164
D. Wrzesi´ nski
Keywords River regime · Flow regime typology · River flow regime change ·
North Atlantic Oscillation · Poland
9.1 Introduction
The country area, even at the regional scale, is characterized by relatively significantly diversified environmental conditions, both climatic, as evidenced by Wo´ s [1],
who distinguished 28 climatic regions, and hydrological, reflected in various water
supply conditions and seasonality of the river flow, which determines the flow regime.
It defines the state and responses of the river system in relation to the climatic system
and physical-geographical characteristics of the basin [2]. Therefore, the river regime
is the regularity of variability of all phenomena occurring in the river in an average in
a multi-year period annual cycle, depending on the properties of the natural environment, mainly climate and the catchment structure. Consequently, the flow regime,
the thermal, ice, chemical regime, etc. may be considered. In this chapter, the analysis refers only to the flow regime of rivers in Poland. The analysis of the temporal
diversity of hydrological phenomena in the annual cycle may refer to the most characteristic and distinctive periods of the hydrological cycle – the high and low water
levels and discharges [3, 4] or it may cover the variability of phenomena in the
yearly cycle. In the latter case, the contractual division of the year into monthly
periods or seasons is applied, or the variability of phenomena is analysed in hydrological seasons, i.e., periods in the annual cycle, which are characterized by a similar
course of climatic and hydrological phenomena and processes.
In order to determine the hydrological regime of rivers, various methods are
applied. The recognition of the regularity of the flow variability in the annual cycle
is based on both the supervised and unsupervised approaches. In the supervised
approach, a few indicators (types of regime) are first defined, and then regularities in
the multi-year monthly or seasonal discharges are sought according to the predefined
indicators. Such an approach can be exemplified by the typologies of the regime
proposed by Pardé [5], Lwowicz [6] or, for rivers in Poland, by Dynowska [7]. In
the unsupervised approach, based mainly on the grouping of variables selected for
the analysis, there are no such indicators, and determination of the type of regime is
made on the basis of data structure so that objects within a single type are as similar
as possible. Such an approach was proposed by Gottschalk [8] in the hydrological
regionalization of Sweden, and by Rotnicka [9, 10] in Poland. While in the first
approach, determining a priori an indicator that decides about the type of regime,
exhibits its certain subjectivity, in the second, objectified, unsupervised approach the
result of the analysis is affected by the so-called ‘stop rule’ and the acceptance of a
certain degree of compliance within the identified groups.
The earliest, more extensive works on the regime of rivers in Poland were
published in the 1970s. D˛ ebski [11] classified our rivers as of a nival-pluvial type in
four variants: complex mountain (e.g. the Odra River at gauge Poł˛ eck), complex Tatra
Mountain (e.g. the Vistula River at gauge Karsy), oceanic (the Słupia River at gauge
D. Wrzesi´ nski
Keywords River regime · Flow regime typology · River flow regime change ·
North Atlantic Oscillation · Poland
9.1 Introduction
The country area, even at the regional scale, is characterized by relatively significantly diversified environmental conditions, both climatic, as evidenced by Wo´ s [1],
who distinguished 28 climatic regions, and hydrological, reflected in various water
supply conditions and seasonality of the river flow, which determines the flow regime.
It defines the state and responses of the river system in relation to the climatic system
and physical-geographical characteristics of the basin [2]. Therefore, the river regime
is the regularity of variability of all phenomena occurring in the river in an average in
a multi-year period annual cycle, depending on the properties of the natural environment, mainly climate and the catchment structure. Consequently, the flow regime,
the thermal, ice, chemical regime, etc. may be considered. In this chapter, the analysis refers only to the flow regime of rivers in Poland. The analysis of the temporal
diversity of hydrological phenomena in the annual cycle may refer to the most characteristic and distinctive periods of the hydrological cycle – the high and low water
levels and discharges [3, 4] or it may cover the variability of phenomena in the
yearly cycle. In the latter case, the contractual division of the year into monthly
periods or seasons is applied, or the variability of phenomena is analysed in hydrological seasons, i.e., periods in the annual cycle, which are characterized by a similar
course of climatic and hydrological phenomena and processes.
In order to determine the hydrological regime of rivers, various methods are
applied. The recognition of the regularity of the flow variability in the annual cycle
is based on both the supervised and unsupervised approaches. In the supervised
approach, a few indicators (types of regime) are first defined, and then regularities in
the multi-year monthly or seasonal discharges are sought according to the predefined
indicators. Such an approach can be exemplified by the typologies of the regime
proposed by Pardé [5], Lwowicz [6] or, for rivers in Poland, by Dynowska [7]. In
the unsupervised approach, based mainly on the grouping of variables selected for
the analysis, there are no such indicators, and determination of the type of regime is
made on the basis of data structure so that objects within a single type are as similar
as possible. Such an approach was proposed by Gottschalk [8] in the hydrological
regionalization of Sweden, and by Rotnicka [9, 10] in Poland. While in the first
approach, determining a priori an indicator that decides about the type of regime,
exhibits its certain subjectivity, in the second, objectified, unsupervised approach the
result of the analysis is affected by the so-called ‘stop rule’ and the acceptance of a
certain degree of compliance within the identified groups.
The earliest, more extensive works on the regime of rivers in Poland were
published in the 1970s. D˛ ebski [11] classified our rivers as of a nival-pluvial type in
four variants: complex mountain (e.g. the Odra River at gauge Poł˛ eck), complex Tatra
Mountain (e.g. the Vistula River at gauge Karsy), oceanic (the Słupia River at gauge