## 3 Results and Discussion
### Analysis of Time Series of Inflow to the Volga-Kama Cascade Reservoirs
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multirow{2}{*}{**The Long-Term Series of Inflow, Seasons**} & \multicolumn{4}{c}{**Inflow Volume for Years of Different Reliability by Flow, Cubic km**} \\ \cline{2-7}  & **2\%** & **25\%** & **50\%** & **75\%** & **95\%** & **98\%** \\ \hline Year, series 1916–1978 & 331 & 264 & 233 & 203 & 163 & 148 \\ \hline Year, series 1979–2020 & 367 & 300 & 272 & 248 & 217 & 206 \\ \hline
**\% volume change** & **10.9\%** & **13.6\%** & **16.7\%** & **22.2\%** & **33.1\%** & **39.2\%** \\ \hline High water, series 1916–1978 & 221 & 172 & 150 & 128 & 98.6 & 87.3 \\ \hline High water, series 1979–2020 & 208 & 171 & 153 & 135 & 108 & 96.5 \\ \hline
**\% volume change** & **-5.9\%** & **-0.6\%** & **2.0\%** & **5.5\%** & **9.5\%** & **10.5\%** \\ \hline Summer–Autumn Low Water, series 1916–1978 & 101 & 67 & 54.1 & 43.4 & 31.1 & 26.9 \\ \hline Summer–Autumn Low Water, series 1979–2020 & 124 & 86.1 & 73 & 62.5 & 50.7 & 46.6 \\ \hline
**\% volume change** & **22.8\%** & **28.5\%** & **34.9\%** & **44.0\%** & **63.0\%** & **73.2\%** \\ \hline Winter Low Water, series 1916–1978 & 33.4 & 21.4 & 17.4 & 14.5 & 11.5 & 10.5 \\ \hline Winter Low Water, series 1979–2020 & 53.3 & 37.6 & 32.3 & 28.2 & 23.6 & 22.1 \\ \hline
**\% volume change** & **59.6\%** & **75.7\%** & **85.6\%** & **94.5\%** & **105.2\%** & **110.5\%** \\ \hline Pre-flood Drawdown, series 1916–1978 & 21.3 & 11.5 & 8.22 & 5.81 & 3.41 & 2.7 \\ \hline Pre-flood Drawdown, series 1979–2020 & 30 & 15.7 & 12 & 9.43 & 6.9 & 6.13 \\ \hline
**\% volume change** & **40.8\%** & **36.5\%** & **46.0\%** & **62.3\%** & **102.3\%** & **127.0\%** \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Comparison of inflow volumes for two long-time series, different runoff reliability years, and different seasons. Figure 9: Reliability graphs of inflow reliability for two long-time series and different seasons. a year with 2% reliability, the annual inflow for the 1979-2020 series increased by 10,9% compared to the 1916-1978 series, the inflow of summer-autumn low water increased by 22,8%, the inflow of winter low water increased by 59,6%, and inflow in March (pre-flood drawdown) increased by 40,8%; in a year with 25% reliability, the annual inflow increased by 13,6%, the inflow of summer-autumn low water increased by 28,5%, the inflow of winter low water increased by 75,7%, and the inflow in March increased by 36,5%; in a year with 50% reliability, the annual inflow increased by 16,7%, the inflow of summer-autumn low water increased by 34,6%, the inflow of winter low water increased by 85,6%, and the inflow in March increased by 46%; in a year with 75% reliability, the annual inflow increased by 22,2%, the inflow of summer-autumn low water increased by 44%, the inflow of winter low water increased by 94,5%, and the inflow in March increased by 62,3%; in a year with 95% reliability, the annual inflow increased by 63%, the inflow of winter low water increased by 105,2%, and the inflow in March increased by 102,3%; in a year with 98% reliability, the annual inflow increased by 39,2%, the inflow of summer-autumn low water increased by 73,2%, the inflow of winter low water increased by 10,5%, and the inflow in March increased by 127%. A particularly large increase in inflow occurs in dry and extremely dry years (during the winter low-water season and in March, the inflow more than doubled). The physical reasons for the increase in runoff in the region of the VKC reservoir basin are most likely associated with warming and, as a result, increased precipitation and inflow to rivers in the region of the Arctic Ocean seas (Barents Sea, White Sea, Kara Sea, Laptev Sea, East Siberian Sea, and Chukchi Sea). All these seas border the territory of Russia in the north and affect the inflow of the basins of the Upper and Middle Volga and Kama rivers, but the authors did not conduct studies on the relationship of these processes.