Changes in River Runoff during Winter Low Water Periods in the Basin of the Ural River

Abstract

The trends in river runoff during the winter lower water period in the Ural River basin have been analyzed in this work. The long-term dynamics of the runoff parameters has been studied. Concurrently, consideration has been given to the phases with a different river water content. It was found that the water regime of the rivers in the study basin is characterized by a stable trend of a decreasing share of the spring runoff and an increasing share of the winter runoff. The growth of the share of winter runoff is caused by an increase in the frequency and duration of positive temperature anomalies and the share of basic (underground) river feeding. Comparison of the annual runoff and 30-day values of the minimum runoff in the winter period illustrates a certain interdependence in the changes of their values. In spite of the general trend of the increasing winter low water discharges, certain differences have been revealed for the rivers of the basin studied due to the heterogeneous conditions under which the runoff is formed. The regional features of the formation of the winter low water runoff confirm the different dates for occurrence of the maximum (complete) depletion of the river runoff. The significant increase in the water content of the rivers in winter affects the decrease in the variability of daily discharges, which is consistent with the previously established trend of decreasing interannual variability of the river runoff in the basin of the Ural River. The increase in the winter low water runoff is of great practical importance, because the runoff value for a given period is the limiting factor that determines the guaranteed and sustainable water consumption. Accordingly, the current trends in the change in the water regime of the rivers of the Urals basin must be taken into consideration when determining the regulations and norms for the use of water resources in the steppe zone.