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ImpactsofRe-greeningtheDesertifiedLandsinNorthwesternChina:ImplicationsfromaRegionalClimateModelExperiment

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Journal of the Meteorological Society of Japan, Vol. 82, No. 6, pp. 1679--1693, 2004 1679

Impacts of Re-greening the Desertified Lands in Northwestern China:

Implications from a Regional Climate Model Experiment

Omer Lutfi SEN

Istanbul Technical University, Eurasia Institute of Earth Sciences, Maslak, Istanbul, Turkey

Bin WANG and Yuqing WANG

International Pacific Research Center, School of Ocean and Earth Science and Technology, University ofHawaii, Honolulu, Hawaii, USA

(Manuscript received 8 August 2003, in final form 19 August 2004)

Abstract

This paper describes a study that investigates the local and regional effects of vegetation restorationin northern China via regional climate model simulations, and reports implications for the sustainabilityof vegetation under the altered rainfall regime. Ensemble simulations with the current vegetation coverand an idealized re-greening scenario for a test area in northwestern China (90�–110�E and 36�–42�N)were performed using large scale boundary forcing derived from 1998. The results indicate that suchre-greening has both significant local and regional effects on the atmospheric circulation and rainfalldistribution.

Replacing desert and semi-desert areas with grass in the test area increases net radiation at thesurface, and hence total heat flux from the surface to the atmosphere. This results in enhanced ascend-ing motions and moisture supply to the atmosphere over the test area. Consequently, rainfall increasesin the whole test area. However, the increase in rainfall largely occurs due to an increase in intensityrather than an increase in frequency. Lack of frequent rainfall, especially in the lowlands of the testarea, makes it very difficult to maintain a vegetated surface. This implies that the current vegetationrestoration activities will be largely limited to areas where water resources are relatively abundant, orthey will depend heavily on irrigation. The increased runoff at higher elevations could be important forproviding water for irrigation in the lowlands. The increase in rainfall in the highlands and far easternparts of the test area, which already receive more frequent rainfall, may help support a restored vege-tation cover in these regions.

The enhanced ascending motions over the test area are compensated by increased subsidence to theeast, centered over Yellow River Delta and Shandong Peninsula, resulting in a higher-pressure and an-ticyclonic circulation anomaly there. Consequently, rainfall decreases at these areas. This anticyclonicanomaly provides significant northeasterly low-level anomalous winds that enhance cyclonic shear vor-ticity in the Yangtze River Basin and South China when they meet southwesterly monsoonal flow. Thiscauses strong ascending anomalies over southern China and the Sichuan Basin, and increases rainfall inthese regions.

1. Introduction

It is broadly recognized that land-surfacedegradation can have significant impact on theoverlying atmosphere, thus on the regional cli-

Corresponding author: Omer L. Sen, ITU, EurasiaInstitute of Earth Sciences, 34469 Maslak Is-tanbul, Turkey.E-mail: senomer@itu.edu.tr( 2004, Meteorological Society of Japan

mate, as it alters the surface-atmosphere inter-action processes. Desertification and deforesta-tion are two types of land-surface degradationsthat have been a major research focus of thescientific community over the last two decadesor so because the land areas subject to de-sertification and deforestation expanded rap-idly during the last century (e.g., Charney et al.1975; Dickinson and Henderson-Sellers 1988;Lean and Warrilow 1989; Shukla et al. 1990;Nobre et al. 1991; Henderson-Sellers et al.1993; Lean and Rowntree 1993; McGuffie et al.1995; Xue 1996; Hahmann and Dickinson 1997;Kanae et al. 2001; Zeng et al. 2002; Sen et al.2004).

Desertification refers to land surface degra-dation in arid, semi-arid, and dry semi-humidareas that has resulted from human activitiessuch as overcultivation of marginal land, un-sustainable ‘slash-and-burn’ agricultural prac-tice, logging for fuelwood, poor irrigation tech-niques, and overgrazing (Wang and Jenkins2002). Desertification increases surface albedo,hence reducing net radiation at surface, whichleads to radiative cooling of the surface. Thisenhances sinking motions in the atmospherethat decreases precipitation. The reduction inrainfall decreases soil moisture, which leads toa reduction in evaporative flux. Consequently,the Bowen Ratio (BR; the ratio of sensible heatflux to latent heat flux) increases, that is, at-mospheric humidity decreases, which leads to afurther reduction in precipitation. The changein surface temperature due to desertification isprimarily related to the competing effects of thechanges in albedo and latent heat flux (Wangand Jenkins 2002): an increase in albedo coolsthe surface, whereas a reduction in latent heatflux, especially in wet season when latent heatflux is relatively large, warms the surface. Thetotal effect is, therefore, highly season depen-dent, and the surface is usually cooler in thedry season but could become warmer in the wetseason.

China is one of the countries that have ex-perienced profound desertification during thelast several decades. Desertification is affectingone third of the country. Annual expansion isreaching to a rate well over 2400 km2/year(Zhao et al. 2002). China has made plans tobring its growing land desertification undercontrol by 2010 through massive restoration of

vegetation across the country. Western ChinaDevelopment Plan that has been implementedin China aims to replace farmlands and re-green the desertified lands with forest andgrass to fight against desertification (Shi andWang 2003). The sustainability of the re-stored vegetation cover, however, remains abig question. Reversing the desertification pro-cess largely depends on a persistent increasein precipitation, especially in its frequency, tosupport restored vegetation.

In order to investigate whether a relativelylarge-scale vegetation restoration effort can im-prove local rainfall enough to help maintainvegetation in once desertified lands, we carriedout an idealized land-cover change experimentusing the International Pacific Research Cen-ter Regional Climate Model (IPRC-RegCM).We also extended the study to see how such alarge-scale surface cover change affects theEast-Asian summer monsoon and its rainfall.

The present paper is organized as follows. Abrief introduction of the regional climate modelis given in Section 2.1. The modeling experi-ment is described in Section 2.2. East Asiansummer monsoon is briefly described in Sec-tion 2.3. The results including local changes insurface variables and regional changes in rain-fall, rainfall frequency, runoff, and large-scalecirculation are presented in Section 3. Con-clusions are summarized in Section 4.

2. Model, experimental design, andEast Asian summer monsoon

2.1 ModelThe IPRC-RegCM model (Wang et al. 2003)

uses hydrostatic primitive equations in spher-ical coordinates with sigma (pressure nor-malized by surface pressure) as the verticalcoordinate. To facilitate accurate long-term in-tegration, the model uses a fourth-order advec-tive conservative finite-difference scheme (Xueand Lin 2001) on an unstaggered longitude/latitude grid system and a second-order leap-frog scheme with intermittent use of Eulerbackward scheme for time integration. Themodel has 28 vertical levels with variable reso-lution, the highest resolution being in the plan-etary boundary layer. The model physics arestate-of-the-art. The comprehensive cloud mi-crophysics scheme developed by Wang (1999,2001) represents the grid-scale moist processes.

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Subgrid convective processes, such as shallowconvection, midlevel convection, and penetra-tive deep convection, are based on the mass-flux cumulus parameterization scheme origi-nally developed by Tiedtke (1989) and latermodified by Gregory et al. (2000). This modifiedversion uses a CAPE closure and considers theorganized entrainment and detrainment basedon a simple cloud-plume model. The subgrid-scale vertical mixing is accomplished by the so-called E-e turbulence closure scheme in whichboth turbulent kinetic energy and its dissipa-tion rate are prognostic variables (Detering andEtling 1985). Surface fluxes over oceans arecalculated based on the Monin-Obukhov simi-larity theory (Wang 2002). The radiation pack-age was originally developed by Edwards andSlingo (1996) and further improved by Sun andRikus (1999). Cloud amount is diagnosed byusing the semi-empirical cloudiness parame-terization scheme developed by Xu and Ran-dall (1996) based on the results from cloud-resolving model simulations.

For the land-surface processes, the modeluses the Biosphere-Atmosphere TransferScheme (BATS) developed by Dickinson et al.(1993). BATS incorporates one canopy andthree soil layers, and it requires land cover/vegetation (18 types), and soil texture (12types) maps for spatial applications as in aGCM. In our application, these datasets wereobtained from the U.S. Geological Survey (thesecond version of the USGS 1-km resolutionland-cover classification dataset), and the U.S.Department of Agriculture (global 10-km soildata). Similar to most other grid-point regionalclimate models, a one-way nesting is used toupdate the model time-integration in a bufferzone near the lateral boundaries within whichthe model prognostic variables are nudged tothe reanalysis data with a linear nudging coef-ficient.

2.2 Experimental designThe IPRC-RegCM was used to carry out two

ensemble simulations, each with 5 memberswith different initial conditions spanning 5days centered on April 20, 1998. The currentsurface cover was used in one ensemble (here-after CURRENT) while a re-greening scenarioin another (hereafter GRASS). The CURRENTsimulations are the same as the control simu-

lations used in Sen et al. (2004). In the GRASSsimulations, the grids with the ‘‘desert’’ and‘‘semi-desert’’ land-cover classes of BATS—those falling between 90�–110�E and 36�–42�N(referred as ‘‘test area’’ in this paper; see thebox in Fig. 1)—were replaced with the ‘‘shortgrass’’ vegetation class. The test area involvesserious vegetation restoration efforts supportedby the government of China (Shi and Wang2003).

Table 1 gives some of the parametersand their values associated with the above-mentioned three land-cover/vegetation classesin BATS. By definition in BATS, maximumfractional vegetation cover can be as high as0.80 for grass, but zero for desert and only 0.10for semi-desert. The large value assigned tothe parameter—fraction of water extracted byupper-layer roots (see Table 1)—indicates thatgrass depends heavily on soil moisture in thisrelatively thin soil layer. The layer can quicklydry in dry conditions, and imposes large stresson vegetation that significantly limits transpi-ration. Albedo of grass is smaller than thatof desert, but, in wet soil conditions, albedo ofdesert can have values as small as those of ve-getated surfaces. Roughness of soil surfaceis 0.05 m in BATS. Roughness of grass is alsoassigned the same value. A larger roughness(0.10 m) is assigned to vegetation in semi-desert ‘‘biomes’’ in BATS.

In the experiments described above, the Eu-ropean Center for Medium Weather Forecasts(ECMWF) global analysis data, available at12 h intervals with a resolution of 2:5� � 2:5� inthe horizontal and 15 pressure levels up to10 hPa, were used to define the driving fields,which provide both initial and lateral boundaryconditions to the regional climate model. Seasurface temperatures (SSTs) over the oceanwere obtained from the Reynolds weekly SSTdata with horizontal resolution of 1� � 1� (Rey-nolds and Smith 1994), and were interpolatedinto the model grids by cubic spline interpola-tion in space and linearly in time. Soil moisturefields were initialized in such a way that theinitial soil moisture depends on the vegetationand soil type defined for each grid cell (depth ofsoil � field capacity � porosity).

The model domain (see Fig. 1) covers the areabetween 0�N–55�N, 80�E–140�E with a hori-zontal grid spacing of 0.5�, thus including 121

O.L. SEN, B. WANG and Y. WANG 1681December 2004

by 111 grid points. The USGS high-resolutiontopographic dataset (0:0833� � 0:0833�) wasused to obtain the model topography (Fig. 1).The high-resolution vegetation type data fromUSGS is reanalyzed to represent the dominantvegetation type in each grid box, except inthe GRASS experiment in which the grid cellswith ‘‘desert’’ and ‘‘semi-desert’’ types in thetest area were just replaced with ‘‘shortgrass’’. In addition to model domain, land cover/vegetation type and topography, Fig. 1 showsthe approximate locations of the places that areoften referred in the text. The dashed 3000-mcontour in the figure separates for demon-stration purposes ‘‘highlands’’ or ‘‘higher ele-vations’’ (> 3000 m) from ‘‘lowlands’’ or ‘‘lowerelevations’’ (< 3000 m) in the test area, thesewords being frequently used in the text to showthe fairly different responses these regions giveto the modeled land cover change.

The model simulations were initialized from00Z on April 20, 1998, and integrated con-tinuously through August 31. The results arereported in terms of the averages of each en-semble. As reported briefly in the next section,

Fig. 1. BATS vegetation cover in the model domain. Contours are showing the topography. Thedashed contour delineates 3000 m, which is arbitrarily used to separate ‘‘lowlands’’ from ‘‘high-lands’’. The dashed rectangle is the area where ‘‘desert’’ and ‘‘semi-desert’’ grid cells are replacedwith ‘‘short grass’’.

Table 1. Some of the parameters andtheir values for desert, semi-desert, andgrass land cover/vegetation types inBATS.

DesertSemi-Desert Grass

Maximum fractionalVegetation cover

0.0 0.10 0.80

Roughness Length(m)

0.05 0.10 0.05

Depth of the uppersoil layer (mm)

100 100 100

Depth of the rootingzone soil layer(mm)

1000 1000 1000

Fraction of waterextracted byupper layer roots(saturated)

0.90 0.80 0.80

Vegetation albedofor wavelengths< 0.7 mm

0.20 0.17 0.10

Vegetation albedofor wavelengths> 0.7 mm

0.40 0.34 0.30

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1998 had a wet summer with floods in YangtzeRiver. In that sense, this experiment quantifiesthe regional effects of the aforementioned sur-face cover change for an extreme wet year. Al-though it is difficult to generalize the resultsto other years (i.e., climatology), the results arestill relevant as they may represent wet yearsthat have very important consequences for theregion, such as flooding.

2.3 The 1998 East Asian summer monsoonBecause the present study investigates the

effect of northern China’s re-greening on theEast Asian summer monsoon (EASM), we willprovide a brief description of the EASM and its1998 evolution. Detailed information can befound in Ding (1994), Ding and Liu (2001), andWang et al. (2003). Ding (1994) identifies threeairflows in the lower troposphere that causeand affect monsoon processes over East Asia:The Indian monsoonal westerlies, which carryabundant moisture from the Indian Ocean; thecross-equatorial airflow over northern Austra-lia and its neighboring sea region; and thetropical western Pacific easterlies associatedwith the western Pacific subtropical high pres-sure system (WPSH).

The onset of the EASM is widely recognizedby the appearance of the westerlies over theSouth China Sea region around mid-May. Asthe summer monsoon develops, the primaryrain belt over East Asia advances northward.This seasonal rain belt becomes somewhat sta-tionary over South China, the Yangtze-HuaiheRiver Basin and North China, respectively,during its two notable northward jumps (Dingand Liu 2001). When the monsoon rainbandreaches the Yangtze-Huaihe River Basin in thefirst half of June, it marks the beginning of theso-called Mei-Yu season in China (Wang andLinHo 2002). The Mei-Yu season, which peaksin late June, is characterized by persistent andtorrential rainfall associated with the quasi-stationary Mei-Yu front. The withdrawal of themonsoon rainy season from China occurs inlate August.

The summer of 1998 was marked with heavyrainfalls that caused severe floods (eight floodpeaks between June and September) in theYangtze River Basin, the largest since 1954summer. More than 3000 deaths and large eco-nomic losses in China were associated with

these floods. An unusual second Mei-Yu periodoccurring in the 1998 summer (Ding and Liu2001) was believed to increase the losses sig-nificantly. The abnormal monsoon rainfall wasalso related to the prolonged impact of the1997–1998 El Nino event, which was thestrongest in the last century (Wang et al. 2000).

3. Results

3.1 Model performanceThe performance of the model was primarily

assessed through its ability to simulate spatialand temporal variations in rainfall, as rainfallis a stringent criterion and the main concern inthis study. A gridded version of the daily rain-fall data from approximately 950 stations (mostof them in China, the Korean Peninsula, Mon-golia, Thailand and Vietnam) was utilized toevaluate the model simulations. Because thestatistics related to control simulations (CUR-RENT) are published in Sen et al. (2004),readers are referred to that publication inorder to avoid repetition in the present paper.As mentioned there, the model simulated wellthe majority of the precipitation events asso-ciated with both southward propagating coldfrontal systems and the quasi-stationary Mei-Yu fronts. The overall performance of the modelis, therefore, deemed adequate to carry out thissensitivity study.

3.2 Local changesAs mentioned earlier, re-greening the de-

sertified lands is expected to change thelocal weather and climate through altering ex-changes of energy, water vapor and momentumbetween surface and atmosphere. This sectionreports the changes in surface variables bothtemporally and spatially over the test area.Hereafter, the analysis concentrates, in gen-eral, on combined effects in June, July and Au-gust (JJA) as JJA marks the mature phase ofEASM. The beginning of JJA also comes suffi-ciently later than the initialization date of thesimulations, which lessens concerns about themodel’s ‘‘spin-up’’.

Figure 2 shows daily variations of net surfaceradiation, Bowen Ratio (BR), and rainfall fortwo ensembles averaged for the whole testarea. Note that the area contains some un-changed vegetation (see Fig. 1), albeit only asmall fraction. Changing the surface cover from

O.L. SEN, B. WANG and Y. WANG 1683December 2004

desert or semi-desert to grass increases thenet surface radiation; the magnitude of the in-crease persists over time because this change ismostly driven by a change in the albedo, whichis a characteristic of the surface. The simulatedlandscape change reduces the BR over thetest area, indicating moister conditions. Thechanges in surface fluxes (not shown here) in-dicate that the reduction in the area-averagedBR is a result of the increase in latent heatflux. The area-averaged sensible heat flux

does not show any large change (not shown).The modeled surface change seems to increaserainfall over the test area in general, but theincrease occurs mostly as enhancement of therainfall within the rainfall generating systems.

Figure 3 shows the changes (GRASS-CURRENT) in latent heat flux, sensible heatflux, surface layer soil moisture, and air tem-perature (2 m) in JJA over a domain includingprimarily the test area. Switching to grass in-creases latent heat flux over most of the test

Fig. 2. Daily variations of (a) net radiation (W m�2), (b) Bowen Ratio, and (c) total rainfall (mmday�1) averaged over the test area. Solid line is from CURRENT, and dashed line is from GRASSensemble.

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area, but the changes are not uniformly dis-tributed, and the largest increases occur athigher elevations. Latent heat flux outside ofthe test area changes little (not shown). Figure3b shows that sensible heat flux increases atlower elevations but decreases at higher ele-vations in the test area (probably the reasonwhy the area-averaged sensible heat flux doesnot change much between two ensembles), andit does not change much outside (not shown).The changes in surface layer soil moisture (Fig.3c), which is the main source for grass transpi-ration, and the changes in air temperature(Fig. 3d) depict somewhat similar patterns tothat of sensible heat flux. The large positive

difference in soil moisture at mostly lowlands ofthe test area comes from the difference in theinitializations of the simulations, whereas thenegative difference at high elevations is causedby rather quick recharge of the surface layer inthe CURRENT simulations, in which moistureis not depleted as much as that in the GRASSsimulations that is subject to higher rates ofevapotranspiration. These differences can beseen better in the next two figures that providetime series of some surface variables for twoareas; one at a higher and the other at a lowerelevation.

Figure 4 shows daily variations in rainfall,soil moisture of both surface and rooting layers,

Fig. 3. Changes in (a) Latent Heat Flux (W m�2), (b) Sensible Heat Flux (W m�2), (c) surface layersoil moisture, and (d) 2-m air temperature (K) in JJA over a domain including mainly the test area(dashed box). For negative anomalies, dashed contours are used in addition to shading. Solid con-tour delineates 3000 m.

O.L. SEN, B. WANG and Y. WANG 1685December 2004

Fig. 4. Daily variations of (a) total rain-fall (mm day�1), (b) soil moisture inboth surface and rooting layers, (c) La-tent Heat Flux (W m�2), (d) SensibleHeat Flux (W m�2), and (e) minimumand maximum temperatures (K) aver-aged for a ‘‘highland’’ area between 36–37�N and 92–94�E.

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latent heat flux, sensible heat flux, and mini-mum and maximum temperatures in an areabetween 36–36�N and 92–94�E. This area isselected to demonstrate the changes in surfacevariables at higher elevations in the test area.The modeled surface cover change generallyincreases rainfall (Fig. 4a) at higher elevations.The changes appear to be increases in therainfall intensity within the rainfall events,and they are mostly substantial as they canamount to 40% or more over the rainfall gen-erated in the CURRENT ensemble. The en-hancement of the rainfall events may indicate acontribution from the increased local moistureas well as other atmospheric effects due to thechanges in the land surface. The infiltration ofrainfall into the soil clearly recharges the sur-face and rooting layers (Fig. 4b) in the CUR-RENT simulations, which then give rise to la-tent heat flux (Fig. 4c), especially during Julyand August. The soil moisture in the GRASSsimulations, which is further recharged by theincreased rainfall, helps the vegetated surfacemaintain a comparatively high amount of la-tent heat flux throughout the whole summer.Sensible heat flux (Fig. 4d) is reduced at highelevations, but the changes are usually smallerthan those in latent heat flux.

The re-greening also lowers daily minimumtemperatures but the daily maximum temper-atures remain similar between the two ensem-bles (Fig. 4e). The decrease in albedo as a resultof land-cover change leads to more net radia-tion to heat the surface, but it seems that theshift in energy partitioning (especially the in-crease in latent heat flux), which cools the sur-face, balances albedo effect during daytime, sothe daily maximum temperatures do not differmuch. The diurnal cycles of energy balancecomponents (not shown) indicate that surfacegreening reduces the heat flux into the soilduring daytime. Consequently, the surface be-comes cooler during the night because of lessheating from the soil layers below where theheat is stored during daytime. This leads tosmaller daily minimum temperatures.

Figure 5 shows the same variables as in Fig.4 but for the area between 40–41�N and 92–94�E. This area represents most of the low-lands in the test area. The area receives verylittle rain (Fig. 5a) indeed, and therefore, isvirtually dry. Yet, switching to grass seems

to increase the rainfall amount in the rainfallevents significantly. It seems that the soilmoisture (Fig. 5b) in GRASS ensemble dropsquickly to around wilting point in the surfacelayer by the beginning of June. The lack ofadequate rainfall to recharge soil layers resultsin zero latent heat flux (Fig. 5c) in the CUR-RENT simulations and limits latent heat fluxsubstantially in the GRASS simulations. Thedaily level of latent heat flux in the latter isprimarily maintained by the soil moisture inthe rooting layer that shows a slow but steadydecrease. Unlike at the high elevations, sensi-ble heat flux (Fig. 5d) at the low elevationsincreases as, in the absence of adequate soilmoisture, less energy is partitioned for evapo-transpiration from the energy surplus obtainedas a result of albedo decrease. Consequently,both daily minimum and maximum temper-atures (Fig. 5e) become slightly higher thanthose in the CURRENT simulations. Note thatright after the largest rainfall event (11–14August), the daily minimum temperature fromGRASS simulations falls below that fromCURRENT simulations for several days.

3.3 Changes in rainfall and runoffFigure 6 shows the changes (GRASS-

CURRENT) in rainfall and whether thesechanges are significant at 90% confidence level.Rainfall significantly increases over the wholetest area (all the hatching in the test area in-dicates significant increase in rainfall althoughthe shading used in Fig. 6 does not show it be-cause the increases are relatively small). Thelargest changes occur in the southern sectionsof the test area that have high elevations.Rainfall is also increased over the eastern flankof Tibetan Plateau, South China and the lowerreaches of the Yangtze River significantly.Rainfall is significantly reduced in the northernparts of South China Sea and northern YellowSea. The frequency of rainfall over 16 mmday�1 (not shown) increases in southern Chinaby 1–4 days month�1, and decreases over theShandong Peninsula and northern parts ofKorean Peninsula by 1–3 days month�1. Thefrequency of the rainfall less than 4 mm day�1

(not shown) decreases 1–4 days month�1 overa band that extends from the test area tosouthern China. The largest changes occur atthe high elevations of the test area, the Sichuan

O.L. SEN, B. WANG and Y. WANG 1687December 2004

Fig. 5. Same as Fig. 4 but for a ‘‘lowland’’area between 40–41�N and 92–94�E.

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Basin and the areas to the east. The number ofdays with rainfall less than 4 mm increases inthe lower reaches of the Yellow River, KoreanPeninsula and northern parts of Vietnam. As-sociated with the changes in rainfall, surfacerunoff (Fig. 7) increases in southern China andthe lower reaches of the Yangtze River Basinand decreases in northeastern China andsouthwestern China.

3.4 Large-scale circulation changesThis section will focus on the description of

the downstream impacts on East Asian large-scale circulation features. Figure 8 shows dif-ferences (GRASS-CURRENT) in geopotentialheight, wind speed, vertical velocity, and watervapor mixing ratio at three pressure levels;500 mb, 700 mb and 850 mb. The most strikingchange in the large-scale circulation in theEast Asian region is characterized by a dipoleanomaly: a high pressure and anticyclonic

anomalies located in the northern China anda low pressure and cyclonic anomalies overthe southern China (Figs. 8a–c, and d–f ). Thenorthern anticyclone is centered over the Yel-low River Delta, and the Shandong Peninsula,including the northern Yellow Sea and BohaiBay (the bay to the north of Shandong Penin-sula). For convenience of discussion, it will bereferred to as North China high. The southerncyclone is centered over Hunan province, justsouth of the middle Yangtze River. For short, itwill be referred to as South China low. Both ofthese anomalous circulation systems show anequivalent barotropic structure, in particularfrom the surface up to 700 hPa. The center overthe 500 hPa shows a slight southward shift.Dynamically consistent with this pressure di-pole, large scale descending and ascending mo-tions occur in the North China high and SouthChina low, respectively (Figs. 8g–i). Similarly,the moisture is depleted (accumulated) over theNorth China high (South China low) so that themixing ratio shows a similar north-south dipolepattern (Figs. 8j–l).

The above changes in the large-scale atmo-spheric fields connect well with the changes inregional rainfall. The links between them willbe discussed in the next section.

Fig. 6. Spatial distribution of rainfallchange (mm month�1; shaded) in JJA.For negative anomalies, dashed con-tours are used in addition to shading.The hatching is for statistically signifi-cant areas at 90% confidence level. Thecontours are showing the topography(at the 1000 and 3000 m heights). Thedashed box shows the test area.

Fig. 7. Same as Fig. 6 but for surfacerunoff change (mm month�1) in JJA.

O.L. SEN, B. WANG and Y. WANG 1689December 2004

Fig. 8. Changes (GRASS-CURRENT) in geopotential height (m) of (a) 500 mb, (b) 700 mb,(c) 850 mb, in wind strength (m/s) and streamlines at (d) 500 mb, (e) 700 mb, (f ) 850 mb, in verti-cal velocity (10�5 hPa/s) at (g) 500 mb, (h) 700 mb, (i) 850 mb, in water vapor mixing ratio (g/kg) at(j) 500 mb, (k) 700 mb, and (l) 850 mb in JJA. The contours are showing the topography (at the1000 and 3000 m heights).

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4. Conclusions and discussion

The present study investigates the local andregional effects of re-greening the desertifiedlands in northern China using a regional cli-mate model, in particular whether the changesin rainfall induced by landscape change arelarge enough to support a restored vegetationcover. The results of the numerical experimentindicate that such a surface-cover change hasboth significant local and regional effects onrainfall and large-scale circulation. Rainfall in-creases significantly over the whole test area.The re-greening of the desertified lands innorthwestern China increases net surface radi-ation in the test area. This increases total heatflux (latent heat flux plus sensible heat flux)from surface to atmosphere, which in turnenhances upward motions over the test areaand supplies more moisture to the atmosphere.These two processes should primarily be re-sponsible for the increase in precipitation overthe whole test area, but owing most likely tothe dynamic effect of the topography, the pre-cipitation increases more over the higher ele-vations towards the Tibetan Plateau. The fur-ther cooling of the surface at higher elevations,hence overlying atmosphere, as a result of theincreased latent heat flux and the decreasedsensible heat flux may have contributed to in-crease in rainfall at the highlands. The rainfallincrease in the test area seems to be associatedwith an increase in intensity rather than fre-quency whose increase at lowlands would bemore valuable to support a restored vegetationcover. In general, enhanced ascending motionsand more moisture transfer from soil to atmo-sphere appear to be the primary processes thatincreased rainfall in the test area.

Rainfall changes outside of the test area aswell. It increases in southern China, the lowerreaches of the Yangtze River, and eastern partsof the Tibetan Plateau. Significant reductionsin rainfall occur mostly over the marginal seas,particularly South China and Yellow Seas. Be-cause these remote changes should be relatedto the landscape change in the test area, below,we discuss a possible mechanism to link theland surface change in the test area to regionalchanges in rainfall. The enhancement of up-ward motions over the test area seems to bepartly compensated by an increase in subsi-

dence to the east over the Shandong Penin-sula and Yellow River Delta, resulting in theNorth China high and anticyclonic circula-tion anomalies. The North China anticyclonicanomaly provides significant northeasterly low-level anomalous winds that stretch from theKorean Peninsula to the middle reaches ofYangtze River. This low-level flow brings rela-tively cold air from north and meets withsouthwesterly monsoon in Southeast China,enhancing cyclonic shear vorticity in the Yang-tze River Basin and South China including theSichuan Basin. The enhanced upward motionsover these areas lift the moisture of monsoonalair to higher levels in the atmosphere andcause significant increases in rainfall, espe-cially in southern China. The latent heat re-leased in the precipitation further feedbacksto strengthen the South China low and low-level cyclonic anomalies. The moist processesenlarge the establishment of the north-southdipole pattern. Note that the development ofSouth China low is also associated with en-hanced southwesterly monsoon flow along theSoutheast China coast. This low-level jet in be-tween the western pacific subtropical high andSouth China low creates anticyclonic shearvorticity over the northern South China Sea,which induces descending motion and reducesrainfall there.

The results of this idealized sensitivity ex-periment provide important clues for the proj-ects such as Western China Development Plan,which aims to restore vegetation in the deserti-fied lands of China. The results suggest thatreclaiming the desertified lands through vege-tation restoration is quite difficult as the localclimate, even after a complete vegetation resto-ration in a relatively large test area, can hardlysupport vegetation. Rainfall increases but theincrease occurs in rainfall intensity and not inrainfall frequency, the latter being probablymore important for the maintenance of the re-stored vegetation in such an environment. Thisimplies that the current vegetation restorationactivities will be largely limited to areas wherewater resources are relatively abundant, orthey will depend heavily on irrigation. Thereare, however, regions in our test area that maysupport vegetation because they receive morefrequent rainfall. These regions are mostly inthe highlands towards the Tibetan Plateau and

O.L. SEN, B. WANG and Y. WANG 1691December 2004

in the eastern parts of the test area (east of108�E), which may be a natural expansion ofthe eastern grasslands towards the west.

The numerical experiments in the presentstudy were performed for only one year (1998)in which there were severe precipitation andflooding events in southern China. In thissense, the results of the experiment, particu-larly the regional effects. apply to that particu-lar year, or at most, to wet years in general.Also, the experiment quantifies the local andregional effects under an idealized landscape-change scenario, which seems infeasible to thatextent in practice despite serious vegetationrestoration efforts in the test area that aresupported by the government of China. Never-theless, the results of the present study arevery relevant as they provide important im-plications on the sustainability of vegetation insuch an environment.

Acknowledgments

This study has been supported in part bya NASA grant to the International PacificResearch Center, which is sponsored in partby the Frontier Research System for GlobalChange. One of the authors, Bin Wang, ac-knowledges the support from NSF and NOAA/PACS program. We acknowledge the UK MetOffice to allow us use its radiation scheme inthe IPRC regional climate model. We appreci-ate the editorial assistance provided by GiselaE. Speidel, and helpful comments of two anon-ymous reviewers.

This paper is SOEST contribution number6510 and IPRC contribution number 304.

References

Charney, J.G., P.H. Stone, and W.J. Quirk, 1975:Drought in the Shara: A biogeophysical feed-back mechanism. Science, 187, 434–435.

Detering, H.W., and D. Etling, 1985: Application ofthe E-, turbulence model to the atmosphericboundary layer. Bound. Layer Meteor., 33,113–133.

Dickinson, R.E., and A. Henderson-Sellers, 1988:Modeling tropical deforestation: a study ofGCM land-surface parameterization. Quart. J.Roy. Meteor. Soc., 114, 439–462.

Dickinson, R.E., A. Henderson-Sellers, and P.J. Ken-nedy, 1993: Biosphere-Atmosphere TransferScheme (BATS) version 1e as coupled to theNCAR community climate model NCAR. Tech.

Note NCAR/TN-378þSTR, 72 pp.Ding, Y., 1994: Monsoons over China. Kluwer Aca-

demic Publishers, 419 pp.Ding, Y., and Y. Liu, 2001: Onset and the evolution

of the summer monsoon over the South ChinaSea during SCSMEX Field Experiment I 1998.J. Meteor. Soc. Japan, 79, 255–276.

Edwards, J.M., and A. Slingo, 1996: Studies with aflexible new radiation code. I: Choosing a con-figuration for a large-scale model. Quart. J.Roy. Meteor. Soc., 122, 689–719.

Gregory, D., J.-J. Moncrette, C. Jakob, A.C.M. Bel-jaars, and T. Stockdale, 2000: Revision of theconvection, radiation and cloud schemes in theECMWF model. Quart. J. Roy. Meteor. Soc.,126, 2685–2710.

Hahmann, A.N., and R.E. Dickinson, 1997: RCCM2-BATS model over tropical South America: Ap-plications to tropical deforestation. J. Climate,10, 1944–1964.

Henderson-Sellers, A., R.E. Dickinson, T.B. Dur-bidge, P.J. Kennedy, K. McGuffie, and A.J.Pitman, 1993: Tropical deforestation: modelinglocal- to regional-scale climate change. J. Geo-phys. Res., 98, 7289–7315.

Kanae, S., T. Oki, and K. Musiake, 2001: Impact ofdeforestation on regional precipitation over theIndochina Peninsula. J. Hydrometeor., 2, 51–70.

Lean, J., and D.A. Rowntree, 1993: A GCM simula-tion of the impact of Amazonian deforestationon climate using an improved canopy repre-sentation. Quart. J. Roy. Meteor. Soc., 119,509–530.

Lean, J., and D.A. Warrilow, 1989: Simulation of theregional climatic impact of Amazon deforesta-tion. Nature, 342, 411–413.

McGuffie, K., A. Henderson-Sellers, H. Zhang, T.B.Durbidge, and A.J. Pitman, 1995: Globalclimate sensitivity to tropical deforestation.Global and Planetary Change, 10, 97–128.

Nobre, C.A., P.J. Sellers, and J. Shukla, 1991: Ama-zonian deforestation and regional climatechange. J. Climate, 4, 957–988.

Reynolds, R.W., and T.M. Smith, 1994: Improvedglobal sea surface temperature analyses usingoptimum interpolation. J. Climate, 7, 929–948.

Sen, O.L., Y. Wang, and B. Wang, 2004: Impactof Indochina deforestation on the East-Asiansummer monsoon. J. Climate, 17, 1366–1380.

Shi, W., and H. Wang, 2003: The regional climate ef-fects of replacing farmland and re-greening thedesertification lands with forest or grass inwest China. Adv. Atmos. Sci., 20(1), 45–54.

Shukla, J., C. Nobre, and P.J. Sellers, 1990: Amazondeforestation and climate change. Science, 247,

Journal of the Meteorological Society of Japan1692 Vol. 82, No. 6

1322–1325.Sun, Z., and L. Rikus, 1999: Improved application of

exponential sum fitting transmissions to in-homogeneous atmosphere. J. Geophys. Res.,104D, 6291–6303.

Tiedtke, M., 1989: A comprehensive mass fluxscheme for cumulus parameterization in large-scale models. Mon. Wea. Rev., 117, 1779–1800.

Wang, B., and LinHo, 2002: Rainy season of theAsian-Pacific summer monsoon. J. Climate, 15,386–398.

Wang, B., R. Wu, and X. Fu, 2000: Pacific-East Asiateleconnection: How does ENSO affect EastAsian climate? J. Climate, 13, 1517–1536.

Wang, G., and G.S. Jenkins, 2002: Deserts anddesertification. Encyclopedia of AtmosphericSciences, J.R. Holton, J.A. Curry, and J.A.Pyle, Eds., Academic Press, 633–640.

Wang, Y., 1999: A triply nested movable meshtropical cyclone model with explicit cloudmicrophysics—TCM3. BMRC Research ReportNo. 74, 81pp, Bureau of Meteorology ResearchCenter, Australia. [Available from Bureau ofMeteorology Research Centre, Melbourne,Australia, VIC 3001.]

Wang, Y., 2001: An explicit simulation of tropicalcyclones with a triply nested movable meshprimitive equation model—TCM3. Part I:Model description and control experiment.Mon. Wea. Rev., 129, 1370–1394.

Wang, Y., 2002: An explicit simulation of tropical

cyclones with a triply nested movable meshprimitive equation model—TCM3. Part II:Model refinements and sensitivity to cloud mi-crophysics parameterization. Mon. Wea. Rev.,130, 3022–3036.

Wang, Y., O.L. Sen, and B. Wang, 2003: A highly re-solved regional climate model (IPRC_RegCM)and its simulation of the 1998 severe precipi-tation event over China. Part I: Model descrip-tion and control experiment. J. Climate, 16,1721–1738.

Xu, K.-M., and D.A. Randall, 1996: A semiempiricalcloudiness parameterization for use in climatemodels. J. Atmos. Sci., 53, 3084–3102.

Xue, Y., 1996: The impact of desertification in theMongolian and the inner Mongolian grasslandon the regional climate. J. Climate, 9, 2173–2189.

Xue, M., and S.-J. Lin, 2001: Numerical equivalenceof advection in flux and advective forms andquadratically conservative high-order advec-tion schemes. Mon. Wea. Rev., 129, 561–565.

Zhao, J.Z., G. Wu, Y.M. Zhao, G.F. Shao, H.M. Kong,and Q. Lu, 2002: Strategies to combat deserti-fication for the twenty-first century in China.International Journal of Sustainable Develop-ment and World Ecology, 9(3), 292–297.

Zeng, Y., G. Yu, Y. Qian, M. Miao, X. Zeng, and H.Liu, 2002: Simulations of regional climatic ef-fects of vegetation change in China. Quart. J.Roy. Meteor. Soc., 128, 2089–2114.

O.L. SEN, B. WANG and Y. WANG 1693December 2004