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How Climate Change Affects River and Lake Water Temperature in Central-West Poland—A Case Study of the Warta River Catchment
Climate change has a significant impact on the abiotic and biotic environment. An increase in air temperatures translates into higher temperatures of water constituting the habitat of a wide range of species. The purpose of this study is to present the direction and extent of water temperature increases in eight rivers and three lakes on a monthly and annual basis. The analysis of river water temperatures used both measured data and data reconstructed using artificial neural networks from the period of 1984–2020. The analysis of the direction and extent of changes in air and water temperatures was performed using Mann-Kandall tests and a modified Sen test. The analysis of water temperature changes was conducted against the background of climatic conditions and catchment characteristics. The results indicate that in the Warta River basin in the period of 1984–2020, the average annual temperature rise reached 0.51 °C decade−1, ranging from 0.43 to 0.61 °C decade−1. This translated into an increase in mean annual water temperatures in lakes in a range from 0.14 to 0.58 °C decade−1, and for rivers in a range from 0.10 to 0.54 °C decade−1. The greatest changes in air temperature occurred in April, June, August, September, and November. It was reflected in an increase in water temperature in lakes and rivers. However, these changes did not occur in all rivers and lakes, suggesting the role of local factors that modify the effect of climate change. The study showed that the extent of air temperature changes was significantly higher than the extent of water temperature changes in rivers.
Seven Decades of Surface Temperature Changes in Central European Lakes: What Is Next?
Lakes are vital components of the hydrosphere, holding both environmental and economic significance. In recent times, they have undergone transformations in one of their key characteristics—water temperature. Assessing the scale and pace of these changes depends on the length and accuracy of the available data. This study focuses on the two lakes in Poland (Białe Augustowskie and Studzieniczne) with the longest continuous water temperature records, ranging from 1954 to 2023. The results reveal a relatively stable thermal regime until the late 1980s (with changes that were statistically insignificant) and a significant shift over the past three decades, during which the water temperature increased at a rate of 0.5 °C per decade. Importantly, simulations indicate further warming of the water by the end of the 21st century. Depending on the chosen climate change scenario, the warming of both lakes is expected to continue, with the Shared Socioeconomic Pathways (SSP585) scenario projecting a steady increase of 0.5 °C per decade. Given the fundamental importance of water temperature in determining factors such as water quality, these future changes present a significant challenge for water management authorities in terms of maintaining and managing these ecosystems.