ESTIMATION OF THE IMPACT OF CLIMATIC AND ANTHROPOGENIC FACTORS ON THE FORMATION OF THE EXTREME LOWFLOW PERIOD IN THE DON RIVER BASIN DURING 2007-2016ESTIMATION OF THE IMPACT OF CLIMATIC AND ANTHROPOGENIC FACTORS ON THE FORMATION OF THE EXTREME LOWFLOW PERIOD IN THE DON RIVER BASIN DURING 2007-2016

The Don River is the largest river in the southwestern part of European Russia and the second largest river system in European Russia. The Don River basin is one of the most water deficient regions in Russia and the long term average water usage in the basin amounts to 45%. The period 2007-2016 was the longest long-term low-flow period observed, with an estimated total water resources deficit of 40.4 km3 over 8 years. The main reason for this deficit were anomalously warm winters (2-4 degrees over average) with a low degree of soil frost penetration. This resulted in low spring flood volume (37% of the average) due to heavy seepage losses combined with thin snow cover. A similar low-flow situation was observed in 2014, when the drought caused great damage to ecosystem of Tsimlianskoye water reservoir and the River Don. Most of the fish breeding grounds had dried up by May 2014. This caused the number of round fish whitebait to drop 5-10 times below the 2002-2014 average. Inland shipping and hydropower industry also sustained losses of 42 million euro (according to interview from State Shipping company) due to low water level. This study shows that the main reasons for the 2007-2016 extreme hydrological drought are exceptional hydro-climatic conditions and anthropogenic transformations in the watershed, such as urbanisation growth and afforestation. The analysis shows that the main cause in water deficit is associated with the left tributaries of Don – Khoper and Medveditsa, while the flow in Upper Don remained more or less normal. The results can be interpreted as a “warning sign” to reduce water consumption in these sub-basins to avoid similar drought situations in future.