Ice regime of the rivers of the Debed basin, Armenia

Abstract

For the first time, the ice regime and its changes in 1939–2018 was analyzed for one of the largest river basins in Armenia – the Debed River. The main material for the analysis was data from observations at six weather stations and 15 river posts of the Hydrometeorological Service of Armenia, which are located at different altitude levels – from the upper reaches of the tributaries at 1600–1900 m down to 450 m at the lower section. Ice phenomena on the rivers of the basin are diverse. More often these are shore ices, shuga (frazils), freeze-up, less often – ice dams and ice-drift, but everywhere they are poorly developed. The reason is the positive average monthly water temperature in winter in almost all the rivers of the basin. In most catchments, all ice formations exist for a short period – usually no longer than 50–100 days; a freeze-up is not formed everywhere and not every year, although on some of the highest tributaries it can last up to 40 days. An analysis of the long-term course of air temperature in the basin showed that against the background of its significant interannual fluctuations, a clear change took place in the early – mid-1990s. Over the 30­year period from the early 1960s, temperature trends in all seasons of the year had only a small positive trend, but after the mid-1990s and until 2018, the temperature rise was accelerated significantly and steadily.The ice regime of the rivers at the beginning of the XXI century was affected not only by the warming of winters by almost 0.7 °C. A significant rise of the spring temperatures by 1.4 °C noriceably displaced the dates of the end of the ice phenomena and decreased duration of them. During the 80-year observation period, the beginning of the ice regime in the middle course of the basin rivers (at altitudes of 1000–2000 m) shifted to a later date by 10–15 days, and its end is observed 15–20 days earlier, the total duration of the ice regime decreased by 25–35 days.