Thermal Regime of River Water as a Response to Climatic Processes in the Upper Don Drainage Basin

Abstract

The modern thermal regime of the Upper Don rivers formed in the conditions of regional climate change in response to the challenge of global climate. The increase in the annual mean temperature of the atmospheric surface layer in the Upper Don in the first decade of the current century nearly by 1°С on average changes the thermal regime of the river water, which, in its turn, reflects the constant interaction between two spheres of the geographic envelope, namely, the atmosphere and hydrosphere. The water mass is concurrently in contact with the streambed, which affects thermal state of the water. Under the conditions of constant interaction and the interference of various environments, the thermal state of the atmosphere does not always remain the leading factor in behavior of the river-water temperature. In light of the unidirectional trend in the behavior of the regional air temperature and the increase in the latter over the entire Don River drainage area, the character of the water temperature response proves to be ambiguous and even contradictory. The maximum water temperature consistently declines in the right-bank Don River tributaries, such as the Krasnaya Mecha, Devitsa, and Chernaya Kalitva rivers, etc., which feed into the main stem from the Central Russian Uplands. The temperature rises in the left-bank Don River tributaries, e.g., Voronezh and Bityug, which feed into the Don River from the Oka–Don Lowlands. The Podgornaya River, which is also a left-bank tributary that feeds into the Don River from the Kalachskaya Uplands, exhibits a drop in temperature. A slight temperature increase is recorded in the streambed of the Don River itself. The ambiguous temperature response of the upper water layer can be attributed to the intra-annual redistribution of drainage, reduced snowmelt, and increase in the proportion and role of groundwater recharge during the formation of the maximum water temperature.