6.4 Evapotranspiration
Assessment of evapotranspiration (ET) is the very problematic for this
region due to the lack of the data. Annual values of ET for goltsy
landscape at the Morozova Creek watershed (altitude range 1100-1700 m
a.s.l.) was estimated based on the water balance data of the Kolyma
water balance station (KWBS) in the range from 70 mm (Lebedeva et al.,
2017) to 92 mm (Makarieva et al., 2018a). In the Upper Wolf-Creek
catchment (part of the southern headwaters of the Yukon River, Canada)
with tundra and shrub-tundra environment and elevation reaching 2250 m
annual value of ET reached 135 mm (Janowicz et al., 2004). The
assessment for the Upper Kuparuk (elevation range of 698-1464 m) and
Imnavait River basins (elevation range from 844 to 960 m) (Alaska) from
tundra landscape was about 140 and 178 mm respectively (Schramm et al.,
2007). In the the Tana River Basin (Finnish Tenojoki), with the mean air
temperature -6˚C at the highest mountain tops (1010 m), annual values of
snow sublimation and evapotranspiration was estimated as 90 and 58 mm
respectively (Dankers & Chrisrensen, 2005). The assessment of total
annual evaporation at the Axel Heiberg Island at the Canadian Arctic
Archipelago was about 140 mm (Ohmura, 1982).
The observations of ET from the ground surface at the Suntar-Khayata
station were carried in 1958 (Grave, 1959). Two land evaporimeters
GGI-500 were used (Makarieva et al., 2018a). The evaporimeters were
installed in early June 1958, when the snowpack was continuous, had not
started melting yet, and ground temperature was below zero. Evaporation
tanks were filled with soil from the Suntar-Khayata Station site and
left under snow until it completely melted at the site on July 20-27,
1958. The observations continued throughout August 1958. Evaporation
tanks were weighted every 5 days, precipitation was registered daily in
direct proximity to them (Grave, 1959). In August 1958 observed values
of precipitation accounted for 77 mm, infiltration rate – 36 mm, ET –
44 mm (about 1.4 mm per day).
Compared to the ET assessments for the KWBS watersheds where free-snow
season lasts twice longer and mean summer values of air moisture deficit
are 1.5 times higher than at the Suntar-Khayata Station, we question
this single result of observations and suggest that the value of 44 mm
is significantly overestimated.
In the Hydrograph model the amount of ET is calculated taking into
account the potential evaporation, initial amount of moisture in soil
layers, maximum water holding capacity of the soil, the fraction of
contribution of a given soil layer to total evaporation, the value of
which depends on soil and vegetation type (Semenova et al., 2013). To
estimate ET we adopted the evaporation coefficient parameter from the
modelling studies conducted for the Kolyma water-balance station
(Semenova et al., 2013; Makarieva et al., 2020). Its value for goltsy
landscape is 9*10-10 m (hPa*s)-1.
Simulated ET values were 19 mm in August, 1958 and 43 mm on average
during snow free season for the whole period of simulations. Adding 11
mm of snow evaporation it gives us about 54 mm of annual total
evaporation at the goltsy landscape.