VARIABILITY OF WINTER RUNOFF OF THE OKA RIVER AND ITS RELATIONSHIP WITH CLIMATE CHANGE

Abstract

Response of a river flow in a winter low-water period to the climate changes is analyzed by the example of theOkaRiver(245 thousand km2). The analysis was done for each individual month from December to March during the period 1980–2015. The data were obtained for the hydrometric section Oka–Gorbatov. The following climatic characteristics were used for the analysis: 1) the number of days with positive air temperatures; 2) the temperature of the upper soil layer; 3) the sum of precipitation (data of meteorological station); 4) water equivalent of snow (the data from the satellite ESA GlobSnow, SWE version 2). Accuracy of the satellite data was estimated with respect to the observational data. In 1981–2010, significant increase in winter runoff occurred in December and March. This period was divided into two phases: 1) the end of the 20th century which was characterized by increasing of precipitation, the soil temperature, number of days with positive temperatures, and that resulted in the growth of the water equivalent of snow; 2) the beginning of the 21st century – by significant fluctuation in precipitation, number of days with positive temperatures as well as by a drop in the soil temperature and water equivalent of snow. The runoff volume was found to be in a direct relationship with the number of days with positive temperatures, the soil temperature, the precipitation sum, and in the inverse relationship with the water equivalent of snow. Both, the regression and dispersion analyses indicated that the above set of climatic characteristics was sufficient to explain changes in the winter runoff. According to the degree of influence on the winter runoff, these characteristics can be ranked as follows: the number of days with positive temperatures; the average soil temperature; the water equivalent of snow; the precipitation sum. The effect of the water equivalent on the runoff becomes significant from midwinter and remains the most significant factor by the end of snowmelt.