(frequency and temporal distribution) appear the most important. In this regard,
temporal variability of precipitation and flood dynamics were analysed in order to
search for possible trends that can be brought about by climate change.
Analysis of precipitation in the Biebrza Valley was done on the basis of data
recorded in rain gauges located in Laskowiec (1996–2011 dataset) and Burzyn
(1970–2010) (see location on the Fig. 14.1). Flood analysis was done on the basis of
discharge data for the River Biebrza in Osowiec in the years 1951–2011. The flood
threshold of river discharge (bankful flow) was set up on the basis of multi-year
observations as 25 m
3 /s (Grygoruk et al. 2011b). Also the largest floods (over the
threshold of the median of the highest annual discharges of Biebrza in Osowiec:
Q > 84.1 m
3 /s, which is a flood of 50 % exceedence frequency) were analysed in
order to reveal the temporal dynamics of flooding in particular seasons. Those
sizeable floods are important from an ecological point of view, as they cover a large
extent of the valley and induce the development and function of riparian zones as
well as a network of ox-bow lakes, entailing water exchange between the river and a
large share of the floodplain.
Temporal variability in amounts of precipitation recorded in the Burzyn rain gauge
during hydrological “summer” (May–October) and “winter” (November–April) was
analysed for each particular year (Fig. 14.2a), as well as the ratio of winter to summer
precipitation (Fig. 14.2b). A slightly decreasing trend in summer volumes of precipitation within the years 1970–2010 can be observed, along with the considerable trend
in increasing winter precipitation. One can conclude that the share of precipitation in
the cold part of the year increases in the total amount of annual precipitation. However,
a vast increase in rainfall intensity in the summer can be observed (Fig. 14.2c) –
although in general summers seem to be drier, the increasing temporal concentration
of precipitation entails possible flooding and remains a challenge for management and
ecosystems. This observation confirms the results of Liszewska and Osuch (2000),
who stated that more extreme weather conditions can occur as a major consequence of
climate change in Central Europe. Similar results for the analysis of precipitation data
recorded in the climate monitoring station of the IMGW (Institute of Meteorology and
Water Management) in Białystok (50 km from the Biebrza Valley), in the years
1971–2010, were observed by Grygoruk et al. (2011a). Hence, the precipitation
dynamics and their temporal distribution analysed herein on the basis of data from
the Laskowiec and Burzyn rain gauges most likely reflect the long-term regional trend.
The increasing temporal concentration and intensity of summer sums of rainfall
correspond with the results of temporal analysis of the largest floods (Fig. 14.2e). It
indicates a significant increase in summer flooding in the first decade of the twentyfirst century, compared to the second half of the twentieth century. Also, the total
volume of individual summer floods (calculated as the amount of water momentary
stored in the Lower Biebrza Basin during the flood events; Fig. 14.2f) increased in
the last 15 years. Temporal analysis of snowmelt floods in the Biebrza Valley
(Fig. 14.2d) indicates the continuing trend of the earlier occurrences of floods in
1950–2012. The analysis of the start of the spring flood was emphasised since this
process induces the ecosystem services of marshes, such as their role in strictly
temporal fish spawning and nutrient removal (Okruszko et al. 2011). It was
214
M. Grygoruk et al.
temporal variability of precipitation and flood dynamics were analysed in order to
search for possible trends that can be brought about by climate change.
Analysis of precipitation in the Biebrza Valley was done on the basis of data
recorded in rain gauges located in Laskowiec (1996–2011 dataset) and Burzyn
(1970–2010) (see location on the Fig. 14.1). Flood analysis was done on the basis of
discharge data for the River Biebrza in Osowiec in the years 1951–2011. The flood
threshold of river discharge (bankful flow) was set up on the basis of multi-year
observations as 25 m
3 /s (Grygoruk et al. 2011b). Also the largest floods (over the
threshold of the median of the highest annual discharges of Biebrza in Osowiec:
Q > 84.1 m
3 /s, which is a flood of 50 % exceedence frequency) were analysed in
order to reveal the temporal dynamics of flooding in particular seasons. Those
sizeable floods are important from an ecological point of view, as they cover a large
extent of the valley and induce the development and function of riparian zones as
well as a network of ox-bow lakes, entailing water exchange between the river and a
large share of the floodplain.
Temporal variability in amounts of precipitation recorded in the Burzyn rain gauge
during hydrological “summer” (May–October) and “winter” (November–April) was
analysed for each particular year (Fig. 14.2a), as well as the ratio of winter to summer
precipitation (Fig. 14.2b). A slightly decreasing trend in summer volumes of precipitation within the years 1970–2010 can be observed, along with the considerable trend
in increasing winter precipitation. One can conclude that the share of precipitation in
the cold part of the year increases in the total amount of annual precipitation. However,
a vast increase in rainfall intensity in the summer can be observed (Fig. 14.2c) –
although in general summers seem to be drier, the increasing temporal concentration
of precipitation entails possible flooding and remains a challenge for management and
ecosystems. This observation confirms the results of Liszewska and Osuch (2000),
who stated that more extreme weather conditions can occur as a major consequence of
climate change in Central Europe. Similar results for the analysis of precipitation data
recorded in the climate monitoring station of the IMGW (Institute of Meteorology and
Water Management) in Białystok (50 km from the Biebrza Valley), in the years
1971–2010, were observed by Grygoruk et al. (2011a). Hence, the precipitation
dynamics and their temporal distribution analysed herein on the basis of data from
the Laskowiec and Burzyn rain gauges most likely reflect the long-term regional trend.
The increasing temporal concentration and intensity of summer sums of rainfall
correspond with the results of temporal analysis of the largest floods (Fig. 14.2e). It
indicates a significant increase in summer flooding in the first decade of the twentyfirst century, compared to the second half of the twentieth century. Also, the total
volume of individual summer floods (calculated as the amount of water momentary
stored in the Lower Biebrza Basin during the flood events; Fig. 14.2f) increased in
the last 15 years. Temporal analysis of snowmelt floods in the Biebrza Valley
(Fig. 14.2d) indicates the continuing trend of the earlier occurrences of floods in
1950–2012. The analysis of the start of the spring flood was emphasised since this
process induces the ecosystem services of marshes, such as their role in strictly
temporal fish spawning and nutrient removal (Okruszko et al. 2011). It was
214
M. Grygoruk et al.