3.3 Input data
Daily air temperature and humidity, and daily precipitation totals from
meteorological stations of the hydrometeorological network within or
nearby the basin were used as meteorological inputs for hydrological
modelling. Four of them, Suntar-Khayata, Nizhnyaya Baza, Vostochnaya and
Agayakan, were used for the period 1957-1964 and two, Agayakan and
Vostochnaya, for the period 1966-2012 (Table 3, Fig. 1). Data from
meteorological stations are interpolated to each RP. The interpolation
is based on the triangulation method, when ideally each RP is inside a
triangle, in the corners of which there are weather stations. Linear
interpolation is conducted between the stations if only two are
available.
The study area is characterized by
temperature inversions. Annual average monthly temperature and air
saturation deficit lapse rates were estimated using the data from the
Suntar-Khayata and Agayakan meteorological stations (the range of
elevation is 1292 m), they change from +1.1 ºС and +0.01 mbar per 100 m
elevation increase in January to -1.3 ºС and -0.35 mbar per 100 m in
June. The estimated values were used to correct interpolated temperature
and saturation deficit from meteorological stations to RPs depending on
the difference in elevation.
Data
from four meteorological stations (Suntar-Khayata, Nizhnyaya Baza,
Vostochnaya and Agayakan) from Reference book (1968) and the information
of snow surveys at high mountain elevation (Grave, 1960) were used to
analyze the distribution of precipitation at different altitudes for
warm (May – August) and cold (September – April) periods of the year.
Annual precipitation at the
Suntar-Khayata Station exceeds the precipitation amount observed at the
foothills by more than twofold. The precipitation gradient for the
altitude range 777 to 1350 m a.s.l. is 7 mm (5-7%) per 100 m, and at
the altitude range 1350 to 2068 m a.s.l. it exceeds 35 mm (15-16%).
Snow survey data for 1957-1959 (Grave, 1960) has demonstrated that
altitudinal gradients of precipitation increase are steady and equal on
average to 35 (5-8%) and 30 (4-5%) mm per 100 m for the altitude
ranges of 2068-2257 and 2257-2477 m a.s.l. correspondingly.
Solid precipitation share at 777 m
a.s.l. is approximately 25% of the annual total, and at 2068 m a.s.l.
it increases to 60%. Mean annual precipitation from 1957 to 1964 at the
Suntar-Khayata Station is 555 mm.
Correct estimation of precipitation is difficult in mountainous areas
wheresignificant biases occur especially for winter precipitation
because of the effect of wind on snowfall (Groisman et al., 2014). There
are several methods for precipitation corrections. They are mainly based
on the coefficient on wind speed and wind protection, air temperature
and precipitation type (WMO Report no. 67, 1998; Yang & Goodison,
1995). In Reference Book (1968) some adjustments are recommended for
wind underestimation and wetting loss, which can reach up to 1.7 times
(1.6 on average in cold season) for solid precipitation, and 1.3 times
(1.16 times on average in warm season) for liquid precipitation, which
leads to the annual precipitation amounts of 688 mm at 2068 m a.s.l.
(Reference Book, 1968), and 800 mm at the mountain peaks (Vasiliev &
Torgovkin, 2002).
Corrected values of precipitation at
meteorological stations were used to develop the relationships between
both liquid and solid precipitation amount and terrain elevation in the
basin. Precipitation amount for each RP is assessed according to those
relationships based on elevation and interpolated daily solid and liquid
sums of precipitation are normalized.
4. Results
We used available observational data from the Suntar-Khayata Station to
verify the model parameterization for the goltsy landscape.