Current Changes in the Maximum Runoff of the Rivers of the Ural River Basin

Abstract

The purpose is to reveal spatio-temporal features of changes in the parameters of maximum runoff in the Ural River basin. Materials and methods. Series of hydrological observations for 12 gauging stations were taken as initial data for the analysis of long-term dynamics of the share of spring fl ood runoff . The choice of gauging stations is based on diff erences in the physical and geographical conditions of runoff formation and the degree of anthropogenic impact on river runoff . Conclusions about the spatial features and trends in the maximum runoff in the study basin are formulated on the basis of statistical data analysis methods, taking into account the threshold year of water content change (1978). Results and discussion. Long-term changes in the spring fl ood runoff of the rivers of the Ural River basin are characterised by certain spatial diff erences. The minimum share in the annual volume of runoff is typical for the upper reaches of the Ural River and its large tributaries (the rivers Sakmara, Bolshoy Kizil, etc.). The most signifi cant reduction in the share of spring fl ood runoff is characterised by the rivers with a regulated regime. The relationship between the reduction in the share of spring fl oods in the annual runoff volume and the reduction in the average and absolute values of maximum discharges has been established, fi rst of all, for the regulated river sections (Ural – Orenburg; Ilek – Vesely) and some watercourses with a conditionally natural regime (Ural – Verkhneuralsk; Or – Istemes; Salmysh – Bulanovo). Conclusion. It has been established that the rivers of the studied basin are characterised by current trends in the maximum runoff changes observed in the European territory of Russia. The transformation of the seasonal distribution of runoff towards an increase in the share of low water fl ows (especially winter runoff ) and a decrease in the share of spring fl ood runoff has been revealed. As a result, changes in the intra-annual distribution of river runoff cause a certain alignment of the hydrograph of the annual river runoff with the Kazakhstan type of water regime.