Climate Change Impact on the Annual and Maximum Runoff of Russian Rivers: Diagnosis and Projections

The article provides an overview of publications devoted to assessing changes in the water regime of Russian rivers under the conditions of current and projected climate changes. The most recent summary of the relevant publications is contained in the national assessment reports of Roshydromet. Since the publication of these fundamental works, a large number of studies have been published, clarifying the conclusions of the national reports. The purpose of this review is to summarize the modern ideas about the impact of climate change on the territory of the Russian Federation on the mean annual and maximum river flow, primarily based on the publications in recent years. The review is divided into two parts. The first part presents the results of the diagnosis of changes in the long-term norms of the annual and maximum flow of Russian rivers that occurred during the period of instrumental observations in the XX–early XXI centuries. Due to the geographical differences in the direction and magnitude of climate changes and associated changes in the water regime of rivers, the review is given separately for the rivers of the European and Asian territories of Russia. It is shown that the annual runoff over the territory of European Russia in recent decades has a tendency to increase, associated with a general rise in the humidity of the territory. However, for most of the analyzed river basins, the changes are statistically insignificant. The annual runoff of rivers from the territory of Siberia and the Far East into the Arctic seas of Russia has also slightly increased on average. The changes in the maximum runoff are more pronounced and differently directed. The second part of the article provides an overview of publications that present projections of changes in the water regime of Russian rivers until the end of the XXI century. The projections were obtained in ensemble experiments with climate models or with regional hydrological models. The conclusions made in the Second Assessment Report of Roshydromet regarding the insignificant positive anomalies of the annual runoff rate for most of the territory of Russia under moderate anthropogenic warming scenarios in the XXI century have been confirmed. The most pronounced positive anomalies of the snowmelt and rainfall runoff in the XXI century are possible on large rivers of Siberia in the case of implementation of the RCP8.5 scenario of anthropogenic radiation impact.