5.2.1 Distribution of air temperature and humidity with elevation
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 RP depending on the difference of elevation.
5.2.2 Distribution of precipitation with elevation
The data of 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 foothills by more than twofold. Precipitation gradient at 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) had 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 according to the rain gauge data is 555 mm.
Correct estimation of precipitation is difficult in mountainous areas, significant biases occur especially for winter precipitation under effect of the 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 mountains peaks (Vasiliev & Torgovkin, 2002).
Corrected values of precipitation at meteorological stations were used to develop the dependencies between both liquid and solid precipitation amount and terrain elevation in the basin. Precipitation amount for each RP is assessed according to those dependencies based on its elevation and interpolated daily solid and liquid sums of precipitation are normalized.
6. Hydrograph model verification based on special observation
We used available observational data from the Suntar-Khayata Station to verify the model parameterization for the goltsy landscape.