A numerical simulation study of the impacts ofvegetation change on regional climate in China* Qiaoping Li 1, Yihui Ding 2(1:Institute of Atmospheric Physics, Chinese Academy of Sciences,Bejing,100029,China
2: National Climate Center, China Meteorological Administration,Bejing,100081,China)* e-mail: Lqp70@163.com
Abstract
By using the regional climate model (RegCM_NCC), two modeling experiments are undertaken to investigate theregional climate impacts of changed vegetation cover in China, one with heavy desertification in North of China andanother with reforestation in Northwest China. Results indicate that these land cover modifications in large regions not only
have significant local and regional effects on rainfall and air temperature, but also have far-reaching effects on the East
Asian monsoon, so being one of main influence factors of the regional climate change.
Keyword: land cover change, regional climate, numerical simulation

Model Introduction

Experimental design and simulation analysis

The regional climate model (RegCM_NCC) used in thestudy is developed based on the second generation of theregional climate model of NCAR/RegCM2 (Giorgi et al.,1993a, b). By modifying and assembling the various
physical process parameterization schemes in the RegCM2,
the RegCM_NCC has been established during 1996-2000
and has been used in climate simulation and seasonal
prediction (Ding et al.,1998). Table 1 lists the details of thephysical schemes options for this study, the lateralboundary data are provided every 12 hours, the sea surface
temperature data is updating per 7 days. Figure1 shows thesimulation domain and terrain height.
Tible1 Physical process schemes
Model Configuration
RegCM_NCC
Horizontal grids
60km
Vertical layers (top)16 sigma layers (50 hPa)
Cumulus convection
Betts-Miller(Betts A K,1986)
Moisture scheme
implicitPBL
Holtslag(Holtslag et al.,1990)
Radiation
CCM3(Kiehl et al.,1996)
Land surface
LPMⅡ( Shi et al.,2000)
Boundary condition
Exponential laxation
Initial, boundary data NCEP/NCAR Reanalysis II( SST)(NOAA:OI.V2)
Simulation period
1997.12~ 1999. 02

Three experiments were carried out, there are controll
run with current vegetation cover in China (hereafterCTRL), two sensitivity experiments with changed land
cover in some regions. The desertifacation test area isselected in North China between 95º-120ºE and37º-45ºN(refer as “DE” test in this paper; see the box1 inFigure1), in which area, the vegetation class was replacedwith desert or semi-desert, some parameters values waschanged associated with these land cover classes in LPMⅡ.
In the reforestation experiment(refer as “RE” test), thevegetation class in Box2 between 85º-110ºE and 35º-43ºN(shows in Figure1) was replaced with various forest, it isconsistent with the project of tree planting over Northwest
China. Each of the experiments is integrated for 15 months(1997.12~1999.02), and the analysis is started from Mar,
1998, with the fore 3 month being regarded as the model’s“spin-up” time. The effects of land cover change on
climate are investigated based on difference between
vegetation sensitivity experiments and controll simulation.
Results of DE test show that heavy desertification innorth of China result in rainfall decreasing over many
regions, especially in North China and Northwest China,
but rainfall increasing in South China. Figure2 just presentsmean precipitation difference in summer between DE andCTRL, rainfall over the test area remarkable decrease tends
to make the water lacked regions (such as In-Mongolian
and north of Shanxi Province) more droughty. However,rainfall over Northeast China increase significantly, rainfall
also increase in south of the Yangtze valley basins. In otherseasons, rainfall in the test area also decrease consistently.
The temperature difference change mainly over thedesertification area, with temperature remarkableincreasing in all seasons except for winter, with themaximum warming center value being 2ºC (shows inFigure3), but temperature in winter is cooler than CTRL,these changes would make the local climate becoming
more arid and unsuitable for vegetation regrowing.

Fig.1 Model domain and terrain heightbecause of the change of character concerned to vegetation
type, such as albedo, roughness length, and so on, thelatent (sensible) heat flux is reduced (increased) over the
degraded area, but the magnitude of the energy change is
not uniformly in different season. In the RE experiment,changes of the heat flux is nearly contrary to the DE test.
The solar radiation flux also presents remarkable variationin the experiments.

Fig.2 summer precipitation difference in DE test
(DE-CTRL)（the rectangle box shows the test area）(Unit:mm/mon)Fig.4 summer precipitation(RE-CTRL) (Unit: mm/mon)Fig.3 summer air temperature difference in DE test
(DE-CTRL) (Unit: ºC)
On the contrary, the results in RE experiment are
obvious different to DE , reforestation in Northwest Chinatends to increase local rainfall, especially in Yellow Riverbasin, and hence, lightening drought over there in somedegree, but rainfall in Yangtze valley basins and south
China decrease in summer (sees in figure4), which tends todecrease flood occurrence in these regions. On the otherhand, air temperature in the re-greening area become
warmer in winter and cooler in summer (figure5 just showssummer temperature difference), while more moisturesupply to lower layer atmosphere and near ground winddecrease, thus may be reduce dust storm weather in someregions.
Furthermore, land cover change also have obviously
effects on the intensity of East Asian monsoon, results
indicate that summer monsoonal flow in East China isweaken while the northwest or northeast winter monsoonal
wind are enhanced in the desertification experiment. In
contrast, reforestation in Northwest China results instronger summer monsoon, with more warm and wet airtransporting from south to north then make for rainfall in
North China increasing, but in winter, the monsoonal windbecome weak, so may be reduce the occurrence of cold
events weather in some regions.
Energy analysis indicate that, in DE experiment,

difference

inRE

test

Fig.5 summer air temperature difference in RE test
(RE-CTRL) (Unit: ºC)

Results and discussion
The land cover change has significant local andfar-reaching effects on regional climate over China.
1. Heavy desertification in north of China result inrainfall decreasing in local and around regions, butincreasing in North China and South China, with surface
air temperature remarkable increasing over the test region,
as a result, the local climate become more arid.
2. Reforestation in Northwest China tends to increase
rainfall in Yellow River basin, and hence, lightening
drought over there, but rainfall over Yangtze valley basin
decrease in summer, while the local air temperature
become warmer in winter and cooler in summer.
3. Vegetation change also have obviously effects on
the East Asian monsoon, including the summer monsoonal
flow in east China weakening while the winter monsoon
enhancing after desertification. In contrast, reforestation inNorthwest China result in stronger summer monsoon andweaker monsoon in winter, which could reduce occurrenceof cold events.
The investigation provide us some important clues on
how land cover change affects Chinese climate, but it also
has some limitations, such as, the vegetation changes isexaggerated and the experiments are performed only on
more than one year, which was relatively short for climate
response, therefore, the results should be testified throughfurther study.

References
Giorgi, F., M.R. Marinucci, G. De Canio and G.T. Bates, 1993a:
Development of a second generation regional climate model(RegCM2) I, Boundary layer and radiative transfer processes.
Mon. Wea. Rev., 121, 2794-2813.
Giorgi, F., Marinucci, M.R. and Bates, G.T. 1993b: Developmentof a second-generation regional climate model (RegCM2), Part II:
convective processes and assimilation of lateral boundary
conditions. Mon. Wea. Rev., 121:10, 2814-2832.
Ding, Y.H., Qian, Y.F., Yan, H., Gao, K., Shen, T.L., Miao, M.Q.,
Li, W.L., Liu, Y.M., Zhao, N., Yi, L. and Shi, X.L., 1998:
Improvement of high-resoulution regional climate model and its
application to numerical simulation of prolonged heavy rainfalls
in East Asia. In Development of Operational Short-term Climate
Model series.2. Y.H., Ding, ed. China Meteorological Press,Beijing, 217-231.