<p>The most urgent tasks facing hydrologists of Ukraine and the world include identifying patterns of rivers hydrological regime against the background of global warming, and assessing these changes. Changes in the annual runoff distribution under climate change impact require separate investigation of anthropogenically altered catchments, such as the Siverskyi Donets River Basin. Siverskyi Donets is the largest river in Eastern Ukraine and the main source of water supply for Kharkiv, Luhansk and Donetsk regions.</p><p>The annual runoff distribution of the Siverskyi Donets River Basin was evaluated by two periods: to the beginning of pronounced climatic changes and the current period. The research is proposed for three water year types: wet year, average year and dry year. The Siverskyi Donets Basin is a complicated water body with peculiar physico-geographical conditions, because of that annual runoff distribution is somewhat different for the left-bank tributaries, right-bank tributaries and, in fact, the Siverskyi Donets River itself.</p><p>It is found that the most runoff of the wet year for both periods is in the spring months. The current period is characterized by a much smaller runoff of spring flood (from the volume of annual runoff) than in the previous period. The annual runoff distribution is offset. Some differences can be observed between the left and right tributaries. For the left-bank tributaries, which has less anthropogenic load, climate change has led to a significant increase of winter and summer-autumn low flow periods. On the right tributaries of the Siverskyi Donets, which are flowing within the industrial part of the Donbass, the low flow period has not changed, or even decreased. Such situation is due to the decrease of mine water disposal because of the industrial production decrease in the region.</p><p>The largest part of the annual runoff in the average year falls on February and March. In the current period, the spring flood has decreased, but the summer and autumn low flow period has increased. The left-bank tributaries runoff during the winter low period is decrease. Instead, the runoff attributable to the autumn and winter low period has increased for the right-bank tributaries and the Siverskyi Donets itself.</p><p>Analyzing the runoff distribution of dry year, we can conclude that the most wet is February. At present, in dry years, spring flood practically are not allocated from the hydrograph; the baseflow months runoff significantly increased. The volume of winter runoff of the Siverskyi Donets River Basin is increased. Actually, for the Siverskyi Donets River the runoff of the summer period has increased and the runoff of the winter and autumn periods has decreased at the present stage.</p><p>The annual runoff distribution of the Siverskyi Donets River Basin in the current climate change has undergone significant changes: the spring flood has decreased and the summer-autumn low flow has increased.</p>
Changes of total annual runoff distribution, high and low discharges in Latvian rivers
