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  longterm ­
  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.