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Based on observational data from 70 hydrological stations in the North Caucasus an evaluation of present values of mean annual runoff, minimum monthly winter and summer runoff was carried out. Series of maps was drawn. Significant changes in mean annual. minimum monthly and maximum runoff during last decades have been revealed in the North Caucasus. A rise in both amount of water availability and potential natural hazard is characteristic of the most of the North Caucasus that is considered to be caused by recent climate change. Mean annual runoff during 1978-2010 increased compared to 1945-1977 by 5-30 % in the foothills and by 30-70% in the plain area. An increase in winter minimum monthly runoff is as well most intensive in the plain part of study area (>100%). Within the foothills it amounts to 50-100%. In mountainous area long-term oscillation of winter minimum monthly discharge strongly depends on local factors, such as geological structure. The rate of the increase in summer minimum monthly discharge regularly grows from central foothill part of Northern Caucasus (30-50%) to the Western plain territory (70-100%). In Kuban river basin 30% of analyzed gauging stations show positive trend in maximum instantaneous discharge, while 9% negative. On the contrary, in the Eastern part – Terek river basin – negative trend in maximum instantaneous discharge is prevalent: 38% of gauging stations. Positive trend in Terek river basin is characteristic of 9.5% of analyzed gauging stations.

The effect of climate on the present day formation conditions of the regimes of annual and base runoff in Eastern Siberia rivers and changes in those regimes are studied. The significant climate warming in Eastern Siberia in recent decades is shown to be accompanied by not only an increase in air temperature and some increase in precipitation, but also by a considerable changes in the annual and seasonal values of river and groundwater runoff. Hydrometeorological data are used to analyze variations in the mean annual and mean base runoff over the entire observation period divided into subperiods of 1940-1969 and 1970-2005. Plots, diagrams, and tables are constructed for the most representative gauges. The zoning of the territory by the runoff formation conditions was carried out and new estimates were derived for total water resources and natural groundwater resources for 1970-2005 with the construction of maps in ArcMap program.

ABSTRACT. This paper reviews the changes in river flow of the European part of Russia during the low-flow period, characterizing groundwater flow feeding. River flow oscillations were analyzed for winter and summer periods. Statistical analyses of average low flow and the minimum monthly summer and winter discharges for 1946-1977 and 1978-2010 showed significant positive trends for all parameters of low-water period. The greatest increase is observed in the Middle Volga, where low flow has almost doubled.The low flow discharges increased by up to 50-70 % in the center of the European part of Russia and the Upper Don and its tributaries, ranging from 0 to 30 % for the northern rivers. Despite the low flow increase, the lack of water in 2010 and 2014 caused economic damage. It is shown that the observed hydrological hazards occur as a result of snow melt draughts and water management instability.KEY WORDS: low flow, lack of water, climate change, extreme hydrological events.

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