4.4 Evapotranspiration
Assessment of evapotranspiration (ET) is very problematic for this
region due to the lack of 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, the 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 Tana
River Basin (Finnish Tenojoki), with a mean air temperature -6˚C at the
highest mountain tops (1010 m), annual values of snow sublimation and
evapotranspiration was estimated to be 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 out 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 weighed every 5 days, and precipitation was registered daily
in direct proximity to them (Grave, 1959). In August 1958 observed
values of precipitation accounted for 77 mm, infiltration rate was 36
mm, and ET was 44 mm (about 1.4 mm per day).
Compared to the ET assessments for the KWBS watersheds where the
snow-free season lasts twice as long 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 the
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 the snow free season for the whole
period of simulations. Adding 11 mm of snow evaporation gives us about
54 mm of annual total evaporation from the goltsy landscape.