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River water temperature (TW) is a key environmental factor that determines the quality of the fluvial environment and its suitability for aquatic organisms. Atmospheric warming, accompanied by more frequent extreme weather phenomena, especially heat waves and prolonged drought, may pose a serious threat to the river environment and native river ecosystems. Therefore, reliable and up-to-date information on current and anticipated changes in river flow and thermal conditions is necessary for adaptive water resource management and planning. This study focuses on semi-natural mountain river systems to reliably assess the magnitude of water temperature change in the Polish Carpathians in response to climatic warming. The Mann–Kendall test was used to detect trends in water temperature series covering the last 35 years (1984–2018). Significant, rising trends in annual water temperature were found for all studied sites, with differences in intensity (0.33–0.92 °C per decade). Trends in TW were strongest in summer and autumn (0.75–1.17 and 0.51–1.08 °C per decade), strong trends were found in spring (0.82–0.95 °C per decade), and weaker in winter (0.25–0.29 °C per decade). Simultaneous air temperature trends were broadly consistent with water temperature trends. This indicates the urgent need for adaptive management strategies to counteract thermal degradation of the fluvial environment under study.

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Widespread, human‐induced land cover (LC) transitions in areas surrounding national parks and nature reserves, accompanied by changing climate conditions, can trigger serious consequences for these natural environments and their ecosystems. The aim of the study was to assess the direction and magnitude of transitions in LC in the Polish Carpathians since 1990 for determining the current status of land degradation neutrality and future degradation risk as well as to analyze concomitant changes in climate conditions to enable sustainable land management. The study area encompasses six national parks with the United Nations Educational, Scientific, and Cultural Organization biosphere reserves, several dozen nature reserves, and landscape parks and is a key source of drinking water in Poland. We studied detailed changes in LC (13 classes). The Wilcoxon signed rank test indicated significant increases in built‐up areas (urban fabric and industrial/transport infrastructure), waters, dense forest cover, and herbaceous vegetation but a decrease in heterogeneous agricultural areas. On the basis of two new methods, we assessed the LC transitions for 20 mountain catchments and for the entire Polish Carpathians. Although we found a slight positive transition in LC for the entire Polish Carpathians, clearly negative transitions occurred in the five analyzed catchments, including those covering two national parks. These LC transitions are accompanied by changing climate conditions with significant increases in air temperature and precipitation. The ongoing intensive urbanization in the studied mountain region, which is accompanied by significant regional warming, implies the need to apply sustainable management practices that will avoid or reduce degradation in the catchments involved.

The main objective of the paper is to determine the role of mountain reservoirs in shaping the dominant cyclicity and energy of river flows. The paper compares a large complex composed of two reservoirs (Czorsztyn–Sromowce Wyżne) with a smaller reservoir (Besko). These reservoirs are located in the Polish Carpathians and are characterised by very different parameters and functions. Moreover, they operate on rivers (the Dunajec and the Wisłok) with different hydrologic regimes. Using Fourier spectral analysis of daily inflows, outflows and water levels in reservoirs for the period 1998–2012, it has been possible to identify the dominant frequencies of the considered time series with a percentage of spectral energy for these frequencies. Moreover, for signals created by river flow rates, changes in signal energy are associated with adequate changes in river energy. Therefore, by calculating the energy of the signal in the time domain, changes in signal energy can be observed before and after the water passes through the reservoir. Data on cyclicity of water levels in these reservoirs forms the background to the analysis of reservoir‐induced changes in cyclicity of river flows. The conducted analysis revealed that reservoirs strengthen the regularity of the annual periodicity of stream flow in the studied rivers. Besides, these reservoirs significantly reduce the energy of water flowing out of them compared to the energy of inflow. Copyright © 2015 John Wiley & Sons, Ltd.

This study analyzes changes in long-term patterns of precipitation and river flow, as well as changes in their variability over the most recent 60 years . The study area is situated in the mountain basin of the Dunajec River, encompassing streams draining the Tatra Mountains in southern Poland. The focus of the study was to evaluate how regional warming translates into precipitation changes in the studied mountain region, and how changes in climate affect sub-regional hydrology. Monthly time series of precipitation measured at several sites were compared for two 30-year periods (1986-2015 versus 1956-1985). The significance of the difference between the periods in question was evaluated by means of the Wilcoxon signed rank test with the Bonferroni correction. The identified shifts in precipitation for 6 months are statistically significant and largely consistent with the revealed changes in river flow patterns. Moreover, significant differences in precipitation variability were noted in the study area, resulting in a significant decrease in the repeatability of precipitation over the most recent 30 years . Changes in the variability of the river flow studied were less visible in this particular mountain region (while significant for two months); however, the overall repeatability of river flow decreased significantly at the same rate as for precipitation.

A thermal regime of aquatic ecosystems determines the possibility of survival and development of aquatic biota. Thermal stratification of river water impounded by dam reservoirs can cause a permanent disturbance in the naturally existing waterair temperature relationship downstream of reservoirs. This article aims at determining the role of dam reservoirs in the disturbance of naturally shaped synchronous behaviour of water-air temperatures. The object of the analysis is the Carpathian river Dunajec downstream of a reservoir complex built in 1994-1997. Results of spectral analysis indicate that the annual scale is the main scale of water temperature (WT) variation, and this scale corresponds to the main frequency of phase synchronisation. However, following the reservoirs construction, the definite synchronous behaviour of interacting air and WTs was apparently distorted, because the response time of WT to changing atmospheric conditions has considerably increased in comparison with the predam period.