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Abstract

Climate change is one of the main drivers of river warming worldwide. However, the response of river temperature to climate change differs with the hydrology and landscape properties, making it difficult to generalize the strength and the direction, of river temperature trends across large spatial scales and various river types. Additionally, there is a lack of long-term and large-scale trend studies in Europe as well as globally. In this study, we investigated the long-term (25years; 132 sites) and the short-term (10years; 475 sites) river temperature trends, patterns and underlying drivers within the period 1985-2010 in seven river basins of Germany. The majority of the sites underwent significant river warming during 1985-2010 (mean warming trend: 0.03°Cyear-1, SE=0.003), with a faster warming observed during individual decades (1985-1995 and 2000-2010) within this period. Seasonal analyses showed that, while rivers warmed in all seasons, the fastest warming had occurred during summer. Among all the considered hydro-climatological variables, air temperature change, which is a response to climate forcing, was the main driver of river temperature change because it had the strongest correlation with river temperature, irrespective of the period. Hydrological variables, such as average flow and baseflow, had a considerable influence on river temperature variability rather than on the overall trend direction. However, decreasing flow probably assisted in a faster river temperature increase in summer and in rivers in NE basins (such as the Elbe basin). The North Atlantic Oscillation Index had a greater significant influence on the winter river temperature variability than on the overall variability. Landscape and basin variables, such as altitude, ecoregion and catchment area, induced spatially variable river temperature trends via affecting the thermal sensitivity of rivers, with the rivers in large catchments and in lowland areas being most sensitive.

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... Da lokale Sturzfluten nahezu ausschließlich in kleinen und mittleren Einzugsgebieten ohne Pegelaufzeichnungen auftreten, existieren auch in der Regel keine belastbaren Datengrundlagen für eine häufigkeitsstatistische Auswertung des beobachteten Sturzflutgeschehens in Deutschland. Hinzu kommt, dass die Bandbreite der Zukunftsprojektionen dabei für kleine Einzugsgebiete erheblich breiter ist, wodurch es beispielsweise zu einer Trendumkehr für Niedrigwasser und Hochwasser kommen kann (Arora et al. 2016, LAWA 2017a. Zudem zeigen aktuelle Simulationsergebnisse, dass die klimamodellbedingte Unsicherheit so groß ist, dass sie die Empfindlichkeit des hydrologischen Systems verdecken kann (Hattermann et al. 2018 Im Zuge der Projektarbeit konnte zunächst bestätigt werden, dass unter allen betrachteten hydroklimatischen Variablen die Lufttemperaturänderung als die Hauptursache für die Änderung der Gewässertemperatur heraus zu stellen ist, da sie die stärkste Korrelation mit dieser aufweist (z. ...
... Zudem zeigen aktuelle Simulationsergebnisse, dass die klimamodellbedingte Unsicherheit so groß ist, dass sie die Empfindlichkeit des hydrologischen Systems verdecken kann (Hattermann et al. 2018 Im Zuge der Projektarbeit konnte zunächst bestätigt werden, dass unter allen betrachteten hydroklimatischen Variablen die Lufttemperaturänderung als die Hauptursache für die Änderung der Gewässertemperatur heraus zu stellen ist, da sie die stärkste Korrelation mit dieser aufweist (z. B. Arora et al. 2016). Eine Temperaturerhöhung hat dabei einen direkten Einfluss auf die terrestrischen und aquatischen Ökosysteme über die funktionellen Regimes, die Produktion und Respiration. ...
... Since local flash floods occur almost exclusively in small and medium-sized catchments without gauge data records, there are also generally no reliable data bases for a frequency-statistical evaluation of the observed flash flood occurrence in Germany. In addition, the range of future projections is considerably broader for small catchments in this context, which can lead to a trend inversion for low-flow and high-flow events, for example (Arora et al. 2016, LAWA 2017a). In addition, recent simulation results show that climate model-related uncertainty is so considerable that it can mask the sensitivity of the hydrological system (Hattermann et al. 2018). ...
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Gewässer und deren Management stehen im Hinblick auf den prognostizierten Klimawandel vor großen Herausforderungen. Intensiver werdende Extremereignisse, wie Hochwasser, Starkregen oder lang anhaltende Trockenphasen mit hohen Temperaturen werden zukünftig verstärkt das sensible ökologische Gleichgewicht der Oberflächengewässer mit deren Flora und Fauna beeinträchtigen. Für eine Aufrechterhaltung der Lebensgrundlage "Wasser" und "biologischen Vielfalt" in Fließgewässern und Seen werden wirksame Anpassungsmaßnahmen benötigt. Demnach stehen sämtliche Akteure der Wasserwirtschaft vor der Herausforderung, die komplexen Wirkungszusammenhänge der vom Menschen beeinflussten Ökosysteme besser zu verstehen und gezielt die Anpassungsfähigkeit aquatischer Ökosysteme zu verbessern. Auf Seiten der Fachinstrumente ist auf EU-Ebene für die Wasserrahmenrichtlinie (EG-WRRL) zu hinterfragen, inwieweit sich deren Methoden und Bewertungssysteme unter sich ändernden klimatischen Randbedingungen als nutzbar erweisen. Zur Untersuchung der Auswirkungen der prognostizierbaren klimatischen Entwicklungen auf die ökologische Beschaffenheit von Oberflächengewässern wurden im Forschungsvorhaben anhand einer umfassenden Literaturrecherche und ergänzenden Expert*inneninterviews zunächst der derzeitige Wissensstandes und bestehende Wissenslücken ermittelt. Anschließend wurde die EG-WRRL als Handlungsinstrument auf ihre künftige Anwendbarkeit überprüft und Vorschläge hinsichtlich einer Anpassung des Methoden- und Bewertungssystems der EG-WRRL abgeleitet. Für die analysierten Wirkungszusammenhänge wurden zudem Verfahrensschritte und derzeitige Umsetzungsgrenzen eines Modellierungskonzeptes beschrieben. Weiterhin erfolgt eine Zuarbeit zur Ermittlung des Indikators "Wasserstress" gemäß der Ziele für nachhaltige Entwicklung der Vereinten Nationen für die Bundesrepublik Deutschland. Im Fokus standen hier die methodischen Ansätze zur Untersuchung des sogenannten "ökologischen Mindestwasserbedarfs" bzw. „Gesamtumweltwasserbedarfs“ für Deutschland. Sämtliche (Zwischen-)Ergebnisse wurden ausgewählten Expert*innen im Rahmen eines Fachworkshops vorgestellt und diskutiert. Die somit identifizierten Kernaussagen und Erfordernisse wurden in Handlungsempfehlungen zusammengefasst und werden über den vorliegenden Bericht Akteuren der Forschung, Verwaltungs- und Fachbehörden, sowie der Planungspraxis bereitgestellt.
... Generally, the T a warming rates have a difference of less than 5 %. Arora et al. (2016) showed a mean T w warming rate in northern and northeastern German rivers of 0.03 • C yr −1 (1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000) and 0.09 • C yr −1 (2000-2010). Regarding our time period , these values are plausible. ...
... Basarin et al. (2016) found a maximum increase in T w at the Danube at Bogojevo (1950-2012) of 0.05 • C yr −1 , which matches the maximum increase at Basel. T a increased by 0.02 • C yr −1 between 1985 and 2010 in the study by Arora et al. (2016). We found a steeper slope at all stations. ...
... The reason could be the hiatus of global warming (Hartmann et al., 2014), which is a flattening of the T a increase between 1998 and 2012. This period is fully included in the Arora et al. (2016) study and our data set, but we investigated further until 2018, when the warming of T a already increased again (Hu and Fedorov, 2017). Michel et al. (2020) investigated T w at 52 river gauges in Switzerland, representing most of the Rhine catchment area at Basel. ...
Article
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River temperature is an important parameter for water quality and an important variable for physical, chemical and biological processes. River water is also used by production facilities as cooling agent. We introduced a new way of calculating a catchment-wide air temperature using a time-lagged and weighed average. Regressing the new air temperature vs. river water temperature, the meteorological influence and the anthropogenic heat input could be studied separately. The new method was tested at four monitoring stations (Basel, Worms, Koblenz and Cologne) along the river Rhine and lowered the root mean square error of the regression from 2.37 • C (simple average) to 1.02 • C. The analysis also showed that the long-term trend (1979-2018) of river water temperature was, next to the increasing air temperature , mostly influenced by decreasing nuclear power production. Short-term changes in timescales < 5 years were connected with changes in industrial production. We found significant positive correlations for the relationship.
... Changes in RWT will directly impact the ecological conditions of habitats and the variability of fish populations in freshwater ecosystems [15][16][17]. However, the reaction of rivers differs depending on the hydrological properties and environmental conditions of catchment areas, which makes it difficult to generalize the strength and direction of their temperature trends in large spatial scales and for distinct river types [18,19]. ...
... Analysis of a number of other temporal series demonstrate a general increasing tendency in water temperature in European rivers and lakes ranging from 0.05 to 0.8 • C per decade, and in some cases exceeding 1 • C per decade [6,21,22]. Statistically significant tendencies of water temperature increase in the last three-four decades have been confirmed, among others for the Devon River in Great Britain [23], the Austrian rivers [24], the Danube River [25,26], selected rivers of Germany [18] and rivers with the alpine and lowland regime in Switzerland [27]. These studies have confirmed that in the years 1977-1990 considerable tendencies of water temperature increase were associated with changes in air temperature, and also with changes in land use, as proved by the results of research by Webb and Walling [22]. ...
... Research conducted on this topic allowed it to be determined that the trend commenced in the 1980s and was associated with climatic patterns over the Northern and Eastern Atlantic. According to Arora et al. [18], the impact of the North Atlantic Oscillation (NAO) index is particularly visible in the variability of the winter temperature of rivers, and to lesser extent in its general variability. Also regarding the Polish rivers, in recent papers [49] the authors have demonstrated a significant impact of NAO on RWT in the winter season. ...
Article
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The study determined water temperature trends of rivers in Poland in the period 1971–2015, and also their spatial and temporal patterns. The analysis covered daily water temperature of 53 rivers recorded at 94 water gauge stations and air temperature at 43 meteorological stations. Average monthly, annual, seasonal and maximum annual tendencies of temperature change were calculated using the Mann–Kendall (M–K) test. Regional patterns of water temperature change were determined on the basis of Ward’s hierarchical grouping for 16 correlation coefficients of average annual water temperature in successive 30-year sub-periods of the multi-annual period of 1971–2015. Moreover, regularities in monthly temperature trends in the annual cycle were identified using 12 monthly values obtained from the M–K Z test. The majority of average annual air and water temperature series demonstrate statistically significant positive trends. In three seasons: spring, summer and autumn, upward tendencies of temperature were detected at 70%–90% of the investigated water gauges. In 82% of the analysed rivers, similarity to the tendencies of change of monthly air temperature was concluded, with the climatic factor being recognised as of decisive importance for the changes in water thermal characteristics of the majority of rivers in Poland. In the winter months, positive trends of temperature were considerably weaker and in general statistically insignificant. On a regional scale, rivers with a quasi-natural thermal regime experienced temperature increases from April to November. In the other cases, different directions of change in river water temperature (RWT) were attributed to various forms of human impact. It was also found that for the majority of rivers the average annual water temperature in the analysed 30-year sub-periods displayed upward trends, statistically significant or close to the significance threshold. Stronger trends were observed in the periods after 1980, while a different nature of water temperature change was detected only in a couple of mountainous rivers or rivers transformed by human impact. In the beginning of the analysed period (1971–2015), the average annual water temperature of these rivers displayed positive and statistically significant trends, while after 1980 the trends were negative. The detected regularities and spatial patterns of water temperature change in rivers with a quasi-natural regime revealed a strong influence of climate on the modification of their thermal regime features. Rivers characterised by a clearly different nature of temperature change, both in terms of the direction of the tendencies observed and their statistical significance, were distinguished by alterations of water thermal characteristics caused by human activity. The results obtained may be useful in optimising the management of aquatic ecosystems, for which water temperature is a significant indicator of the ongoing environmental changes
... A mean trend of +0.3 • C per decade has been observed in England and Wales over the period from 1990 to 2006 by analysing more than 2700 stations (Orr et al., 2015). A similar mean trend is found in Germany for the period from 1985 to 2010 over 132 sites (Arora et al., 2016). While the warming is more pronounced in summer in Germany and in France (Moatar and Gailhard, 2006), the results in Wales and England show the opposite with a stronger warming in winter. ...
... This later rate corresponds to about 95 % of the con-temporary air temperature warming rate. Similar mean trends have been observed in Germany, Wales, and England over comparable periods (Orr et al., 2015;Arora et al., 2016). At the individual catchment scale, air and water temperature trends are poorly correlated, suggesting the large influence of local conditions and hydrological processes on water temperature. ...
... At the individual catchment scale, air and water temperature trends are poorly correlated, suggesting the large influence of local conditions and hydrological processes on water temperature. The warming is more pronounced in summer and less important in winter, creating a gradually increasing winter to summer stream temperature difference, which is in agreement with results found by Moatar and Gailhard (2006), Webb and Nobilis (2007), and Arora et al. (2016) in France, Austria, and Germany, respectively, but differs from the observations in Wales and England (Orr et al., 2015), that can be easily explained by the different climate conditions over Great Britain. In spring, the water temperature trend is more pronounced than the air temperature trend (consistent with Huntington et al., 2003 andWebb andNobilis, 2007). ...
Article
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Stream temperature and discharge are key hydrological variables for ecosystem and water resource management and are particularly sensitive to climate warming. Despite the wealth of meteorological and hydrological data, few studies have quantified observed stream temperature trends in the Alps. This study presents a detailed analysis of stream temperature and discharge in 52 catchments in Switzerland, a country covering a wide range of alpine and lowland hydrological regimes. The influence of discharge, precipitation, air temperature, and upstream lakes on stream temperatures and their temporal trends is analysed from multi-decadal to seasonal timescales. Stream temperature has significantly increased over the past 5 decades, with positive trends for all four seasons. The mean trends for the last 20 years are +0.37±0.11 ∘C per decade for water temperature, resulting from the joint effects of trends in air temperature (+0.39±0.14 ∘C per decade), discharge (-10.1±4.6 % per decade), and precipitation (-9.3±3.4 % per decade). For a longer time period (1979–2018), the trends are +0.33±0.03 ∘C per decade for water temperature, +0.46±0.03°C per decade for air temperature, -3.0±0.5 % per decade for discharge, and -1.3±0.5 % per decade for precipitation. Furthermore, we show that snow and glacier melt compensates for air temperature warming trends in a transient way in alpine streams. Lakes, on the contrary, have a strengthening effect on downstream water temperature trends at all elevations. Moreover, the identified stream temperature trends are shown to have critical impacts on ecological and economical temperature thresholds (the spread of fish diseases and the usage of water for industrial cooling), especially in lowland rivers, suggesting that these waterways are becoming more vulnerable to the increasing air temperature forcing. Resilient alpine rivers are expected to become more vulnerable to warming in the near future due to the expected reductions in snow- and glacier-melt inputs. A detailed mathematical framework along with the necessary source code are provided with this paper.
... Approximately 7% of the global population would suffer from a severe reduction in renewable water resources with a 1 • C rise in global mean temperature [2]. Global warming research has motivated the widespread application of statistical change analysis in observed time series of hydrometeorological variables [3][4][5][6][7]. Trend detection is one branch of change detection methods, focusing on gradual changes that have far-reaching effects on the effectiveness of current water management policies. ...
... After bias correction, the upper and lower tails of Z S still align with the Normal curve and further provide a proper rejection ratio (see Figure 2b). In the following analysis, the usefulness of the original Sen's trend test was evaluated using the bias-corrected variance in Equation (4). ...
... A total of 500 sets, each with 500 representations of the AR(1) and FGN time series, were generated, and subsequently V(S) was estimated using these simulated time series. The theoretical values of V 0 (S) were computed using Equation (4). In this study, the synthetic FGN data were simulated using the function "simFGN0" in the R package "longmemo." ...
Article
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Trend detection in observations helps one to identify anthropogenic forces on natural hydrological and climatic systems. Hydrometeorological data are often persistent over time that deviates from the assumption of independence used by many statistical methods. A recently proposed Sen’s trend test claimed to be free of this problem and thereby received widespread attention. However, both theoretical derivation and stochastic simulation of the current study implies that persistence inflates the trend significance, leading to false trends. To tackle this problem, we incorporate the feature of persistence into the variance of the trend test statistic, whereby an innovative variance-corrected Sen’s trend test is developed. Two theoretical variances of the trend test statistic are newly derived to account for short-term and long-term persistent behavior. The original variance for independent data is also corrected because of its negative bias. A stepwise procedure, including steps to specify the underlying persistent behavior and to test trend with new statistic, is outlined for performing the new test on factual data. Variance-corrected Sen’s trend test can effectively restore the inflated trend significance back to its nominal state. This study may call for the reassessment of published results of the original Sen’s trend test on data with persistence.
... A mean trend of +0.3 • C per decade has been observed in England and Wales over the period from 1990 to 2006 by analysing more than 2700 stations (Orr et al., 2015). A similar mean trend is found in Germany for the period from 1985 to 2010 over 132 sites (Arora et al., 2016). While the warming is more pronounced in summer in Germany and in France (Moatar and Gailhard, 2006), the results in Wales and England show the opposite with a stronger warming in winter. ...
... This later rate corresponds to about 95 % of the con-temporary air temperature warming rate. Similar mean trends have been observed in Germany, Wales, and England over comparable periods (Orr et al., 2015;Arora et al., 2016). At the individual catchment scale, air and water temperature trends are poorly correlated, suggesting the large influence of local conditions and hydrological processes on water temperature. ...
... At the individual catchment scale, air and water temperature trends are poorly correlated, suggesting the large influence of local conditions and hydrological processes on water temperature. The warming is more pronounced in summer and less important in winter, creating a gradually increasing winter to summer stream temperature difference, which is in agreement with results found by Moatar and Gailhard (2006), Webb and Nobilis (2007), and Arora et al. (2016) in France, Austria, and Germany, respectively, but differs from the observations in Wales and England (Orr et al., 2015), that can be easily explained by the different climate conditions over Great Britain. In spring, the water temperature trend is more pronounced than the air temperature trend (consistent with Huntington et al., 2003 andWebb andNobilis, 2007). ...
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Stream temperature is a key hydrological variable for ecosystem and water resources management and is particularly sensitive to climate warming. Despite the wealth of meteorological and hydrological data, few studies have quantified observed stream temperature trends in the Alps. This study presents a detailed analysis of stream temperatures in 52 catchments in Switzerland, a country covering a wide range of alpine and lowland hydrological regimes. The influence of discharge, precipitation, air temperature and upstream lakes on stream temperatures and their temporal trends is analysed from multi-decade to seasonal time scales. Stream temperature has significantly increased over the past 5 decades, with positive trends for all four seasons. The mean trends for the last 20 years are +0.37 °C per decade for water temperature, resulting from joint effects of trends in air temperature (+0.39 °C per decade) in discharge (−10.1 % per decade) and in precipitation (−9.3 % per decade). For a longer time period (1979–2018), the trends are +0.33 °C per decade for water temperature, +0.46 °C per decade for air temperature, −3.0 % per decade for discharge and −1.3 % per decade for precipitation. We furthermore show that in alpine streams, snow and glacier melt compensates air temperature warming trends in a transient way. Lakes, on the contrary have a strengthening effect on downstream water temperature trends at all elevations. The identified stream temperature trends are furthermore shown to have critical impacts on ecological temperature thresholds, especially in lowland rivers, suggesting that these are becoming more vulnerable to the increasing air temperature forcing. Resilient alpine rivers are expected to become more vulnerable to warming in the near future due to the expected reductions in snow- and glacier melt inputs.
... Climate change forecasts assume further increase in air temperature, which may contribute to an increase in water temperature (on average by 0.8-1.6 °C), and changes in the thermalice regime (Caldwell et al., 2015;IPCC, 2018;Olsson et al., 2015;Taniwaki et al., 2017;van Vliet et al., 2013). According to the forecasts, the greatest increases in river water temperature will occur among others in Europe, where earlier research revealed its increase in a range of 1-3 °C (Arora et al., 2016;Basarin et al., 2016;Pekarova et al., 2008). The tendency for an increase in water temperature was also confirmed in the case of rivers in Poland, where the issues of thermal conditions of rivers represent an important trend of hydrological research (Graf, 2019;Graf and Wrzesiński, 2020;Łaszewski, 2020;Ptak, 2018). ...
... Van Vliet et al. (2011) emphasise that during low flows, water temperature is the most sensitive to the effect of atmospheric conditions, and can reach high values. According to Arora et al. (2016), a decrease in water flow probably contributed to a faster increase in temperature in the river in summer and in the catchments of NE Europe (e.g. in the Łaba River catchment). In the case of the Ticino River (northern Italy), maximum water temperatures were determined to be correlated with low discharges recorded in the summer period (August) (Salmaso et Fig. 4. Changes in mean annual water temperature (blue) in Vistula and air temperature (red) in the period 1971-2017. ...
Article
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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 oc-curring in river ecosystems. Given the scale of changes, fast measures should be undertaken to slow down the warming.
... Temperature -Current knowledge of recent warming in rivers is scarce due to a lack of long-term and large-scale studies in various parts of the world (Bolotov et al., 2018). However, a rapid rise in water temperature in temperate lotic systems in recent decades has been confirmed (Arora et al., 2016). Recent studies reveal that among hydro-climatological variables, change in air temperature, which is a response to climate forcing, is the main driver of river temperature change because it had the highest correlation with river temperature irrespective of period (Arora et al., 2016;Basarin et al., 2016). ...
... However, a rapid rise in water temperature in temperate lotic systems in recent decades has been confirmed (Arora et al., 2016). Recent studies reveal that among hydro-climatological variables, change in air temperature, which is a response to climate forcing, is the main driver of river temperature change because it had the highest correlation with river temperature irrespective of period (Arora et al., 2016;Basarin et al., 2016). The data on monthly mean variation in air, water and sediment temperatures from tropical river Tunga at different stations is presented in Fig. 1a. ...
Conference Paper
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A total of 19 environmental variables have been monitored from 14 stations for a period of one year at monthly intervals in the upstream of Tunga River from Kudrekmukha National Park to backwaters of Tunga reservoir (Mandagadde Bird Sanctuary) in the Western Ghats of Karnataka. The monthly average air, water and sediment temperatures varied from 25.41 to 27.58 o C, 23.92 to 26.96 o C and 23.79 to 26.75 o C. The monthly mean values of total, suspended and dissolved solids were 169.15, 90.11 and 81.31 mg/l respectively. The observed pH value of Tunga river water ranged from 5.7 at station Korakanahalla (Gurige) stream during September 2003 to 8.84 at station 14 in Tunga River during March. The high concentration of dissolved oxygen was in upper reaches of Tunga River basin and in the downstream the demand for oxygen by microorganisms is more. The tributaries located in the upper stretch (<34 mg/l) of the river Tunga showed lower values of alkalinity than the tributaries located in the lower stretch (>45 mg/l). The chloride concentration was maximum (25.56 mg/l) in Nadti stream near Thirthahally during April 2003 and the minimum was 4.26 mg/l in Tudur stream during June 2003. The river water from the upper stretch of Tunga River showed low values of total hardness. The surface runoff during the south west monsoon season from the montane forest area could have contributed high iron content in the Tunga river water and was further enhanced by inflow of water with high content of iron from tributaries. The monthly mean values of nitrate content varied from 0.14 to 0.51 mg/l. The sulfate, silicate and phosphate contents were high in tributaries of Tunga River. The large amount of correlation present among the environmental variables indicated that these variables may be grouped into homogenous sets of variables based on their correlation patterns and thereby used as indicators of water quality.
... As temperatures for both lakes and streams are projected to rise in the future, these negative effects would not be expected to become less severe or frequent [65][66][67]. European river temperatures are projected to increase with 1.6-2.1 °C 2071-2100 compared to the recorded river temperatures in 1971-2000 [66]. ...
Article
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Urban areas with dark and impermeable surfaces are known to have a heating effect on air and still water compared to surrounding areas, called the urban heat island effect (UHI). UHI and stormwater discharges’ collective impact on stream temperature, especially regarding seasonal changes, is a less-studied field. In this study, the temperature effect of the urban village Aarslev on Stream Vindinge in Southern Denmark was examined. Loggers (ID A–L) were placed in Stream Vindinge in 2020–2021, measuring temperature (°C) and pressure (kPa). Outlets were analyzed with respect to origin: Direct stormwater outlets (rain ÷ basin), stormwater delayed by ponds (rain + basin), common overflow, and common sewage from WWTP. Data showed the stream temperature rise through Aarslev village in all months (except March) with 0.3–1.9 °C, most notably in the summer months. A one-way ANOVA confirmed that the upstream station A and downstream station K were significantly different (p-values < 0.001). No significant difference in temperatures between the different outlet types was found. An increase in stream temperature was observed in response to rain events, followed by a temperature decrease. This was assumed to be a “first heat flush”. This was speculated to mean less optimal conditions for trout and sensitive macroinvertebrates not because of heat shock, but rather to lower O2 concentrations and higher mineralization. River and lake temperatures are projected to increase, and this effect might become more pronounced. A decrease in stream temperature was observed after the village (station L). Therefore, it was concluded that the rise in temperature through the village was due to UHI.
... The results are also comparable with the other studies in Europe. For example, Orr et al. (2015) found that during the 17-year period (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006), annual mean RWT increased by 0.3 • C per decade on average for rivers in England and Wales; the results of Arora et al. (2016) showed that annual mean RWT increased by 0.3 • C per decade on average during 1985-2010 for seven river basins of Germany. Fig. 5 presented the ratio of warming rate of RWT and T a . ...
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Study region The study region comprises 125 water gauges from 70 rivers covering the whole territory of Poland. Study focus The air2stream model was used to reconstruct daily river water temperature (RWT) from 125 water gauges in 70 Polish rivers for the period 1966–2020 (55 years). Then, the annual and seasonal warming trends of RWT, and a biologically relevant metric (the annual number of days when water temperature exceeded 20 °C) were evaluated. New hydrological insights for the region The modelling results showed that the air2stream model performed well for RWT modeling (the averaged Root Mean Square Error (RMSE) values for the calibration and validation periods are 1.21 and 1.32 °C, and Nash-Sutcliffe efficiency coefficient (NSE) for the two periods are 0.96 and 0.95 respectively). Annual averaged RWT of 121 gauges (96.8 % of the 125 gauges) showed clear warming trend in the past 55 years with the warming rate ranging between 0.08 and 0.44 °C/decade (average: 0.25 °C/decade). The warming trends of river waters on the main rivers and their tributaries are spatially differentiated. Seasonal RWT trends showed that summer is warming fastest, followed by spring and then by autumn and winter. Long-term increases in RWT were typically correlated with increases in air temperatures. For the three large rivers (Vistula, Odra, and Warta), the biologically relevant metric (the annual number of days when water temperature exceeded 20 °C) increased synchronously with the warming of RWT. The results reported in this study will be useful to stakeholders and the reconstructed dataset will be useful to the community for the further study of river thermal dynamics and aquatic habitats in Poland.
... While only a slight increase in water temperatures was found at Palzem, the mean temperatures of the river Rhine increased by 1.7 °C at the Upper Rhine and by 1.2 °C (0.36 °C per decade) in Koblenz (Middle Rhine) between 1978 and 2011 [12]. Similar trends of 0.3 °C per decade were observed for the Elbe and Danube [13] and for Northern and Eastern Germany [14]. In the UK [15], river warming was less pronounced (0.22 °C per decade), with April being the fastest-warming month (+0.63 °C per decade on average). ...
Article
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Reductions in industrial pollutant loads and the introduction and modernization of wastewater treatment facilities have improved the quality of inland waters in Europe and elsewhere, but climatic change, changes in runoff and the legacy of mine wastes may increase pressures on many aquatic environments. In the present study, data obtained by monitoring the French–German river are collated to visualize long-term trends in the pollution, river discharges and temperatures of Moselle waters. While air temperatures and accumulated heat sums in the catchment area showed an upward trend, precipitation and discharge levels as well as river temperatures were less affected by the ongoing climatic change. At the same time, the electric conductivity, i.e., the total suspended solids, did not show the anticipated reductions, while oxygen levels and pH values have showed upward trends since the 1990s. Despite the improvements in classical water quality parameters, the flooding of abandoned mines, increased water abstraction for cooling and agriculture and untreated old and emerging pollutants may aggravate environmental problems in the future. Climatic change will probably modify the runoff of pollutant loads by increasing the severity of flash floods and by concentrating water pollutants in drought spells.
... Interest in studying the impact of the development of water temperature processes in open watercourses concerns numerous ecological and other aspects that have proliferated in recent decades (e.g., [10][11][12][13][14][15][16][17][18][19][20], etc.). Open watercourses are under pressure from global climate change and aggressive and poorly controlled anthropogenic interventions. ...
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The air temperature trends measured at the central meteorological station Varaždin and the water temperature measured at the Botovo station on the Drava River were analyzed from 1 January 1969 to 31 December 2021. Analyses were performed for three different time scales: year, month, and day. Mann–Kendall testing statistically determined the significant trends over the analyzed period and found increasing air and water temperatures. From 1975 to 1989, three reservoirs of different volumes and water surface areas were built. The Botovo water measuring station is 11 km from the third largest reservoir and 28 km from the mouth. Applying the day-to-day (DTD) method, we determined that the variations in the daily air temperatures are significantly higher than the simultaneous variations in the daily water temperatures. Also, the rise in water temperatures at the downstream water measuring station Botovo was influenced by the construction of reservoirs. The commissioning of the second reservoir in 1982 caused a significant rise in water temperature at the Botovo station. Trends in water temperature increase during all months of the year were statistically significant, while air temperature trends were statistically significant during the warm parts of the year.
... One of the most elementary water properties is its temperature, which considerably determines the course of all processes that occur in water. Considering the currently observed [1,2] as well as forecasted climate changes [3,4], as well as the close relationship between air and water temperature [5,6], knowledge on these relationships is particularly important. Numerous studies point to an increase in the temperature of inland waters [7,8], which plays and will continue to play an important role in the transformation of their properties. ...
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Water temperature in rivers is the key property determining the biotic and abiotic processes occurring in these ecosystems. In many regions of the world, the significant lack of measurement data is a serious problem. This paper presents reconstruction of water temperature for selected Polish rivers with monitoring discontinued in the period 2015–2020. Information regarding air temperature and water temperature in lakes provided the basis for the comparison of three models: multiple linear regression, random forest regression, and multilayer perceptron network. The results show that the best reconstruction results were obtained with a multilayer perceptron network model based on water temperatures in the lake and air temperatures from three meteorological stations. The average values of mean error, root mean square error and standard error were for the rivers in Poland: 1.52 °C, 5.03%, and 0.47 °C. The course of mean yearly water temperature in the years 1987–2020 showed a statistically significant increase from 0.18 to 0.49 °C per decade. The results show that the largest increases occurred in June, August, September, November, and December.
... In our case, a handful of important variables was sufficient to predict in-stream NO 3 removal (NO 3 concentration, water temperature) and floodplain denitrification rates (flood duration, soil fine material content, NO 3 concentration) reasonably well. While, we estimated the water temperature from the air temperature, it is to a lesser degree also dependent on other factors including average and low flow (Arora et al., 2016). However, considering these additional factors would only slightly improve our estimates for the Table 2 Total nitrogen (TN) emissions, loads and removal in the river systems. ...
Article
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Floodplains remove nitrate from rivers through denitrification and thus improve water quality. The Danube River Basin (DRB) has been affected by elevated nitrate concentrations and a massive loss of intact floodplains and the ecosystem services they provide. Restoration measures intend to secure and improve these valuable ecosystem services, including nitrate removal. Our study provides the first large-scale estimate of the function of large active floodplains in the DRB to remove riverine nitrate and assesses the contribution of reconnection measures. We applied a nutrient emission model in 6 river systems and coupled it with denitrification and flooding models which we adapted to floodplains. The floodplains have the capacity to eliminate about 33,200 t nitrate-N annually, which corresponds to 6.5 % of the total nitrogen emissions in the DRB. More nitrate is removed in-stream at regular flow conditions than in floodplain soils during floods. However, increasing frequently inundated floodplain areas reveals greater potential for improvement than increasing the channel network. In total, we estimate that 14.5 % more nitrate can be removed in reconnected floodplains. The largest share of nitrogen emissions is retained in the Yantra and Tisza floodplains, where reconnections are expected to have the greatest impact on water quality. In absolute numbers, the floodplains of the lower Danube convert the greatest quantities of nitrate, driven by the high input loads. These estimates are subject to uncertainties due to the heterogeneity of the available input data. Still, our results are within the range of similar studies. Reconnections of large floodplains in the DRB can, thus, make a distinct contribution to improving water quality. A better representation of the spatial configuration of water quality functions and the effect of floodplain reconnections may support the strategic planning of such to achieve multiple benefits and environmental targets.
... Resulting reduced DO levels can affect stream metabolism, chemical reactions and nutrient cycling (Hoak, 1961;Kinouchi et al., 2007;Poole and Berman, 2001). A general increase of such effects can be expected by global warming (Arora et al., 2016;Webb and Walling, 1992). For instance Song et al. (2018) suggested that global increases of River mouths at confluences and estuaries are integral reflectors of catchments and their water quality depending on factors including geology, geomorphology, hydrological conditions, land cover, climate and human interactions (Lintern et al., 2018;Pinckney et al., 2001). ...
Thesis
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Oxygen and carbon cycles play a pivotal role for the functioning of terrestrial freshwater ecosystems because both are indicators of energy storage and transfer with large scale relevance for global climate. Their availabilities are strongly influenced by the balances of abiotic and biotic sinks and sources with photosynthesis (P), ecosystem respiration (R), air-water gas exchange (G) and water mixing as the most important ones. However, anthropogenic transformations of natural environments and ongoing climate change have increasingly outbalanced these processes, resulting in a reduced species diversity and degradation of ecosystem services for man and nature. To deepen our understanding of oxygen and carbon cycles in aqueous environments investigations of their stable isotopes (expressed as δ18O, δ13C) have proven valuable to differentiate sources and sinks. New combinations of traditional freshwater monitoring approaches with such sophisticated methods might help to develop improved management strategies to counteract continuing degradation of freshwater habitats. In this thesis a comprehensive literature review combined with statistical analyses provides detailed understanding of dissolved oxygen (DO) transfer and turnover processes in river networks that integrate ecological states of entire catchments. This is particularly important because rivers connect surface and subsurface aquatic compartments including lakes, reservoirs, dams, hyporheic zones (HZs), soil waters, springs and groundwaters. With the relevance of DO for aerobic life and a myriad of redox processes, most important sinks and sources in these compartments are addressed. Special attention is given to DO cycles in HZs as a biogeochemically highly active mixing zone of river- and groundwater. Here, so far poorly understood processes such as the iron cycle and residence times of DO are elucidated in greater detail. In addition to this literature review, statistical analyses of the GLobal RIver CHemistry (GLORICH) database indicated a dominance of DO-undersaturated river waters, as well as a negative global trend of DO concentrations at higher water temperatures due to reduced physical solubilities. These analyses could determine critical thresholds of DO relationships between hydrochemistry and catchment properties including land use. This large-scale background served as a basis for a case study of three mid-latitude European headwater streams to obtain more detailed insights in site-specific diel DO and δ18ODO patterns also in context of land use types and proportions. With the first such application in Europe a new DO stable isotope modelling approach combined with detailed knowledge about land use backgrounds. The work helped to quantify key DO drivers P, R and G in each stream section. They revealed a clear trend with heterotrophic conditions at mostly forest-dominated stream sites up to dominance of P at stream sites with highest proportions of agricultural and urban land use proportions. Such small-scale investigations with modelling approaches are useful to estimate vulnerabilities of freshwater ecosystems with regard to future environmental changes. In a complementary study, a pond with seasonal cyanobacteria blooms was investigated with regard to its carbon cycle, including most important dissolved and particulate inorganic and organic phases (DIC, DOC, POC). This study helped to unravel dynamics and causes for the extreme primary productivity rates. DIC and POC concentrations and their respective stable isotope values (δ13CDIC, δ13CPOC) were the most dynamic carbon phases with highest POC concentrations and δ13CPOC values during pronounced growth periods. Such δ13CPOC increases are plausible for the carbon concentrating mechanism (CCM) of cyanobacteria, that enhanced incorporations of the 13C-enriched bicarbonate (HCO3−) when dissolved CO2 (CO2(aq)) became depleted as the primary carbon source. These analyses also revealed unexpected critical thresholds of the activation of the CCM at a pCO2 below 150 µatm and a pH higher than 8.9. Such new understanding of highly dynamic carbon cycles in terrestrial freshwater systems can help to mitigate future deleterious effects of climate change and land use.
... It was caused by the negative effects of the human impact, including an increase in temperature in the majority of rivers as a result of climate warming. The rate of the increase in RT in the North Hemisphere over the last several decades was in a range from approximately 0.01 to more than 0.1 • C year − 1 (among others Kaushal et al., 2010;Arora et al., 2016). ...
Article
Temperature is one of the most important properties of rivers. Interest in river temperature (RT) has been rapidly increasing in the current period of climate change. It is related to among others the application of models for the development of scenarios of RT increase. The article presents an attempt to identify one of the most important elements of fluvial regime: river thermal seasons (RTS). No attempts have been undertaken to date to determine such seasons, although they are among the most important elements of fluvial regime. This paper proposes another approach to the issue of changes in RT. It involves the designation of river thermal seasons RTS based on unique daily data from a period 1961-2020. The thermal season was defined as a sequence of days with intrinsic similarity resulting from mean multiannual water temperature, its variability in the multiannual period, and autocorrelation. A total of 18 types of RTS were designated in 5 groups of RTS: very cold (0.0-1.0°C), cold (1.1- 4.0°C), moderate (4.1-10.0°C), warm (10.1-15.0°C), and very warm (15.1-20.0°C). Moroever, two sub-periods were designated: namely 1961-1992 and 1993-2020, permitting the identification of the character of RTS in both sub-periods, and the assessment of changes in their distribution. The applied method allowed for conducting comparative analyses between rivers of various sizes. The occurrence of different thermal seasons was evidenced, as well as various directions and effects of changes resulting from climate warming. The greatest contribution in a year was reached by the group of very warm seasons (34.9%). In comparison with sub-period 1961-1992, it increased by 5.1%. A smaller share was determined for the group of cold seasons (29.0%) which also increased (by 10%) in comparison to the earlier sub-season. An increase in the contribution of cold seasons resulted from a considerable reduction of the duration of seasons from the moderate (from 27.5% to 16.5%) and very cold group (from 9.1% to 1.7%). The proposed study method is universal. It can be applied to analyses of river temperature in other climate zones.
... In addition to the observed warming of air temperature, this study shows that the stream water warmed significantly since 2003, 20 ÷ 25 years after the rise of air temperature and at a rate of 0.22 ∘ C y −1 between 2003 and 2020, similar to what was observed in the last decade in several streams, such as in northern Germany (Arora et al., 2016). In 2020, the annual mean of the maximum daily water temperature reached 8.1 ∘ C at 2642 m a.s.l. and 2.4 ∘ C at 2858 m a.s.l., with increments of 4.4 and 1.6 ∘ C, respectively, with respect to the pre-2003 averages. ...
Article
We evaluated the effect of global warming on invertebrate communities at high altitudes using data from the Careser system. We procured data on air temperature, which was obtained over 50 years at altitudes above 2600 m a.s.l., and data on water temperature, which was available for approximately 30 years. We sampled thrice in the past 20 years (2001, 2014, 2018) at three sampling sites (CR0-metakryal, CR1-hypokryal, CR2-glacio-rhithral) of the Careser glacier-fed stream and its main non-glacial tributary (CR1bis-krenal). Warmer climates were observed in the last decade compared to the 1980s, with a mean maximum summer air temperature (mTmax) increase of 1.7 °C at 2642 m a.s.l. and 1.8 °C at 2858 m a.s.l. Compared to air temperatures, the rise in water temperature was delayed by approximately 20 years; water mTmax started to increase in 2003, reaching 8.1 °C at 2642 m a.s.l. and 2.4 °C at 2858 m a.s.l in the year 2020. The invertebrate community exhibited a delayed response approximately 13 years from the water warming; there was a sequential increase in the number of taxa, Shannon diversity, and after 17 years, functional diversity. In the kryal sites, taxonomical and functional diversity changed more consistently than in the glacio-rhithral site in the same period, due to the arrival of taxa that were previously absent upstream and bearers of entirely new traits. Progressive taxonomical homogenisation was evident with decreasing glacial influence, mainly between glacio-rhithral and krenal sites. The numbers of Diamesa steinboecki, an insect that was adapted to the cold, declined in summer (water mTmax >6 °C and air mTmax >12 °C). This study highlights the mode and time of response of stream invertebrate communities to global warming in alpine streams and provides guidelines for analysing changes in the stream invertebrate communities of other glacial systems in alpine regions.
... Deliberate nutrient addition could therefore mitigate some adverse effects of climate change by maintaining sufficient prey availability and supporting growth and production as streams warm. However, a further complication is that warmer downstream receiving waters may be more vulnerable to oligotrophication (Arora, Tockner & Venohr, 2016;Bolotov et al., 2018). ...
Article
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1. Freshwater catchments can experience nutrient deficits that result in reduced primary and secondary productivity. The most commonly limiting nutrients are nitrogen and phosphorus, either separately or together. This review considers the impact of increasing nutrient limitation in temperate basin stream and river systems, focusing on upland areas that currently or previously supported wild Atlantic salmon (Salmo salar) populations. 2. Anthropogenic changes to land use and increases in river barriers have altered upland nutrient dynamics, with particular impacts on salmon and other migratory fish species which may be net importers of nutrients to upland streams. Declining salmon populations may further reduce nutrient sources, reducing ecosystem and fisheries productivity below desired levels. 3. Experimental manipulations of nutrient levels have examined the impacts of this cultural oligotrophication. There is evidence that growth and biomass of juvenile salmon can be increased via appropriate additions of nutrients, offering potential as a conservation tool. However, further research is required to understand the long-term effects of these additions on salmon populations and stream ecosystems, and to assess the vulnerability of downstream habitats to eutrophication as a result. 4. Although purposeful nutrient addition with the aim of enhancing and conserving salmonid populations may be justified in some cases, it should be undertaken in an adaptive management framework. In addition, nutrient addition should be linked to nutrient retention and processing, and integrated into large-scale habitat restoration and recovery efforts. 5. Both the scientific and the management community should recognize that the ecological costs and benefits associated with adding nutrients to salmon streams may change in a non-stationary world.
... For the Swiss Plateau catchments, the errors in river temperature (RMSE) obtained during the calibration and validation periods are far below the CC signal for RCP4.5 and RCP8.5, which underlines the robustness of the simulated trends. The results obtained are coherent with past and current observations in Switzerland and in central Europe (Moatar and Gailhard, 2006;Webb and Nobilis, 2007;Arora et al., 2016;Michel et al., 2020) and are in agreement with other results in the literature, both in terms of predicted changes in discharge and water temperature and in terms of processes and CC sensitivity Ficklin et al., 2014;Du et al., 2019;Leach and Moore, 2019;Wondzell et al., 2019;Muelchi et al., 2021a;Piotrowski et al., 2021). The studied catchments can be assumed to be representative of undisturbed Swiss catchments in general (Michel et al., 2020). ...
Article
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River ecosystems are highly sensitive to climate change and projected future increase in air temperature is expected to increase the stress for these ecosystems. Rivers are also an important socioeconomic factor impact-ing, amongst others, agriculture, tourism, electricity production , and drinking water supply and quality. In addition to changes in water availability, climate change will impact river temperature. This study presents a detailed analysis of river temperature and discharge evolution over the 21st century in Switzerland. In total, 12 catchments are studied, situated both on the lowland Swiss Plateau and in the Alpine regions. The impact of climate change is assessed using a chain of physics-based models forced with the most recent climate change scenarios for Switzerland including low-, mid-, and high-emission pathways. The suitability of such models is discussed in detail and recommendations for future improvements are provided. The model chain is shown to provide robust results, while remaining limitations are identified. These are mechanisms missing in the model to correctly simulate water temperature in Alpine catchments during the summer season. A clear warming of river water is modelled during the 21st century. At the end of the century (2080-2090), the median annual river temperature increase ranges between +0.9 °C for low-emission and +3.5 °C for high-emission scenarios for both lowland and Alpine catchments. At the seasonal scale, the warming on the lowland and in the Alpine regions exhibits different patterns. For the lowland the summer warming is stronger than the one in winter but is still moderate. In Alpine catchments, only a very limited warming is expected in winter. The period of maximum discharge in Alpine catchments, currently occurring during midsummer , will shift to earlier in the year by a few weeks (low emission) or almost 2 months (high emission) by the end of the century. In addition, a noticeable soil warming is expected in Alpine regions due to glacier and snow cover decrease. All results of this study are provided with the corresponding source code used for this paper.
... In addition to the observed warming of air temperature, this study shows that the stream water warmed significantly since 2003, 20 ÷ 25 years after the rise of air temperature and at a rate of 0.22 ∘ C y −1 between 2003 and 2020, similar to what was observed in the last decade in several streams, such as in northern Germany (Arora et al., 2016). In 2020, the annual mean of the maximum daily water temperature reached 8.1 ∘ C at 2642 m a.s.l. and 2.4 ∘ C at 2858 m a.s.l., with increments of 4.4 and 1.6 ∘ C, respectively, with respect to the pre-2003 averages. ...
Article
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It is known that pesticides and other organic pollutants are transported from lowlands and alpine valleys to high alpine summits, where they are stored in glaciers until melting occurs between July and September. In this study, we aimed to map glacial contamination by measuring the concentrations of currently used pesticides, synthetic fragrances, and polycyclic aromatic hydrocarbons (PAHs) in glacial and non-glacial meltwater from six sites in the Italian Alps located within the protected Adamello-Brenta Natural Park. We subsequently characterised the ecological risk of these contaminants to aquatic fauna. Chlorpyrifos, chlorpyrifos-methyl, terbuthylazine, galaxolide, tonalide, and PAHs were detected in July and September 2019 and 2020 across all sites. Risk characterisation indicated that PAHs posed a low risk to the alpine ecosystem at most of the sites, and medium risk was associated only with fluoranthene and pyrene at Mandrone in 2020. Regarding fragrances, herbicides, and chlorpyrifos-methyl, the calculated risk to aquatic biocenosis was acceptable under current European guidelines. Only chlorpyrifos posed an unacceptable risk to aquatic invertebrates at two sites: Amola (in July 2019) and Mandrone (in July and September 2019 and 2020). A risk refinement of chlorpyrifos, calculated using the species sensitivity distribution, indicated an acceptable level of risk, as concentrations were consistently below the effect level. Chlorpyrifos is not the only potential threat to Alpine aquatic ecosystems; therefore, it is advised to continue monitoring other equally potentially dangerous compounds that could reach high-altitude environments through medium-range atmospheric transport. To preserve the ecological and social value of the Adamello-Brenta Natural Park, natural capital is a priority. In this context, the results of this study assume strategic importance in supporting the development of future environmental conservation initiatives and water management policies.
... In addition to the observed warming of air temperature, this study shows that the stream water warmed significantly since 2003, 20 ÷ 25 years after the rise of air temperature and at a rate of 0.22 ∘ C y −1 between 2003 and 2020, similar to what was observed in the last decade in several streams, such as in northern Germany (Arora et al., 2016). In 2020, the annual mean of the maximum daily water temperature reached 8.1 ∘ C at 2642 m a.s.l. and 2.4 ∘ C at 2858 m a.s.l., with increments of 4.4 and 1.6 ∘ C, respectively, with respect to the pre-2003 averages. ...
... Due to climate change and anthropogenic activities, river thermal dynamics in many regions have undergone tremendous changes [1,9,14,28,44,49]. River damming, as one of the main human interventions to the river systems, plays a vital role in reshaping the river thermal conditions. ...
Article
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Background River damming inevitably reshapes water thermal conditions that are important to the general health of river ecosystems. Although a lot of studies have addressed the damming’s thermal impacts, most of them just assess the overall effects of climate variation and human activities on river thermal dynamics. Less attention has been given to quantifying the impact of climate variation, damming and flow regulation, respectively. In addition, for rivers that have already faced an erosion problem in downstream channels, an adjustment of the hydroelectric power plant operation manner is expected, which reinforces the need for understanding of flow regulation’s thermal impact. To fill this gap, an air2stream -based approach is proposed and applied at the Włocławek Reservoir in the Vistula River in Poland. Results In the years of 1952–1983, downstream river water temperature rose by 0.31 ℃ after damming. Meanwhile, the construction of dam increased the average annual water temperature by 0.55 ℃, while climate change oppositely made it decreased by 0.26 ℃. In addition, for the seasonal impact of damming, autumn was the most affected season with the warming reached 1.14 ℃, and the least affected season was winter when water temperature experienced a warming of 0.1 ℃. The absolute values of seasonal average temperature changes due to flow regulation were less than 0.1 ℃ for all the seasons. Conclusions The impacts of climate variation, damming, and flow regulation on river water temperatures can be evaluated reasonably on the strength of the proposed methodology. Climate variation and damming led to general opposite impacts on the downstream water temperature at the Włocławek Reservoir before 1980s. It is noted that the climate variation impact showed an opposite trend compared to that after 1980s. Besides, flow regulation below dam hardly affected downstream river water temperature variation. This study extends the current knowledge about impacts of climate variation and hydromorphological conditions on river water temperature, with a study area where river water temperature is higher than air temperature throughout a year.
... Due to the influence of many factors which shape the features of the thermal regime of waters, predictions of changes and forecasts of TRW are a complex process [3]. Predictive and prognostic models of TRW changes take into account relationships with meteorological and hydrological factors, as well as morphological parameters [4][5][6][7]. Brosofske et al. [8], conducting research in western Washington, showed that significant changes in the reference characteristics of RWT are also caused by the features of the microclimate in the riparian zones of streams, which are often transformed by various forms of anthropogenic activity. In their opinion, a buffer 45 m wide (on each side of the stream) is necessary to maintain a natural riparian microclimatic environment along the streams. ...
Article
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The temperature of river water (TRW) is an important factor in river ecosystem predictions. This study aims to compare two different types of numerical model for predicting daily TRW in the Warta River basin in Poland. The implemented models were of the stochastic type-Auto-regressive (AR), Moving Average (MA), Autoregressive Moving Average (ARMA) and Autoregres-sive Integrated Moving Average (ARIMA)-and the artificial intelligence (AI) type-Adaptive Neuro Fuzzy Inference System (ANFIS), Radial Basis Function (RBF) and Group Method of Data Handling (GMDH). The ANFIS and RBF models had the most fitted outputs and the AR, ARMA and ARIMA patterns were the most accurate ones. The results showed that both of the model types can significantly present suitable predictions. The stochastic models have somewhat less error with respect to both the highest and lowest TRW deciles than the AIs and were found to be better for prediction studies, with the GMDH complex model in some cases reaching Root Mean Square Error (RMSE) = 0.619 °C and Nash-Sutcliff coefficient (NS) = 0.992, while the AR(2) simple linear model with just two inputs was partially able to achieve better results (RMSE = 0.606 °C and NS = 0.994). Due to these promising outcomes, it is suggested that this work be extended to other catchment areas to extend and generalize the results.
... Given overall trends of stream warming due to climate change, the constriction and loss of habitat that supports coldwater species, such as salmonids, is a particular concern in land and water management [8,[12][13][14]. Globally, warming of thermal landscapes are a direct product of climate change [15][16][17]. Across the United States, projections show nearly 50% of cold-water habitat could be lost due to climate change [8,18], though this decline varies widely depending on species, their thermal constraints, and landscape resistance to dispersal [18]. These changes are compounded by the regulation effects of dams. ...
Article
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Stream temperature science and management is rapidly shifting from single-metric driven approaches to multi-metric, thermal regime characterizations of streamscapes. Given considerable investments in recovery of cold-water fisheries (e.g., Pacific salmon and other declining native species), understanding where cold water is likely to persist, and how cold-water thermal regimes vary, is critical for conservation. California’s unique position at the southern end of cold-water ecosystems in the northern hemisphere, variable geography and hydrology, and extensive flow regulation requires a systematic approach to thermal regime classification. We used publicly available, long-term (> 8 years) stream temperature data from 77 sites across California to model their thermal regimes, calculate three temperature metrics, and use the metrics to classify each regime with an agglomerative nesting algorithm. Then, we assessed the variation in each class and considered underlying physical or anthropogenic factors that could explain differences between classes. Finally, we considered how different classes might fit existing criteria for cool- or cold-water thermal regimes, and how those differences complicate efforts to manage stream temperature through regulation. Our results demonstrate that cool- and cold-water thermal regimes vary spatially across California. Several salient findings emerge from this study. Groundwater-dominated streams are a ubiquitous, but as yet, poorly explored class of thermal regimes. Further, flow regulation below dams imposes serial discontinuities, including artificial thermal regimes on downstream ecosystems. Finally, and contrary to what is often assumed, California reservoirs do not contain sufficient cold-water storage to replicate desirable, reach-scale thermal regimes. While barriers to cold-water conservation are considerable and the trajectory of cold-water species towards extinction is dire, protecting reaches that demonstrate resilience to climate warming remains worthwhile.
... Resulting reduced DO levels can affect stream metabolism, chemical reactions and nutrient cycling (Hoak, 1961;Kinouchi et al., 2007;Poole and Berman, 2001). A general increase of such effects can be expected by global warming (Arora et al., 2016;Webb and Walling, 1992). For instance Song et al. (2018) suggested that global increases of river water temperatures by 1 • C would increase their heterotrophic status by 24% which would then enhance DO consumption. ...
Article
Oxygen is one of the most crucial elements on earth and equally affects life and inorganic redox processes. After its transition to water with moderate solubility and slow diffusion rates, most aquatic organisms depend on permanent renewal of dissolved oxygen (DO). Recharge of this pivotal aqueous gas may become hampered by anthropogenic and climatic influences with so far unknown consequences for surface freshwater systems and entire ecosystems. Because rivers integrate biogeochemical information of catchments, their oxygen dynamics may also reflect ecosystem and landscape health. Here we summarize the most important sources and sinks of DO and its role in river systems. These considerations also extend to associated water compartments and fluxes including lakes, reservoirs, soils, groundwater and the hyporheic zone. In addition, for continental-scale considerations, we analysed the GLObal RIver CHemistry (GLORICH) database with 170,369 DO measurements. These analyses revealed that DO in rivers relates to water temperature, pH and nutrient availability. On larger scales, it is also influenced by catchment area, slope, ratios of forests to managed land and population density. Our review also highlights important links between physical and biological influences on DO transfer as well as its sources and sinks in streams and rivers. We conclude that DO monitoring should be combined with novel interdisciplinary tracing techniques such as stable isotope ratios, radon gas and biological analyses. Such combined analyses have the potential to improve our understanding of transfer and transformations of oxygen in rivers as essential integrators of landscapes.
... It should be emphasized that river water temperature is correlated with air temperature [42,43]. The statement was confirmed in three out of four cases analyzed in the paper, where the rate of increase in water temperature and the corresponding air temperatures in the nearest meteorological stations were similar. ...
Article
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The paper presents long-term changes in water temperature in two rivers, Oder and Neman, with catchments showing different climatic conditions (with dominance of marine climate in the case of the Oder and continental climate in the case of the Neman River). A statistically significant increase in mean annual water temperature was recorded for four observation stations, ranging from 0.17 to 0.39 °C dec−1. At the seasonal scale, for the winter half-year, water temperature increase varied from 0.17 to 0.26 °C dec−1, and for the summer half-year from 0.17 to 0.50 °C dec−1. In three cases (Odra-Brzeg, Odra-Słubice, Niemen-Grodno), the recorded changes referred to the scale of changes in air temperature. For the fourth station on Neman (Smalininkai), an increase in water temperature in the river was considerably slower than air temperature increase. It should be associated with the substantial role of local conditions (non-climatic) affecting the thermal regime in that profile. Short-term forecast of changes in water temperature showed its further successive increase, a situation unfavorable for the functioning of these ecosystems.
... We demonstrate the ability of the developed model chain to reliably simulate the water temperature of a variety of catchments over Switzerland. The results obtained for water temperature and discharge for the near future with 21 CC scenarios are 5 coherent with past and current observations in Switzerland and in central Europe (Moatar and Gailhard, 2006;Webb and Nobilis, 2007;Arora et al., 2016), and with other modelling studies using the same forcing scenarios over Switzerland. ...
Preprint
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Rivers are ecosystems highly sensitive to climate change and projected future increase in air temperature is expected to increase the stress for these ecosystems. Rivers are also an important socio-economical factor. In addition to changes in water availability, climate change will impact the temperature of rivers. This study presents a detailed analysis of river temperature and discharge evolution over the 21st century in Switzerland, a country covering a wide range of Alpine and lowland hydrological regimes. In total, 12 catchments are studied. They are situated both in the lowland Swiss Plateau and the Alpine regions and cover overall 10% of the country’s area. This represents the so far largest study of climate change impacts on river temperature in Switzerland. The impact of climate change is assessed using a chain of physics-based models forced with the most recent climate change scenarios for Switzerland including low, mid, and high emissions pathways. A clear warming of river water is modelled during the 21st century, more pronounced for the high emission scenarios and toward the end of the century. For the period 2030-2040, median warming in river temperature of +1.1°C for Swiss Plateau catchments and of +0.8°C for Alpine catchments are expected compared to the reference period 1990-2000 (similar for all emission scenarios). At the end of the century (2080-2090), the median annual river temperature increase ranges between +0.9°C for low emission and +3.5°C for high emission scenarios for both Swiss Plateau and Alpine catchments. At the seasonal scale, the warming on the Swiss Plateau and in the Alpine regions exhibits different patterns. For the Swiss Plateau, the spring and fall warming is comparable to the warming in winter, while the summer warming is stronger but still moderate. In Alpine catchments, only a very limited warming is expected in winter. A marked discharge increase in winter and spring is expected in these catchments due to enhanced snowmelt and a larger fraction of liquid precipitation. Accordingly, the period of maximum discharge in Alpine catchments, currently occurring during mid-summer, will shift to earlier in the year by a few weeks (low emission) or almost two months (high emission) by the end of the century. In summer, the marked discharge reduction in Alpine catchments for high emission scenarios leads to an increase in sensitivity of water temperature to low discharge, which is not observed in the Swiss Plateau catchments. In addition, an important soil warming is expected due to glacier and snow cover decrease. These effects combined lead to a summertime river warming of +6.0°C in Alpine catchments by the end of the century for high emission scenarios. Two metrics are used to show the adverse effects of river temperature increase both on natural and human systems. All results of this study along with the necessary source code are provided with this manuscript.
... Warming of stream water is observed in all seasons, but is more pronounced in summer than in winter, creating a gradually increasing winter to summer stream temperature difference, which agrees with results found by Moatar and Gailhard (2006), Webb and Nobilis (2007), and Arora et al. (2016) in France, Austria, and Germany, respectively. In spring, the water temperature trend is more pronounced than the air temperature trend (consistent with Huntington et al., 2003 andWebb andNobilis, 2007). ...
... Lower precipitation and runoff volumes in summer (under possitive NAO) favour more rapid heating and cooling of river flows, with less buffering by diminished groundwater inputs (Webb et al., 2003;Arora et al., 2016). Headwater streams are particularly vulnerable due to their relatively low volume of water, increasing their sensitivity to solar heating. ...
Article
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Water temperature (Tw) is a primary determinant of river ecosystem health and function that is strongly controlled by climate variability and change but mediated by catchment properties. We apply a nested analysis to: (1) evaluate how annual and seasonal mean Tw varied across England during the period 2000–2018; (2) assess the extent to which these regional-temporal dynamics correlate with the North Atlantic Oscillation (NAO); and (3) quantify the impact of local climate variability on modelled daily maximum Tw for open, shaded and spring-fed river reaches. Such information is used to identify sentinel locations for long-term monitoring and reporting, to evaluate the true benefit of riparian shade management, and to assess the impacts of climate change on Tw. We draw on a national archive of nearly 1 million Tw values and data from a high-resolution field experiment in central England. Nationally, annual mean Tw changed by −0.4 °C/decade over the period 2000 to 2018, broadly in line with Central England Temperatures, although summer Tw changed by +0.6 to +1.1 °C/decade in parts of central and northern England. There were significant associations between summer Tw and NAO (rho = 0.64, p
... These changes in air temperature determine in turn the water temperature, as water temperature tracks air temperature (shown for European streams by Webb and Nobilis, 1994;Langan et al., 2001;Mouthon and Daufresne, 2006). In this direction, a recent analysis of river temperature trends in northern Germany reported a mean warming trend of 0.03ºC year -1 over the period 1985-2010 (Arora et al., 2016), that is, 1.05ºC increase over the considered period. However, meteorological time series reveal not only a trend of increasing air temperature values but also an increase in the frequency and magnitude of extreme events (i.e., heat waves; Benestad, 2004). ...
... With these data, the annual mean and minimum (consisting of the mean temperature from the months December, January and February) temperature from the year of the sampling as well as the maximum (consisting of the mean temperature from the months June, July and August) temperature of the year prior to sampling were estimated for each site and year [40]. Air temperature was used as a proxy for water temperature [33,34] due to the lack of water temperature measurements with adequate and comparably high temporal and spatial resolution and the strong linear relationship with stream temperature [3,17,38]. We further collected data on annual precipitation from the German Meteorological Service (www.dwd.de) and openly available information on land use changes from 2000 and 2012 using the CORINE land use dataset from the metadata catalog of the Federal Environment Agency (www.gis.uba.de). ...
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Background Benthic invertebrate communities are an integral and longstanding component of stream biomonitoring. However, multiple stressors driven by global change threaten benthic invertebrate communities. In particular, climate warming is expected to disrupt freshwater ecosystems. While an increasing number of studies have shown changes in benthic invertebrate community composition in response to climate warming, the effect on stream assessments has rarely been investigated. As several community composition metrics are also used in stream assessments, we predicted that climate warming would worsen stream assessment results. Therefore, we used a comprehensive data set of 2865 benthic invertebrate samples taken between 2000 and 2014 from small central European low mountain streams. We examined the effects of changes in temperature on common community and stream assessment metrics. We used 31 metrics covering composition, richness, tolerance and function of communities, of which many are used in various stream assessment schemes. Results Against our expectations, we identified a decreasing air temperature trend of − 0.18 °C over 15 years. This trend was accompanied by significant changes in community composition, for example, increases in species richness and decreases in the community temperature index (CTI). Further, we identified slight concomitant improvements of various globally used stream quality assessment metrics, such as a decreasing saprobic index and an increasing BMWP. Conclusions While temperature increased by + 0.9 °C during the past 30 years (1985–2014), our 15-year study period (2000–2014) showed a decrease by − 0.18 °C. Therefore, we regard the concomitant improvement in several assessment metrics as a recovery from prior increasing temperatures. In turn, we assume that increases in water temperature will lead to opposite effects and therefore cause declining assessment results. Water managers should be aware of this linkage that in turn could provide a chance to mitigate the effects of global warming by, for example, planting trees along the rivers and the removal of artificial barriers to increase current velocity to minimize a warming effect.
... First, the role of climatic changes was assessed by estimating the relations between the mean monthly temperature in the range 1998-2018 and the observed trends of diversity indexes. Mean air temperature can be considered a valid proxy for watercourses temperature, when time series for water temperature are not available (Arora et al., 2016;Culler et al., 2018;Isaak et al., 2012;Laizé et al., 2017;Orr et al., 2015;Piccolroaz et al., 2018;Pletterbauer et al., 2018), especially when considering long term trends. Spring fed rivers can show a buffered response to air temperature excursions, yet their long term trends are in general well correlated (Beaufort et al., 2020;Kurylyk et al., 2014). ...
Article
Freshwater fish communities are impacted by multiple pressures, determining loss of functional diversity and redundancy. Our aim was to disentangle the roles and relevancies of different pressures in shaping fish communities in small streams of the Po plain (North Italy). Long term trend (1998–2018) of functional diversity of 31 fish communities was assessed and modeled in respect to three potential pressures: temperature increase, intensity of exotic fish invasion, and habitat quality degradation. Ecological traits mostly influenced by the pressures were also identified. Reduction of functional richness mostly due to local extinction or contraction of cold adapted predators, such as salmonids, was linked to increasing temperatures. Warming probably also led to a shift of generalist and dominant species, which became more abundant in streams hosting mixed communities of salmonids and cyprinids, and determined the increase of functional dispersion and uniqueness. Reduction of functional redundancy and increasing functional dispersion were both also related to the introduction of new ecological traits brought by expanding exotic species. Low functional overlap was found among native and exotic species, indicating that the invasion process was mainly controlled by competitive interactions and/or resource opportunism. Functional response to habitat quality was not clearly evident. In conclusion, the impact of temperature increase and exotic species on fish functional diversity was effective, idiosyncratic and mediated by the scale of analysis and by the intensity of pressures.
... Although focusing on summer temperature only, our results imply that the warming rate has risen considerably in the last years, which was also found in other streams (e.g. accelerated warming of northern German streams in recent years in comparison to previous decades, Arora, Tockner, & Venohr, 2016). ...
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The accelerating climate crisis intensifies environmental changes in high-altitude ecosystems worldwide, with rising air temperature among the main stressors. While past research in Alpine streams has primarily focused on how retreating glaciers might affect the ecology of glacier-fed streams on the long run, observations of real-time alterations of water temperature in such pristine environments are rare. Using long-term measurements of water temperature (2010-2017) together with datasets on benthic invertebrate communities from 18 glacial and non-glacial alpine and sub-alpine streams in the European Alps, we illustrate significant ecological relationships of water temperature regimes and the identity of benthic communities and forecast changes thereof due to considerable warming of stream water. Besides reporting multiannual warming of all observed streams during summer with a mean rate of 2.5 (±0.6) °C decade-1, this work re-defines temperature optima and ranges using robust regression modelling and thereby identifies potential winners and losers among the invertebrate species. We conclude that the various invertebrate taxa in Alpine stream networks will respond differently to thermal alterations and that the herein modelled temperature ranges of invertebrates is an essential step towards the understanding of future shifts in species distributions and success.
... Thackeray et al., 2016;Shrestha et al., 2018;Raman Vinna et al., 2018), and, in recent years especially frequently for climate change studies (e.g. Watts et al., 2015;Arora et al., 2016;Knouft and Ficklin, 2017;Leach and Moore, 2019;Paul et al., 2019). However, some doubts have been expressed regarding the usefulness of specific stream temperature models for studying the impact of climatic change on water temperatures in rivers (Arismendi et al., 2014, Leach and Moore, 2019, Wondziell et al., 2019. ...
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Although deep learning applicability in various fields of earth sciences is rapidly increasing, shallow multilayer-perceptron neural networks remain widely used for regression problems. Despite many clear distinctions between deep and shallow neural networks, some techniques developed for deep learning may help improve shallow models. Dropout, a simple approach to avoid overfitting by randomly skipping some nodes in a net during each training iteration, is among methodological features that made deep learning networks successful. In this study we give a review of dropout methods and empirically show that, when used together with early-stopping, dropout and its variant dropconnect could improve performance of shallow multi-layer perceptron neural networks. Shallow neural networks are applied to streamwater temperature modelling problems in six catchments, based on air temperature, river discharge and declination of the Sun. We found that when training of a particular neural network architecture that includes at least a few hidden nodes is repeated many times, dropout reduces the number of models that perform poorly on testing data, and hence improves the mean performance. If the number of inputs or hidden nodes is very low, dropout only disturbs training. However, nodes need to be dropped out with a much lower probability than in the case of deep neural networks (about 1%, instead of 10–50% for deep learning), due to a much smaller number of nodes in the network. Larger probabilities of dropping out nodes hinder convergence of the training algorithm and lead to poor results for both calibration and testing data. Dropconnect turned out to be slightly more effective than dropout.
... River water temperature without reservoir operation showed an increasing trend. The observed rate of increase in the mean water temperature during the last ten years before impoundment was 0.06 • C/year, among the highest rates observed globally in aquatic systems [61,62]. These rather rapid climatic changes proceeded in addition to reservoir construction and underlined the importance of also incorporating longer-term variability and trends into assessments and process-based analysis of the hydrological, thermal, and also biogeochemical and ecological impacts of cascading reservoirs. ...
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We analyzed the alteration of discharge and water temperature caused by two newly established reservoirs in the lower reaches of the Jinsha River. In comparison to longer-term observations from the pre-impoundment period, the seasonal flow variability was significantly affected by the larger, upstream-located Xiluodu reservoir, with higher discharge in spring and reduced discharge in summer. The smaller, downstream located Xiangjiaba reservoir did not contribute significantly to the total hydrological alteration caused by the reservoir cascade. Thermal stratification occurred in spring and summer in the Xiluodu reservoir, but was not observed in the Xiangjiaba reservoir. The vertical structure and seasonal dynamics of thermal stratification were mainly governed by the water temperature of the inflow and the depth of the water outlet. Despite the different thermal structure, both reservoirs reduced the amplitude of annual temperature variations and delayed the seasonal temperature cycle in the downstream river water. In contrast to discharge variation, thermal effects were cumulative along the cascading reservoirs. Homogenization and delay effects can be expected to increase further with the completion of ongoing reservoir construction upstream of the two studied reservoirs. Based on our findings, we discuss the larger-scale impacts of cascading hydropower developments and emphasize the need for taking water temperature and its variation into account when developing optimized operation or mitigation strategies for these systems.
... Apart from stream temperature forecasting (see e.g. Ouellet-Proulx et al., 2017 and references therein), stream temperature models are frequently needed to project the stream temperatures in future climatic conditions (Webb et al., 2008;Watts et al., 2015;Arora et al., 2016;Knouft and Ficklin, 2017;Soto, 2018), or to evaluate the water temperatures in rivers where it is not measured (Grabowski et al., 2016;Sohrabi et al., 2017;Jackson et al., 2017Jackson et al., , 2018. In such cases the applicability of physically-based models is limited, and hence simpler models are needed. ...
Article
Among various stream temperature models those based on nonlinear regression frequently attract attention due to their simplicity and small number of required variables. Among such approaches the logistic regression model developed twenty years ago for weekly data is still widely used in various scientific studies that require quick and simple calculation of stream water temperature. The model has been modified a number of times in recent years to capture the relationship between daily stream water temperatures, air temperatures and discharge. In this study, we propose further modifications of the logistic regression model that do not require any additional variables that may be hard to measure. The proposed models capture the relationship between the stream temperature and the declination of the Sun, the air temperature and the discharge from a number of recent observations. The proposed approaches are tested on six rivers located in diverse orographic conditions of temperate climate zones of Europe and USA. Although the proposed models remain very simple, their performances are competitive against the performances of more advanced semi-physical or data-driven models.
... Because stream temperature is more closely correlated with air temperature than with discharge [25], streams are generally expected to warm with climate change [26][27][28][29]. However, buffering sources are expected to moderate stream temperature into the foreseeable future [3,8]; shade is predicted to be a potentially significant buffer [14,22,25]. ...
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Until recently, stream temperature processes controlled by aquatic macrophyte shading (i.e., the riverine canopy) was an unrecognized phenomenon. This study aims to address the question of the temporal and spatial scale of monitoring and modeling that is needed to accurately simulate canopy-controlled thermal processes. We do this by using unmanned aerial vehicle (UAV) imagery to quantify the temporal and spatial variability of the riverine canopy and subsequently develop a relationship between its growth and time. Then we apply an existing hydrodynamic and water temperature model to test various time steps of canopy growth interpolation and explore the balance between monitoring and computational efficiencies versus model performance and utility for management decisions. The results show that riverine canopies modeled at a monthly timescale are sufficient to represent water temperature processes at a resolution necessary for reach-scale water management decisions, but not local-scale. As growth patterns were more frequently updated, negligible changes were produced by the model. Spatial configurations of the riverine canopy vary interannually; new data may need to be gathered for each growth season. However, the risks of inclement field conditions during the early growth period are a challenge for monitoring via UAVs at sites with access constraints.
... Some studies have noted trends over time in stream temperatures and attributed them to changing climate, but they were unable to unable to identify whether there were land use or riparian cover changes during the study periods (Arora et al., 2016;Kaushal et al., 2010;Isaak et al., 2012;Soto, 2016). Others have used air temperature over time as a surrogate of stream temperatures (Durance and Ormerod, 2007); these may overestimate or underestimate stream temperature trends. ...
Article
This paper presents retrospective simulations and future projections of daily time series of discharge and stream temperature for 52 278 reaches over the Loire River basin (10 5 km 2) in France, using a physical process-based thermal model coupled with a hydrological model. Retrospective simulations over the 1963-2019 are based on the Safran meteorological reanalysis over France. 21st century projections are based on a subset of the DRIAS2020 ensemble projection dataset, derived from the Euro Cordex data set through the ADAMONT statistical bias correction. Such a dataset at this large scale and high spatial resolution stands out from existing datasets, and is the first one in France derived from a physical process-based thermal model. The dataset is freely available for other studies and can be downloaded as NetCDF format from https://doi.org/10.57745/LBPGFS
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This paper presents retrospective simulations and future projections of daily time series of discharge and stream temperature for 52 278 reaches over the Loire River basin (105 km2) in France, using a physical process-based thermal model coupled with a hydrological model. Retrospective simulations over the 1963–2019 are based on the Safran meteorological reanalysis over France. 21st century projections are based on a subset of the DRIAS2020 ensemble projection dataset, derived from the Euro Cordex data set through the ADAMONT statistical bias correction. Such a dataset at this large scale and high spatial resolution stands out from existing datasets, and is the first one in France derived from a physical process-based thermal model. The dataset is freely available for other studies and can be downloaded as NetCDF format from https://doi.org/10.57745/LBPGFS (Seyedhashemi et al., 2022a).
Article
The alterations in the hydrosphere dynamics are undeniable. However, the analysis of hydrological alterations provides a benchmark to identify the potential environmental consequences and triggers of the evinced deviations. Hydra-Eflow is a free download and integrated hydro-informatics tool to assess gauged site discharge timeseries deviations for two non-concomitant samples through the Hydrologic Alteration Indices on Rivers (IAHRIS, acronym in Spanish). Its modules allow data quality verification, traditional frequency analysis, alteration analysis, and desktop environmental flow prescription. In addition, Hydra-Eflow supplies recommendations by an expert-based adjacency matrix to guide forward cascading studies and provide helpful rules for robust models. A case study at the Balsas River Basin is shown to verify the consistency of the information generated by Hydra-Eflow. Results show that 96 out of 129 hydrometric stations are altered due to changes in the discharge regime derived from the densified number of dams and impoundments in the streams for a wide range of purposes. Furthermore, the middle northern sub-basins exhibit a high alteration degree which may cause appalling water resources management since they submit more than 25% of the drinking water consumed in Mexico City. Finally, Hydra-Eflow supplied information to improve the heuristics of hydrologic alteration in the Balsas River Basin.
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Springs are considered relatively stable aquatic environments and possible thermal refugia for cold-adapted taxa under climate change. However, permanent and pristine spring fens in the Western Carpathians show between-site variation in thermal stability with significant effects on macroinvertebrate assemblages. In this study, we investigated the impact of the thermal stability on microcrustaceans (Harpacticoida, Ostracoda). We disentangled various parameters of thermal stability, such as mean summer and winter temperatures, annual amplitude, and daily fluctuations, and related it to mesoclimate, vegetation cover, and water table. We found that the relative abundance of cold-stenothermal species decreased significantly with increasing mean water temperature in summer, which had a significant effect on species composition. Surprisingly, ostracods were completely indifferent to thermal stability despite including cold-stenotherms and crenobionts, suggesting that these species might have broader thermal tolerance. In contrast, harpacticoids significantly responded to both summer and winter mean temperatures, showing upper and lower limits of thermal tolerance. While vegetation cover significantly suppressed daily fluctuations in summer, no effect of daily fluctuations on microcrustaceans was found. The effect of water table was also significant but independent of thermal stability. We assume that the less thermally stable sites will not support the occurrence of cold-stenothermic harpacticoids as air temperature rises. However, an increase in winter temperatures may results in higher overall abundance of harpacticoids. We discuss that the spring fens are probably most threatened by the combination of drought and increasing temperature.
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Stream temperature appears to be increasing globally, but its rate remains poorly constrained due to a paucity of long-term data and difficulty in parsing effects of hydroclimate and landscape variability. Here, we address these issues using the physically based thermal model T-NET (Temperature-NETwork) coupled with the EROS semi-distributed hydrological model to reconstruct past daily stream temperature and streamflow at the scale of the entire Loire River basin in France (105 km2 with 52 278 reaches). Stream temperature increased for almost all reaches in all seasons (mean ∘C decade−1) over the 1963–2019 period. Increases were greatest in spring and summer, with a median increase of + 0.38 ∘C (range to +0.76 ∘C) and +0.44 ∘C (+0.08 to +1.02 ∘C) per decade, respectively. Rates of stream temperature increases were greater than for air temperature across seasons for the majority of reaches. Spring and summer increases were typically greatest in the southern part of the Loire basin (up to +1 ∘C decade−1) and in the largest rivers (Strahler order ≥5). Importantly, air temperature and streamflow could exert a joint influence on stream temperature trends, where the greatest stream temperature increases were accompanied by similar trends in air temperature (up to +0.71 ∘C decade−1) and the greatest decreases in streamflow (up to −16 % decade−1). Indeed, for the majority of reaches, positive stream temperature anomalies exhibited synchrony with positive anomalies in air temperature and negative anomalies in streamflow, highlighting the dual control exerted by these hydroclimatic drivers. Moreover, spring and summer stream temperature, air temperature, and streamflow time series exhibited common change points occurring in the late 1980s, suggesting a temporal coherence between changes in the hydroclimatic drivers and a rapid stream temperature response. Critically, riparian vegetation shading mitigated stream temperature increases by up to 0.16 ∘C decade−1 in smaller streams (i.e. < 30 km from the source). Our results provide strong support for basin-wide increases in stream temperature due to joint effects of rising air temperature and reduced streamflow. We suggest that some of these climate change-induced effects can be mitigated through the restoration and maintenance of riparian forests.
Chapter
The Rhine is a 1233 km-long pivotal river in Central Europe. Its catchment harbors about 60 million inhabitants in nine countries from the Alps to the North Sea. On most of its course, this heavily modified water body is managed in favor of industrial production, urbanization, and transport. The 1816 commission on navigability was the first European institution. In the channelized and dammed Upper Rhine and in the Lower and Delta Rhine, several restoration actions combined with flood protection are underway. Being one of the most polluted water bodies in Europe after WWII, the river showed a remarkable water quality improvement in the past decades, due to efficient international collaboration. Several migratory fish species returned. Water plants established indicating reoligotrophication. However, its recent connectivity to the Ponto-Caspian area and sea harbors, homogenization of the main channel habitats, loss of natural flow regime, and strong water temperature increase make the Rhine a roundabout for invasive species.
Chapter
The British Isles, comprising the United Kingdom (Scotland, England, Wales, and Northern Ireland) and the Republic of Ireland, lies at the northwest Atlantic seaboard of Europe. The latitude and longitude ranges from around 50°N to 61°N and 2°E to 11°W. As the landmasses of mainland Britain and the island of Ireland are small, the sea is always close, and the rivers are small in comparison with continental Europe. Despite this, the area has marked differences in climate, geology, and population densities that result in a diverse range of rivers with distinctive physical, chemical, and ecological characteristics and varying degrees of human impact.
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In the majority of studies aiming at stream temperature warming due to climate change just a single water temperature model is used. Choosing a single model may highly impact the conclusions from the study. In this paper four relatively different empirical or semi-empirical models: perceptron neural networks, product unit networks, extended logistic regression and air2stream were applied to project the impact of climate change on water temperature in rivers located in temperate climatic zones of the USA and Poland. The models were driven by daily air temperature and streamflow projected by the rainfall-runoff model. In the first step, the models were calibrated and validated. Then the projections of water temperature were derived for the historical periods and two future periods taking into account: (a) climate simulations from the CORDEX initiative (NA-CORDEX and EURO-CORDEX), (b) the GR4J rainfall-runoff model and (c) different water temperature models. The obtained results indicate that due to global warming, the stream temperatures are expected to increase by about 1–2 °C for 2021–2050 and by 2–3 °C for 2071–2100 periods. These changes are not uniformly distributed throughout the year. The largest warming in the USA is found in the summertime, in Poland – in spring and autumn. For some months the discrepancies in the projected stream temperature between various stream temperature models are large. Product unit neural network, logistic regression-based model or air2stream occasionally led to projections that differ from those obtained by the majority of models even by 2 °C. We strongly recommend using at least a few stream temperature models for analysing the impact of climate change on water temperatures or the fate of the aquatic ecosystem.
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Water temperature is one of the most important indicators of aquatic system, and accurate forecasting of water temperature is crucial for rivers. It is a complex process to accurately predict stream water temperature as it is impacted by a lot of factors (e.g., meteorological, hydrological, and morphological parameters). In recent years, with the development of computational capacity and artificial intelligence (AI), AI models have been gradually applied for river water temperature (RWT) forecasting. The current survey aims to provide a systematic review of the AI applications for modeling RWT. The review is to show the progression of advances in AI models. The pros and cons of the established AI models are discussed in detail. Overall, this research will provide references for hydrologists and water resources engineers and planners to better forecast RWT, which will benefit river ecosystem management.
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Alpine headwaters in subarctic regions are particularly sensitive to climate change, yet there is little information on stream thermal regimes in these areas and how they might respond to global warming. In this paper, we characterize and compare the hydrological and thermal regimes of two subarctic headwater alpine streams within an empirical framework. The streams investigated are located within two adjacent catchments with similar geology, size, elevation and landscape, Granger Creek (GC) and Buckbrush Creek (BB), which are part of the Wolf Creek Research Basin in the Yukon Territory, Canada. Hydrometeorological and high‐resolution stream temperature data were collected throughout summer 2016. Both sites exhibited a flow regime typical of cold alpine headwater catchments influenced by frozen ground and permafrost. Comparatively, GC was characterized by a flashier response with more extreme flows, than BB. In both sites, stream temperature was highly variable and very responsive to short‐term changes in climatic conditions. On average, stream temperature in BB was slightly higher than in GC (respectively 5.8 °C and 5.7 °C), but less variable (average difference between 75th ‐ 25th quantiles of 1.6 °C and 2.0 °C). Regression analysis between mean daily air and stream temperature suggested that a greater relative (to stream flow) groundwater contribution in BB could more effectively buffer atmospheric fluctuations. Heat fluxes were derived and utilized to assess their relative contribution to the energy balance. Overall, non‐advective fluxes followed a daily pattern highly correlated to short‐wave radiation. Generally, solar radiation and latent heat were respectively the most important heat source and sink, while air‐water interface processes were major factors driving nighttime stream temperature fluctuations. This article is protected by copyright. All rights reserved.
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The Giant Freshwater Pearl Mussel (Margaritifera auricularia) is one of the rarest invertebrate species worldwide. This two-volume book aims to bring together all the so far available information on the species. Both volumes are independent books, although they can be seen as complimentary, giving scientific and technical information. They result from work by the authors in the context of the LIFE+ project 13BIO/FR/001162 „Conservation of the Giant Freshwater Pearl Mussel (Margaritifera auricularia) in Europe“ and include additional work by the contributors from other conservation and research projects. Volume 1 is dedicated to a synopsis of the current knowledge about the species, their biology and ecology, environmental impacts that have led to the reduction of the populations, as well suggestions to save this and other unionoid species in the Anthropocene. For a review on conservation and rearing techniques, please refer to Volume 2.
Book
Full-text available
The Giant Freshwater Pearl Mussel (Margaritifera auricularia) is one of the rarest invertebrate species worldwide. This two-volume book aims to bring together all the so far available information on the species. Both volumes are independent books, although they can be seen as complimentary, giving scientific and technical information. They result from work by the authors in the context of the LIFE+ project 13BIO/FR/001162 „Conservation of the Giant Freshwater Pearl Mussel (Margaritifera auricularia) in Europe“ and include additional work by the contributors from other conservation and research projects. Volume 1 is dedicated to a synopsis of the current knowledge about the species, their biology and ecology, environmental impacts that have led to the reduction of the populations, as well suggestions to save this and other unionoid species in the Anthropocene. For a review on conservation and rearing techniques, please refer to Volume 2.
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Streamflow observations from near-natural catchments are of paramount importance for detection and attribution studies, evaluation of large-scale model simulations, and assessment of water management, adaptation and policy options. This study investigates streamflow trends in a newly-assembled, consolidated dataset of near-natural streamflow records from 441 small catchments in 15 countries across Europe. The period 1962–2004 provided the best spatial coverage, but analyses were also carried out for longer time periods (with fewer stations), starting in 1932, 1942 and 1952. Trends were calculated by the slopes of the Kendall-Theil robust line for standardized annual and monthly streamflow, as well as for summer low flow and low flow timing. A regionally coherent picture of annual streamflow trends emerged, with negative trends in southern and eastern regions, and generally positive trends elsewhere (especially in northern latitudes). Trends in monthly streamflow for 1962–2004 elucidated potential causes for these changes, as well as other changes observed in hydrological regimes across Europe. Positive trends were found in the winter months in most catchments. A marked shift towards negative trends was observed in April, gradually spreading across Europe to reach a maximum extent in August. Low flows have decreased in most regions where the lowest mean monthly flow occurs in summer, but vary for catchments which have flow minima in winter and secondary low flows in summer. The study largely confirms findings from national and regional scale trend analyses, but clearly adds to these by confirming that these tendencies are part of coherent patterns of change, which cover a much larger region. The broad, continental-scale patterns of change are congruent with the hydrological responses expected from future climatic changes, as projected by climate models. The patterns observed could hence provide a valuable benchmark for a number of different studies and model simulations.
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Much study has been devoted to the possible causes of an apparent decrease in the upward trend of global surface temperatures since 1998, a phenomenon that has been dubbed the global warming "hiatus." Here we present an updated global surface temperature analysis that reveals that global trends are higher than reported by the IPCC, especially in recent decades, and that the central estimate for the rate of warming during the first 15 years of the 21st century is at least as great as the last half of the 20th century. These results do not support the notion of a "slowdown" in the increase of global surface temperature. Copyright © 2015, American Association for the Advancement of Science.
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The distribution and future fate of ectothermic organisms in a warming world will be dictated by thermalscapes across landscapes. That is particularly true for stream fishes and cold-water species like trout, salmon, and char that are already constrained to high elevations and latitudes. The extreme climates in those environments also preclude invasions by most non-native species, so identifying especially cold habitats capable of absorbing future climate change while still supporting native populations would highlight important refugia. By coupling crowd-sourced biological datasets with high-resolution stream temperature scenarios, we delineate network refugia across >250 000 stream km in the Northern Rocky Mountains for two native salmonids-bull trout (BT) and cutthroat trout (CT). Under both moderate and extreme climate change scenarios, refugia with high probabilities of trout population occupancy (>0.9) were predicted to exist (33-68 BT refugia; 917-1425 CT refugia). Most refugia are on public lands (>90%) where few currently have protected status in National Parks or Wilderness Areas (<15%). Forecasts of refuge locations could enable protection of key watersheds and provide a foundation for climate smart planning of conservation networks. Using cold water as a 'climate shield' is generalizable to other species and geographic areas because it has a strong physiological basis, relies on nationally available geospatial data, and mines existing biological datasets. Importantly, the approach creates a framework to integrate data contributed by many individuals and resource agencies, and a process that strengthens the collaborative and social networks needed to preserve many cold-water fish populations through the 21st century. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.
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Change in river water temperature has important consequences for the environment and people. This review provides a new perspective on the topic by evaluating changes in river water temperature for the UK over the 20th century and possible changes over the 21st century. There is limited knowledge of space-time variability in, and controls on, river temperature at the region scale and beyond over the 20th century. There is historical evidence that UK river temperature has increased in the latter part of the 20th century, but low agreement on the attribution of changes to climatic warming because river temperature is a complex, dynamic response to climate and hydrological patterns moderated by basin properties and anthropogenic impacts. Literature is scarce to evaluate changes to UK river temperature in the 21st century, but it appears as likely as not that UK river temperature will increase in the future. However, there are a number of interlinked sources of uncertainty (related to observations, scenarios, process interactions and feedback) that make estimating direction and rate of temperature change for rivers across the UK with confidence very challenging. Priority knowledge gaps are identified that must be addressed to improve understanding of past, contemporary and future river temperature change.
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Monthly mean air temperature (AT) at 85 sites and instantaneous stream-water temperature (WT) at 129 sites for 1960–2010 are examined for the mid-Atlantic region, USA. Temperature anomalies for two periods, 1961–1985 and 1985–2010, relative to the climate normal period of 1971–2000, indicate that the latter period was statistically significantly warmer than the former for both mean AT and WT. Statistically significant temporal trends across the region of 0.023 °C per year for AT and 0.028 °C per year for WT are detected using simple linear regression. Sensitivity analyses show that the irregularly sampled WT data are appropriate for trend analyses, resulting in conservative estimates of trend magnitude. Relations between 190 landscape factors and significant trends in AT-WT relations are examined using principal components analysis. Measures of major dams and deciduous forest are correlated with WT increasing slower than AT, whereas agriculture in the absence of major dams is correlated with WT increasing faster than AT. Increasing WT trends are detected despite increasing trends in streamflow in the northern part of the study area. Continued warming of contributing streams to Chesapeake Bay likely will result in shifts in distributions of aquatic biota and contribute to worsened eutrophic conditions in the bay and its estuaries.
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