Runoff Change in the Neman River Basin

Project
«River basin management and climate change adaptation in the
Neman River basin »
Runoff Change in the Neman River Basin
Edvinas Stonevičius
Vladimir Korneev
Egidijus Rimkus
Aliaksandr Pakhomau
Vilnius, Minsk, 2012
Introduction
There has been much evidence of climate change impact on river flow regime in the world
(IPCC 2007) and in the Baltic Sea region (BACC... 2008). Investigation of long-term trends of river
runoff is an important step in river basin management and climate change adaptation. The knowledge
of how the rivers in Neman basin have reacted to the resent changes of climate may help to understand
the changes which may happen in the future. The analysis of the historical runoff records allows
estimating the river runoff sensitivity to climate variability and allows roughly judge about the ability
to adapt to climate and runoff changes.
This project is the first attempt to estimate the recent runoff changes in the whole transboundary
Neman basin.
Data and methods
This study analyzes the changes of meteorological parameters in the Nemunas river basin in
1961-2010. Climatic database was created in the first stage of the investigation. Initial monthly data
were taken from the archives of Lithuanian and Belarus Hydrometeorological Services. The data from
24 hydrological stations were used (Table 1).
Table 1 Hydrological stations whose data were used in research
Name of the
water body
Neman
Neman
Neman
Isloch River
Gavya River
Schara River
Svisloch River
Vilija River
Vilija River
Naroch River
Oshmyanka
River
Dubysa
Jūra
Merkys
Šešupė
Minija
Šventoji
Šventoji
Žeimena
Neman
Neman
Neman
Vilija
Vilija
Station
Longtitude
Latitude
Stolbtsy
Mosty
Grodno
Borovikovshina
Lubiniata
Slonim
Sukhaya Dolina
Steshytsy
Mikhalishki
Naroch
26° 42' 56" E
24° 32' 10" E
23° 48' 23" E
26° 44' 16" E
25° 38' 40" E
25° 19' 37" E
24° 01' 33" E
27° 23' 39" E
26° 09' 59" E
26° 43' 33" E
53° 28' 43" N
53° 24' 11" N
53° 40' 43" N
53° 57' 26" N
53° 59' 26" N
53° 04' 56" N
53° 28' 04" N
54° 33' 50" N
54° 48' 50" N
54° 33' 24" N
Bolshiye Yatsiny
Lyduvenai
Taurage
Puvociai
K. Naujamestis
Kartena
Anykščiai
Ukmerge
Pabrade
Druskininkai
Nemajūnai
Smalininkai
Vilnius
Jonava
26° 12' 57" E
23° 5' 14.1" E
22° 16' 45.0" E
24° 18' 12.0" E
22° 51' 49.2" E
21° 28' 48.2" E
25° 5' 52.7" E
24° 46' 8.0" E
25° 46' 21.0" E
23° 58' 48.7" E
24° 4' 26.3" E
22° 35' 15.6" E
25° 16' 36.5" E
24° 16' 54.9" E
54° 44' 27" N
55° 30' 23.1" N
55° 15' 4.0" N
54° 7' 4.3" N
54° 46' 37.5" N
55° 54' 59.2" N
55° 31' 29.9" N
55° 14' 48.0" N
54° 59' 1.7" N
54° 1' 9.4" N
54° 33' 14.8" N
55° 4' 22.3" N
54° 41' 31.1" N
55° 4' 10.2" N
Catchment area,
km2
3070
25600
33600
624
920
4860
1720
1200
10300
1480
1480
1134
1664
4300
3179
1230
3600
5440
2580
37100
42800
81200
15200
24600
Changes of water discharge during the observation period were studied by splitting the 1961–
2010 year period into two parts 1961-1985 and 1986-2010. The difference of annual, monthly,
maximum flood, minimum summer-autumn and winter discharges were calculated between 1961-1985
and 1986-2010. Mapping of obtained results was made in order to highlight regional differences of
changes. Student's test was used to assess whether the differences between the two periods were
statistically significant. The statistical significance level of 0.05 was chosen.
Results
Annual water runoff
The tendencies off mean annual water runoff changes in 1961-2009 in different parts of the
Neman basin differ. The positive changes are predominant in the northern part of the basin and the
negative changes are more common in the southern part (Figure 1, Table 2). The annual water
discharge change pattern correlates with the changes off annual precipitation (Rimkus et al., 2012), but
the formation of runoff is a complicated process due to the different size, different land use and soil
types of catchments. Therefore the runoff pattern has more complex structure then the precipitation.
On the other hand, the annual runoff trends in 1961-2009 in many stations of Neman basin are
not statistically significant. Only the annual negative runoff trend in Oshmyanka River exceeds the 5
% significance level according to (Student’s test).
Figure 1 Annual water discharge changes (%) in 1961-2009 in Neman river basin.
The largest slope of positive trend is in Šventoji river upstream, while the largest negative slope
is in the nearby station of Vilnius (Vilija river) (Figure 2). The trends in these stations are different, but
the correlation of annual runoff is good (r=0.69).
Figure 2 Two cases of largest positive and negative anuall runoff trend slopes in 1961-2009 in
Neman basin.
Table 2 Changes of runoff parameters (%) in 1961-2009 in Neman river basin
Maximum
Minimum water Minimum
Average
water
Name of the
Catchment
discharge
water
Station
annual
water
discharges
water body
area, km2
during summer- discharge
discharge
during
autumn
during winter
spring-flood
Neman
Stolbtsy
3070
-11.76
-9.56
3.72
-53.07
25600
Neman
Mosty
-3.49
-2.16
2.19
-35.52
33600
Neman
Grodno
-2.69
-4.01
16.90
-29.23
624
Isloch River
Borovikovshina
4.40
26.33
40.90
-52.42
920
Gavya River
Lubiniata
4.22
-8.62
-3.73
-37.36
4860
Schara River
Slonim
-8.75
-3.74
-4.58
-39.81
1720
Svisloch River Sukhaya Dolina
-0.56
20.02
47.61
-42.48
1200
Vilija River
Steshytsy
13.09
1.82
27.42
-33.46
10300
Vilija River
Mikhalishki
-6.01
-6.76
-0.22
-38.63
1480
Naroch River
Naroch
4.10
-2.05
36.57
-36.50
1480
Oshmyanka River Bolshiye Yatsiny
10.87
32.90
38.56
-25.31
Dubysa
Lyduvenai
1134
8.06
8.15
48.99
-28.68
Jūra
Taurage
1664
3.61
35.76
17.54
-5.24
Merkys
Puvociai
4300
6.37
3.66
10.83
-20.19
Šešupė
K. Naujamestis
3179
13.19
24.78
15.33
-3.78
Minija
Kartena
1230
9.71
7.20
12.28
3.17
Šventoji
Anykščiai
3600
2.72
13.00
19.36
-16.45
Šventoji
Ukmerge
5440
13.52
29.65
30.55
-14.07
Žeimena
Pabrade
2580
6.51
2.88
7.17
-10.37
Neman
Druskininkai
37100
-2.68
-4.17
9.75
-29.61
Neman
Nemajūnai
42800
-2.85
-3.87
17.71
-27.98
Neman
Smalininkai
81200
1.18
8.22
15.69
-20.16
Vilija
Vilnius
15200
-2.08
0.27
9.12
-34.62
Vilija
Jonava
24600
4.34
2.75
0.36
-23.20
The same could be said about all rivers in Neman basin. The correlation of annual runoff data
of all stations with data in the nearest to Nemunas river mouth Smalininkai hydrological station is
strong. The correlation coefficient is higher than 0.60 in all cases except Svisloch river (Sukhaya
Dolina). High correlation coefficient means that dry and wet years in all basin rivers are usually
concurrent.
Seasonal distribution
Not only the magnitude of annual runoff changes over the time, the sasonal distribution off
runoff changes as well. The larggest changes in 1961-2010 in Neman river runoff regime were in the
January and February and in April (Figure 3 A, B, D). In the first two months of the calendar year the
runoff has increased in all rivers of Neman Basin. This increase can be reletaed to the increaeas of
precipitation amount in these months and due the increase in winter temperature (Rimkus et al., 2012).
The higher winter temperature leads to more frequent thaws (Gečaitė and Rimkus, 2010) an to the
change of the composition of precepitation. Liquid precipitation begins to prevail in winter. As a
consequence the water content in snow cover in the end of winter has decreased in Neman River
Basin.
The changes in March are different in the southern and northern parts of Neman basin (Figure
3 C). March is transitional month between winter and spring. The increase of runoff in March in the
northern part and decrease of runoff in southern part of Neman basin can be related to slightly different
time of spring flood time. In the northern part the spring flood is usually later than in southern part.
Due to shift of spring flood end date the runoff in May decreased in 1961-2009 in largest part of the
Neman basin.
The thinner snow cover and smaller amount of water in it at the end of winter may be the
main reason why the runoff in April has decreased in all rivers in Neman basin (Figure 3 D).
The magnitude of runoff changes in May were much smaler than in April, but the decrease of
runoff is tipical for the largest part of the Neman basin (Figure 3 E). The exception is the basin part
near the Baltic Sea where the runoff has slightly increased.
In June (Figure 3 F) the runoff changes gradually shifts from positive in the north to negative
in the south, but the magnitude of changes are relatively small. In July, August and September (Figure
3 G, H and I) the changes remain very small; however the runoff rise prevailed in these months in
1961-2009. In the end of the year the runoff decreased in south western part of Neman basin and
increased in the north eastern part (Figure 3 J, K and L).
The majority of Neman is upstream of Smalininkai, so this hydrological station represents the
integrated changes in largest part of the basin. A comparison of the 1980-2009 average and 1812-1980
30-year moving averages in Smalininkai hydrological station confirms that recent changes in runoff
are exceptional in the context of long term observations (Figure 4). The 1980-2009 changes in January
and February are higher than any 30-year changes from 1812-1980. Monthly runoff values in April,
May and August are among the lower ones. This means that the last 30-year period is characterized as
a period with a very high winter and a very low spring flow.
Figure 3. Monthly water discharge changes (%) in 1961-2009 in Neman river basin. (January
A, February B, March C, April D, May E, June F, July G, August H, September I, October J,
November K, December L)
1600
1400
1200
1000
800
600
400
200
0
m3/s
1
1812-2009 max-min
1812-2009 average
1980-2009
2
3
4
5
6 7 8
Months
9
10 11 12
Figure 4 Comparison of the 1980-2009 monthly discharge averages and 1812-2009 30-year
moving averages in Neman upstream Smalininkai.
The changes in seasonal distribution also affects the magnitude of seasonal extremes. The
maximum water dishcarge during spring flood in 1961-2009 has decreased in the whole Neman Basin
(Figure 5, Table 2). In majority hydrological stations the maximum water discharge has decreased by
20-30 % (Table 2). The smallest changes are in the western part of Neman basin where unstable snow
cover is common. The maximum discharge during spring flood has increased only in Minija river
upstream Kartena. (Figure 5, Table 2). The negative trends are statistically significant (p < 0.05) in all
rivers except Minija, Jura, Šešupe and Oshmyanka.
Figure 5 Maximum spring flood discharge changes (%) in 1961-2009 in Neman river basin.
Figure 6 Minimum summer-autumn water discharge changes (%) in 1961-2010 in Neman river basin.
Figure 7 Minimum winter water discharge changes (%) in 1961-209 in Neman river basin.
The minimum water discharge during summer-autumn has slightly decreased in the Neman
upstream Nemajūnai hydrological station and in most hydrological stations on Vilija River (Figure 6,
Table 2). The decrease of runoff was also observed Gavya, Schara and Naroch rivers. In all mentioned
rivers the magnitude of decrease is low and the trends are not statistically significant at 0.05 level. In
other parts of the Neman basin the minimum summer-autumn water discharge has increased, but
statistically significant trends were only in five hydrological stations: Isloch, Borovikovshchina;
Svisloch River, Sukhaya Dolina; Oshmyanka River, Bolshiye Yatsiny; Jūra, Taurage and Neman,
Smalininkai (Figure 6, Table 2).
Other minimum of discharge in Neman basin is usually in winter. As mentioned before the
monthly runoff in winter months has increased consequently the minimum water discharge in winter
has also increased in whole Neman basin (Figure 7, Table 2). The smallest changes are expected in the
southern and central parts of the basin (Figure 7). The changes in the other part are large and
statistically significant.
References
BACC Author Team 2008 Assessment of climate change for the Baltic Sea basin. Heidelberg:
Springer.
Gečaitė and Rimkus, 2010 Snow cover regime in Lithuania. Geografija 46 (1-2), 17-24 (in
Lithuanian).
IPCC 2007 Climate Change 2007: Impacts, Adaptation and Vulnerability - Working Group II
Contribution to the Intergovernmental Panel on Climate Change - Fourth Assessment Report (M. L.
Parry, O. F. Canziani, J. P. Palutikof, P. J. van der Linden, C. E. Hanson eds.) Cambridge University
Press, Cambridge, United Kingdom.
Rimkus E., Korneev V., Pakhomau A., Stonevičius E. 2012 Climate Change in the Nemunas
River Basin: Observed Trends and Future Predictions. Project “River basin management and climate
change adaptation in the Neman River basin” report.