Definition

Siberia: a region of northern Asia of Russia, stretching from the Ural Mountains to the Pacific Ocean.

Continental air mass: vast body of air that forms over the interior of a continent, excluding mountainous areas.

Anticyclone: weather phenomenon in which there is a descending movement of the air and a high pressure area over the part of the planet’s surface affected by it.

Continental arctic air: air that are extremely cold and dry due to their continental source region between 60o and 90o north latitude.

Tundra: a biome in which tree growth is hindered by low temperatures and short growing seasons.

Taiga: a biome characterized by coniferous forests.

Introduction

Siberia has the largest area of permafrost in the world. Furthermore, the freshwater in the large Arctic rivers of Eurasia that flow from Siberia to the Arctic Ocean plays an important role in the control of the global thermohaline circulation by modifying salinity and sea-ice formation in the Arctic Ocean. In addition, snow and ice greatly affect the lives of the people inhabiting Siberia. This article discusses the characteristics of snow and ice in Siberia.

Geography and climate

Siberia occupies the Asian part of Russia and consists of three major subregions shown in Figure 1a. In the west, abutting the Ural Mountains, is the huge West Siberian Plain, drained by the Ob and Yenisey rivers. It varies little in relief and includes wide tracts of swampland. East of the Yenisey River is central Siberia, a vast area that consists mainly of plains and the central Siberian Plateau. Farther east, the basin of the Lena River separates central Siberia from the complex series of mountain ranges, upland massifs, and intervening basins that make up East Siberia.

Siberia, Figure 1
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Map of Siberia. (a) Topography map for geography indicated West, central, and East Siberia and (b) vegetation map for climate for tundra and taiga of West and East Siberia.

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According to Climates of the U.S.S.R. by Borisov (1965), there are four major climate zones in Siberia. The climate zones of West and East Siberia are each subdivided into two climate zones according to the dominant vegetation, tundra or taiga. Here, West Siberia as used here includes the central Siberian Plateau. West Siberia is characterized by many days dominated by continental arctic air and East Siberia by prevailing continental temperate climate and continental arctic air masses, which converge to form mainly extensive anticyclones, especially in winter. The taiga corresponds with regions of subarctic and cold continental climate with long, severe winters (up to 6 months with mean temperatures below freezing) and short summers as characteristic, as has a wide range of temperatures between the lows of winter and highs of summer. On the other hand, tundra corresponds with the regions of polar climate with extremely short growing season (6–10 weeks) and long, cold, dark winters. Tundra occupies the region between tree line and polar ice cap. Tundra–taiga boundary is corresponding to the arctic front (Bryson, 1966).

Figure 1b denotes the four major climate regions. The West Siberian tundra region is characterized by contrast in the intensity of solar radiation during the year and by a long, severe winter with frequent passage of low-pressure systems accompanied by violent gales and heavy snowstorms. In contrast, a high-pressure system typically develops over the East Siberian tundra region in winter, leading to stable winter weather and a negligible snow cover. Because of its great continentality, the region is characterized by contrasting conditions between summer and winter. The West Siberian taiga region is characterized by the active movement of air masses from the Atlantic and Arctic oceans with the continental air mass and anticyclones formed in Siberia. The East Siberian taiga region is characterized by marked continentality such as the prevalence of clear-cut anticyclonic weather conditions, very frosty and cold cloudless winter weather and hot summers with high solar radiation, and the sudden onset of seasons.

Frozen ground

Permafrost is the dominant component of the Siberian soil; about 80% of area in the subsurface in Siberia is composed of permafrost. Kondratjeva et al. (1993) showed that permafrost in Siberia mostly developed in the Late Pleistocene during the Sartanian glaciation (Late Wisconsinan/Weichselian, 18,000–27,000 years ago). The average air temperature at that time was 8–10°C lower than at present, and under these very cold conditions, permafrost spreads over Siberia, eventually extending its southern boundary to 48–49° N during the Sartanian glaciation. Subsequently, in the Holocene, the spatial extent of the permafrost was greatly reduced in West Siberia, where the southern permafrost border has been displaced northward to 60° N. Although in East Siberia the permafrost has retained almost the same spatial coverage as during the last glacial period, it has likely become reduced in thickness. Duchkov (2006) showed that permafrost reaches its greatest thickness (more than 1 km) in Yakutia, central Siberia, where it forms the lowest temperature block of lithosphere in northern Eurasia. Terrestrial heat flow acts as one of the heat sources for permafrost to determine the lower limit of the permafrost depth. Terrestrial heat flow in the area of Yakutia does not exceed 30 mW m–2, in contrast to other Siberian regions, where terrestrial heat flow is 50–70 mW m–2 and the permafrost is no more than 400–600-m thick.

The top layer of soil above the permafrost layer thaws seasonally and is called the active layer. The active layer affected direct runoff and peak flow in a small permafrost watershed, as shown by Yamazaki et al. (2006). Water within the active layer has a role of memory in previous years, because water within the active layer has a residence time of more than a half year and it affects snowmelt runoff due to the change of the capability of infiltration into frozen ground (Suzuki et al., 2006a) and transpiration due to recovering shortage of water for transpiration from the thawing ground water during the summer (Sugimoto et al., 2003). Rest of the parts of Siberia without permafrost are covered by seasonal frost, where the ground freezes in winter and thaws in summer. Zimov et al. (2006) showed that the permafrost stores a large amount of carbon, and if it were to thaw, a great deal of carbon would be released. One of the pathways for terrestrial carbon cycle in permafrost region is carbon transport in the rivers. Suzuki et al. (2006b) showed that a large quantity of dissolved organic matter is transported from the upper catchments of the Lena river to the Arctic Ocean.

Snow

During winter, snow covers all of Siberia. The snowpack structure in Siberia is characterized by a thick layer of depth hoar at the bottom, which forms as a result of the large temperature gradient between the relatively warm soil and cold air. Kitaev et al. (2005) analyzed the distribution of snow over Russia from 1936 to 2000. In East Siberia, the mean snow depth, snow cover days from 1936 to 2000, and snow water equivalent from 1966 to 1996 were 34 cm, 220 days, and 90 mm, respectively, and in West Siberia, they were 34 cm, 192 days, and 133 mm, respectively. In both West and East Siberia, snow depth and snow cover days generally increased from 1936 to 2000.

The presence of snow cover influences the depth of the active layer and of seasonal frost in Siberia. In addition, snowmelt runoff contributes greatly to the discharge of Siberian Rivers, rather than rain. Tree growth as indicated by tree ring width is related to winter precipitation as snow, because recent tree growth is not only related to air temperature but also to the timing of snow disappearance (Vaganov et al., 1999). A few snow researches have been carried out in the southern mountain region of East Siberia, where Suzuki et al. (2006c) showed that sublimation accounts for nearly 10% of snow ablation beneath larch forest. Furthermore, Suzuki et al. (2006c) found that snow albedo is related to snow density. In the tundra region of East Siberia, Hirashima et al. (2004) developed a land surface model that incorporated blowing snow and estimated that about 40% of winter precipitation sublimated during blowing snow events. Tundra regions of Siberia are characterized by a shallow snowpack and a heterogeneous snow cover because of the small topographic relief, because strong wind induced blowing snow events occasionally, but taiga regions tend to have a uniform snow cover since forest canopy reduced wind speed and large snow-folding capacity.

Glaciers and river and lake ice

Ice in Siberia occurs in glaciers and as river and lake ice. The large volume of ice constitutes an important water resource and influences the inhabitants of Siberia. According to Kotlyakov et al. (1996) and UNEP (United Nations Environment Programme) (2007), from 1950 to 1970, Siberia’s glaciers were widely dispersed on mountain ranges, from the Ural Mountains to Kamchatka, covering a total area of about 3,600 km2 (USSR Glacier Inventory). Since 1970, Siberian glaciers have generally retreated, mainly from lower elevations and southern latitudes, and the amount of retreat has a wide variety in the places.

River and lake ice are of more importance to the people living in Siberia than glaciers because they are an important freshwater resource. The timing of the break-up or freeze-up of lake ice depends primarily on air temperature. Walter et al. (2006) reported that during thaws, a lake in northern East Siberia emits a large amount of methane.

The break-up of river ice in spring occasionally causes large floods in Siberia, especially in permafrost-dominated regions. By incorporating river ice into a river run-off model, Ma et al. (2005) showed that river ice volume greatly affects estimations of snowmelt run-off in the Lena River. Vuglinsky (2002) noted that the knowledge of river ice is important for understanding run-off processes, and the duration of river ice each year also greatly affects the use of large rivers for transporting cargo from or to the sea. Smith (2000) showed that the river ice in central and East Siberia is melt onset 1–3 weeks earlier since 1930s but found no trend in West Siberian river.

Thick icing is commonly observed in the permafrost regions of the northern hemisphere, including Siberia. Icing is often seen on the river in Siberia. In southern East Siberia, aufeis (icing) can be 5–10-m thick. Icing contributes about 10% of annual river discharge (Sokolov and Vuglinsky, 1997). Icing may be an important indicator of groundwater movement in permafrost regions of Siberia.

Summary

Because of the extremely cold winter climate of Siberia, the region is characterized by a thick and extensive winter snow cover and many frozen water bodies in winter. However, people in Siberia are more aware of global warming and its effects on snow and ice in Siberia are posing a threat to infrastructures due to thawing snow and ice. Warming air temperature by itself can cause the shorter periods or less volume of snow and ice in Siberia, but it cannot explain all of the observed changes such as the small changes of timing of river ice freeze-up or permafrost thawing. Vegetation characteristics also influence how warmer air temperatures affect snow and ice in Siberia. Most of Siberia is covered by taiga forest. In East Siberia, the taiga forests consist mainly of larch, which is a deciduous conifer, whereas West Siberia is characterized by wetlands and evergreen coniferous forest. Suzuki et al. (2007) showed that a moss layer protects the soil from heating by the atmosphere and helps to maintain a constant ground temperature and moisture content. Thus, the vegetation type affects snow and ice in Siberia and complicates our understanding of snow and ice cover changes in Siberia. In the future, this subject should be studied by a multidisciplinary approach.

Cross-references

Icing

Inverted Cup Depth Hoar Crystals

Lake Ice

Permafrost

River Ice Hydrology

Snow Hydrology