Hydrometeorological conditions of grassland vegetation in Central Mongolia andtheir impact for leaf area growth*Shin Miyazaki1 2, Tetsuzo Yasunari3, 4, Tadashi Miyamoto5, Ichirow Kaihotsu6, 7
Gambo Davaa8, Dambarajaa Oyunbaatar8, Luvsan Natsagdorj8, and Taikan Oki1
(1: IIS, University of Tokyo, Japan, 2: JST-CREST, Japan, 3: HyARC, Nagoya University, Japan, 4: FRCGC, Japan
5: Nomura Research Institute, Japan, 6: Faculty of Integrated Arts and Sciences, Hiroshima University, 7: DPRI,
Kyoto University, Japan, 8: Institute of Meteorology and Hydrology, Mongolia)* Institute of Industrial Science, University of Tokyo, Japan, 153-8505, Komaba,
Meguro Tokyo, Japan. e-mail: miyashin@iis.u-tokyo.ac.jp
Abstract
The long-term observation of surface heat and water budget and hydro-meteorological elements has been carried out over a
grassland site at Arvaikheer (46.23 N, 102.82 E) in central Mongolia as the framework of the GAME-AAN (GEWEX Asian
Monsoon Experiment-Asian Automatic Weather Station Network). The purpose of this study is to clarify the relationshipbetween vegetation and climate using long-term data (1982-2000) of satellite-derived LAI and climatic data observed at
Arvaikheer. Furthermore, we aimed to reveal physical process by comparing soil moisture, and heat and water budgets in1999 and 2000 as a case study of good and poor vegetation growth. Significant positive correlations with 99% confidence
levels were found for July precipitation (P) and the LAI in July LAI (0.538), August (0.826) and September (0.564).
Composite analysis for five highest (H5) and lowest (L5) LAI years showed the significant positive anomalies of P in Julyand LAI in July and August for H5. In June and July 1999, soil moisture and P values were higher than values in 2000; thispattern was reversed in August and September. The mean LAI during the 1999 growing season (1.0) was about twice that of2000 (0.6). In 1999, the ratio of evapotranspiration (ET) to P (ET/P) and change of stored soil moisture ( ∆W ) to P
( ∆W /P) were 0.79 and 0.15, respectively. In 2000, ET/P and ∆W /P were 0.94 and 0.0, respectively. These results suggestthat the P and ∆W before July had the most influent on grass growth in central Mongolia.
Keyword: Mongolia, Grassland, Leaf area index, Soil moisture, Rainfall, Evapotranspiration

1. Introduction
Few studies have examined the relationship between
vegetation and climate in Mongolia. Kondoh and Kaihotsu(2003) found that Mongolian grasslands showed a clear
relationship between total summer precipitation and the
NDVI amplitude. Ni (2003) noted that grasses showed apositive relationship to precipitation and aridity index(mean annual precipitation divided by mean air
temperature plus 10 degrees) in north-east China andsouth-east Mongolia. Suzuki et al. (2003) pointed out that
the Mongolia showed 11 weeks later start of green-up than
Kazakh, while Mongolia and Kazakh located in almost
same latitude. They suggested that Kazakh had more soil
moisture from snowmelt than its in Mongolia. However,neither study clarified physical or physiological processes
together with inter-summer variation of precipitation andvegetation.
The long-term observation of surface heat and water
budget in association with hydro-meteorological elements
has been carried out over a grassland site at Arvaikheer(46.23 N, 102.82 E) in central Mongolia as the frameworkof the GAME-AAN (GEWEX Asian Monsoon
Experiment-Asian Automatic Weather Station Network;
Sugita et al. 2003). The purpose of this study is to clarify
the relationship between vegetation and seasonal andinterannual variability of rainfall using long-term data
(1982-2000) of satellite-derived LAI and climate variables
observed at Arvaikheer (Miyazaki et al., 2004).
Furthermore, we aimed to reveal physical process bycomparing surface climate, soil moisture, and heat andwater budgets of in 1999 and 2000 as a case study of goodand poor vegetation growth.

2. Data and methods
Long-term observations of hydro-meteorologicalelements and surface flux have been conducted by using
Automatic Weather Station (AWS) at the site in Arvaikheer
in central Mongolia since 17 September 1997. Annual
mean air temperature and annual precipitation (P) areo

0.4 C and 245 mm, respectively. All the vegetation at
this site is C3-type grasses, mainly in the Gramineae (e.g.,
Stipa Gobica), Compositae (e.g., Artemisia adamsii), andCyperaceae (e.g., Carex duriuscula) families. The soil
consists of brown humus and sand from the surface to 20
cm, brown soil with rock from 20-70 cm, and brown silt
below 70 cm. Winds prevail from the north-west andhomogeneous grasslands extend more than 5 km aroundthe site. Surface flux was observed at 7.8 m height by
Portable Automated Mesonet III (PAM III: Miltzer et al.
1995) Automatic Weather Station (AWS) developed by the
National Center for Atmospheric Research (NCAR) in the
United States. The observational height of surface flux toensure sufficient fetch, since surface fluxes are considered
100-times greater than the measuring height (780 m; Horst
and Weil, 1994).
Mongolia’s Institute of Meteorology and Hydrology(IMH) provided daily P data from 1999 to 2000 at
Arvaikheer. The IMH also provided long-term 10-day
mean air temperature and 10-day P data from 1982 to 2000.
In addition to station data provided by IMH, we usedsummarized global data on daily mean air temperature,daily mean dew point temperature, and daily precipitation
amounts and snow depths. These data were obtained fromthe Global Climate Observing System (GCOS) Surface
Network (GSN), produced by the National Climate Data
Center (NCDC), and are available via the NCDC web
server (http://www.ncdc.noaa.gov/).
In this study, we used a global LAI dataset derived fromglobal composites of maximum NDVI values. The data arepart of the National Oceanic and Atmospheric
Administration (NOAA) Pathfinder Advanced Very High
Resolution Radiometer (AVHRR) Land dataset (PAL) Ver.
3. The global composites were created using an algorithm
that incorporates results from a three-dimensional radiativetransfer model and a six-biome classification scheme, as
described in Myneni et al. (1997). The data containmonthly LAI values at a 16 x 16 km spatial resolution from
July 1981 to May 2001 and are available online at
http://cybele.bu.edu. We used the data from the grid near
Arvaikheer (46.175-46.325 N, 102.66-102.86 E).

3. Results and Discussion
3.1 Relationship between local climate and LAI
The monthly mean air temperature (T) at Arvaikheeroexceeds 5 C in May and the monthly mean T drops lowerothan 5 C in October. It is common that the monthly mean
T with 5 degrees is the threshold for vegetation activity.
Moreover, most precipitation (about 90% of annual
precipitation) and growth of vegetation at Arvaikheer
occurs from May to September. Therefore, we define thevegetation growing season (GS) as May to September.
To clarify the seasonal variation of T, P and LAI at thesite, we present the time series of monthly T, P and LAI
averaged from 1982 to 2000 with standard deviations (SD)(figures are not shown). The seasonal maximum of both T

showed for P in August and the LAI in August or
September, or for P in September and the LAI in
September, implying that after August, P has less effect on
grass growth.
Table 1. Correlation matrix of P and the LAI. The boldvalues are significant correlation coefficient. *: the 95%
significance level. **: the 99% significance level.
LAI
P-month 5678950.245 0.482* 0.074 0.069 0.086
6-------- 0.458* 0.445 0.050 0.053
7------- ------- 0.538** 0.826** 0.564**8------- ------- ------ -0.141 -0.065
9------- ------- ------ ------- -0.009
To reveal the actual phenomena guiding relationships
between P and the LAI, we created the composites of years
with the five highest (H5; in the years of 1984, 1985, 1990,
1997, and 1998) and five lowest (L5; in the years of 1982,
1986, 1988, 1995, and 2000) for mean LAI value during
GS. We present the anomalies of P and LAI for comparing
H5 and L5 composite in Fig. 1 (a) and (b). P of H5 in July
had significant (larger than SD) positive anomaly with 45.4
mm while P of L5 had nearly significant negative anomaly
with 44.4 mm. The LAI of H5 in July and August had thesignificant positive anomaly with 0.7 and 0.6, while the
LAI of L5 from July to September had the almost
significant negative anomaly with 0.5. In other months, nosignificant difference showed for P and the LAI. These
results support findings of large, significant positive
correlations for P in July and the LAI from July to
September. This suggests that plenty of July rainfall is themost important factor for grass growth.
50

oAnomaly of precipitation (mmoseasonal minimum of both T (8.9 C ) and P (14.7 mm)
appeared in September. P had large SD from June toAugust with more than 30mm, while T had small SD from
June to August with less than 1.5 degrees. LAI increased
from May (0.4) to June (1.2) rapidly then became nearly
constant until September with slight maximum in August(1.3). From 1982 to 2000, T during GS had significant
increasing trend (0.1 degree/year) with 99% confidence
level. In same period, P and LAI during GS had no
significant trend.
To evaluate the relation between climate and vegetation,
it is useful to calculate correlation between T, P and LAI.
No significant correlation showed for T and LAI. Table 1
shows statistical correlations between P and the LAI from1982 to 2000. Nineteen data points were used for thisanalysis. Thus, the degree of freedom for correlation
analysis was 17, and the lower limits for significant
correlation were 0.529 and 0.456 at 99% and 95%
confidence levels, respectively. Positive significant
correlations at 99% confidence levels were found for P in
July and the LAI in July (0.538), August (0.826) and
September (0.564). Positive significant correlations at 95%
confidence levels were found for P in May and the LAI in
June, and for P in June and the LAI in June. No correlation

P -lo w
P - H ig h

40
30
20
10
0
-1 0
-2 0
-3 0
-4 0
-5 0

M a y -P

J u n -PJ u l-P

A u g -PS e p -P

89

M o n th0 .8

L A I -lo w
L A I -h ig h

0 .6
0 .4

Anomaly of LA(16.1 C ) and P (77.0 mm) appeared in July, while the

0 .2
0
-0 .2
-0 .4
-0 .6
-0 .8
5

6

7
M o n thFig. 1 Comparison of (a) P (b) LAI by composites of thefive years with the highest LAI values and five years withthe lowest LAI values, which was chosen from mean LAI
value during growing season. Error bars show the standard
deviation over 19 years (1982-200).

Annual P in both years (150 mm) was about 60% ofthat in normal years (240 mm) while seasonal variability in
P differed in these years. We used these two years in a casestudy to examine results from the previous section further.
From May to July, 1999 had a higher P frequency (43.5%
of total days) than 2000 (33% of total days; Figure was notshown). In 1999, P values exceeding 3 mm/day occurred
on 13 days from May to July; only 7 days in the same
period in 2000 exceeded 3 mm. From August to September,
both 1999 and 2000 showed the same frequency of P. In
1999, no day had a P value greater than 10 mm/day; four
such days were observed in 2000.
The surface condition is the most important parameter
controlling heat and water budgets. Soil moisture is a
useful parameter for expressing the surface condition.
Figure 2 shows the time series of 5-day mean θ at
depths from 5 to 20 cm, on average, during the growing
season. In both 1999 and 2000, θ responded to P very
well. The θ in 1999 was higher than in 2000 in June andJuly, and lower than in May and August. Erdenetsetseg(1997) showed the soil moisture regime at typical sites
with long-term observation. The temporal variation of θ
in 1999 resembled with the long-term mean soil watercontent in steppe region, while the temporal variation ofθ in 2000 was similar to that in desert region shown in
Erdenetstseg (1997). The frequency of P in 1999 was about
1.5 times of its in 2000. This also affected the different
intra-seasonal variation of θ between in 1999 and 2000.
Volumetric soil water content at 0-0.2m depth

0 .2
0 .1 89900

0 .1 60 .1 40 .1 20 .1

September 2000 were higher than in 1999. P in June andJuly 2000 were significant smaller than the average P from1982 to 2000. It implies that the small P caused low θ inJune and July 2000. These results point out that higher θin early 1999 GS may have an impact on the LAI, since the1999 LAI was significantly greater than the 2000 LAI.
Figure 3 shows a time series of 5-day mean sensible
heat flux (H) and latent heat flux (LE) during the GS. From
May to June, H was the dominant component of the surface−2

heat budget with about 15 to 20 MJm /day in both years;
during this same period, H reached its annual maximum of−2−2

20.2 MJm /day and 22.3 MJm /day in early June 1999
and mid-June 2000, respectively. In 1999, LE exceeded H
in three periods (mid-June, early August, and late
September), in response to soil moisture increases after
heavy rainfall. In 2000, LE surpassed H in mid-June andearly August during high soil moisture conditions. In 1999,
LE reached its annual maximum in mid-July at about 14.7
−2

MJm /day that was about 60% of Rn, while LE in 2000
attained an annual maximum in early August at about 12.4
−2

MJm /day that was about 50% of Rn. This result isdifferent from the results of Japanese grassland (Saigusa etal. 1998) which the ratio of LE to Rn was same between
wet and dry year. This difference may imply that theMongolian grassland is more sensitive for the difference ofclimate than the Japanese grassland where there is enoughprecipitation for the grass growth.
25

Heat budget (MJ/m^2/day)

3.2 Comparison of summer climate and vegetationin 1999 and 2000

H 99
LE 99
H 00
LE 00

20

15

10

5

0 .0 80 .0 60
126

0 .0 40 .0 20
126 136

146

156

166 176

186 196 206 216
D a y o f Y ea r

226 236 246

256

266

Fig. 2 Comparison of 5-day mean volumetric soil watercontent averaged from 5- to 20-cm depths from May to
September in 1999 and 2000.
The mean LAI during the 1999 GS (1.0) was about
twice that in 2000 (0.6). The annual maximum LAI value
reached 1.6 in June 1999 and 0.7 in June 2000. The
uncertainty in the LAI estimate may be order of 0.5 LAI(Myneni et al. 1997). Therefore, the difference of annual
maximum LAI is significant. The LAI peak in June 1999
likely related to the θ in root zone deeper than 10cm inJune. In May and June 1999, the frequency of P was about
twice of its in May and June 2000. The days with P morethan 5 mm/day were four times in middle and late May
1999 while there was no day with P more than 5 mm/day in
May and June 2000. In June and July 1999, θ values
were higher than in 2000, while θ values in August and

136

146

156

166

176

186 196 206 216
D ay of Y ear

226

236 246

256 266

Fig.3 Comparison of 5-day mean sensible heat flux andlatent heat flux values from May to September in 1999 and2000.
Figures 4 (a) and (b) show the time series of 5-day
cumulative values for each component (P, ET, and ∆W ) of
the water budget during the 1999 and 2000 growing
seasons, respectively. Change in observed soil watercontent was used to calculate ∆W . The cumulative P
before July was 96.7 mm and 60.7 mm in 1999 and 2000,
respectively. The rain gauge using in Mongolia is
Tretyakov type with wind shield and measured at 2m. The
average catch ratios range from 81 to 97% for rain (Yang etal. 1995), which corresponds from 4.5 to 28.5mm whenannual precipitation was 150mm. Therefore, the differenceof cumulative P (36 mm) before July was significant. In
1999, cumulative ∆W gradually increased in May andabruptly increased from 4.7 to 20.7 mm following an
increase in cumulative P; cumulative ∆W remainednearly zero until the end of July 2000. In mid-July 1999,
cumulative ∆W reached an annual maximum of 27.1
mm when θ reached its annual maximum (cf., Fig. 2). In
mid-August 2000, cumulative ∆W reached an annual
maximum of 14.9 mm when θ was at its annual
maximum (cf., Fig. 2). In 1999, averaged ET/P and∆W /P during the GS were 0.79 and 0.15, respectively. In
2000, averaged ET/P and ∆W /P during the GS were 0.94
and 0, respectively. The water budget was thus notcompletely closed. The remaining water, however, is only
about 5% of P, which is less than the uncertainty inevaluating evaporation and measuring P. Results suggestthat about 15% of precipitation was stored in the soil layer,
and approximately 80% evaporated in 1999, which
resembled results from the mean value of the classicalestimation of evaporation near Arvaikheer (Tuvedendorzh
and Myagmarzhav, 1985), and Selenge river basin in
Mongolia (Ma et al. 2003). In contrast, almost all P
evaporated and little to no water was stored in the soil in
2000, which is similar to the highest value of Selenge river
basin (Ma et al. 2003) and the characteristics of whole
Mongolia (Natsagdorj, 2000).
140

ET
P
∆W

Cumulative ET or P orΔW (mm)

120
100
80
60
40
20
0
125

135

145

155

165

175

185

195

205

21 5

225

235 245

2 55

265

D ay of Y ear

Cumulative ET or P orΔW (mm)

140
120
100

ET
P
∆W

80
60
40
20
0
126 136 146 156 166 176 186 196 206 216 226 236 246 256 266-20
Day of Year

Fig.4 Time series of 5-day cumulative precipitation,
evapotranspiration, and stored moisture values from May
to September in (a) 1999 and (b) 2000.

4. Summary and remarks
In this study, we investigated the impacts of seasonaland interannual variability on vegetation as well as soil
moisture and evapotranspiration over a grassland at
Arvaikheer, central Mongolia. Correlations were
determined for 19 years (1982-2000) of monthly mean LAI
and climate data. The largest and significant correlation
was found for P in July with LAI in July, which continued

until September. Furthermore, significant correlation
showed for P in May and LAI in June, P in June and LAI in
June. In the composite analysis of H5 and L5, thesignificant positive anomalies of P (45.4 mm) in July and
LAI in July (0.6) and August (0.6) were found, which wascorresponded to the correlation analysis. It implies that the
P in July had the largest impact for grass growth.
To study the physical processes of grass growth, we
conducted a case study using energy and water budget datawith hydro-meteorological elements from 1999 and 2000.
In both 1999 and 2000, total precipitation during GS was
almost same about 130 mm. However, the intra-seasonal
distribution of rainfall was different. P in 1999 before July
was about 70% of total P during GS while P in 2000 before
July was about 40%. These intra-seasonal distribution of P
caused the difference of the intra-seasonal variation of
surface θ . The θ in upper 20cm in June and July 1999
was higher than in 2000. The LAI from June to September
in 1999 was always larger than in 2000. These differencesof surface conditions were closely related with the average
ET between 1999 (1.3mm/day) and 2000 (0.7mm/day). In
1999, averaged ET/P and ∆W /P during the growing
season were 0.79 and 0.15, respectively. In contrast, ET/Pand ∆W /P during the growing season were 0.94 and 0,
respectively. There was almost no stored water in the soilin 2000 because of low P frequency and the small P
amounts in June and July 2000.
The results of this study suggest that grass growth incentral Mongolia is influenced by P and ∆W before July.
High amounts of P, provided after August, did notcontribute to grass growth. Although this study focused on
one site, it is the first study to examine physical processes
related to seasonal rainfall variation and its impact on grass
growth in central Mongolia. To generalize our results, weare conducting further analyses using LAI data and datafrom other stations.

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