RECENT CHANGES OF ANNUAL FLOW DISTRIBUTION OF THE VOLGA BASIN RIVERS

摘要

Modern features of the annual flow distribution of the Volga Basin were analyzed. Statistical analysis of the annual flow data for the spring, summer-autumn, and winter seasons were carried out to study the changes of the water regime of the Volga Basin Rivers in 1946–2010, 1946–1977, and 1978–2010 observation years. Using the data of 207 stations, new maps of seasonal flow were created and changes in the natural river flow regulation were shown. In recent decades, the water regime of the rivers in European Russia and their annual flow distribution has changed greatly. A statistically significant decrease in the river flow irregularity after 1946 has been revealed for the most of the Volga Basin Rivers. It resulted in the increase in the natural regulation index φ, change of the seasonal flow, primarily in low-water period, and especially in winter. The increase in the φ index during the last 30 years is approximately 30%, compared to the similar previous period. Such a change of the φ value took place due to the reduction of the spring flood flow and the increased significance of the groundwater flow. In the second half of the 1970s, the rivers of the Volga Basin were characterized as “snowfeeding”; at the end of the XXth century, they became the rivers with “mixed feeding” or even “mixed feeding with prevailing groundwater feeding” according to B.D. Zaikov’s river classification. This has resulted in the significant increase in the natural flow regulation comparable to the effect of seasonal storage reservoirs.