Tendencje zmian przepływu rzek Polski w drugiej połowie XX wieku
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Date
2009
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Wydawnictwo Poznańskiego Towarzystwa Przyjaciół Nauk
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Abstract
A study was made of multi-year tendencies in monthly, seasonal and yearly series of streamflow in Poland in
the second half of the 20th century. To establish changes in the time series, use was made of the non-parametric
Mann-Kendall test. The analysed flow series came from 148 profiles located on 91 Polish rivers and covered 9 time
intervals: two 20-year periods (1951-1970 and 1981-2000), two 25-year ones (1951-1975 and 1976-2000), two
30-year ones (1951-1980 and 1971-2000), two 40-year periods (1951-1990 and 1961-2000), and the years
1951-2000.
Over the years 1951-2000, the directions of change in the series of mean monthly, seasonal and yearly
streamflow in Poland were clearly different in the first and second part of this period. In all the flow series starting
in 1951, upward trends decidedly prevail, being the most frequent in the years 1951 -1980. Statistically significant
trends can then be observed in more than 30% of the series under analysis. Nearly 60% of the mean yearly flow
series display then statistically significant growth, recorded on most of the rivers in the country except in the
Mazurian Lakeland. A statistically insignificant increase in streamflow can be noted from January to April. In the
remaining months the discharge figures grow markedly, although the growth varies in space and time. From May to
July the discharges rise mostly on rivers in the eastern part of the country, in the Narew and Wieprz catchments, in
May in the Warta catchment, and in June also in the upper Oder catchment. From August to October a significant
increase in streamflow can be observed on most rivers in the country except lakeland rivers and upper reaches of
the Carpathian tributaries of the Vistula. A similar distribution occurs in the remaining months, with the proportion
of statistically significant trends in December dropping to 38% of the series under analysis. After 1961 the direction
of variations in streamflow changes and negative trends start to predominate. The largest number of downward
trends, in more than 70% of the series, although usually statistically insignificant, can be observed in the period
1971-2000. An exception is the March and April flow series when upward trends predominate. An increase in
streamflow in the winter-spring season can then be observed on the rivers of the Pomeranian Lakeland (February
and March) and the Carpathians (February and April). In the summer-autumn season the discharges of most rivers
in this multi-year period tended to decline.
Mean annual discharges on most of the studied rivers tended to grow between 1951 and 2000, but usually in a
statistically insignificant way. An increase can generally be noted on rivers flowing in the eastern parts of the
Vistula and Oder catchments and on coastal rivers, while a decrease, on rivers in the western parts of those
catchment, not counting the upper reaches of the Sudeten tributaries of the Oder. Still, upward trends, statistically
significant, are only characteristic of rivers of the Pomeranian Lakeland and locally those in the Narew catchment
and some Carpathian streams. A statistically significant upward trend in the winter season on rivers in the
north-east of the country, and also locally on the Sudeten and Carpathian rivers, shows that circulation factors may
be responsible for the higher discharges of those rivers. This is corroborated by a diagram of isocorrelates of
streamflow in those regions in the winter season with the winter NAO index, as well as differences in flows
between a positive and a negative stage of this macro-scale type of circulation (WRZESIŃSKI 2008). An analysis of the spatial variability of the tendencies of change in streamflow is also made difficult by the physical-geographic
conditions of the catchments and by human activity. These are elements of major importance in the shaping of flow
conditions and specific features of stream regimes. The reversal observed in flow tendencies in the 1970s requires
further studies to confirm the statistical significance of this change and to determine when upward trends turned
into downward ones.
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Citation
Badania Fizjograficzne, Seria A, Tom 60, 2009, s. 147-162
Seria
Seria A - Geografia Fizyczna TOM 60;
ISBN
978-83-7654-057-3
ISSN
0067-2807