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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.