♦ First ice 
Average first ice ♦ Last ice 
Average last ice 
87 
t— 
Csl 
CO 
m 
CO 
1^ 
CO 
CD 
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T— 
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CO 
CD 
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CD 
CD 
CD 
CD 
CD 
CD 
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T- 
T- 
T- 
T- 
T- 
T- 
T- 
T- 
T- 
Csl 
Csl 
Csl 
Csl 
Csl 
Ice winter (1991=1990/91) 
Figure 9.9. Beginning of freezing and end of ice season in strong ice winters in Szczecin Lagoon 
♦ Karnin ▲ Kamminke ■ Ueckermunde Average number of the days with ice 
t— 
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CO 
in 
CO 
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T— 
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I - 
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Ice winter (1991=1990/91) 
Figure 9.10. Number of days with ice in strong ice winters in Szczecin Lagoon 
Figure 9.11 shows the monthly deviations of the ice parameter „number of days with ice“ from the 
mean value of the 1961-1990 period at the Ueckermunde station. In November, ice formation is rare in 
Szczecin Lagoon, but there has been a slight upward trend in the past 20 years. In December, the 
same number of days with ice is counted on average as in the 1961-1990 period. In the winter months 
of January and February to mid-March, there is a very high probability of ice occurrence in Szczecin 
Lagoon but, in comparison with the reference period, a clearly negative trend has been observed for 
the past 20 years. It is only in strong or very strong ice winters that the last ice in Szczecin Lagoon 
melts as late as April. An analysis of the deviations of days with ice from the normal value does not 
show any development trend for April. 
Analogous to the parameters described above, the monthly deviations of air temperatures from their 
1961-1990 mean value were determined for the Ueckermunde station, see Figure 9.12. November 
temperatures in the past 20 years have decreased slightly, which explains the small increase in the 
number of days with ice in that month. In December, the air temperature hardly deviated from the 
mean value. A clearly positive trend is observed for January and particularly February. Also the mean 
temperatures in March and April have risen slightly in the past few years. 
The parallels in the trends of air temperatures and numbers of days with ice again show clearly that 
ice formation and ice development in calm and smaller waters depend primarily on the air tempera 
ture. Other factors are of secondary importance. But despite the upward trend in air temperatures 
there has not been a single winter in the past twenty years in which Szczecin Lagoon was completely 
free of ice.