LONG-TERM CHANGES IN WATER INFLOW INTO THE KAMA RESERVOIR

Abstract

The article deals with long-term changes in water inflow into the Kama Reservoir. According to the results of the study, in all months (except May, June, and September) there was a trend toward the inflow increase, in the winter months (November-March) the trends were significant (p>0.05). An analysis of changes in air temperature and precipitation by seasons has revealed an increasing trend in the data series. These trends are statistically significant for air temperature in all seasons and for precipitation in the winter season. Over 1978-2021, the average air temperature increased by 0.2-0.3°C per decade, precipitation also increased by 2-10 mm per decade. The authors studied the influence of ongoing climate change on the volume of water inflow for two periods before and after the pronounced changes in the runoff: 1954-1977 and 1978-2021. In 1978-2021, there was an increase in water inflow in all seasons: by 5% during the spring season, by 17% during the summer-autumn season, and by 30% during the winter season. Changes in inflow during the winter season were statistically significant. There was also a redistribution of runoff within seasons, which began to correspond to the following ratio in % of the annual: winter season – 16% (+3%), spring season – 59% (-4%), and summer-autumn season – 25% (+1%). A combined analysis of the cyclicity of water inflow, air temperature, and precipitation has found that the volume of inflow during the winter season has similar cycles with the average air temperature. The best correlation of inflow cycles with precipitation has been revealed for the spring and summer-autumn seasons. High correlation of cycles is noted during the periods of the winter drawdown r=0.92 and summer-autumn stabilization r=0.73. In the spring period, the correlation of cycles is lower r=0.48 since the formation of the inflow is also influenced by other factors that change significantly from year to year.