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 Station Longtitude Latitude

Catchment area,

km2

Neman Stolbtsy 26° 42' 56" E 53° 28' 43" N 3070

Neman Mosty 24° 32' 10" E 53° 24' 11" N 25600

Neman Grodno 23° 48' 23" E 53° 40' 43" N 33600

Isloch River Borovikovshina 26° 44' 16" E 53° 57' 26" N 624

Gavya River Lubiniata 25° 38' 40" E 53° 59' 26" N 920

Schara River Slonim 25° 19' 37" E 53° 04' 56" N 4860

Svisloch River Sukhaya Dolina 24° 01' 33" E 53° 28' 04" N 1720

Vilija River Steshytsy 27° 23' 39" E 54° 33' 50" N 1200

Vilija River Mikhalishki 26° 09' 59" E 54° 48' 50" N 10300

Naroch River Naroch 26° 43' 33" E 54° 33' 24" N 1480 Oshmyanka

River Bolshiye Yatsiny 26° 12' 57" E 54° 44' 27" N 1480

Dubysa Lyduvenai 23° 5' 14.1" E 55° 30' 23.1" N 1134 Jūra Taurage 22° 16' 45.0" E 55° 15' 4.0" N 1664

Merkys Puvociai 24° 18' 12.0" E 54° 7' 4.3" N 4300 Šešupė K. Naujamestis 22° 51' 49.2" E 54° 46' 37.5" N 3179 Minija Kartena 21° 28' 48.2" E 55° 54' 59.2" N 1230 Šventoji Anykščiai 25° 5' 52.7" E 55° 31' 29.9" N 3600 Šventoji Ukmerge 24° 46' 8.0" E 55° 14' 48.0" N 5440 Žeimena Pabrade 25° 46' 21.0" E 54° 59' 1.7" N 2580 Neman Druskininkai 23° 58' 48.7" E 54° 1' 9.4" N 37100 Neman Nemajūnai 24° 4' 26.3" E 54° 33' 14.8" N 42800 Neman Smalininkai 22° 35' 15.6" E 55° 4' 22.3" N 81200

Vilija Vilnius 25° 16' 36.5" E 54° 41' 31.1" N 15200 Vilija Jonava 24° 16' 54.9" E 55° 4' 10.2" N 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

Name of the

water body Station

Catchment

area, km2

Average

annual water

discharge

Minimum water

discharge

during summer-

autumn

Minimum

water

discharge

during winter

Maximum

water

discharges

during

spring-flood

Neman Stolbtsy 3070 -11.76 -9.56 3.72 -53.07

Neman Mosty 25600 -3.49 -2.16 2.19 -35.52

Neman Grodno 33600 -2.69 -4.01 16.90 -29.23

Isloch River Borovikovshina 624 4.40 26.33 40.90 -52.42

Gavya River Lubiniata 920 4.22 -8.62 -3.73 -37.36

Schara River Slonim 4860 -8.75 -3.74 -4.58 -39.81

Svisloch River Sukhaya Dolina 1720 -0.56 20.02 47.61 -42.48

Vilija River Steshytsy 1200 13.09 1.82 27.42 -33.46

Vilija River Mikhalishki 10300 -6.01 -6.76 -0.22 -38.63

Naroch River Naroch 1480 4.10 -2.05 36.57 -36.50

Oshmyanka River Bolshiye Yatsiny 1480 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)

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.

0

200

400

600

800

1000

1200

1400

1600

1 2 3 4 5 6 7 8 9 10 11 12

m3/s

Months

1812-2009 max-min

1812-2009 average

1980-2009

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.