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P. Jokiel and P. Tomalski
transformed that their final form and spatial distribution differ strongly from the
input. For example, different types of retention create a specific hydrological memory
that increases flow inertia, while reshaping and slowing down precipitation events
advancing downstream the catchment [11].
The annual, more or less clear repeatability of hydrological events in Poland is an
obvious consequence of climate-dependent changes in seasons and hence repeated,
seasonal changes in the size and type of precipitation and its redistribution. Spring
is expected to bring snowmelt, rainfall and high flows in rivers. Summer features
low water and occasional rainfall-related floods. Low water levels caused by limited
or lack of precipitation in the summer may further drop in the autumn or revert due
to increased moisture and reduced evaporation. In the winter, river flows usually
build up and are later transformed into mid-winter and then spring thaws. It seems
therefore that the annual cycle is closed and its phases clearly outlined. However, its
repeatability over years is only relative. This is because winters can be frosty and long
or mild and short. They can also be snowy or nearly snowless. These six parameters
are enough to generate 12 types of winter with features triggering a highly variable
course of hydrological events. They would affect not only winter, but also spring and
even summer events, as Poland has large retention related flow inertia, and water
resources in the country are formed mainly in the winter half-year (October-April).
Other seasons also show high multiannual variability of climatic conditions and
features. As a result, the times of floods and low waters change rather freely over the
year timeline. These changes in timeline position bring about variations in the event
parameters and causes. If we combine the already noticeable hydrological effects
of permanent or temporary climatic changes and human pressure, it is clear that the
term “flow seasonality” is increasingly imprecise and requires clarification or even
periodic redefinition [9].
Large physical and geographical variations (relief, geological structure, groundwater, climate, land cover) of the Vistula and the Oder basins affect not only the
conditions and factors determining the river flow but also change the course of water
concentration, drainage, and transport along the river beds. In consequence, water
regimes of the Vistula and the Oder vary along their length, as they become resultants
of an increasing number of factors and conditions occurring within a growing and
more diversified area. The aim of this work is therefore to identify the level and the
character of flows seasonality in the Vistula and the Oder and their fluctuations with
the increasing length of the rivers, their catchment areas and physical and geographical diversity (Fig. 10.1). We will also attempt to assess changes in flow seasonality
of the rivers over a multiannual period to identify various spatial and temporal regularities. The study will be based on four seasonality metrics: seasonality index IS,
concentration date PK, seasonality coefficient GMO, and half-flow date TPO.
P. Jokiel and P. Tomalski
transformed that their final form and spatial distribution differ strongly from the
input. For example, different types of retention create a specific hydrological memory
that increases flow inertia, while reshaping and slowing down precipitation events
advancing downstream the catchment [11].
The annual, more or less clear repeatability of hydrological events in Poland is an
obvious consequence of climate-dependent changes in seasons and hence repeated,
seasonal changes in the size and type of precipitation and its redistribution. Spring
is expected to bring snowmelt, rainfall and high flows in rivers. Summer features
low water and occasional rainfall-related floods. Low water levels caused by limited
or lack of precipitation in the summer may further drop in the autumn or revert due
to increased moisture and reduced evaporation. In the winter, river flows usually
build up and are later transformed into mid-winter and then spring thaws. It seems
therefore that the annual cycle is closed and its phases clearly outlined. However, its
repeatability over years is only relative. This is because winters can be frosty and long
or mild and short. They can also be snowy or nearly snowless. These six parameters
are enough to generate 12 types of winter with features triggering a highly variable
course of hydrological events. They would affect not only winter, but also spring and
even summer events, as Poland has large retention related flow inertia, and water
resources in the country are formed mainly in the winter half-year (October-April).
Other seasons also show high multiannual variability of climatic conditions and
features. As a result, the times of floods and low waters change rather freely over the
year timeline. These changes in timeline position bring about variations in the event
parameters and causes. If we combine the already noticeable hydrological effects
of permanent or temporary climatic changes and human pressure, it is clear that the
term “flow seasonality” is increasingly imprecise and requires clarification or even
periodic redefinition [9].
Large physical and geographical variations (relief, geological structure, groundwater, climate, land cover) of the Vistula and the Oder basins affect not only the
conditions and factors determining the river flow but also change the course of water
concentration, drainage, and transport along the river beds. In consequence, water
regimes of the Vistula and the Oder vary along their length, as they become resultants
of an increasing number of factors and conditions occurring within a growing and
more diversified area. The aim of this work is therefore to identify the level and the
character of flows seasonality in the Vistula and the Oder and their fluctuations with
the increasing length of the rivers, their catchment areas and physical and geographical diversity (Fig. 10.1). We will also attempt to assess changes in flow seasonality
of the rivers over a multiannual period to identify various spatial and temporal regularities. The study will be based on four seasonality metrics: seasonality index IS,
concentration date PK, seasonality coefficient GMO, and half-flow date TPO.