Trends in the Minimum Winter River Flow on the Territory of the Basin of Lake Sevan

This work is devoted to assessing the features of the distribution of spatiotemporal changes in the characteristics of the minimum 30-day winter flow of rivers in the basin of Lake Sevan. The problem of spatiotemporal changes in the minimum river flow is especially relevant for regions with insufficient and unstable moisture, like the basin of Lake Sevan, most of which is located within the steppe zone. The purpose of this work is to summarize modern ideas about the impact of climate change on the characteristics of the minimum 30-day winter river flow based on the authors’ own research, to analyze and evaluate the spatiotemporal variability of long-term fluctuations, and to identify nonstationarity in the series of minimum winter flow. The characteristics of the minimum flow have been determined, their spatiotemporal changes have been studied, and the dates of violations of homogeneity in the series of long-term runoff observations have been discovered. Using statistical parameters and difference integral curves, we assessed the representativeness of time series of minimum 30-day winter water flows at 12 sites during the period of instrumental observations. Nonstationarity in the series of minimum winter runoff in the basin of Lake Sevan has been revealed, and the dates for changes in stationary regimes have been determined. For most of the watersheds analyzed, the changes are statistically significant. Maps of the date of violation of the stationarity of the series under consideration based on information up to 2021 are presented, including a map of the distribution of the module of the minimum 30-day runoff for the winter period and maps on the nature of changes in the minimum 30-day winter flow. It is shown that changes in the minimum 30-day winter flow have a multidirectional nature, but mainly for the minimum 30-day winter flow, on average, over the territory of the lake basin. In recent decades, Lake Sevan has shown an increasing trend associated with rising air and soil surface temperatures. For some of the watersheds analyzed, the changes are statistically insignificant. On the territory of the Vardenis, Lichk, and Bakhtak river basins, on average, the minimum 30-day winter flow decreases by 20–30%, which will lead to an increase in environmental risk, requiring the adoption of appropriate measures. The obtained statistical materials will serve as the basis for scientific generalizations of research on the territory under consideration and can also be used for practical purposes in hydraulic engineering design and assessment of natural hazards and in making appropriate preventive decisions.