Search

Study region: Pannonian Ecoregion, Hungary. Study focus: Bridging the gap between atmospheric influences and aquatic environments, this study embarked on a comprehensive reconstruction of daily surface water temperatures across lakes and rivers within the Pannonian Ecoregion over an extensive period of 150 years (1870–2021). New hydrological insights for the region: The analysis revealed a clear warming trend in waters over the past 150 years, and majority of this warming occurred in recent three to four decades (average warming rate: 0.317 °C/decade). Seasonal patterns indicated that winter and spring exhibited faster warming rates, followed by autumn and summer. There has been a significant increase in the number, duration, and intensity of heatwaves in both lakes and rivers, particularly pronounced in the last 30–40 years, and with the rise of air temperatures, river and lake heatwaves tend to intensity. These findings underscore the escalating impact of climate change on freshwater systems in the Pannonian Ecoregion, emphasizing the urgent need for mitigation measures. As the first study on river and lake heatwaves in Hungary and one of the few studies on river heatwaves worldwide, this study will provide reference for analysing extreme thermal events in aquatic systems.

Rivers worldwide are warming due to the impact of climate change and human interventions. This study investigated river heatwaves in the Vistula River Basin, one of the largest river systems in Europe using long-term observed daily river water temperatures from the past 30 years (1991–2020). The results showed that river heatwaves are increased in frequency and intensity in the Vistula River Basin. The total number of river heatwaves showed clear increasing trend with an average rate of 1.400 times/decade, the duration of river heatwaves increased at an average rate of 14.506 days/decade, and the cumulative intensity of river heatwaves increased at an average rate of 53.169 °C/decade. The Mann-Kendall (MK) test was also employed, showing statistically significant increasing trends in the total number, duration, and intensity of heatwaves for all rivers, including the main watercourse of the Vistula River and its tributaries, with few exceptions. Air temperature is the major controller of river heatwaves for each hydrological station, and with the increase of air temperatures, river heatwaves will increase in frequency and intensity. Another impacting factor is flow, and with the increase of flow, river heatwaves tend to decrease in number, duration and intensity. The results suggested that mitigation measures shall be taken to reduce the effect of climate change on river systems.

Water temperature is an important physical indicator of rivers because it impacts many other physical and biogeochemical processes and controls the metabolism of aquatic species in rivers. Having a good knowledge of river thermal dynamics is of great importance. In this study, an advanced machine learning based model that is fast, accurate and easy to use, namely the nonlinear autoregressive network with exogenous inputs (NARX) neural network, was coupled with Bayesian Optimization (BO) algorithm for optimizing the number of NARX hidden nodes and lagged input/target values and the Bayesian Regularization (BR) backpropagation algorithm for the NARX training, to forecast daily river water temperatures (RWT). Long-term observed data from 18 rivers of the Vistula River Basin, one of the largest rivers in Europe, were used for model testing, and model performance was compared with the air2stream model. The results showed that the NARX-based model performs significantly better than the air2stream model in the calibration and validation stages, and can better capture the seasonal pattern and peak values of RWT. Input combinations impact the performance of the NARX-based model in RWT modeling, and air temperature and the day of the year (DOY) are the major inputs, while streamflow and rainfall play a minor role on modeling RWT at the Vistula River Basin. Considering that future times series of air temperatures are easily accessible from climate models and DOY is easy to be considered in the model, the NARX-based model can serve as a promising tool to investigate the impact of climate change on river thermal dynamics.

Study region: Lowland lakes located at Poland. Study focus: There are thousands of lowland lakes in Poland, however, many of them don’t have observed data of water temperatures. How can we simply estimate lake surface water temperature (LSWT) is challenging, and a few studies tried to deal with this issue. In this study, we proposed a simple method using the air2water model for regional estimation of LSWT for Polish lowland lakes: Firstly, a literature review was conducted to collect parameter values of the air2water model applications in different lakes with diverse lake morphologies (e.g., mean depth). Secondly, correlations of model parameters with mean lake depth were analyzed. Finally, model parameters of the Polish lowland lakes (25 lakes with three lakes for testing) were derived using the corresponding mean lake depth and model performance was evaluated afterwards. New hydrological insights for the region: The results showed that the proposed method performs generally well for the 25 Polish lowland lakes, better than the previous method. Reasonable results were obtained for three Polish lakes that were not used for regression analysis, what encourages application of the proposed approach on unmonitored lakes. The results indicated that the method proposed in this study can be used to estimate LSWT of Polish lowland lakes as daily data of air temperatures are readily available in most of the meteorological stations.

Study region: The study region comprises 25 lowland Polish lakes in the northern part of the country. The studied lakes provide domestic, industrial and agricultural water supply, and are major attractions for tourism, thus playing a significant role in the Polish economy. Study focus: The expected impact of future climate change on lake surface water temperature (LSWT) was predicted using the air2water model, which relies solely on daily air temperature (AT) as model input. LSWT and AT observations for the period 1987–2016 were used for model calibration and validation. Then, historical (1987–2005) and future (2006–2100) AT time series from nine EURO-CORDEX climate models were used to project future LSWT under emission scenarios RCP4.5 and RCP8.5. New hydrological insights for the region: The results showed that air2water can well reproduce daily LWST with root mean square errors lower than 1 °C on average. The warming trends of both AT and LSWT are expected to be lower than those observed in the past decades (after the 1980s), and ice cover and weak stratification conditions are expected to partially buffer the LSWT response to the high AT warming expected in future winters. However, the overall enduring warming will substantially alter future thermal dynamics, leading to a shortening of ice cover and inverse stratification periods, possibly leading to serious consequences for lake water quality and ecosystem health.

This article presents a quasi-static and dynamic study of the energy absorption of aluminium and composite foams by investigating four types of cast foams produced by different technologies: foaming in liquid state, casting metal around granule and gas foaming and continuous rolling. Aluminium alloys were the base material.The main intention of the article is to present the results confirming the possibility of using aluminium-based foams in the liquefied natural gas tanks. For this reason, the main goal of the research was to evaluate the energy absorption and structural stability at sub-zero as well as extremely high temperatures. The low temperature of liquefied methane (−163 °C) was particularly important because low temperatures can reduce the strength of aluminium foams, which decreases their durability and influence the overall structural safety. The combustibility of aluminium foams and composite foams was also tested. The composite foam named 445, manufactured by the authors, underwent a combustibility test and retained its original dimensions, while other foams were partially melted. The advantageous durability at extremely low (−175 °C) and high (750 °C) temperatures suggest that such materials can significantly increase the safety and durability of liquefied natural gas tanks against fire, quasi-static and impact loading.