Baltic Sea Environment Fact Sheet 2016, Published on 23 March 2018
Author: Johannes Johansson
In contrast to the runoff in 2015, the total runoff in
2016 was slightly below the 1950 – 2015 mean value. When looking at the period
from 1950 to present, alternating between dry and wet periods in the length of
decades is common. One example of a dry period occurred between 1968 and 1980
and the following decade (1981-1990) was a rather wet one. The five year
running mean has been increasing since 2004, but it went down slightly with the
2013 runoff. It is still above the long term mean value though.
The total runoff to the Baltic Sea in 2016 was very
close to average for the given time period. The rather large runoff to the Gulf
of Finland, +11% compared to mean the value, was compensated with a lower than
average runoff to the Gulf of Bothnia, -9%. The less prominent runoffs to the
Baltic Proper and the Gulf of Riga was +2% and -3% respectively. The total
runoff to the Baltic Sea in 2016 was hence -1% compared to the long term mean
of the annual runoff.
During the period 1950 – 2016, the total runoff to the Baltic Sea shows
no long-term trend. This time period is characterised by dry and wet periods
lasting for a couple of years to a decade generally following the NAO index.
Figure 1. Total runoff deviation during the period 1950 – 2016 to
the Baltic sub-basins based on annual mean values. The mean runoff value and
the 2016 value for each sub-basin are written in the top left corner in each
panel. The black line represents the five year running mean. The blue lines on
the map represent all the major rivers within the Baltic region.
the assessment of this report, the E-HYPE model (http://hypeweb.smhi.se/)
was used to estimate the runoff to the Baltic Sea. E-HYPE produced runoff values
for the period 1981-2016, for the earlier period 1950-1980 the runoff is based
on observations. Previous years the latter period was simulated by a
combination of observations and two models HBV-model (Graham 1999) and
et al. 2012). The HBV- and the Balt-HYPE model are no longer operational, thereby
the switch to the E-HYPE model.
to the change of data for this assessment, the results are somewhat different
from fact sheets in the past (until 2015). In general the E-HYPE model
estimates a larger runoff in relation to data published in the past, the
overall patters are more or less the same though.
is a quantitative background indicator of the freshwater discharge, carrying
the nutrients from the drainage areas to the coast.
is an important parameter for the change of pressure of nutrient supply due to
varying climate and climate change. Also change in land-use can influence
runoff. To evaluate the change of pressure of nutrient supply to the Baltic
region it is necessary to know the variability of runoff and normalise for this
natural variability. Dry periods, like the one during the 70’s, can mask the
marine eutrophication since the runoff was lower than average and hence also
the total load of nutrients. Extended dry periods should also lead to a slight
increase in surface layer salinity. During wet periods, the total nutrient load
(pressure) increases, making marine eutrophication (effects) even worse.
indicator shows the annual runoff from drainage areas integrated over the
Baltic sub-regions. Runoff is governed by the precipitation - evaporation on
land areas and is also influenced by air temperature. It is the sum of direct
river and diffusive runoff. In all sub-regions a strong seasonal, annual and
decadal variability can be distinguished. Especially wet and dry periods are
characterising the runoff. The 70’s was a fairly dry period compared with the
80’s and the later part of the 90’s. Geographically, the runoff is of about the
same size in the Gulf of Finland and the Baltic Proper, whereas the Gulf of
Riga contributes to a lesser extent and the Gulf of Bothnia to a larger extent
to the total runoff.
different sub-basins are described by the deviation from their mean values
based on runoff during 1950 to 2015. The mean values and the 2016 values are
shown in each sub-basin panel (Figure 1). Years with higher runoff compared to
the mean value are displayed as red bars and lower values with blue bars. A
five year running mean is displayed as a black line overlaying the bars in the
figure. The sub-basins are displayed in the centre of Figure 1 and the
sub-basins described are the Baltic Proper, the Gulf of Riga, the Gulf of
Finland and the Gulf of Bothnia. A figure with the sum of the Baltic Sea
sub-basins is also included, partly to give an overview of the entire Baltic
Sea and partly to compare the annual changes to the NAO index.
the period 1950 – 2016, there is no obvious trend in the annual runoff, neither
in the total runoff to the Baltic Sea area, or in the sub-regions. Instead,
this time period is characterised by dry and wet periods lasting for a couple
of years to a decade. During 2016 the runoff were above mean values in the
Baltic Proper and the Gulf of Finland, while in the Gulf of Riga and the Gulf
of Bothnia the runoff were below mean values, see Table 1.
Table 1. 2016
runoff values [m3s-1] are compared to the 1950-2015 mean of the
annual averages for the sub-basins in the Baltic Sea and the difference in %
times, there have been similar features in the changes of runoff values for all
the sub-basins. Other time periods, the changes are similar only in some of the
sub-basins. All the sub-basins had low runoff values in the early to mid-70’s
and higher in the end of the 90’s. In the Baltic Proper, the Gulf of Riga and
the Gulf of Finland, there were high values from the mid 50’s to the beginning
of the 60’s. In the Gulf of Bothnia, the Gulf of Riga and the Gulf of Finland,
there was an episode of increasing values during the 80’s while in the Baltic
Proper, there was a tendency of decreasing values. There were low values in the
Baltic Proper in the early 90’s while there were high values in the end of the
80’s and at the start of the 90’s in the Gulf of Riga, the Gulf of Finland and
the Gulf of Bothnia.
total runoff to the Baltic Sea is mostly influenced by the sub-basins with the
largest contributions, obviously. The highest contribution is from the Gulf of
Bothnia followed by the Gulf of Finland and the Baltic Proper. When comparing
the Gulf of Bothnia to the Gulf of Finland, there is a rather good correlation
in the features of the running mean values. When comparing the Gulf of Bothnia
to the Baltic Proper, there are some correspondences but also some deviations
in the patterns. The panel displaying the total runoff to the Baltic Sea
represents, however, the general features of the different sub-basins rather
well. Hence, only the panel displaying the total runoff to the Baltic Sea is
compared to the NAO index.
Figure 2. Panel A: The integrated deviations of the runoff to the Baltic Sea. B:
Total runoff deviation during 1950 – 2016 to the Baltic Sea. C: NAO index
during 1950 – 2016 based on winter mean values of the NAO index. Positive index
indicates stronger westerly winds bringing warmer and wetter winters to
Scandinavia. D: NAO index during the years 1864 – 2016. B-D: The black line
represents the five year running mean for each panel.
Figure 2 displays the total runoff deviation during 1950 to 2016 to the Baltic Sea, both as integrated difference (A) (sum of abnormalities from the mean (1950-2016), starting and ending with 0 km3) and with bars displaying the year to year deviation from the mean (B). The integrated difference gives an idea of the total amount of runoff in the Baltic Sea. The NAO index during the years 1950 – 2016 based on winter mean values of the NAO index is presented in panel C. The black line shows the five year running mean. By comparing the running means of panel B and C between 1952 and onwards, the features correspond rather well with each other. Note though, that there are exceptions where the NAO index does not reflect the total runoff from the Baltic Sea e.g. in 1962, 1976 and 2010.
Figure 3. Correlation patterns between the NAO index and the total runoff to the
Baltic Sea for different time periods. A: Time period 1950-2016. B: 1960-1979.
C: 1990-2009. A low p-value (<0.05) is often used to determine a statistical
significance of a dataset. A high r-value is used to determine how strong a
correlation is, r-values >0.5 is considered to be a moderate correlation.
However, based on a
positive correlation with a p-value of 0.0015 (Figure 3), the NAO indices may
be used to indicate general runoff to the Baltic Sea back in time. This
motivates the inclusion of the NAO indices for longer time series presented in
panel D (Figure 2). Furthermore, looking at certain time periods, the
correlation between the NAO index and total runoff deviation is rather good
(r=0.55, 1990-2009). For other time periods there seems to be no correlation at
all (r=0.12, 1960-1979), which indicates a more stochastic behaviour of the
cohesion between Baltic Sea runoff and NAO index.
have focused on whether global warming would increase river runoff in the
Baltic Sea region, as suggested by most models and climate scenarios. A 500 year reconstruction of river runoff has, on the other hand,
indicated a decrease of the total runoff to the Baltic Sea with increasing
temperature as an effect of increased evaporation (Hansson et al., 2010). There are clearly uncertainties associated to river runoff that need to be further
Arheimer, B., Dahné J., and Donnelly, C. 2012.
Climate change impact on riverine nutrient load and land-based remedial
measures of the Baltic Sea Action Plan. Ambio 41, No 6, 600-612.
S. and B. Carlsson 1994. River runoff to the Baltic Sea 1950 – 1990. AMBIO Vol.
23, No. 4-5, 280-287.
Phil 1999. Modelling runoff to the Baltic Sea. AMBIO Vol. 28, No. 4, 328-334.
A., Elken, J., Lehmann, A., Leppäaranta, M., Meier, H., Myrberg, K., &
Rutgersson, A. 2014. Progress in
physical oceanography of the Baltic Sea during the 2003-2014 period. Progress in Oceanography, 128,
D., Eriksson, C., Omstedt, A., Chen, D. 2010. Reconstruction of river runoff to the Baltic Sea, AD 1500-1995.
International Journal of Climatology, 31.5 (2011): 696-703.
are collected at the BALTEX Hydrological Data Centre (http://www.smhi.se/sgn0102/bhdc/bhdc.htm)
(1950-1980), whereas modelled data is obtained at SMHI using the E-HYPE model
There might be some inconsistencies regarding the result from the observations
and the model. The NAO indices are collected from https://climatedataguide.ucar.edu/sites/default/files/nao_station_djfm.txt
For reference purposes, please cite this Baltic Sea environment fact sheet as follows:
[Author's name(s)], [Year]. [Baltic Sea environment fact sheet title]. HELCOM Baltic Sea Environment Fact Sheets. Online. [Date Viewed], http://www.helcom.fi/baltic-sea-trends/environment-fact-sheets/.