International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 6
Number 1
March 2012
123
1 INTRODUCTION
Storm surges, as water level extremes, have been in-
vestigated quite extensively as they represent a ma-
jor threat to the coastal population. Considerable
technical and scientific effort has been invested
worldwide to reduce the impacts of such phenome-
na, which may reach catastrophic proportions. Storm
surges do occur within the Baltic coastal zone
where, in addition to causing a direct threat to the
seashore and inundation of the coastal area, they af-
fect safety of navigation and operation of the ports.
Climate change and sea-level rise will increase the
frequency and severity of storm surges (based on the
SRES scenarios in range 0.2-0,8 m/century). Ob-
served climate changes are characterized with great-
er dynamics of weather phenomena. A number of
weather and hydrological phenomena already now
characterized by the increase in the prevalence of
their presence and intensity of natural disasters.
Translocating storms induce surges, characteristic
for specific seashore regions and, depending on a
row of factors, the surges reach various sizes. To
compare the risk of the storm surges at various water
areas the new methods had to be worked out. Taking
the above into consideration, there had been under-
taken the works focused on classification of the
storm surges sizes and developing a concept of the
storm surge indicator, including analyzing the indi-
cator values in relation to the South Baltic coast. The
identification of the hydro-meteorological factors
and the height of storm surges were done.
Thus the storm surge indicator is used to compare
the storm surges related risks, occurring at various
water areas. In the above studies there were analyzed
the data gathered within a period of over 50 years, it
means from 1955 to 2008 at stations of Świnoujście,
Ustka and Hel. It was accepted (in accordance with
the definition given by A. Majewski) that any hydro-
logical situation, when the sea level is reaching or
extending 570 cm, stands for a storm surge. (thus for
Hel the alarm level was decided to be at 570 cm, for
Ustka 600 cm and for Świnoujście - 580 cm).
2 METHODS
Sea level changes along the coasts are generated in
connection with several factors, however mainly
with the wind impact. Affecting sea surface by wind
results in changes of the sea surface which appear in
a form of storm surges of water. Within a time from
November till March the largest number of storms
used to occur; they generate extreme changes of sea
Storm-surges Indicator for the Polish Baltic
Coast
I. Stanislawczyk
Institute of Meteorology and Water Management, Maritime Branch in Gdynia, Poland
ABSTRACT: Storm surges appear in the coastal zone of the Baltic Sea and, depending on row of factors,
have different sizes, specifically characteristic for each region of the sea-coast. Observed climate changes are
characterized with greater dynamics of weather phenomena. To compare the risk of storm surges to different
areas, a new method had to be developed. Storm-surges indicator is used to compare the risks to the South
Baltic water areas, varied along with conditions therein and the hydro meteorological and local conditions.
The studies on the relations between the parameters and the occurrence of storm surges were carried out as
well. The storm surges indicator “W” is related to the number of storm surges observed at the stations in the
particular regions, the maximal wind velocity and the max sea level occurring during the same storm surges.
The storm surges indicator was calculated for the period of 1955-2008 for the Polish coastal zone. The inten-
tion is to use this indicator for research and forecasting purposes. Assessment of the tendencies and variability
of the regional phenomena indicators in timescale prove occurrence of certain regional changes of hydrome-
teorological conditions.
124
levels. The most intensive deterioration of the sea-
shore occurs in a time of severe storms. The sea
coastal zone is an area covering both – on-shore part
(coastal zone) as the off-shore one. The storm surges
are threatening about 500 km of the coastline. The
variable route of the coastline results in differentiat-
ed exposure of individual sections to wind condi-
tions. In spite of considerable equalization of our
coastline, there exist sections of different exposition
to wind directions, characterized with diverse regime
in meteorology and hydrodynamics.
Storm surges occur in the coastal zone of the Bal-
tic Sea and, depending on a row of factors, have dif-
ferent sizes, characteristic for each region of the sea-
coast. Of essential influence are however, the local
conditions. The magnitude and the character of the
changes depend on the coast line configuration, on
the bathymetry of the adjacent sea basin, on the ex-
position of a particular coast part to the actual wind
etc. However the most spectacular deformation of
the water surface at the Baltic Sea shores can occur
due to the already mentioned off- or on-shore,
stormy, sometimes hurricane-like winds.
Mostly active depressions with the fronts systems
move eastwards from over the Atlantic Ocean. Well
developed low-pressure troughs and their frontal
systems moving across the coast are accompanied by
gale-force backing winds as the fronts approach, and
by veering winds after they have passed. The pres-
sure gradient becomes very steep and the wind, ini-
tially gale-force, increases in severity and finally
reaches hurricane force. In the forefield of a depres-
sion winds prevail of a strong southern component,
behind the fronts usually veering. The winds in the
forefield of a depression are offshore in relation to
the southern coasts of the North and Baltic Seas.
This situation normally causes sea level oscillations.
The mean sea level and a number of storm surges
in the southern Baltic Sea have visibly increased
during the last century. Figure 1 shows the number
of storm surges in Świnoujście in 1950-2008, from
1950/1951 (from August 1950 to July 1951) to
2007/2008, when maximum occurrence of storm
surges is for the autumn – winter months, from No-
vember to January – February.
The storm surges are not a regular annual event.
Their number may vary as in the case of Świnoujście
- from no occurrence at all to as many as twelve.
The linear trend of this parameter values indicates an
increasing tendency of the storm surges number (lin-
ear trend in Świnoujście is described as follows:
y = 1,6407+0,0619*x). Also a threat of storm surges
got increased towards the end of the 20 century near-
ly twice as compared to the middle of 20 century in
the Southern Baltic Sea. Within 1950-1979 (almost
half the entire period) 72 storm surges occurred,
whereas in 1980-2008 as many as 129.
Distribution of the annual sea level maxima on
the Polish coast (Świnoujście - on the western part
and Gdańsk - on the eastern part of the Polish coast)
changed also within 1955-2008. The annual sea lev-
el maxima frequency distribution (for 10 cm inter-
vals) in Gdańsk (Fig. 2) in two periods - of 1955-
1981 and of 1982-2008 illustrates the changes oc-
curred in the period of issue.
Figure 2. Frequency distribution of annual sea level maxima
(for 10 cm intervals, e.g. 550-559, ect.), Gdańsk, 1955-1981
and 1982-2008
Figure 1. Long term variation of number of storm surges in Świnoujście, 1955-2008 (from 1950/1951 to 2007/2008).
0
5
10
15
20
25
30
35
40
550
560
570
580
590
600
610
620
630
640
650
660
670
frequency [%]
sea level [cm]
1955-1981
1982-2008
0
2
4
6
8
10
12
14
number of storm surges
years
number of storm surges
trend
125
The annual sea level maxima in Gdańsk varied
from 570 cm (as in the definition - for Gdańsk the
alarm level was 570 cm, although the lowest value
of the annual sea level maxima is 557 cm) to 644 cm
and the most frequent were values ranging between
590 and 600 cm in 1955-2008 (intervals are left-
closed). In 1955-1981 period the most frequent were
the peak values of the annual sea level maxima rang-
ing between 600 and 610 cm (22%), then followed
the values between 560 and 600 cm (the same val-
ues). The maximal values of the sea level ranged be-
tween 630 and 640 cm. In 1982-2008 the frequen-
cies of the annual sea level maxima have been
shifted to the higher values. However, the most fre-
quent were the peak values between 590 and 600
cm, but the maximal annual sea level was in the
higher range of 640-650 cm.
The frequency distribution of the annual sea level
maxima (for 10 cm intervals) in Świnoujście within
two periods - of 1955-1981 and of 1982-2008 is
shown in the Figures 3. The distribution of the sea
level maxima in Świnoujście differs from that of
Gdańsk, but the frequencies of the annual sea level
maxima in 1982-2008 haves been shifted also to the
higher values.
Figure 3. Frequency distribution of annual sea level maxima
(for 10 cm intervals, e.g. 550-559 ect.), Świnoujście, 1955-
1981 and 1982-2008
In Świnoujście the annual sea level maxima var-
ied from 580 cm (as in the definition - for
Świnoujście the alarm level was 580 cm) to 669 cm,
and in 1955-2008, maximum was between 580-590
cm (intervals are left-closed). Thus the maximal an-
nual values of sea level were shifted from a range of
630-640 cm to 660-670 cm. Distribution of the an-
nual mean sea level (frequencies) indicates also an
increase in their amount in a last period and trend of
changes is also growing.
On base these of results one can ascertain, that in
nearest period threat of storm surges on sea-coast
will grow, what will influence on necessity of more
precise forecasts and of information on theme of
storm surges, flooding and coastal erosion hazard.
2.1 Storm surges indicator for the Polish coast
Proper classification is in terms of conditions of
storm surges occurrence, gives the opportunity to
compare and assess the risks of different and often
separated areas. The storm surges indicator ”W” in-
dicator has been worked out to satisfy researches on
climate, weather forecasting, navigation and sea
ports operation planning. General aim is the devel-
opment of innovative methods for mitigation of haz-
ard in the context of increasing storminess and sea
level rise. In addition, the research works were
aimed at assessment of the storm surges threat to
various water areas of the Polish Baltic coastal zone
and correlativeness of the regional indicators and
climate variability. The appropriate classification of
regions in respect of surge occurrence conditions of-
fers a possibility of comparison and assessment of
the threat to differential, located often at quite a dis-
tance apart water areas and in future, a possibility of
seasonal storm surges forecasting.
There has been preformed identification of fac-
tors, conditioning and determining storm surges oc-
currence at the Polish sea coast. The meteorological
and hydrological factors have been indicated, analy-
sis of the selected parameters carried out. There has
been examined correlativeness of the maximal surge
height and other parameters and magnitudes: atmos-
pheric circulation, atmospheric pressure, wind veloc-
ity and direction, differences in water and air tem-
peratures, also the mean monthly temperature of air
within the specific years of the period in question in
Świnoujście. The obtained considerable values of
the correlation coefficients were used to select the
parameters conditioning a storm surge size. On such
a basis the concept of the storm surges indicator
“W” has been worked out.
2.1.1 Storm surges indicator “W”
The indicator “W” is related to the number of storm
surges observed at stations in the particular region
and the maximal wind velocity and the maximal sea
level occurring in a time of the same storm surge.
The storm surges indicator “W” comprises the pa-
rameters specified below; thus:
i
H
V
i
W
∑
×
=
1.0
1
2
where i = number of observing storm surges in
month, year or season; V = maximal wind velocity
[m/s] observed within a time of a singular surge; H =
maximal high of sea level [m] within a time of a sin-
gular surge; and 0.1 = numerical coefficient [m/s
2
].
Thus; the storm surges indicator ”W” is used to
compare a threat with storm to different areas. It also
displays a potential risk which may occur in circum-
stances of changing the meteorological conditions –
126
a path of low, which is a random phenomenon, and,
what is followed therewith, eventual wind force and
direction changes to more unfavorable and more
danger. The suggested formula of calculation of the
indicator enables to assess estimatively a threat with
high surges even basing on non-homogenous values
and analyzed periods.
3 RESULTS
To estimate (potential risk) the threat of storm surg-
es on the Polish sea coast, selected were the data
from 3 sea areas, representatives of different kind of
hydrographic conditions. In storm surges occurrence
there can be seen regional differentiation, reflected
in regional diversification of the storm surge indica-
tor.
To determine the South Baltic storm surges indi-
cator (seashore of Poland) there have been selected
stations, representing dissimilar types of hydro-
graphic conditions: Świnoujście (the Pomeranian
Bay), Ustka (open waters of central seaside) and Hel
(area of the open sea) In the analysis there were ap-
plied the homogeneous sequences of data collected
by the mentioned stations within a period of over 50
years (1955 – 2008). Distribution of the indicator’s
values is different in specific regions of Polish sea
coast. The results are presented in Table 1.
Table 1 Statistical parameters of the storm surges indicator
“W” on the Polish coast, 1955-2008 and 1971-1990.
__________________________________________________
Area Storm surges indicator
_______________________________________
1955-2008 1971-1990
__________________ __________________
Max Min Mean Max Min Mean
__________________________________________________
Świnoujście 7.4 0.2 2.8 6.3 0.8 3.1
Ustka 7.5 0.2 2.6 5.4 0.2 1.8
Hel 6.8 0.2 2.2 5.2 0.3 2.2
__________________________________________________
The values of the regional storm surges indicator
range from 7.5 to 0.2, but in substance to zero (zero
value proves that no storm surge occurred in a given
time period). A number of years with no storm surge
occurrence is as follows: within the mentioned peri-
od in Świnoujście - 5 years with no storm surges, in
Ustka - 9 years and in Hel 12 years. The highest
storm surges indicator ”W” values within the whole
period, i.e. 1955-2008, is related to Ustka (7,5),
slightly lower in Świnoujście (7.4), and even in Hel
(6.8), anyhow the mean indicator values are highest
for Świnoujście (2.8), then for Ustka (2.6); the low-
est for Hel (2.2). The storm surges indicator values
for the period of 1971-1990 (period of reference is
30 years) for all the stations - Świnoujście, Ustka
and Hel, were lower than the values for the whole
period in question. Then, the mean values were
higher in Świnoujście, but lower in Ustka, whereas
for the Hel locality the mean value of the indicator
was the same for the whole period of the investiga-
tions.
For Świnoujście the indicator value’s standard
deviation is 1.35, variance 1.8. The value of median,
the average, it means such a value, of which 50% of
surges were sever and 50% were mild is 2.7. The
90
th
percentile, it means a value, above which 10%
of all the cases fall in, was equal to 4.8. For the Hel
locality in turn, a value of the storm surges indicator
is of standard deviation equal to 1.2, the variance is
1.4. The value of median is 1.8, the 90
th
percentile
was equal to 3.9. For Ustka, the standard deviation is
1.5, the variance 2.2. The value of median is 2.4,
90
th
percentile was equal to 4.5.
The annual storm surges indicator within 1955-
2008 period at the stations of Świnoujście, Ustka
and Hel is presented respectively in Figures 4, 5 and
6. In Świnoujście the indicator is definitely of higher
frequency, also its mean values are higher. The an-
nual storm surges indicator changes within a range
from zero to values above 5.
Figure 4. Variability of annual storm surges indicator, Świnoujście, 1955-2008.
0
1
2
3
4
5
6
1955
1957
1959
1961
1963
1965
1967
1969
1971
1973
1975
1977
1979
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
storm surges indicator
years
Świnoujście - storm surges indicator
8-years moving average
trend
127
Figure 5. Variability of annual storm surges indicator, Ustka, 1955-2008.
Figure 6. Variability of annual storm surges indicator, Hel, 1955-2008.
Values above 4 confirms frequent occurrence of
high surges in storms of significant strength. A value
close to 1 indicates a majority of storms, with slight-
ly exceeded state of emergency. There also happen
years with no high surges at all. A values of the in-
dicator may change significantly even from year to
year. The highest values of the annual storm surges
indicator have been observed in Świnoujście in
2006, 1965 and 1986, in Ustka in 2000, 1955 and
2004 and in Hel in 1980, 1964 and 1967.
In Hel and Świnoujście localities there remains a
stable value of the annual storm surge indicator (on-
ly in the nineties in Świnoujście there are of the con-
siderably lower values), whereas in Ustka there oc-
curred a high growth thereof since the middle of
nineties, what confirms a course of anomalies of the
annual storm surge indicator. The differences in the
indicator variability course, fairly equal before (8 -
years moving averages) is observed from the begin-
ning of the eighties.
The indicator’s value reflects not only the risk
caused by surge, which occurs with very high sea
level. It shows a possibility of much higher risk in
case of wind direction changing to less favorable, al-
so in case of a lower surge and very strong wind of
not as much danger direction. For example: in Hel in
1999 the indicator value was 5.0, sea level was
580cm, the mean wind velocity 17m/s, but the wind
direction only 260 grades, it means from the west di-
rections. If only the wind direction had changed to
less favorable, the north one, a potentiality of a very
high surge would be much higher.
Anomalies of the storm surge indicator for
Świnoujście, Ustka and Hel localities also confirm
its regional character (Fig.7, 8 and 9). The results for
various stations (areas) differ considerably from
each other. Only for Ustka (in the central coast re-
gion) there is observed a clearly growing tendency
in the storm surge course and the increased values
thereof in recent years (approximately last ten years
period).
Figure 7. Anomalies of annual storm surges indicator „W
a
”,
Świnoujście, 1955-2008 (mean W
a
=2,58).
0
1
2
3
4
5
6
1955
1957
1959
1961
1963
1965
1967
1969
1971
1973
1975
1977
1979
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
storm surges indicator
years
Ustka - storm surges indicator
8-years moving average
trend
0
1
2
3
4
5
6
1955
1957
1959
1961
1963
1965
1967
1969
1971
1973
1975
1977
1979
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
storm surges indicator
years
Hel - storm surges indicator
8-years moving average
trend
-3
-2
-1
0
1
2
3
1955
1958
1961
1964
1967
1970
1973
1976
1979
1982
1985
1988
1991
1994
1997
2000
2003
2006
Storm surges indicator
years
128
Figure 8. Anomalies of annual storm surges indicator „W
a
”,
Ustka, 1955-2008 (mean W
a
=2,12).
Figure 9 Anomalies of annual storm surges indicator „W
a
”,
Hel, 1955-2008 (mean W
a
=1,82).
Were analyzed the reasons for this increase, the
differences between the periods 1955-2008 and
1997-2008 are connected with an increased mean
wind velocity which occurred in Ustka in the last pe-
riod, assuming the not changed wind directions dis-
tribution. A growth of the mean wind velocity is the
most intense in case of the north directions, especial-
ly N (north) and NE (north-east) (Fig.10).
Figure 10. Frequency distribution of the mean wind velocity in
Ustka, 1955-2008 and 1997-2008
This increase for mean wind velocity is 2 m/s for
NE (north-east) direction and 1.8 m/s for N (north)
direction. At the remaining stations are not observed
any such changes, on the contrary, the mean wind
velocity for north directions, is lower in recent years
compared with the previous period: slight decrease
in Świnoujście and greater lowering in Hel. The in-
crease of the mean wind velocity is an important in-
dicator, because reflected into an increase of the
strong or stormy winds and higher storm surges. As-
sessment of the tendencies and variation in timescale
of the regional phenomena indicators shows certain
regional changes of climate conditions.
The seasonal storm surge indicators values enable
assessment of its intensiveness within specific year
seasons; it means autumn, winter and springtime, for
the selected stations within a period of 1955-2008,
assuming that autumn comprises months from Sep-
tember to November, winter – December to Febru-
ary and spring – March till May. In summertime the
storm surges usually do not occur, however two cas-
es happened in July 1989 and August 1995 in
Świnoujście. Different seasons vary considerably in
terms of value storm surge indicator for each part of
the Polish coast. The seasonal storm surge indicator
values are highest at all the stations in autumn and
among them the highest value in Świnoujście - 3,1
(Table 2). Next in the order of the season, is winter
and slightly lower values define the severity of the
storm surges conditions during the spring season
(but only in Świnoujście in springtime is higher in-
dicator than in winter - 3,0).
Table 2. Seasonal storm surges indicator on the Polish coast,
1955-2008.
_________________________________________________
Area Storm surges indicator
____________________________________
Autumn Winter Spring
_________________________________________________
Świnoujście 3.1 2.6 3.0
Ustka 2.8 2.6 2.4
Hel 2.5 2.1 2.1
_________________________________________________
A very large influence of local factors, resulting
in large differences in storm surges conditions and
value of storm surges indicator of each areas. In
Świnoujście area storms conditions cause much
more threat than in the other part of the coast.
4 CONCLUSIONS
To compare the risk of the storm surges at various
sea areas, the new methods had to be developed. The
storm surges indicator has been worked out to satis-
fy researches on climate, weather forecasting, navi-
gation and sea ports operation planning. Weather
and hydrological phenomena characterized now by
the increase in their presence and intensity.The pre-
-3
-2
-1
0
1
2
3
4
1955
1958
1961
1964
1967
1970
1973
1976
1979
1982
1985
1988
1991
1994
1997
2000
2003
2006
Storm surges indicator
years
-3
-2
-1
1
2
3
4
1955
1958
1961
1964
1967
1970
1973
1976
1979
1982
1985
1988
1991
1994
1997
2000
2003
2006
Storm surges indicator
years
0
1
2
3
4
5
6
7
8
S
SW
W
NW
N
NE
E
SE
wind velocity (m/s)
wind direction
1955-2008
1997-2008
129
sented storm surge indicator allows for satisfactorily
characterising the conditions of threat with surges to
Polish coastal zone and changes thereof in timescale.
The comparative analysis of the indicator has con-
firmed its regional character. Moreover, the ob-
served conditions variability in the last years proves
that there occurs an increased threat with large surg-
es in storms of considerable severity for a given area
of the coast. In case of Świnoujście the threat is most
intense however it remains at stable level. At the
central area of the coast (Ustka) there can be ob-
served a clearly growing tendency within a course of
the storm surge indicator values (with its increased
values in last ten years). The least threat occurs
around Hel locality; within the many years course of
the annual indicator there is to notice a slightly
growing trend only and fairly low values thereof.
Assessment of the tendencies and variability of the
regional phenomena indicators in timescale prove
occurrence of certain regional changes of climate. It
is planned to carry out further work on the capabili-
ties of the practical application of the indicator and
the relationship between the storm surges indicator
and regional processes and scenarios of changes (to
2030).
ACKNOWLEDGEMENTS
This work was supported by The Programme Inno-
vative Economy under National Strategic Reference
Framework, co-financed from EU resources. Project
KLIMAT under grant No POIG.01.03.01-14-
011/08-00 (The impact of climate change on the en-
vironment, economy and society)
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