6 
Summary 
In Germany, ice observations have been performed routinely for over 100 years now (since the 
winter of 1896/97). The North Sea coast (including Kiel Canal) presently has 55 observation stations, 
and the Baltic Sea coast 78 stations. Up to 80 Ice observers provide dally coded reports to the Ice 
Service which contain details of the Ice situation and navigating conditions In their areas of 
responsibility. The data received are used in preparing daily ice reports and ice maps and are 
evaluated in Ice climatological studies. 
Descriptions of the ice winters on the German coasts have been published routinely since the winter 
of 1899/1900. Due to uniform processing of the observation data, it Is possible to compare ice 
conditions in different years as well as in Individual coastal sections and harbours. This method has 
led to a better understanding of the hydrographic characteristics of the German coasts, which Is highly 
Important for all branches of Industry In the coastal regions and for the coastal population. The long 
term series of systematic observations at a large number of coastal stations also provide an insight 
into possible periodic fluctuations or changes of Ice occurrence on the coasts. 
This report presents descriptions of the past five ice winters from 1999/2000 to 2003/04. A slightly 
more detailed description Is provided of ice winters in the German/Polish boundary waters, Stettlner 
Haff, and Pomeranian Bight. This part of present work has been carried out within the framework of 
the treaty between the Federal Republic of Germany and the Republic of Poland (working group W1). 
The results of the Ice climatological studies, which are aimed at improving the operative Ice Service, 
are reviewed and modified where necessary. 
Ice winters on the German coasts are classified on the basis of the accumulated areal ice volume 
(V AI ), which Is computed on the basis of the size and thickness of the ice cover as well as the duration 
of ice occurrence (Koslowskl, 1989). In the period from 1896/97 to 1998/99, 40 ice winters were 
classified as mild, 40 as moderate, 11 as severe, 8 as very severe, and 4 as extremely severe. As 
regards the past five years, the ice winter of 2002/03 was moderate, and the winters of 1999/2000, 
2000/01, 2001/02, and 2003/04 were mild, continuing the phase of predominantly „Ice-poor“ winters 
which began In 1998. Similar phases of about equal duration occurred also In the 1930s and 1990s, 
which were followed by very strong to extremely strong ice winters. 
The intensity and duration of low-temperature periods In winter Is expressed by the „Wlnterzahl“ (WJ 
used in meteorology. Under certain conditions, the accumulated areal ice volume is closely correlated 
to the Winterzahl (Wz). The empirically determined relation between Vai and Wz Is based on the 
time series from 1897 to 1987. An analysis of the winters following this period confirms that the 
severity of an Ice winter, expressed by Vai, and its meteorological character, expressed by Wz, 
correlate very well. 
The smaller, land-locked coastal waters are very well suited for studying the behaviour of individual 
ice parameters, and particularly ice thicknesses. In an earlier paper (Schmelzer et al., 1999), the 
regression equations influencing the growth of Ice In the Stettiner Haff have been described. The 
dependencies found are based on data from the years 1961-1990. An analysis of the variability of Ice 
winter characteristics In the Stettiner Haff during the past years has shown that there Is a slight 
tendency toward decreasing ice thickness at the maximum of Ice development. This Is due to the 
increase In mild winters Ice during the past 20 years. The maximum ice thicknesses measured in 
moderate or severe to very severe ice winters today reach the same values as in the reference period. 
By analysing the ice parameter „number of days with Ice“, certain developments in Ice formation 
become apparent: Ice in the Stettiner Haff occurs rarely in November, but there has been a slightly 
Increasing trend in the past 20 years. In December, the same number of days with Ice is observed on 
average today as in the years 1961-1990. In the winter months of January and February, until mid- 
March, the probability of ice occurrence in the Stettiner Haff is very high, but compared to the 
reference period there has been a clearly negative trend during the past 20 years. The parallels found 
between the trends In the development of air temperature and that of the Ice parameter „number of 
days with ice“ shows once more clearly that ice formation and Ice development in small, calm bodies 
of water depend primarily on the air temperatures. Other factors are of lesser importance. 
Despite the rising trend of air temperatures, there has not been a single winter during the past 20 
years In which the Stettiner Haff remained completely free of Ice.