Recent trends in Lake Ladoga ice cover

The condition of the ice on a large lake is an important sensitive indicator of regional climate change. We have investigated the ice regime on Lake Ladoga using aircraft surveys and satellite images. Nearly 1,000 surveys of the lake's ice cover covering the years from 1943 to the present were analyzed to determine the first basic statistical characteristics of Ladoga ice cover based on long-term observation. The aim was to estimate long-term trends in the ice cover. Analysis showed that the average period of ice-cover formation is up to 1.5 times longer than the period of ice-cover destruction. The inter-annual trends in first and last ice dates, and in the duration of ice cover, are a few days per century, i.e. significant but rather small. We created the Relative Ice Cover Index (RICI), a dimensionless single-number variable that allowed the characteristics of winter seasons to be compared. A statistically significant downward trend of no more than 12% in RICI was observed over the 63-winter periods. The distribution of RICI was compared with the North Atlantic Oscillation Index (NAO) in an effort to explain the ice cover trend.