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021. Depth of snow cover map

Depth of snow cover map

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Snow cover depth

Mapping fields of snow cover, as well as any geographical fields, are characterized by their spatial and temporal patterns on topological, regional and planetary levels. Information about snow cover is mainly represented by measurements at meteorological stations located in homogeneous standard locations. Snow covers countless diverse landscapes, the characteristics of which are not reflected in meteorological information. Therefore, the primary issue of snow cover mapping is substantiation of its spatial and temporal changes. This goal was achieved by the search of further information through the real data links with better known characteristics of geospace. This approach is implemented on the principles of geographical similarity of processes and statistical regularities.

There was a need to solve a number of other key issues. The first one is dictated by current climate warming. We have complete information on snow cover only till warming, according to the data from references representing measurements for the period up to 1968 [References..., …1968]. Other publications include maps of individual components of snow cover of the late 20th century [Atlas of Irkutsk oblast, 1962; Cisbaikalia and Transbaikalia, 1965; Atlas of Transbaikalia, 1967]. At the same time, thanks to the field work within the Baikal- Mongolia region and personal contacts of the authors, there was an opportunity to get acquainted with climate data of 1951-2010 and 1976-2010 in Transbaikalia and Mongolia, and, accordingly, to fix a tendency of temporarily change of parameters of snow cover in the up-to-date period.

The snow cover of the Baikal basin is formed inhomogenously. Its height decreases from the northeast of the Lena-Angara plateau (50-80 cm) to 5-10 cm in the vast plains of Mongolia and Transbaikalia. This is caused by the interaction of powerful north-eastern air flows with weakened Pacific ones, as well as by precipitation increasing with the altitude and by an increase in the share of their solid constituents. Therefore, in the valleys the snow depth is small, and in the mountains of Cisbaikalia and on the Stanovoe highland it reaches up to 60-100 cm.

Continuous snow cover is typical for the whole Baikal basin, but due to wind transport within basins with inversions, on the windward and leeward slopes it occurs unevenly. These factors make it difficult to reflect its spatial and temporal state, which is traced according to the data of the snow cover measurements. So, on the shores of Lake Baikal within 460-500 m there are about 70 meteorological stations, and on the slopes of the ranges there are no more than 5 stations. This factor defined the search for correlations of the measurement data of snow depth with better studied factors: with precipitation of the cold period, and with altitudes of the area. In this respect, the snow cover was analyzed at least on 900 meteorological stations within the entire Baikal-Mongolian region and adjacent territories. At the same time, a geographical-functional approach to spatial and temporal analysis of the snow cover was developed. Particular attention was given to determining the depth of snow on the slopes of different exposures. On the windward slopes the snow depths increase up to 70 cm at 1500 m of true altitude and up to 125 cm at 2000 m. Within the goletz zone on the leeward slopes the snow cover is constantly reducing up to 7-12 cm at 2000 m. On the plains its average height ranges from 30 to 40 cm. The exception is provided by the Mongolian Plateau, where in February and March, the snow depth does not exceed a few centimeters. It should be emphasized that in snowy winters the snow occurrence over 23-35 cm is covered by ice coating: due to fodder shortage in 2010 the number of livestock in Mongolia decreased from 40 to 28 million.

All contemporary background information is presented in references on climate, published at the end of the last century; after that the planetary warming came. Therefore a map of snow depths based on the data obtained till 1968 was compiled. Further, a correlation between the components of the snow cover of the last century with contemporary data for the warming period (1976-2010) is revealed. Using this approach, the opportunity to evaluate the past changes in snow cover over recent decades presented itself.

From 1975 to 2010, the average annual temperatures increased by 2ºC in extremely arid deserts of southern Mongolia, and by 1ºC in the northern mountain Transbaikalia. However, in Northern Transbaikalia the growth ΣT ≥ 10ºC turned out to be more, i.e. 600ºC, and in arid deserts only 200ºC. In the mountain-taiga landscapes the precipitation remained intact and in arid landscapes it decreased. Consequently, the height of the snow cover in the mountain-taiga landscapes decreased, and the avalanche danger became less threatening. At the same time Mongolian ice coating in Dauria became more active. Livestock deaths increased. Thus, according to the identified correlations, the snow cover map compiled according to the data till 1968 can be considered a basic one.

Regional peculiarity of snow depth formation should be emphasized. First of all, it is dictated by the meeting of wet air masses with the surface of mountain slopes. It is possible to distinguish graphically the snow accumulation on the windward and leeward slopes. Air masses, transporting over the water surface of rivers and lakes, are saturated with water and enhance the amount of snow on opposite slopes. These are the locations of weather stations near Vydrino, Snezhnaya, Tankhoi, Vorontsovka and others. The effect of windward and leeward slopes is leveled by depression inversion and generally irregular dynamics of air masses. The data of meteorological stations are more reliable. On their basis, the reading of snow changes according to the generalized spatial and temporal altitudinal gradient is carried out. So, at the levels of 1000 and 1500 m, the snow depth is 58 - 90 and 56 - 86 cm on the north-western slope and on the south-eastern slope, respectively.

References

Atlas of Irkutsk oblast. (1968). Moscow-Irkutsk: Main Department of Geodesy and Cartography, 182 p.

Atlas of Transbaikalia. (1967). Moscow-Irkutsk: Main Department of Geodesy and Cartography, 176 p.

Atlas of Cisbaikalia and Transbaikalia. (1965). Moscow: Izd-vo "Nauka", 485 p.

Atlas: The economic potential of the Republic of Tuva. (2005). Kyzyl: TuvIKOPR SO RAN, 60 p.

Climate Handbooks. (1968). Leningrad: Gidrometeoizdat, vol. 21-23.

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