:.-.==--i

0 0 0• 20 40 60 80 100

Forest Percentage(%)

F ig . 8.4 A cotnpnriso11 of t he complex rela~ionships between torcst cover raLes a nd observed st ream Oow i11 th ree regions in Northern China (Wang et a l. , 20 I J ).

8 lmp:t < ts of Global Change' 0 11 \VaLPr R<'><>II I'CCS in Dn·l;~11d Eas t Asin - l(i :~

wor ld (Andreassian, 2004.) . These sLudies suggest thaL large-scale fores tat ion

may have serious consequences for water management and sustainable develop­

ment in the dry regions because of the potential stream flow reduction , especially during low-flow periods (Brown ct a!. , 2005). Soil conservation practices such

as reservoir construction can iner<'n.o;e or decrense base flow depending opera­

t. int • sr·l!< •!!I<' S (llwmg alld Zkut g. 21lll l: Zltn n)-!; ('\ ;tl. . 20W-h). IL is in.polrt.; u!l lO

qtt <~ n l i L; l l i H:Iv t 'Y<lht<ll t' h• >\\' lat1 •l cm·t'r cit<lttge Jll<l.\' aflen.tltl: water lwi;~JJCC,. iJt

ar iJ environll l0nt s . Soil co11sern1Lion lllCas urc::. LllaL inclmle bot h bio logical (n:­

forcsLatiou) and engincer i11g appronche~ (check dallls. Lc•tTaciug, etc.) ha.vc been

implemeuted iJ1 arid Northern C lti na, particularly in Lhe Loess Plateau region,

since the 1950s t o reduce soil erosion and sediment loading Lo the Yellow R iver,

which incre<l.ses crop prod 11ctivity a nd improves l he harsh etwironmcnt s.

8.2.3 Agricultura l Irrigation a nd Industrialization

It was estimaLed tha t C hina has 14] .1 million ha cropland, about 25% of which

is paddy lands and 75% dry farmlands (Liu et a l. , 2005). :tvJore Lh<w 30% of farmla nds rely on irrigation that accounts for a large porLion of all water use,

especially fo r the dry north (Lu et a l. , 2012). Irrigation is essent ia l for grow­

ing winter wheat and maize in the Northern China Plain and for producing

cash crops (e.g., cotton, vegetables or fruit trees) in the DEA region . During

1990- 2000, Lhe northeast and nort.ltwcst regions of Chiul'l gained cropland areas

by converLing grasslands, wetlands, and througl1 deforestaLion, while t he norLb

aucl southeas t regirms showed a loss of high-quality croplands due Lo urbaniza­t ion. Tl11 . .! newly ct •'aled croplands in t. lte dry regions in C hina mo:;L likely need

irrigation to achieve profitability, ca using emerging envirom11enLal concems. Jn the I'iortltern C!J ina Plaiu, grou nd water is Lhe utajor source for in igaLion

because surf<H.:c water is not sufficicttl; to meet Lhe high ET demand from I\:fay

to September 11nder the monsoou cl imaLc, in wltich mo:; L precipitat ion occurs

from J une Lo Septeml>er. In somt? areas in the Northern China Plain , pulllpiug

groundwater for irrigation ha.'3 resu I ted ill water table declines of 20- 30 111 over t,he past :.:}0 years and large reductions in stream flow (Jin et al., 200!:J; Foster

et al. , 2004; Liu and Xia, 2004). A grou ndwater monitoring \\·ell in the Daxing

Dis t rieL 00 km outs ide of downtown Bc•ij iug, showed L haL t. lt~ water L<l blc leH•I

of t he surficia l aquifer has declined ;tl a rate of 1 .. J meter pC' r year i 11 t. he las t.

decade (F ig. 8 .5) . In this a rea, large groundwaler withdrawal oecnrrcd during

spring and summer seasons as a result of irrigation bul water labk· decline

recovcrf' <l S a result of groundwater recharge dming fall and \\' inter sca:,-ons wlten

water usc b,v agr icul t ure suLsides. Sit n i larly, rapid ground water level decli nes arc

colllmon in t. hc Heilongji ang Province and smrounding regions, Nor t heastern

J 6·1 - Gc Suu, ct al.

C hi na, whe re H-gTicuiLure accounts for 84% of water nse ( Liu and Xia, 200£1) . OIJ~erved m onllJ!y strea nlflow and raiu l.'a ll data over a period of 35 years (19G'I-

19GG, 1973 2001) fTom the Cltao-B ai ll iver in Hebei Province tha t provides much

of Lhe water supply for Beij iug show t hat human activit ies had bigger impacts on streamflow than climal.c (Wnng ct. al. , 2009) (Fig. 8 .6) . [twas estima ted that,

httn tatt act iviLi<'S (i .e., forc~l cover change, llulllall walcr wit hdrawal , s iltat.ion

dant ami rc~crvoir consLruct ions) and prccipitalion decrenses cont.ribuLed to 70% and 30% of t he observed decrease in r unoff, rcspccti vc•ly. Similar find ings are

-8r-----------------------------------------.

~ 10

.g - 12-c. 0 0 0 ::0 r:: - 16 .... " ~ - 18 -

- 20

-22~~~~~~~~~~~~~~~~~~~~~~ 6 12 6 12 6 12 6 12 6 12 6 12 6 12 6 12 6

Month

F ig. 8.5 Wa l.cr t able level decl ines during 2001- 2009 measured by a well in t he Daxing Dis l.ricl., suburbau Beij ing (Zha ng, Y. ct al., 2012).

1.400.-------------------------------------------- --y- 180

8 1 ,200-!Ar"'-\--'i-'l\-:---:c~\l*+-:&::;-~o;,.;:;o;r---~r----:ck-,lt-..a::......;'\-,....,.::z--f1 160

5 140 ti 1.0004-------1- 1-----------l 0.. 120

60

40

20

Year

F ig. 8 .6 Observed long-lcrnt (1 061- 200!J) t rend of stream II ow cl tangc in t he Chao- !Jni H.iv<>r of I [euci Province, showing a ~ harp decline in surface walcr resources since the early 2000s due l.o humm t wa l.cr 11se. l:lo l.lt precipilat.ion a nd pol.em ia l evapotranspim­Liun \'ariubles have no signific;J nt. t rend .

8 l 111pac 1.~ of C:lnbal Change 0 11 \Va i.<' r Ho•svlliT cs in Dn ond Em;t :\si • - JG!i

reported by Zheng eL al. (2009) to cxpla iu t he observed streamflow decl ine in the

headwaters of the Yellow River Basin. The lower reach of the Yellow River had similar water shortage crisis due to increased waLer consumptio11 for irrigation . Irrigation accounts for nbouL 90% of water consumption in the Yellow River

ba.c;in (Chen et a!., 2003; Xia eL a!.. 200·1). \Vit.lt the rapid inclus t rializ<lLion, \'.'HI <'r <i••tnand b\· ot J., r f'Cunontic ,.;. •c:t or" it !CT!'as< I rapidly a:; \\"I'll iu t ltl' Ydlm\· llivN Bn-< in (Xu l WJ.-,J.

8 .2.4 Climate C h a nge

Clilllale change is hydrologic change, wit idt haH profound impacts on all aspects of water resources. The \\"aLer-lim ited drylands arc especially sensitive lo cli­

mate change, precipitation in particular (.\ Ia el al. , 2008) because :-.urfa ce and groundwater resource;; a rc scarce a nd Lhc hydrologic balances arc dominated by

precipitation variability (Zhcng et a !. , 2009) . China's climate is warming np by 1. 1 ° C over Lite pas t 50 years, faster than

Lhe global a verage of 0.74 ° C (1906- 2005) (JPCC, 2007) or even Lhat of the Nort hent Hemisphere !"o r Lhe same period (Doug ct. a l. , 2009). The wruming has been accelerating since Lhe mid-1980s, pal'Licularly in Northern China. The rise of a ir tem perature is pa rt icularly s ign ificaut. it t winter. The ai r temperature in the Yellow River basin ltas increased 0.29 °C per decade since 1989. T he largest. warrni11g is fotmd in Northeast China , with a !.rend of 0.36 cc p er dccad0, a nd

in IM with 0.4° C per decade (Piao ct. a !. , 20 I 0). T he air temperature in XJ in­creased 1.01 ° C dming 1881- 2001 (Xia c t. a !. , 20 li ) . Precipitation i:; increasing in sou l hcrn aud some western regions a ud dec:rcilsi ng in the north n.nd um"tlt ­east (Tno ct al. , 2003). Jn lhe Tarilll r iver ba:;in, Lhe tempemt.me experienced a s ignificant monotonic l°C rise, and annual precipitation showed a significant decrease in the 1970s, a nd a Significant increase in Lhc1980s and 1990s a t a rate

of G.8 mm per decade. A step chang<' occurn·d i11 both temperat.me a nd pre­cipitat ion time series n.round 1986 clue to glolJal clitnate ch::t.t tge (Chen aud X u,

2005). The c lima te records of Il\:1 snggcsLcd a warmer and drier Lrend from ., %5 to 2005 (Ln et a!. , 2009). The annual daily mean, daily maxill lllll t <UJd daily minimwn tempera! me increased wltcreas the diurnal Le1npenl l ure rang<' tDTR.) decreasccl. The d('ncasing t rend of <tnnual precipitation wa:> ttol. st.al isLically s ignificant. HO\n;:\·cr. Lite Yapor pre~surc ddicit. (VPD) i11creasNl significantly.

By biome region, din ta le in the gras:;laud a ud Lhe dc;;ert bionw,; had tnore pro­nounced change Llta n in the forest biontc. DTI1. and VPD showed the la rgest inLer-biome gracJ ie11l from the lo\\"eSl ra I.e of clta.ngc in the foresl lJiCJ Jlle to the

highcsl rate of cban~c in the deser t biunJC, suggesl. ing drier regions were experi­encing more cl1ange:-. .

lGG - Ge Sun, l!l al.

Chiua experienced a series of severe extended droughts (1920- J 930, 1939- L9..JO, 1956- 1958, 1960- L963, J 965- 1968, 1!:.178-1980 and 1999- 2002) during Lhe 20tll century (Xiao eta!. , 2009). FUture projections for China's climate arc ttncerLain (Piao et a!. , 2010) , buL most studies show climate cha nge will have serious im­pacts on water supply in the dry lands in Northern China. ClimaLc change will like!.'· have a larger impact Oll water supply in light of projected widr~prcad sum­mer drying in mid-la lilucle regions during the 21st century (JPCC, 2007) . Two nmjor waler rcso11rces issues related to climate change arc Slllllttllll'ized below.

1. G lacier retreat

There a re aboul IJG,OOO glaciers CO\'ering all area of 59,000 km2 ill t he Qinghai­Tibetau Pla teau region, Western China (Xia et al. , 2011). Glaciers play a key role in providing waler for Ll1e clryla nd rivers and recharging local groundwaLer systems. There nrc ser ious concerns abouL the s hort- and long-Lcrrn hydrologic impacts of glacier rctreaL on freshwaler supply, irrigation alHI hydropower po­

tential (Immcrzccl et a l. , 2010; Sorg et al., 2012) . It was estimated Lhat roughly 1,400 km2 of glaciers has been lost in Western

Chiua in the pas t 50 years (Xia et al. , 2011). Since 1985 a lone, glacier storage in Lhe dryland a reas i11 \ Veslern Chjna has decreased by 15%. resu!Li ng in 5%

32% increase in a nnua l streamflow. Cousequent.ly, the Tar im Ri ver basin in central XJ saw a s ignificant. rise in the water levels of glacier lakes and an record fioods down slrcalllS in Lhc 1990s (Chen and Xu, 2005; Xia eL al., 2011; Sorg cL al. , 2012). Piao ct. a l. (2010) summarized observed changes in glaciers aL 22 monitori11g slations in Western China. They reported Lhn.L tltc some glaciers have shrunk as itigh as 50% ill the T ianshan Mountains over Lite past 30- 40 years. Tiansitan :rvlounLains , !mown as Lhe "water tower of Centra l Asia", has had shifls of seasona l runoff maxima iu some rivers (Jmmcrzccl eL a l. , 2010; Sorg eL al., 201 2). Titc increasing trend in glacia l runoff, especia lly in spring and early summer , may result, in rednccd ·water availability in late summer and fall and in a water shortage in lite long run. Over Lh~ next 50 years, small glaciers ( < 1 km2 )

may disappear. Overall , 5%- 27o/c of the glacial area is projected Lo disappear by 2050 and 10% 67% by 2100. Glacier melt runoff may increase in t he next few decades and peak a round 2030- 2050 and could gradually decline afterwards (Piao eL al., 2010). Other studies suggesLed that, by 2030, Lite total area of

glaciers in China will s it rink 5.6%-8.5% a nd storage wi ll decrease by 6.1 %-9.3%; consequently, Lola! river fl ow will increase by 9.6%-15%. Loug-Lcnn exhaus t ion of glacial water supply will have a considerable impact on Lhc avail <Lbili ty of water for both ;LgricuiLmal and human consumption in Lhe rcgio11.

2. Surface water and groundwater availability

A11 increase in ;~ir Lcmpcrnture and decrease in prccipitat.ion partially contribuLc Lo the general dryi ng Lrcnd in :"Jor thern China (Xia et al., 20 LJ ). Compared

8 l rnpad~ of Clobal C lr<l.nge on Wa t· •r Ht·~nur<.:£»< in l yland Eas l :\,: i,r - ] r,/

to the t ime period of 1956- 1979, total water resources decreased by about 25%

dming 1980- 2000 in the four major rivers (Yellow River, Huaihe, Haihe, Liaohe) in ~orthern China. An increase in ai r temperat ure wi ll increase water used for irrigation. A 1 °C temperature rise will increase the demand for irrigation by 6%-10% (Cruz et. al. . 2007) . In the past 30 yf'ars, s twarn flo,,· of tlw Yf'llow '!l iver (rec<~r•kd :rt llua~ "' ukou ll .\'( lrologir· '1· :111\lll ;. t midd le t'l'<l ch) h:•: dr ·<'J'C;l '-'ed h.'·

22%. l)urillg 1()7:2 - l!JU:J, tlH· Yellow n \'('(' \\.b f'OII ll d I f) lw dried up rllr ~:- .\ ' {';\!'~

of tJw 2:3-YeHr record. l ll J !J97, t ilt' river ~I uppl'd l'lllllti ttg for 2:2() del\'~ with over 8;--1'/o of t.hc river chaullcl beiug dried up. Scclimcnt. loading has dccrrascd

front J A bil lion tons per yea.r in the 1900s to ouly less t Iran 0.4 hill ion tons in the early 2000s. Climate change (decrease in precipitalion nnd r ise of air temperature), soil conservation activities, and wntcr wit hd rawal upstrca n1 for irrigation a ll cont r ibuted to the hydrologic a nd sed iment dynamics (Xia eL al., 2011 ). Li ei a l. (2009) reported that lhe large climate variability during 1981-

2000 influcHc<•d surface hydrology more significant ly Lltan t.be minor la iJcl 11se change in an agriculture-dominated basin in GS. Overa ll , climate fluctuations and massive land-use changes are the root causes of the water shor tages of the

Yellow River Basin (Yang et a l. , 2004; Xu , 2005) . I t appears that the d isturbance magnitude and form s of laud use changes determine the relative influences of climate change vs. land use change for one particular bas in.

According to several Global Circulation 'tviodels (CClVIs), droughts will likely continue to dominate the Northem China P lain, but precipitation in North­western China may increase in t he next 40 years. \Vater s tress iu the Yellow

River Basin will likely increase clue t.o a rise of water demand (\\' ilske et nl., 2009) . Head water regions of the Yellow llivcr will see mpid soil thawing that. affects wetland resom ces and water ba lances (Sato ei a l. , 2008) . There arc also concerns that an increase of precipi t< rl ion and int ens ilied rain storms will en usc large flooding nnd sediment movcmem events in secUons of the river where t he channel beds a rc already high due t.o chron ic sedimeut deposi tion (Xia eL al. , 2011) .

8.3 Water Resources under Environmenta l

Chan ges : Case Studies

8.3 .1 Loess P lateau

The Loess P lateau, approximately 640,000 km2 in land area, is dominated by grasslands, dry fan nlands, and sltrubh=mds in a semi-arid, cont.inental mon-

16 - Gc Sun , et al.

soon climate in l\orthern China. Annual precipita tion rates vary from 1e.ss Lhan 200 mm per year in the desert to more t han 750 mm in the mow1tains. T he region is well-knO\vn for its high ra te of soil erosion and sediment loading Lo l ite upper and middle reaches of the Yellow ruver (Fu, 1989; La l, 2003). The Loess

Plalcau is one of the most severely Proded areM in l ite world as a consequence of the loose loess soils. s leep slopes, high rainfall intensity. aud poor ,·egetation

cond it ions as a consequence of intensive human dist.urbnncc;-; (Li et al., 2009). Jn l ite pnsL Llu·ec clccaclcs, hrge-scale soil conservaLion eA.'orts tha t, involve

strud urnJ a pproaches (i.e., ter racing, check dams) and vegetation approaches (i.e., rcforc~;taLion) have been devoted to reduci ng soil erosion and improve lite

local p0ople's well-being in this tra.clit ionally economically disadvantaged regiou (F'u el a l. , 2011). The regiona l ecological effects of these long-term efForts a rc being evaluaLcd (Chen el a l. , 2010; Fu et al., 2011; J in cl al. , 2011 ). ::'\umerous

studies arc available in the literature that describe t he combined impacts of climate change and land use change on water resources a l. different spatial scales (Huang et a l. , 2003a, b; Huang and Zhang, 2004; Zhnng et a l. , 2008a, b; Rustomji

el al. , 2008; Li et a l. , 2009; Wang et al. , 2011). vVc couducLcd a. case s tudy t,hat a imed a t understanding the hydrologic efrecls

of a reccnL reforestation campaign: t he Grain-for-Green (GFG) projecL. Spe­cific objectives were to: 1) clelecL the individual and combined roles of climate and land cover in afl"ccting evapotranspiration and water yield across the Loess

Plateau region, 2) understand how climate variabi liLy may enhance or mask the en·ccts or land cover change across the Loess Plateau region, and 3) examine the spa ti<t! ;wei tempora l hydrologic responses to vcgetn.tion in t he Loess Plateau rcgioll so that, we can provide recornmendationl:l to land planners at the regiona l scale. E1n pir ical evapotransp iration models are developed from global eddy Hux mcas lu·clucnts and local watersl1ed hydrological monitoring data. Remote sens­ing data such as vegetation cover type and leaf area index (LAI) derived from 1\ fODlS products are integrated with models to c;xtrapolale site-level hydrologic

measurements to the regional scale a nd arc used for model validations (i.e .. ET val icla.lioll ). Research methods are illuscrated in F ig. 8.7 Lo demonstrate the pro­cesses of model dcvelopmeul, validat.ion and a pplicalion. Details of this study can be found in Feng et a l. (2012).

The ln.nd cover change cousidcred in t he sLucly was most ly a result of Lhc govcn nncnt-funded GFG project tha t involved corwcrLi ng croplands and aban­

doued far111lands into forests and pasture lands. VegctaLiou covers in some areas hn.ve improved grea.tly since tile project was implemented at the end of 1999.

For example, LoLa! vegetat ion cover in nor thern Sha.'ln.x.i Province (combined for planted foresL aud herbaceous vegetation, i.e ., ~:,rrasscs, forbs, herbs) increa.~ed fro111 30% in 1998 to 42% in 2005 as a result of the G rc project (Cao et a!. , 200!J) . 1\ ltilough it is genera lly accepted thai reforesLat ion and soil conservation pnH.:ticcs ean resulL in reduced water yield and sediment (see reYiew in ~vlcVicar

8 Impact ~ oi Ulobal Cha nge on Water Resourr,., iu Drylan·i Ec,,:t Asia - 169

Climat~

• Meteorological Stations

o Watersheds for model validation

• Watersheds for model calibration

Preciptation (mm yr-1) 1790 1i0 }}0

Model Application

.. ·

I 2 3 4 .5 G 7 R 9 I \J I I l2 l\lonth

l\ lod~ l Validation

I Effects of Cl imate 011 crl

F ig. 8 .7 Illustration of t he method to model regional evapotranspiration and water yield across the Loess P lateau region.

et al. , 2007; \VangY. et a l. , 2011), few studies have been conducted to examine the relationship beLween obscn·ed vegetu.t iun change, climate variability, <llld hydrological res pouses at a regioJJal sca le for t he Loc~s Plateau. Suc:h Lypcs of studies are surely needed to expl ain regional chauge paLterns iu ecosystem func­tions such as water availabili ty and soil erosion control (l?u et a l. , 2011). For example, the observed land cover change toward more productive states iu t;he 1990s is perhaps an indication of vegetation recovery due to huwa n intervell­tion, but the contribution of climate variability in the region ca nnot be excluclecl (Fang et al. , 2003).

This case study focuses on the time period from 1999 to 2007 in which year 1999 is designa ted as the "baseline" period u.ucl 2000 to 2007 as t]JC "trealtnent:' period that has different land cover and eli matic coudition::; from the baseline pe­riod. Changes in ET (treatment period- baseline) at both annual and monthly scales are examined. If precipita tion is assumed not to be afl'cd ecl by vegetation cover change, t he effect of land CO\'Cr on wnter yield is considered t.o be equiva­lent to changes in ET. A summnry of findings for t his regional modeling sLudy follow:;.

170 - Ge Sun, ct. al.

Water yield had large spatial and t.emporal variability in the study region (Fig. 8.8a) . In general, lhe vegetation-based ecological restoration efl'ort, GFG project, resulted in an increase of water loss (,hrough evapotra nspiration (Fig. 8.8c) . £lowever, t;be actual impacts on water yield depended on the variabili ty of precipita.tion. Simulation showed that increased precipitation during the project implementation period masked the waLer yield reduction efl'ects; the GFG project might have aggravated water shortages in some areas that received reduced precipitation. Due to Lhe large spatial variability in climate and vegetation characteristics, the magnitude of hydrologic efl:'ects of vegetation change varies across the Loess Plateau (Figs. 8.8b and c). The forested areas that received more precipitation had higher responses than Lhe drier areas in terms of absolute water yield reduction. However , drier areas are more vulnerable to flow reduction, especially in the growing season. The effects of ecological restoration were strongly influenced by precipita­tion variability in the arid region. The current regional vegetation restora­tion projects have variable effects on local water resources across the region

100

I so "0 60 -.; ;;:: ... "' ~ ..... 20

600

0 300 1999 2000 2001 2002 2003 2004 2005 2006 2007

(b)

Year (a)

Water Yield Change (mmyr- 1) ,., 20

lizd -20

(c)

F ig . 8 .8 SinwlaLed mean a nnual wa Ler yield across the Loess P ialeau region during 1999- 2007 (a), efl'ects of la nd use change only {b), aud land use cha nge + climate variabi lity (c) over 2000- 2007 when compared t.o year 19!)9. Positive values indicaLe an iucrease and otherwise a decrease in water yield (Peng el, al., 20 12).

8 lmpads of Global Change on Water Resources in Dryland East As ia - 171

t hat had a large precipitation gradieuL. The future cl imate change in t he

s ludy region is li k<'ly to alter the water ba la nces due to both air warming

and changes in precipitat ion patterns . La nd management p lanning must

r onsider t.he in fluPnces of spatial di rna l<' \'<ll'iability <tnd lon.L;- term cli rn atP f'!J:11 1gP 1111 IV;l f • ••· \' iPJr! ;•·•d l'•'IJSySICIII Sl Jt l'f \11'1'~

8.3.2 Impacts of Future C limate Change on Runoff across D EA

Globa l Cil'Ctrlatiou ::\Jodels (GC!'vi:::) c:a 11 rnore or lc,;s adccjuat.dy r<'prodLIC(' t.hc

annua l variability of ai r tempera lme and precipitation; however , lhey ha,·e la rge

uncertain ties in ruuofl' s imulation due to t he simplified represcnl'ai ion of land surface processes, lack of rWloff routing computation and neglected local hu­

man impacts (i.e., reservoirs) . To eliminate these shortcomings, we a nalyzed

future nmoff changes modeled by a mod ified vers ion of the water ba lance model

(WBMPlus) (Wisser ct. al., 2008; Shiklomanov eL a l., 2013) driven by severa l

AO GC1vls under the IPCC SRES AlB emissiou scenario (Table 8 .1) .

Table 8 .1 Descript ion of Eight IP CC AO GC1vfs.

GCM ~l odcls Country Spa tia l Resolution

ECHAM5/11 fPl-OM Gcrnwny ].9° X 1.9~

CGCM3.1(T63) Canada 2.8° x2.8~

UK l\•10-11adCi'vl :3 <ircal. Bril.;dn 1.25° X l.R75°

UCCR-13Cf\.12 l\onvay 2.8° x 2.8~

::\CAILCCSI\13 USA l . 'l 0 x lA0

IN1\·1-C~I 3 R.AS Russia 3.0° x-l.O"

GFDL-Cf\.12.1 USA 2.0° x2.5"

MJROC3.2( mcdres) .Jap<m 2.8° x2.8"

WBM is a g loual-scale, gridded model Lhn.t sitnulates both the vert ical ex­

change of wrtter beL ween t he ground <lll cl t li0. a tmosphere, a nd t;lie hor izontal

Lransport of ,,·aler through nmofl a nd s Lrcam networ k::;. The u::;ed version of the

model also has Lhe capabil ity to model the i111 pacL of large reservoirs on st.rcam

flow <tnd the roho of irrigation on t. he vertical exchange of w;tter. To ana.lyzc

future ch<mge:; in region<tl hydrolog~', we ran WB~'lPlus with :lOx 30 min spatial

resolut ion a.ud IIIOnLiily t.ime steps nsing future clin tate scenarios generated fro111

eight AO GCMs (Ta ble 8 .1) ( ht lp: / / nccspi.sr .nnl r.edu/ 111a ps/) . Rei'inlls indicate' a l<'ndency lo,,·ard decreases in river muon· across DEA,

a llhoH• ;I ll 1• proj<'ct <d dt<lll!!'~'" an• 1' · 1 sp:lli;dJ.,· ll 'l ifo:· u .. l'r ~nn ~.9 ::.ho"·s

changt' s in n 1 :1Hal rin ·r l'llllt <f. across lJGA by 20IU 20t•U fru n1 the lollg-ttnll

172 - - Ge Sun, el al .

20 .40 Cc.lculntctl l>:~ to~

• 1 E'G EN DH ·

t-.H G E NO .

GFDL Freq~ncy llinograrn fer the Ollcul:l.tcd J);l~

"'r,:;;:;j.::..-1,;,71 " I' "I ~ ,.l_ _j_,

Calcui.J.t:J I)J.u

·~~E G•E.N o·.

NCAR

.66:-."~~~·!:'r·mlor il!r~· l5 . f'~.~IAWra&e "' 6,.&71 . ·· ··l···---~_· 1 30 . .. .• ·J ~

0: 25 ·- --- =a' ~ I

~ 20 -,--- __ , __ ;__

! .J .. ,_, -·· -. . -··-- -·-

- ~(.

Ca:c:ullled D;ata

.lll ta!ifiE G•E NIO i

F ig . 8.!) T he dev i<Jtious o f mean l'l nnual p rojected ru nofr for 2040- 20GO from mean contempora ry runofr over 1959- J 999 under 20c3m scenario simulated wilh \ VBMplus us ing cliO'erenL AO GCMs (lPCC, 2007; Shiklomanov et al., 2013) .

b Jm pacls o f Global C hange on \Val,•r Hcsourccs in Dryland Ea~t :'\sia - li:.l

average (1959- 1999) for GFDL-CM2.1, IN.tvi-CM3 RAS, MPl ECHAM5 and NCAR CCSM3 AO GCMs. The DEA region , in the future, will be drier with a

decliHe in annual rive r runoff aggregated for the entire domain in the range from

- !'i mm to - 11 mm (fig . 8 .~) . Howe\'(>J' . !\CAR CCS:'I.f3. with lh<' lws t. spa!i :=!l

r• .,.,ol11t j,·ll l nnd t l , · IIIOSt " '>phi,;! ica t r·d I l ' JH "c ,.,en! 111 !o 11 of I a 11d ~~ : :'a n· Jll'L'i '•'S'• " ·

1•rojccr,; \·o:11pl<' l.dy dil i· rv1.t fut ure: cli lliillC's wi th high0.r at)!\ '! •I p n ' r·ip iw t j,,n

<llld thus increased a i1111 Hll J'llllOfl' by 16 Ill ill hy 2040 20GO (Fig. x.9). Till iS, t.hc:re

is" great uncertainty in f'utmc runoff project. ions because of a gt t' ~lt. um.:crta inly

of future climate among different IPCC AO C: CMs. T here is a lso a large uncert ainty in Lhe projection of changes in Illonthly and

an nual river discharge l'or t.lte lil.rge regiona l river~ . snrh as lhc ) \ >llow R iver.

SimulaLions for Lhe same location a re preseut.ed in figures 8 .10 and 8.11 . Large

discrepancies among models were found fo r Lhe fal l season. Accordiug lo the

most AO GCM (except NCAR), increa.c;es i11 r iver discharge are projected during

winter and spring mo11ths and decreases dw-ing summer-fall wlJCII water use by

ecosystems and huma ns is highest .

7,000

~ 6,000

: 5,000

5 4,000 " ~ 3,000

....,_ UIU ... tOA i b

..._NCAR Alb

_,._ ECHA:0.1 A I b

-x- 8 GCMs 20c3m

-+- 8 GCJI.-Is A I b ~ 2,000

0 I ,000 0~~~~~~~,~~~~

2 3 4 5 6 rvlonth

7 8 9 10 11 12

Fig. 8 .10 M ean moutl dy discharge simuh~Lcd wiLI 1 t he \.VBi\-fplus tllucl cl for til e Yellow River for 20.40- 2060 (JPCC AlB emission sccn:u·io) and I !J59-1 9!J~ I (l'ur 20th cent ury IPCC AR4 20c3m scenario) from different. G C l\ls .

-UKMO - NCAR -ECHA!Vt ...... g GCI\•ts 5,000 4,500

I "' 4,000 g 3,500 1) 3,ooo I C' ~ 2,500 ] 2,000 i:5 1,500

1,000

500 0 1959 1969 1979 1989 1999 2009 20 19 2029 2039 20·19 2059

Y~ar

F i g . 8 .11 ~,k.,, t ann11 al discharge vari; .J ,i l iLy f',r t. IJc YPII•JW H ivcr :--i i nlil;\ l NI w i t.h the \VB.\fplu~ I'' " ! I . il !'f' l'l'lll C:C\ls n sit l ~ t h· 20· 'h n , , .. uari" Il l .·, l ! lf)() <~lld srn;s A IIJ ;:j IIC\ ..:1}\) I.

174 - Cc Sun, ct. al.

8.4 Conclusions

T his review found that both climate change (e.g., glacier melting due to global warming) and land usc cha nge (e .g., conservation, irrigation) have severely im­pact.ed sLrean t flow in mnny a reas in DEA. The region is raci11 g an uuprece­dcnLcd waLer shortage tha t has caused serious concerns for the sustainabilily o l' the regio11 as a whole . Dra.rualic land use changes driven by populaliou growth, urbanizatiou, iudustrialization , and poorly guided ecologica l rcstoratiou a rc Lhe

root causes for t his water crisis. Global climate warming has a ltered the normal local hydrologic cycles and ecosystem fun ctions in some key regions by melting glaciers, t!J awing frozcu soils, and elevat ing water demand for agTicultural irri­gation and hurnan usc. Continued climate change will have profound impacts on DEA and will likely aggravate tbe cmrent water problems characterized as d iminishiug surface water, groundwater depletion , increased water pollution aud

expansion of soil erosion/ desertification . Solving the wa Ler resource issues in DEA cannot be achieved by looking at. the

water sector a lone. ln fact, single-handed soil and water conservation practices such as reforestation in Northern China have resulted in tmintended environmen­tal conscquc11ccs. An ecosystem approach is needed to manage the trade-offs be­tween a ll ecosystem ser vices (i .c., soil erosion cont·rol, water supply, groundwater

rrccharge, carbo1 r sequestration, and climate moderation) . Integra ted watershed managenrent tha l considers all watershed service needs by humans aud nalura l ·ecosystems should be promoLed . \Vater conservation practices that promote io­·creas ing water use efficiency and implementing demand-based wa ter allocation management in agricuHural irrigation and industry water use may have immedi­ate efrects in tlJe face of rapid economic transformation in Northern China. Pac­ing t he la rge nuccrLa inLy of climate change and socioeconomic changes in DEA, decision-making processes and institutions must adopt a robust and adaptive framework to achieve long-term sustainability in DEA (Lu ct al. , 2012) .

Acknowledgements

~viajor funding for this syuthcsis comes from the USDA Forest Service East­ern Forest, E nvironmenLal Threat Assessment Center, t he LCLUC P rogram of NASA, Lhc Natura l Science Foundation of China, the Chinese Academy of Sciences, the Rcsea rcll Priorities Programme of China (No . 2009CB421104),

the Nationa l NaLural Science Foundation of China (No. 40801070), and the CAS/SAFEA Internationa l Partnersllip Prograrruue Jor JnnovaLion llcsearch Teams of "Ecosysl.cm Processes and Services" . GIMJviS AVHRil-NDVI data

IS l ulpa<:L" ol G lobal C hange un \>Vater !idourcc:; iu l>rylaw 1 Eas~ A sm - 175

and SPOT VEGETATION data were provided from the E nvironmental and Ecological Science Data Center for \Vest China (http:// westdc.westgis .ac.cn) . Also, we would like to thank two anonymous reviewers for their comments aud suggestions that helped to improve t he quality of this C'haptrr .

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Authors Information

Gc Sun 1*, Xiaominp; Feng2 , Jingfeng Xia.o3 , Alex Sluklonranov3 , Shcngping

\Va.ng\ Zbiqiang Zhang5 , Nan Lu2 , Sltuai Waug2 , Licling C ltcn2 , Bojie Fu2 ,

Yaning Chen6 , Jiquan Chcn 7

L. Eastern ForcsL Environmental Tlueat AsscssruenL CenLer, SonLitern H.esearch StaLion, USDA Forest Service, Raleigh , NC 27GOG , USA

2. Resea rciJ Center for Eco-EnvironmcnLa l Scie11ces, Chinese Academy of Sci­ences, Beij ing 100085, P.R. China

3. Eart h Systems Research Center, lnst iLute for the St udy of Earth, Oceans,

and Space, University of New Hampshire, Durham, NH 03824, USA 4. Key Labora tory of Regional Energy System Optimizal ion , ·orlh China Elec­

tric Power Universi ty, Beiji ng 102206, P.R. China

5. Co!Jege of Soil a ud \Vater Conservation , Beiji ng Forestry Uni vers it y. Beijing J00083, P.R. China

G. Xinjiang lnst.it.utc of Ecolog:; and C:cograpl ty, Cltincsc J\cademy of Science, Ur iimqi 830(11 I, P.n .. C ltina

7. Deparllllent. of E uvironmcutal Sciences, Univers ity of Toledo, Toledo, OH I :~GOG-:n~ln. CS1\