Comparison of water and heat balance on grassland and forest in Central Yakutia,
East Siberia.

*Hironori YABUKI1, Yoshiyuki ISHII2, Tetsuo OHATA1(1: Institute of Observational Research for Global Change, JAMSTEC, 2: Institute of Low Temperature Science,
Hokkaido University)* Institute of Observational Research for Global Change, JAMSTEC, 236-0001, Showa-machi,Kanazawa-ku, Yokohama, Japan. e-mail: yabuki@jamstec.go.jp

Abstract
Siberian region is an area dominated by taiga forest but the percentage of it is 70%, other being bare land, grassland
and water bodies such as rivers and lakes. In order to better understand the water and energy cycle on this region, waterand heat characteristics were compare the forest and grassland. The field observation was carried out from April to
September 2000. The tower and mast were used 1-D scale flux observations of forest canopy and grassland, respectively.
Both sites have separated as a distance about 2km. Air temperature and humidity were measured at 22m and 17m inforest site, and 2m and 0.5m in grassland site, respectively. We measured the downward and upward
short-wave/long-wave radiation on top of tower and upward short-wave/long-wave radiation at grassland. Latent heatand sensible heat fluxes were obtained by the Bowen ratio method. And those flues were compared with between forestand grassland sites. At the grassland the sensible heat flux was smaller and latent heat flux larger than those at the forestsite. PAI in forest and grassland were 3.5 and 3.2, respectively, this value of the grassland was smaller than that of theforest site. However, the area of trunk and branch at forest were big, LAI of the forest which contributes to theevapotranspiration was 2.0, this value was smaller than grassland. The difference of this LAI seems to appear thedifference in the latent heat of the forest and the grassland.
Keywords: Siberia, alas, latent heat flux, forest, grassland.
Both sites have separated as a distance about 2km. The
Siberian region is an area dominated by taiga forest but field observation was carried out from April to September
the percentage of it is 70%, other being bare land, 2000.
grassland and water bodies such as rivers and lakes. Theseregions were underlain by permafrost. Especially, in rightbank of the Lena River region, which is the opposite sideof the Yakutsk City, there are many concave landforms
called "alas". An alas is formed after the forest has beencleared by natural collapse and forest fire, cultivation in anarea where the ice content of permafrost was high. The
alas occupying up to 20% of this area. Most alas havelakes and marshes near the center, and the surround of lake
is covered in the grassland. When we consider the waterand heat circulation of this region, it is necessary to clarifywater and heat characteristics of the forest and grassland.
In this study, the water and heat flux observation was
carried out in the forest and grassland area, and the waterand heat balance characteristics was compared. Until now,the simultaneous measurement of sensible heat and latent
heat fluxes in forest and grassland was little, where
weather condition seemed to be almost similar.

1. Introduction

2. Observation Site
Observation site in the right bank of the Lena River iscalled "Ulakhan Sykkhan"(62.15oN, 130.51oE), which islocated at 50km north east part of the Yaktusk city, being
on the middle reaches of the Lena river in a permafrost
region (Fig1). This region is interminglement region ofgrassland called "alas" and Taiga forest. The observation
was carried out in grassland and taiga forest. In forest site,
we install observation tower in a flat larch forest. TheFig.1 Location map and satellite image of Observation
stand density was 4200 tree ha-1. The mean basal diameter
areaof tree was 7.6cm. The mean stand height was 7.6m. The
maximum stand height was 17.3m. In grassland site, weinstalled observation mast in the center of alas. This alas
3. Observation
has oval shape and 0.64km2 area including a 0.1km2 lake
3.1 Forest Siteat the center. The tower and mast were used 1-D scale flux
Figure 2. illustrates a schematic diagram of theobservations of forest canopy and grassland, respectively.

observation system installed in right bank forest station on
Rena river. A temperature and moisture sensor has
ventilation fan, which moves from the before two minutesof the measurement for the reducing power. Air
temperature, relative humidity and wind speeds aremeasured at three levels. Accurate temperature
measurement used thermocouple in respect of thetemperature gradient. Short wave radiation, long wave
radiation and photosynthetically active radiation (PAR) aremeasured above the canopy and on the forest floor withthe upward and the downward radiations. The humidity
and temperature data that measured after two minutes
ventilation collected 10 minutes interval. The radiation
carried out the measurement every 5-second, and it
recorded the average for 10 minutes.

3.2 Grassland site
The observation system of the center of grassland iscomposed of two parts. One is the radiation system, andothers is Bowen ratio system. Radiation system measured
upward short wave, long wave, photosynthetically active
radiation (PAR) and net radiation. The eddy covariancesystem can be measured sensible and latent heat directly.
The eddy covariance system consists of three sensors thatmeasure the fluctuations in vertical wind speed, airtemperature, and water vapor density. K style sensor isthree-dimensional sonic anemometer / thermometer. K
style sonic array has path length of 15cm. The KH-20 is anultraviolet krypton hygrometer, which is similar inprinciple to the Lyman-alpha hygrometer, except that thesource tube contains krypton gas. The KH-20 has afrequency response of 100 Hz. All devices will be
operated by storage batteries power that is charged by thesolar cell.

4. Result and discussion
4.1 Forest site
It was required sensible heat and latent heat by theBowen ratio method in the forest site. The energy balanceis estimated the Bowen ratio method. According to thismethod, sensible heat H, and latent heat lE, are presented
as follows;

H=lE =
Fig2. Schematic map of alas observation( Rn − G )(1 + (1 / β ))(Rn − G )(1 + β )(1)(2)

where Rn is net radiation, G is ground heat flux and β is
the Bowen ratio. The Bowen ratio is defined by followingequation.

β =γ(T2 − T1 )(e2 − e1 )(3)

where γ is humidity coefficient, T1, T2 and e1, e2 were airtemperatures and relative humidity at the heights with z1and z2, respectively.
The equation of the following was used in order to obtain
the daily mean flux.

β=Picture1 .Forest conditon

Picture 2. Grassland conditon(T − T1 )UH=γ 2lE(e2 − e1 )U(4)where U is wind speed.
The seasonal variation of sensible and latent heat flux
calculated by Bowen Ratio method shown in fig. 3. This
figure showed also the seasonal variation of net radiationand ground heat flux and Bowen ratio and forest
condition.
The forest is covered in the snow by 3 May, and theopen and leaf is done from middle of May. The Bowen
ratio decreased with arriving leaf and open leaf of theforest, and the latent heat increased.

Fig 4. The relationship of Bowen ratio used by eddy
correlation method compared with Bowen ratio
calculated from air temperature and vapor pressure.
Fig.3 The seasonal variation of net radiation andground heat flux, sensible and latent heat flux,
Bowen ratio and forest condition

4.2 Grassland site
Though it would be to obtain the sensible and latent
heat fluxes by Bowen ratio method in grassland site, theobservation in the whole period was not possible in thetrouble of the machine. And it used the result by the eddy
correlation method. The heat balance required by the equal
method is important in order to compare 2 sites.
The Bowen ratio was made using the ratio of sensible andlatent heat required by the eddy correlation method. And
sensible heat and latent heat were required using thisBowen ratio. The Bowen Ratio used by eddy correlation
method compared with Bowen ratio calculated from airtemperature and vapor pressure (Fig. 4). We had good
relation, Sensible heat and latent heat of the grassland
were required using the Bowen Ratio used by eddy
correlation method. The seasonal variation of sensible andlatent heat flux calculated by Bowen Ratio method shownin fig. 5. This figure showed also the seasonal variation of
net radiation and ground heat flux and Bowen ratio andgrassland condition.
The grassland is covered in the snow by end of April,
and the grass began to grow in first of June. The grassland in this region was natural condition to end of July,
The mowing was carried out in the end of July, since it isused as the feeds.
When the grass starts the growth, the latent heatincreases. Bowen ratio in the summer is almost 0.1, and it
is very small. In the grassland, Rn-G used as a latent heat.

Fig 5. The seasonal variation of net radiation andground heat flux, sensible and latent heat flux, Bowen
ratio and grassland condition

Table 1. LAI of the grassland
The figures 6 shown the result of sensible and latent
heat compare grassland and the forest. At the grassland theLAI
Point 1
Point 2 Averagesensible heat flux was smaller and latent heat flux larger
2000/5/260.5
0.8
0.7than those at the forest site. LAI of the grassland was
2000/6/6
1.5
1.5
1.5
shown in Table4.
LAI of the grassland did the2000/6/16
2.9
2.9
2.9
measurement in 2 sites. LAI of the grassland becomes 3.2
2000/7/2
3.4
3.0
3.2
on 2 July. LAI of the forest of the measurement in thesame
timebecame2.0. PAI in forest and grassland were 3.5 and 3.2, respectively,
this value of the grassland was smaller than that of theforest site. However, the area of trunk and branch at forest
were big, LAI of the forest which contributes to theevapotranspiration was 2.0, this value was smaller thangrassland. The difference of this LAI seems to appear thedifference in the latent heat of the forest and the grassland.

5. Conclusion
At the grassland the sensible heat flux was smaller andlatent heat flux larger than those at the forest site. PAI inforest and grassland were 3.5 and 3.2, respectively, thisvalue of the grassland was smaller than that of the forestsite. However, the area of trunk and branch at forest werebig, LAI of the forest which contributes to theevapotranspiration was 2.0, this value was smaller thangrassland. The difference of this LAI seems to appear thedifference in the latent heat of the forest and the grassland

Fig 6. The comparison of latent and sensible heat
flux with forest and grassland