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The paper evaluates changes in the water temperature of the Vistula River – one of the longest rivers in Europe. Mean monthly and annual water temperatures from the period 1971–2017 for 11 stations along the entire length of the river revealed the increasing trends. The mean increase in water temperature in the analysed multi-annual period was 0.31 °C dec–1. In the majority of analysed stations, the key factor determining changes in the water temperature of the river was air temperature. The observed water warming in the Vistula River should be considered an exceptionally unfavourable situation in the context of importance of water temperature for a number of processes and phenomena occurring in river ecosystems. Given the scale of changes, fast measures should be undertaken to slow down the warming.

Main aim of the study was to determine the temporal and spatial patterns of relations between monthly and annual average river flow (RF) and water temperature (WT) for 53 rivers in Poland. The research made use of monthly and annual WT and RF for 88 water gauges for the period 1971–2015. Correlations were established using the Spearman’s rank correlation coefficient and the similarity of RF–WT relations was determined using the Ward’s hierarchical grouping. It was demonstrated that correlations between average annual RF and WT were negative (for >85% of water gauges) and statistically significant (p

The main purpose of the research was to determine the conditions affecting ice phenomena, including the three-phase cycle of ice: expansion, retention and decay of the ice cover on selected rivers of the Baltic coastal zone in the Northern Poland (Przymorze region). The analysis has been elaborated for the years 1951–2010 against the backdrop of currently occurring climatic changes, with particular emphasis on the development and phase variability of the NAO. The article presents the impact of the variability in atmospheric circulation which has manifested in an increase in air temperature, over the last 20 years, on thermal conditions during winter periods in the South Baltic Coastal Strip. The increase in air temperature has contributed to an increase in the temperature of river waters, thus leading to a shortening of the duration of ice phenomena on rivers in the Przymorze region. The article also brings to light an increased occurrence of winter seasons classified as cool, and a disruption in the occurrence of periods classified as normal over the last 30 observed years. The research has demonstrated a significant dependence between the seasonal change in air temperature and the variability of thermal conditions of water, which has a direct impact on the variability of the icing cycle of rivers in the Przymorze region. The authors also show that the variability in forms of ice phenomena for individual river sections is determined by the local factors, i.e. anthropogenic activity, impact of urbanized areas or inflow of pollutants.

Assessments of the infiltration recharge of groundwater are performed using various methods and on different scales. Infiltration is dependent of climatic factors, aspects of water circulation, as well as on quasi-stationary and variable environmental features of a specific area, which are frequently difficult to determine on the basis of direct measurements or observations. The objective of the present study was to identify factors conditioning recharge of shallow groundwater in selected catchment areas of the Poznań Upland using the WetSpass simulation water balance model with spatially distributed parameters. Our analysis has indicated favourable and unfavourable conditions for recharge of groundwater in the annual period and in both half-year periods, which are the result of mutual relationships between the physical qualities of these catchment areas and their climatic and hydrological characteristics. The results obtained also confirmed the impact of surface runoff and actual evapotranspiration on the spatial distribution of effective infiltration. With soil types and groundwater depth distributions being similar in the catchment areas, changes in relationships between components of water balance are caused by differences in the type of land usage. Application of the WetSpass model has made it possible to arrive at a more accurate assessment of groundwater recharge. The results obtained may be used for erification of recharge areas and values of effective infiltration, set as a boundary condition in groundwater flow models.

In the paper we present the results of shallow groundwater recharge estimation using the WetSpass GISbased distributed water balance model. By taking into account WetSpass, which stands for Water an Energy Transfer between Soil, Plants and Atmosphere under quasi-Steady State, for average conditions during the period 1961-2000, we assessed the spatial conditions of the groundwater infiltration recharge process of shallow circulation systems in the Poznan Plateau area (the Great Poland Lowland in western Poland), which is classified as a region with observed water deficits. For three temporal variants, i.e. year, winter and summer half-years, we determined using the geological infiltration method by about 5-10% on average, marginally by 20%.

Surface water temperature characteristics of the Vistula River mouth and the Gdańsk Bay were determined on the basis of available observations, remote sensing and hydrodynamic models. The water temperature in the Vistula River and the Gdańsk Bay was found to be much higher than the air temperature. In recent decades, the water temperature in the Vistula River mouth and the Gdańsk Bay has increased significantly. It has been determined that water temperature in the bay is affected not only by air temperature, but also by water discharge of the Vistula River and wind. [ABSTRACT FROM AUTHOR]

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The article presents the results of an analysis of the impact of cumulated series of negative air temperatures (cumulated degree-days) on the formation and persistence of the permanent ice cover on the River Noteć in the period 1987-2013. When assessing ice phenomena, use was made of observations conducted over 24-hour periods at four IMGW-PIB stations located along the River Noteć: Pakość (upper section), Ujście and Krzyż Wielkopolski (middle section) and Nowe Drezdenko (lower section). The authors determined the nature of the distribution of negative series and 24-hour air temperatures in terms of their duration, increase and distribution in years and months, using data from the Piła meteorological station. The primary objective was to specify the threshold values of cumulated degree-days at which the permanent ice cover starts to appear on the river, and the conditions under which this phenomenon is accelerated. When determining the strength of the relation between cumulated degree-days and the probability of appearance of an ice cover, use was made of the logistic regression model. Research showed that in the majority of instances ice cover appeared on the river at values of cumulated degree-days greater than: -16°C in Pakość, -21°C in Ujście and Krzyż Wielkopolski, and -73.5°C in Nowe Drezdenko. During the analysed period, 306 negative air temperature series occurred in the studief catchment area, with those lasting 5-10 days (76 of all instances) being predominant. As regards the River Noteć in Pakość, the logistic regression model confirmed that, on average, a one-degree increase in the value of cumulated degree-days is associated with an increase in the probability of appearance of the permanent ice cover of approximately 2.10%, of approximately 1.17% in Ujście, of 2.72% in Krzyż Wielkopolski, and of approximately 5.70% in Nowe Drezdenko. The more rapid the increase in cumulated series of negative air temperatures, the greater the probability of ice cover appearing and persisting on the River Noteć. The analysis pointed to the usefulness of the cumulated degree-days factor for predicting the appearance of ice cover on the river. The results obtained are significant for maintaining the economic and ecological function of the River Noteć. Information about the icing of the river has a practical dimension, among others as concerns identifying and minimising hazards connected with the occurrence of jams and ice-jam floods, which bring about enormous economic losses and constitute a threat to human life. [ABSTRACT FROM AUTHOR]

In this study, a spatially distributed water balance model WetSpass was used to simulate long-term average annual and seasonal recharge of groundwater, surface runoff and actual evapotranspiration in the Mogilnica catchment, the Wielkopolska Lowland (western Poland). It is a region with the lowest precipitation and runoff in Poland. The simulated hydrological variables in the Mogilnica catchment are made on raster model (xy = 0.0625 km²). A GIS based, WetSpass is a model: Water and Energy Transfer between Soil, Plants and Atmosphere under quasi-Steady State. For water balance components estimations should be carried out concerning the meteorological conditions (precitipation, air temperature, wind speed, potential evapotranspiration), groundwater level and distributed topography, soil texture and land-use. In the Mogilnica catchment the long-term temporal and spatial average annual precipitation of 538 mm was distributed as: recharge of groundwater of 84 mm (15%), surface runoff of 31 mm (6%) and actual evapotranspiration of 425 mm (79%). Sustainable groundwater management and protection requires knowledge of spatial variation in water balance elements. [ABSTRACT FROM AUTHOR]