| | | 21.4 Water level changes |
A long-term sinusoidal fluctuation of the water level (WL) with a period of about 30 years is characteristic of both lakes (Figure 6). Smooth and continuous decreases (1928-1940) and increases (1940-1957; 1965-1990) of WL resemble a long-term trend and can be distinguished only in the context of a long time series. Apparent periodicity is probably associated with large-scale fluctuations in solar activity and atmospheric processes. Similar periodic changes have occurred in other large geographic areas: in lakes Saimaa, Ilmen, and Onega WL fluctuations have a spectral density maximum at 28-32 years [309]; spectral density maxima ranging from 20 to 30 years were stated for different hydrological elements of Lakes Ladoga [305] and Müggelsee [39].
| | | 21.4 Water level changes |