Northern Eurasia accommodates a variety of hydrological conditions and water bodies.
Regions with an abundant moisture supply border on areas with poor water resources such
as, for example, the Caucasus mountains and semi-deserts of the Caspian plain or mountains
and deserts of Central Asia. Rivers, which are among the world's largest (the Yenisey, Ob,
Lena, and Volga) drain the continent; the largest lakes, the Caspian and the Aral, and the
deepest in the world (Lake Baikal), which accounts for 20 per cent of the world fresh
water resources, are located here. Nowhere in the world do wetlands cover such an enormous
area as on the West Siberian plain and nowhere in the world does the development of water
resources take place in such an enormous permafrost area as in Eastern Siberia. Another
unique aspect is the development of the vast internal drainage basin of the Caspian and
Aral Seas. The lack of connection or a weak link to the World Ocean makes aquatic
ecosystems extremely vulnerable to human impact. One of the world's most dramatic examples
of critical human-induced changes is the modern condition of the Aral Sea. At the same
time, due to the remoteness of many regions, especially in the north and in the east, many
water bodies remain in their natural state.
Typical of Northern Eurasia is a water regime with powerful spring floods and low
winter and summer water levels which develop because of the northern location of the
region and continentality of its climate. Because of these factors, river discharge
averaged across Northern Eurasia is lower than the world average.
Regular hydrological observations began in Northern Eurasia in the 18th century and by
the beginning of the 20-th century a relatively dense hydrological network had been
established. This chapter builds on hydrological research conducted by many academic
institutions in the former Soviet Union (FSU). It discusses aspects of water balance, the
hydrology of the largest rivers and lakes, briefly discusses wetlands and artificial
reservoirs, and addresses the issue of human effects on water regimes and quality. Note
that data given in the tables and figures may differ depending on averaging periods and
methods of measurement and estimation.
