9 Flow Regime Patterns and Their Changes
177
the negative phase of the NAO DJFM the most stable types of regime are type 3 (the
nival well-formed regime) and type 4 (the nival-pluvial regime), which in 85% of
river profiles have not changed. Few changes of the regime consist of transformation
from type 3 into type 4, and from type 4 into type 5, which proves an increase in
flows in the summer months. In this phase, a less stable type of regime is type 1
– the nival poorly formed regime, and type 5 – the pluvial-nival regime. In both
cases, in approximately 35% of river profiles representing these types of regime a
transformation of type occurs. In the case of type 1 of regime, there is a change into
the nival moderately formed regime or the nival-pluvial regime, while the pluvialnival regime is transformed into the nival-pluvial one. Most often, in more than 55%
of cases, the nival moderately formed regime is transformed. This regime is changed
into the nival well-formed or the nival-pluvial regime. The observed direction of
transformation indicates that in the negative phase of the NAO DJFM in many rivers,
there is an increase of the spring and summer flows. In the positive phase of the
NAO DJFM , type 3 remains the most stable type of regime – the nival well-formed
regime. It represents 90% of all profiles, at which it was identified for the average
conditions. On a small number of lake-district rivers, this type of regime is changed
into the nival moderately formed one. Compared with the average conditions in the
positive phase of the NAO DJFM , more frequent transformations are subject to type 2
– the nival moderately formed regime (mainly changed into the nival well-formed
one – in some lake-district and upland rivers, and in the Prosna River catchment) and
type 1 – the nival poorly formed regime, which in rivers, mainly of the eastern part
of the Pomeranian Lake District, is transformed into the nival moderately formed
regime. Compared to the average conditions, in the positive NAODJFM phase, types
4 and 5 are of the least stability. The nival-pluvial regime is transformed at almost
70% of profiles into the nival moderately formed type (the middle and lower reaches
of some rivers in the Sudety Mountains and the San River), but mostly into the nival
well-formed type (most of the upper reaches of the Sudety Mountains rivers, the
Vistula and San rivers). The most frequent transformations are observed in the case
of rivers, which in average conditions represent type 5 – the pluvial-nival regime.
In the positive phase of the NAO DJFM they account for only 15% of cases, in the
other cases the regime is changed, mainly into type 4 – the nival-pluvial regime. This
direction of transformation is observed in most rivers in the Dunajec catchment.
Research confirms that there is a temporarily and spatially differentiated impact of
changes in the intensity of the North Atlantic Oscillation on the level of river flows in
Poland. This impact is not strong but noticeable. It is observed with varying intensity
in rivers in many regions of the country, mainly in winter, spring and summer. In the
negative phase of the NAO DJFM , it was observed in 31% of the examined rivers, and
in the positive one – in 43%. In particular, changes in flows of the spring and summer
seasons are crucial due to the adopted typology criteria of the river regime. Thus,
the observed transformations of the regime type in the two NAO DJFM phases against
the background of average conditions are understandable and indicate the possible
destabilization of the characteristics of the flow regime of many rivers in Poland in
the changing climatic conditions caused by the varying intensity of the macroscale
type of circulation, which is the North Atlantic Oscillation.
177
the negative phase of the NAO DJFM the most stable types of regime are type 3 (the
nival well-formed regime) and type 4 (the nival-pluvial regime), which in 85% of
river profiles have not changed. Few changes of the regime consist of transformation
from type 3 into type 4, and from type 4 into type 5, which proves an increase in
flows in the summer months. In this phase, a less stable type of regime is type 1
– the nival poorly formed regime, and type 5 – the pluvial-nival regime. In both
cases, in approximately 35% of river profiles representing these types of regime a
transformation of type occurs. In the case of type 1 of regime, there is a change into
the nival moderately formed regime or the nival-pluvial regime, while the pluvialnival regime is transformed into the nival-pluvial one. Most often, in more than 55%
of cases, the nival moderately formed regime is transformed. This regime is changed
into the nival well-formed or the nival-pluvial regime. The observed direction of
transformation indicates that in the negative phase of the NAO DJFM in many rivers,
there is an increase of the spring and summer flows. In the positive phase of the
NAO DJFM , type 3 remains the most stable type of regime – the nival well-formed
regime. It represents 90% of all profiles, at which it was identified for the average
conditions. On a small number of lake-district rivers, this type of regime is changed
into the nival moderately formed one. Compared with the average conditions in the
positive phase of the NAO DJFM , more frequent transformations are subject to type 2
– the nival moderately formed regime (mainly changed into the nival well-formed
one – in some lake-district and upland rivers, and in the Prosna River catchment) and
type 1 – the nival poorly formed regime, which in rivers, mainly of the eastern part
of the Pomeranian Lake District, is transformed into the nival moderately formed
regime. Compared to the average conditions, in the positive NAODJFM phase, types
4 and 5 are of the least stability. The nival-pluvial regime is transformed at almost
70% of profiles into the nival moderately formed type (the middle and lower reaches
of some rivers in the Sudety Mountains and the San River), but mostly into the nival
well-formed type (most of the upper reaches of the Sudety Mountains rivers, the
Vistula and San rivers). The most frequent transformations are observed in the case
of rivers, which in average conditions represent type 5 – the pluvial-nival regime.
In the positive phase of the NAO DJFM they account for only 15% of cases, in the
other cases the regime is changed, mainly into type 4 – the nival-pluvial regime. This
direction of transformation is observed in most rivers in the Dunajec catchment.
Research confirms that there is a temporarily and spatially differentiated impact of
changes in the intensity of the North Atlantic Oscillation on the level of river flows in
Poland. This impact is not strong but noticeable. It is observed with varying intensity
in rivers in many regions of the country, mainly in winter, spring and summer. In the
negative phase of the NAO DJFM , it was observed in 31% of the examined rivers, and
in the positive one – in 43%. In particular, changes in flows of the spring and summer
seasons are crucial due to the adopted typology criteria of the river regime. Thus,
the observed transformations of the regime type in the two NAO DJFM phases against
the background of average conditions are understandable and indicate the possible
destabilization of the characteristics of the flow regime of many rivers in Poland in
the changing climatic conditions caused by the varying intensity of the macroscale
type of circulation, which is the North Atlantic Oscillation.