Heat and water exchange of the snowpack and permafrost during the snowmelt
season in a larch forest in eastern Siberia* Tetsu Hashimoto1, Takeshi Ohta2,4, Tae Toba2, Trofim Chr. Maximov3(1: ERCBR, Shimane University, 2: Nagoya University, 3: Institute of Biological Problems of the Cryolithozone,
4: Frontier Observational Research System for Global Change)* Forest Science section, ERCBR, Faculty of Life and Environmental Science, Shimane University, Nishikawatsu-cho,
Matsue, 690-8504, Japan. e-mail:tetsu@life.shimane-u.ac.jp
Abstract
To clarify the features of the heat and water balances of the snowpack and their influence on the permafrost during thesnowmelt season, observations of the snow water equivalent, snowmelt rates, water vapor flux at the snow surface, andmeteorological elements were made in a larch forest in the middle reaches of the Lena River basin. The snow temperaturereached 0 ºC only at the snow surface in the pre-melt period, and reached 0 ºC in all layers of the snowpack in the melt
period. The heat balance components were calculated using the bulk method. The heat available to the snowpack included
the net all-wave radiation and the sensible heat flux. The net all-wave radiation contributed more than 60% of the available
heat in both periods. The main consumption heat was the latent heat flux in the pre-melt period and the heat for melt in themelt period, which accounted for 67 and 72% of the consumption heat, respectively. The runoff ratio of meltwater from thesnowpack was estimated from the snow water equivalent and surface snowmelt rates; 44 and 81% of the meltwater in thesnowpack flowed out to the permafrost in the pre-melt and melt periods, respectively. The contribution of evaporation tosnow ablation was as much as 37% in the pre-melt period and 6% in the melt period. In the pre-melt period, the meltwater
was thought to flow down through snow fingers. The meltwater infiltrated the frozen permafrost and raised the temperatureof the frozen soil by releasing the fusion heat of refreezing in both periods.
Keyword: Siberian larch forest, snowmelt, heat balance analysis, snow finger, permafrost

1. Introduction
Siberia is a typical high-latitude area in the EurasianContinent. The Lena River basin is divided into two mainzones: taiga and tundra. The taiga contains boreal forest.
Snowmelt processes and the timing of the snow
disappearance can affect the timing of the thaw. In boreal
forests, the forest canopy has a marked effect on snowmelt.
The characteristics of the snowmelt processes in a forest
are determined by the heat balance in the snowpack, whichis affected by the forest canopy. Heat balance models
reflecting forest canopy structure have been applied toboreal forest.
The meltwater discharge includes water movement in
the snowpack. Flow paths are often formed in thesnowpack. The meltwater discharged from the snowpack
flows on the ground surface or infiltrates the ground. The
infiltration of meltwater into frozen ground in permafrost
or frost regions has been noted. For example, a rise in thetemperature of frozen ground caused by the infiltration of
meltwater has been reported. The water or ice content of
the ground affects the snowmelt stream runoff.
To connect the snowmelt processes in the snowpack to
the timing of the disappearance of snow, the snowmelt
runoff in streams, the permafrost thaw, and the moisture
content in the active layer, it is necessary to grasp the heat
and water exchanges in the snowpack, and their influenceon the permafrost under the snowpack. Taking these factors
into account is important for making good estimates or for
improving the heat balance models used in snowmelt or
runoff models.
The purpose of this study was to clarify the features of
the heat and water balances in the snowpack andpermafrost, during the period from pre-melt to thedisappearance of the snowpack, for the taiga forest in the
middle reaches of the Lena River basin, using observationdata.

2. Observations
The study site is located about 20 km north of Yakutsk
City (62º15'18"N, 129º37'08"E) in the middle of the Lena
River basin, in eastern Siberia. The altitude is 220 m a.s.l.
The topography is essentially flat. The dominant species
around the site is larch (Larix gmelinii). A 32-m-highobservation tower was installed in the forest in August
1996. The water and heat fluxes and the profile ofmeteorological elements have been observed since 17
August 1997 (Ohta et al., 2001). For the 50 x 50-m
quadrate in which the tower is centered, the mean standheight and density were 18 m and 840 trees per hectare,respectively. The site was covered with snow from mid
September 1997 until mid May 1998.
In the larch forest, the decrease in the snow surface,evaporation from the snow surface, density profile of thesnowpack, snow temperature profile, and water equivalentof the snowpack were measured manually from 16 April to
13 May 1998. The evaporation from the snow surface wasmeasured using two small cylindrical lysimeters. The
lowering of the snow surface was measured by thesnow-wire method. We considered the amount of loweringof the snow surface to be the sum of snowmelt andevaporation. The snow density profile was measured using
a 100 cc box-type snow sampler, which was 3 cm high.
The temperature profile of the snowpack in a cross-section
was measured with a thermister thermometer inserting. The
measuring points on the cross-section were at the surfaceof the snowpack, every 10 cm from the snow surface, andat the bottom of the snowpack. Measurements were usually
made at 5:00, 8:00, 10:00, 11:00, 13:00, 14:00, 15:00,
16:00, 18:00, and 20:00 (lowering only). The snow surface
density was measured every day between 14:00 and 16:00.
The snow density profile at 3-cm intervals was measured
around 10:00 and 15:00 every two days. The snow waterequivalent was measured with a cylinder-type sampler
from 8:00 to 9:00 every few days. The internal diameterand length of the sampler were 7 cm and 1 m, respectively.
The times mentioned above are Yakutsk Standard Time.
The atmospheric downward long-wave radiation(MS-201, Eiko) was measured 32.0 m above the ground.
Global solar radiation (CM-6F, Kipp & Zonen), reflectedsolar radiation (CM-6F, Kipp & Zonen), net all-wave
radiation (Q7, REBS), air temperature (HMP-35D, Vaisala),relative humidity (HMP-35D, Vaisala), wind speed(AC-750, Makino), infrared snow surface temperature(4000-4GL, Everest), ground temperature (TS101,
Hakusan Kougyou), and ground heat flux (MF-81, Eiko)were measured above the forest floor. A ventilated shelter
covered the air temperature and relative humidity sensors.
The radiation meters, ventilated shelter, wind speed, andinfrared radiation thermometer for measuring the snow
surface temperature were installed 1.2, 1.8, 1.9, and 1.9 m
above the ground, respectively. The ground temperature
was measured at seven depths (0, 10, 20, 40, 60, 80, and120 cm). The ground heat flux was measured at a depth of
5 cm. All the elements, except radiation items, were
measured every five minutes. These data were stored in adata logger (DATA MARK LS-3300, Hakusan Kougyou)
every five minutes. For the radiation items, the average ofmeasurements made every minute was recorded every fiveminutes.

for Rn, while H and lE were given by the following bulk
equations:

H = c p ρC HU (Ta − Ts )lE = lρCEU (qa − qs )

(3)
(4)

where CH and CE are the bulk coefficient for the sensible
and latent heat fluxes, respectively, cp is the specific heat ofair, U is the wind speed above the snow surface, ρis the
air density, Ta is the air temperature above the snow surface,
Ts is the snow surface temperature, l is latent heat for theevaporation or condensation of water vapor, and qa and qs
are the specific humidity of air and the snow surface,respectively. For U, Ta, Ts, and qa, observed one-hour
averages were used. The bulk coefficient for the sensible
heat flux was assumed to equal that of the latent heat flux.
The bulk coefficient for the latent heat was obtained fromthe relationship between the evaporation rates obtainedusing the lysimeters and the value of ρU (qa – qs) given
by observed data.
The observed one-hour average of the ground heat
flux was used as QB. The daily value of ΔQT was obtainedusing the following equation:n∆QT = ∑ C PS ρ Si ∆Ti ∆Z Si

(5)

i =1

Q M = Rn + H + lE + QB − ∆QT(1)where n is the number of vertical divisions of thesnowpack, the subscript i is the number assigned to a layer,
CPS is the specific heat of ice, ρSi is the density of snow,
ΔTi is the difference in snow temperatures at the medianpoint within the period from 18:00 on one day to theprevious day, and ΔZSi is the snow thickness of a layer.
The snowpack was divided into layers 10 cm thick. ΔTi
was obtained from the snow temperature measured at every
10 cm depth. ΔQS and QD in Eq. (2) were obtained bypartitioning the daily value of QM. The daily runoff ratio
was determined from the observed snow surface lowering,snow surface evaporation, and water equivalent of thesnowpack from the snow density profile.

QM = ∆QS + QD

(2)

4. Results

3. Heat balance equations
To evaluate the heat balance components of the snowpack,
we used the following heat balance equations under thecondition of no precipitation and ignoring the vapor
exchange at the bottom of the snowpack:where QM is the heat of snowmelt, Rn is the net all-wave
radiation, H is the sensible heat flux, lE is the latent heat
flux for exchanging water vapor at the snow surface, QB isthe conductive heat flux at the bottom of the snowpack,
ΔQT is the stored heat that changes the temperature of thesnowpack, ΔQS is the fusion heat for the snowmelt stored
in the snowpack, and QD is the fusion heat for thesnowmelt flowing out from the snowpack as meltwater.
The daily values of each term in Eq. (1) were obtained
as follows. The observed one-hour average value was used

The snow depth was about 50 cm at the beginning of ourmanual measurements. On May 12, snow covered less than
50% of the area and the maximum snow depth in thequadrate was about 20 cm. Our period of analysis was from
17 April to 12 May.
Figure 1 shows the daily mean values of air temperature,
specific humidity, and wind speed above the forest floor.
The mean air temperature and mean specific humidity
increased after May 5. The mean air temperature changed
from below 0 to 1 ºC on that day. The mean wind speed
was very low, below 1.2 m s-1.

2

0

1.5

-2

1

-4
-6

0.5
17 20
25
Apr.,1998

301
5
May

10

0

Fig. 1: Daily mean air temperature, humidty and windspeed above the forest foloor

290

120
280

100

270

80
60

260

40
250

20
0
0.8
0.7
0.6
0.5
0.4
0.3

240

17 20
25
Apr.,1998

10

301
5
May

Shortwave radiation
Net all‑wave radiation
Downward long‑wave radiation
AlbedoFig.2:Radiations in the forest

Snowmelt or evaporation rate (mm day‑1)

Figure 2 shows the daily mean values of the observed
radiation above the forest. The global solar radiation
increased slightly before May 5. The downward
nward
long-wave radiation increased after May 5. This waspartially due to the increase in the downward long-wave
radiation above the forest. The increases in air
temperature and specific humidity shown in Figure 1
could have caused the increase in the downward
long-wave radiation above the forest. The daily net
all-wave radiation in the forest was positive during theperiod. The net all-wave radiation increased more before
May 5 than after that date. This was caused by both theincrease in absorbed solar radiation due to the lowered
albedo and the increase in the downward long-wa
long-waveveradiation in the forest.
Figure 3 shows the daily snowmelt and surface
evaporation rates. The snowmelt occurred during our study
period and increased rapidly, beginning May 5. Minimal
condensation of water vapor occurred on the surface atnight, while the evaporation of water vapor dominated thedaily values. In the study period, the water equivalent of
the snowmelt and evaporation was 90.4 and 9.8 mm,
respectively.
All layers of the snowpack reached 0 ºC for the first timeon 5 May. Before this date, the snow temperature reached 0ºC only at the surface of the snowpack, and was below 0 ºC
below the snow surface.
In this paper, we call the period after May 5 the melt
period, and the period before that date the pre-melt period.
The snow density tended to increase with time of day.
This tendency was strongest between 40 and 50 cm, anddecreased with the distance from the ground. The density
above 20 cm above the ground increased to around 260 kg
m-3 in our study period. The density of the layers above aheight of 20 cm did not vary much with time of day. The
snow density at our site was from 150 to 260 kg m-3.
The snow layer was divided into the portions above andbelow about 20 cm from the ground. The crystals were

140

Downward long‑wave radiation(W m‑2)

2

300

160

Albedo

2.5

Net all‑wave radiation(W m‑2)
Shortwave radiation(W m‑2)

4

3
Air TemperatureSpecific humidity
Wind speed

Specific humidity (g kg‑1)
Wind speed (m s‑1)

Air temperature(℃)

6

16
14
12

Surface evaporation rate
Snowmelt rate

10
8
6
4
2
0
17
20
Apr.
1998

25

30 1
May.

5

10

Fig. 3: Snowmelt and evaporation rates
0.5-2.0 mm in size in the upper layer, and 2.0-4.0 mm in
the lower layer. The snow in the upper layer changed fromcompact to granular snow with time. The snow in the lower
layer changed from dry to wet hoar on May 5.
In addition, the snowpack at our site was alsocharacterized by snow fingers. We found numerous snow
fingers, from 2 to 6 cm in diameter, in the snowpack at oursite on 8 May. The fingers were clearly visible about 5 cm
below the snow surface and extended to the ground. A

Table 1 Heat balance components of the snowpack
PeriodPre-melt
Melt

Available heat Wm-2 (%)
Rn
H
11.6
7.6
(60.4)(39.5)
37.6
14.3(72.5)(27.5)

Consumed heat Wm-2 (%)
lE
QM
∆QS
12.9
5.4
2.6
(67.1)(28.3)(13.6)
13.0
37.2
5.2
(25.0)(71.8)(10.0)

QD
2.8(14.7)
32.0(61.7)

QB
0.6
(2.9)
0.9
(1.7)

QT
0.3
(1.7)
0.8
(1.6)

Pre-melt period: Apr. 17 - May 4 1998, Melt period: May 5-12 1998
snow finger is a water pathway.
On 17 Apr., the first day of our study, the groundtemperature profile was almost constant between –6 and –7ºC. The ground temperature increased gradually in the
pre-melt period and rapidly approached 0 ºC during themelt period.
The slope of the regression line of the relationshipbetween the evaporation rates obtained from the lysimeters
and the value ofρU (qa – qs) given by observed data had avalue og 0.0039, which we adopted as the bulk coefficient.
Using Eq.(4), the evaporation rates were reproduced
satisfactorily. The heat for snowmelt (QM) calculated using
Eq. (1) also were good agreement with the observed valueof the snow surface melt rates.

5. Heat and water balance analysis
The daily runoff ratio was determined from thedifference between snowmelt rates at the surface layer(obtained from the snow surface lowering and snow
surface evaporation) and the water equivalent of thesnowpack from the snow density profile. The runoff ratioof the meltwater was 0.44, 0.81, and 0.71 in the pre-melt,
melt, and all periods, respectively. The evaporation rate asa percentage of the ablation rate was 37%, 6% and 13%
during the pre-melt, melt, and all periods, respectively.
Evaporation contributed markedly to snow ablation in the
pre-melt period. Only the snowpack surface reached 0 ºC
in the pre-melt period. Despite the fact that the temperature
below the snow surface was sub-zero, 44% of the
meltwater reached the ground. We found complete snow
fingers at our study site on 8 May. It is thought that thefingers were formed by the downward flow of meltwater.
Table 1 shows the heat balance of the snowpack during
both periods. The main available forms of heat were the net
all-wave radiation and the sensible heat flux. The mainheats consumed were the latent heat flux of evaporationand the heat for snowmelt. The conductive heat flux at thebottom of the snowpack, and the heat required to change
the snowpack temperature, were relatively small. In both
periods, the net all-wave radiation dominated the available
heat flux. In the melt period especially, the net all-wave
radiation accounted for 72.5% of the available heat flux. In
the pre-melt period, the latent heat flux for evaporationaccounted for 67.1% of the consumed heat, dominating theconsumed heat. By contrast, in the melt period, the heat forsnowmelt was the major consumed heat, accounting for
71.8% of the consumed heat. There was little difference inthe latent heat flux between the pre-melt and melt periods.
As has been already noted, the increase in the heat forsnowmelt from the pre-melt period to the melt perioddepended on the increase in net all-wave radiation.
Therefore, the latent heat, as a percentage of the consumed
heat, showed a relative decrease. Nevertheless, the latent
heat was not negligible as a consumed heat in the melt
period. The heat fluxes from the snowpack to the groundwere the conductive heat at the bottom of the snowpack,and the fusion heat of the meltwater discharged from thesnowpack. The value of the latter was much higher thanthat of the former (Table 1).
In the pre-melt period, 14.7% of the consumed heat, as
the fusion heat for the snowmelt, was discharged from thesnowpack with the meltwater (Table 1). We consider thefusion heat for snowmelt that is stored in the snowpack in
the pre-melt period. The fusion heat for snowmelt stored in
the snowpack accounted for 13.6% of the consumed heat
(Table 1). In our study, the stored heat that changed thetemperature of the snowpack (ΔQT ) was calculated from
Eq. (7), using the observed snow temperature profile. The
calculated value of Δ QT was the stored heat in thesnowpack excluding snow fingers, as the temperatures ofsnow fingers were not measured. We postulate that the
meltwater stored in the snowpack froze again, releasing theheat of solidification, and formed a snow finger in which
the temperature was around 0 ºC. The formation of a snow
finger discharged the heat of fusion for snowmelt, which
accounted for 14.7% of the consumed heat and decreased
the heat stored in the snowpack. This prevented a rapid
increase in the snowpack temperature, resulting in
prolongation of the pre-melt period.
The heat required to increase the ground temperature
was calculated in one-dimension from the time vaiations of
the ground temperature profiles and was compared with thefusion heat of meltwater discharged from the snowpack
and with the conductive heat at the ground surface. In the
result, it was indicated that snowmelt water infiltrated to
the ground was very important to rise the groundtemperature in both period.