174
D. Wrzesi´ nski
a significant decrease in winter flows observed in many rivers, and a delayed increase
in the spring thaw in the 1950s and 1960s. In turn, in the 1970s and 1980s in these
rivers there was a disappearance of the winter low-water stages associated with a
remarkable increase in the winter flow, sometimes prolonging the less pronounced
spring high-water period. These regularities indicate the noticeable impact of changes
in the macroscale intensity of the air circulation type, which is the North Atlantic
Oscillation, on the transformation of the characteristics of the flow regime of rivers
in Poland.
The North Atlantic Oscillation (NAO) is attributed to a very important, climactic
role in Poland [15–18]. There are also more and more papers documenting the impact
of the North Atlantic Oscillation on the flow of rivers in Poland. Kaczmarek [19]
pointed to the impact of the NAO on the magnitude of high-water stages caused by
thaw in the Central European rivers. In the positive phase of the NAO, lower spring
high-water stages are usually observed than in the negative phase. Other studies also
confirmed the impact of the NAO on the Warta River flows [20] and the existence
of asynchronous relationships between the winter NAO indices and flows of some
Carpathian rivers and the Vistula River [21, 22]. Analyses of changes in hydrological
periods and features of the river flow regime in various phases of the NAO DJFM were
made by Wrzesi´ nski [23–26], and Wrzesi´ nski and Paluszkiewicz [27]. The height of
the flow in various NAO DJFM phases is temporally and spatially differentiated. In the
positive NAO DJFM phase in the winter months (January–February), higher flows are
observed in rivers in the north-eastern part of the country and the mountains. In the
spring months, higher flows in rivers almost all over the country are in the negative
phase of the NAO DJFM . Significantly lower than the average flows in the positive
phase of the NAO are observed in the summer months. As a consequence, at this
stage of the NAO DJFM the annual flows in most rivers are lower than average, and in
rivers between the Odra and Vistula by as much as 20–40%. This is also confirmed
on the maps of average flows in rivers in both NAO DJFM phases (see Figs. 9.3 and
9.4).
Wrzesi´ nski [28] presented the directions of the transformation of the types of
the flow regime of rivers in Poland in the years 1971–2010 in various phases of the
NAO DJFM . In that paper, values of the NAO DJFM winter index were used. That index
is the normalized mean difference in the atmospheric pressure from December to
March, between Lisbon and Stykkisholmur and Reykjavik in Iceland [29]. The type
of regime was established in accordance with the criteria proposed by Dynowska [12]
for the entire period 1971–2010 and for 10 years with high (NAO DJFM > 2.20) and
10 years with low (NAO DJFM < −0.23) values of the NAO DJFM winter index. These
numbers correspond to the first and third quartiles from the entire NAO DJFM index set
from the years 1971–2010. In the examined variants, the rivers in the distinguished
types of the regime are characterized by a similar distribution and range of changes
in monthly flows in the average annual cycle. The distinguished groups of rivers
represent the same types of regime. However, they differ in numbers, which has
consequences in a different picture of their spatial distribution (Fig. 9.3). The analysis
shows that in the studied NAO DJFM phases„ there is a frequent transformation of the
flow regime of many rivers. Compared to the average conditions (1971–2010), in
D. Wrzesi´ nski
a significant decrease in winter flows observed in many rivers, and a delayed increase
in the spring thaw in the 1950s and 1960s. In turn, in the 1970s and 1980s in these
rivers there was a disappearance of the winter low-water stages associated with a
remarkable increase in the winter flow, sometimes prolonging the less pronounced
spring high-water period. These regularities indicate the noticeable impact of changes
in the macroscale intensity of the air circulation type, which is the North Atlantic
Oscillation, on the transformation of the characteristics of the flow regime of rivers
in Poland.
The North Atlantic Oscillation (NAO) is attributed to a very important, climactic
role in Poland [15–18]. There are also more and more papers documenting the impact
of the North Atlantic Oscillation on the flow of rivers in Poland. Kaczmarek [19]
pointed to the impact of the NAO on the magnitude of high-water stages caused by
thaw in the Central European rivers. In the positive phase of the NAO, lower spring
high-water stages are usually observed than in the negative phase. Other studies also
confirmed the impact of the NAO on the Warta River flows [20] and the existence
of asynchronous relationships between the winter NAO indices and flows of some
Carpathian rivers and the Vistula River [21, 22]. Analyses of changes in hydrological
periods and features of the river flow regime in various phases of the NAO DJFM were
made by Wrzesi´ nski [23–26], and Wrzesi´ nski and Paluszkiewicz [27]. The height of
the flow in various NAO DJFM phases is temporally and spatially differentiated. In the
positive NAO DJFM phase in the winter months (January–February), higher flows are
observed in rivers in the north-eastern part of the country and the mountains. In the
spring months, higher flows in rivers almost all over the country are in the negative
phase of the NAO DJFM . Significantly lower than the average flows in the positive
phase of the NAO are observed in the summer months. As a consequence, at this
stage of the NAO DJFM the annual flows in most rivers are lower than average, and in
rivers between the Odra and Vistula by as much as 20–40%. This is also confirmed
on the maps of average flows in rivers in both NAO DJFM phases (see Figs. 9.3 and
9.4).
Wrzesi´ nski [28] presented the directions of the transformation of the types of
the flow regime of rivers in Poland in the years 1971–2010 in various phases of the
NAO DJFM . In that paper, values of the NAO DJFM winter index were used. That index
is the normalized mean difference in the atmospheric pressure from December to
March, between Lisbon and Stykkisholmur and Reykjavik in Iceland [29]. The type
of regime was established in accordance with the criteria proposed by Dynowska [12]
for the entire period 1971–2010 and for 10 years with high (NAO DJFM > 2.20) and
10 years with low (NAO DJFM < −0.23) values of the NAO DJFM winter index. These
numbers correspond to the first and third quartiles from the entire NAO DJFM index set
from the years 1971–2010. In the examined variants, the rivers in the distinguished
types of the regime are characterized by a similar distribution and range of changes
in monthly flows in the average annual cycle. The distinguished groups of rivers
represent the same types of regime. However, they differ in numbers, which has
consequences in a different picture of their spatial distribution (Fig. 9.3). The analysis
shows that in the studied NAO DJFM phases„ there is a frequent transformation of the
flow regime of many rivers. Compared to the average conditions (1971–2010), in