Eurasian Arctic Rivers
Changes in the amount and timing of the discharge of major Eurasian Arctic rivers have been well documented, but whether or not these changes can be attributed to climatic factors or to the construction of man made reservoirs remains unclear. A new research report helps to identify the key processes (snow cover and air temperature) that have regulated seasonal stream flow fluctuations in the Eurasian Arctic over the last half-century (1958—1999) and to understand the regional coherence of timing trends, using a set of Eurasian Arctic rivers selected specifically because they are free of known effects of dams. A shift toward the earlier onset of spring runoff as measured by a modest change in the spring pulse onset (26 of 45 stations) and a strong change in the timing (39 of 45 stations). Winter stream flows increased over the period of record in most rivers, suggesting that trends observed by others in larger regulated Eurasian Arctic rivers may not be entirely attributable to reservoir construction.
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. 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.
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 its climate. Because of these factors, river discharge averaged across Northern Eurasia is lower than the world average.
Construction of dams and reservoirs has been another important feature in the development of water resources in Northern Eurasia. In the 1920s, the Soviet Union launched a massive program of development of hydropower. Since then, many large hydraulic dams and reservoirs have been built, mainly in north-western Russia (Karelia and the Kola peninsula), the Moscow region, the Volga region, the Urals, Central Asia, and Southern Siberia. Major rivers such as the Volga, Kama, and Angara have been transformed into a chain of reservoirs. About 45 per cent of the total water volume in Eastern Siberia and the Far East, which accommodate some of the world's largest rivers, belongs to the artificial reservoirs.
The development of hydroelectricity and the construction of reservoirs have substantially modified the regimes of many rivers towards an equalization of seasonal flows. The storage capacity of reservoirs reduces spring flooding substantially.
The new research further states that upward trends in air temperature appeared to have had the largest impact on spring and summer flows for tributaries in the coldest of the major Eurasian Arctic river basins (e.g., the Lena). While the overall duration of snow cover has not significantly changed across the Eurasian Arctic, snow cover disappearance has trended earlier in the year and appears to be related to the increased May and snow melt season fractional flows.
The full article may be found in the current edition of the Journal of Geophysical Research.
For further information: http://www.agu.org/pubs/crossref/2011/2010JD014337.shtml