TY - JOUR A1 - Schmidt, Lena Katharina A1 - Francke, Till A1 - Rottler, Erwin A1 - Blume, Theresa A1 - Schöber, Johannes A1 - Bronstert, Axel T1 - Suspended sediment and discharge dynamics in a glaciated alpine environment BT - identifying crucial areas and time periods on several spatial and temporal scales in the Ötztal, Austria JF - Earth surface dynamics N2 - Glaciated high-alpine areas are fundamentally altered by climate change, with well-known implications for hydrology, e.g., due to glacier retreat, longer snow-free periods, and more frequent and intense summer rainstorms. While knowledge on how these hydrological changes will propagate to suspended sediment dynamics is still scarce, it is needed to inform mitigation and adaptation strategies. To understand the processes and source areas most relevant to sediment dynamics, we analyzed discharge and sediment dynamics in high temporal resolution as well as their patterns on several spatial scales, which to date few studies have done. We used a nested catchment setup in the Upper Ötztal in Tyrol, Austria, where high-resolution (15 min) time series of discharge and suspended sediment concentrations are available for up to 15 years (2006–2020). The catchments of the gauges in Vent, Sölden and Tumpen range from 100 to almost 800 km2 with 10 % to 30 % glacier cover and span an elevation range of 930 to 3772 m a.s.l. We analyzed discharge and suspended sediment yields (SSY), their distribution in space, their seasonality and spatial differences therein, and the relative importance of short-term events. We complemented our analysis by linking the observations to satellite-based snow cover maps, glacier inventories, mass balances and precipitation data. Our results indicate that the areas above 2500 m a.s.l., characterized by glacier tongues and the most recently deglaciated areas, are crucial for sediment generation in all sub-catchments. This notion is supported by the synchronous spring onset of sediment export at the three gauges, which coincides with snowmelt above 2500 m but lags behind spring discharge onsets. This points at a limitation of suspended sediment supply as long as the areas above 2500 m are snow-covered. The positive correlation of annual SSY with glacier cover (among catchments) and glacier mass balances (within a catchment) further supports the importance of the glacier-dominated areas. The analysis of short-term events showed that summer precipitation events were associated with peak sediment concentrations and yields but on average accounted for only 21 % of the annual SSY in the headwaters. These results indicate that under current conditions, thermally induced sediment export (through snow and glacier melt) is dominant in the study area. Our results extend the scientific knowledge on current hydro-sedimentological conditions in glaciated high-alpine areas and provide a baseline for studies on projected future changes in hydro-sedimentological system dynamics. Y1 - 2022 U6 - https://doi.org/10.5194/esurf-10-653-2022 SN - 2196-632X SN - 2196-6311 VL - 10 IS - 3 SP - 653 EP - 669 PB - Copernicus Publications CY - Göttingen ER - TY - GEN A1 - Schmidt, Lena Katharina A1 - Francke, Till A1 - Rottler, Erwin A1 - Blume, Theresa A1 - Schöber, Johannes T1 - Suspended sediment and discharge dynamics in a glaciated alpine environment: identifying crucial areas and time periods on several spatial and temporal scales in the Ötztal, Austria T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Glaciated high-alpine areas are fundamentally altered by climate change, with well-known implications for hydrology, e.g., due to glacier retreat, longer snow-free periods, and more frequent and intense summer rainstorms. While knowledge on how these hydrological changes will propagate to suspended sediment dynamics is still scarce, it is needed to inform mitigation and adaptation strategies. To understand the processes and source areas most relevant to sediment dynamics, we analyzed discharge and sediment dynamics in high temporal resolution as well as their patterns on several spatial scales, which to date few studies have done. We used a nested catchment setup in the Upper Ötztal in Tyrol, Austria, where high-resolution (15 min) time series of discharge and suspended sediment concentrations are available for up to 15 years (2006–2020). The catchments of the gauges in Vent, Sölden and Tumpen range from 100 to almost 800 km2 with 10 % to 30 % glacier cover and span an elevation range of 930 to 3772 m a.s.l. We analyzed discharge and suspended sediment yields (SSY), their distribution in space, their seasonality and spatial differences therein, and the relative importance of short-term events. We complemented our analysis by linking the observations to satellite-based snow cover maps, glacier inventories, mass balances and precipitation data. Our results indicate that the areas above 2500 m a.s.l., characterized by glacier tongues and the most recently deglaciated areas, are crucial for sediment generation in all sub-catchments. This notion is supported by the synchronous spring onset of sediment export at the three gauges, which coincides with snowmelt above 2500 m but lags behind spring discharge onsets. This points at a limitation of suspended sediment supply as long as the areas above 2500 m are snow-covered. The positive correlation of annual SSY with glacier cover (among catchments) and glacier mass balances (within a catchment) further supports the importance of the glacier-dominated areas. The analysis of short-term events showed that summer precipitation events were associated with peak sediment concentrations and yields but on average accounted for only 21 % of the annual SSY in the headwaters. These results indicate that under current conditions, thermally induced sediment export (through snow and glacier melt) is dominant in the study area. Our results extend the scientific knowledge on current hydro-sedimentological conditions in glaciated high-alpine areas and provide a baseline for studies on projected future changes in hydro-sedimentological system dynamics. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1296 Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-576564 SN - 1866-8372 IS - 1296 SP - 653 EP - 669 ER - TY - JOUR A1 - Rottler, Erwin A1 - Vormoor, Klaus Josef A1 - Francke, Till A1 - Warscher, Michael A1 - Strasser, Ulrich A1 - Bronstert, Axel T1 - Elevation-dependent compensation effects in snowmelt in the Rhine River Basin upstream gauge Basel JF - Hydrology research : an international journal / Nordic Association of Hydrology ; British Hydrological Society N2 - In snow-dominated river basins, floods often occur during early summer, when snowmelt-induced runoff superimposes with rainfall-induced runoff. An earlier onset of seasonal snowmelt as a consequence of a warming climate is often expected to shift snowmelt contribution to river runoff and potential flooding to an earlier date. Against this background, we assess the impact of rising temperatures on seasonal snowpacks and quantify changes in timing, magnitude and elevation of snowmelt. We analyse in situ snow measurements, conduct snow simulations and examine changes in river runoff at key gauging stations. With regard to snowmelt, we detect a threefold effect of rising temperatures: snowmelt becomes weaker, occurs earlier and forms at higher elevations. Due to the wide range of elevations in the catchment, snowmelt does not occur simultaneously at all elevations. Results indicate that elevation bands melt together in blocks. We hypothesise that in a warmer world with similar sequences of weather conditions, snowmelt is moved upward to higher elevation. The movement upward the elevation range makes snowmelt in individual elevation bands occur earlier, although the timing of the snowmelt-induced runoff stays the same. Meltwater from higher elevations, at least partly, replaces meltwater from elevations below. KW - compensation effects KW - elevation-dependency KW - Rhine River KW - snowmelt KW - timing Y1 - 2021 U6 - https://doi.org/10.2166/nh.2021.092 SN - 2224-7955 VL - 52 IS - 2 SP - 536 EP - 557 PB - IWA Publ. CY - London ER - TY - JOUR A1 - Rottler, Erwin A1 - Vormoor, Klaus Josef A1 - Francke, Till A1 - Bronstert, Axel T1 - Hydro Explorer BT - an interactive web app to investigate changes in runoff timing and runoff seasonality all over the world JF - River research and applications N2 - Climatic changes and anthropogenic modifications of the river basin or river network have the potential to fundamentally alter river runoff. In the framework of this study, we aim to analyze and present historic changes in runoff timing and runoff seasonality observed at river gauges all over the world. In this regard, we develop the Hydro Explorer, an interactive web app, which enables the investigation of >7,000 daily resolution discharge time series from the Global Runoff Data Centre (GRDC). The interactive nature of the developed web app allows for a quick comparison of gauges, regions, methods, and time frames. We illustrate the available analytical tools by investigating changes in runoff timing and runoff seasonality in the Rhine River Basin. Since we provide the source code of the application, existing analytical approaches can be modified, new methods added, and the tool framework can be re-used to visualize other data sets. KW - global runoff database KW - interactive web app KW - R Shiny KW - runoff KW - seasonality KW - runoff timing Y1 - 2021 U6 - https://doi.org/10.1002/rra.3772 SN - 1535-1459 SN - 1535-1467 VL - 37 IS - 4 SP - 544 EP - 554 PB - Wiley CY - New York ER - TY - JOUR A1 - Rottler, Erwin A1 - Kormann, Christoph Martin A1 - Francke, Till A1 - Bronstert, Axel T1 - Elevation-dependent warming in the Swiss Alps 1981-2017 BT - Features, forcings and feedbacks JF - International journal of climatology : a journal of the Royal Meteorological Society N2 - Due to the environmental and socio-economic importance of mountainous regions, it is crucial to understand causes and consequences of climatic changes in those sensitive landscapes. Daily resolution alpine climate data from Switzerland covering an elevation range of over 3,000m between 1981 and 2017 have been analysed using highly resolved trends in order to gain a better understanding of features, forcings and feedbacks related to temperature changes in mountainous regions. Particular focus is put on processes related to changes in weather types, incoming solar radiation, cloud cover, air humidity, snow/ice and elevation dependency of temperature trends. Temperature trends in Switzerland differ depending on the time of the year, day and elevation. Warming is strongest during spring and early summer with enhanced warming of daytime maximum temperatures. Elevation-based differences in temperature trends occur during autumn and winter with stronger warming at lower elevations. We attribute this elevation-dependent temperature signal mainly to elevation-based differences in trends of incoming solar radiation and elevation-sensitive responses to changes in frequencies of weather types. In general, effects of varying frequencies of weather types overlap with trends caused by transmission changes in short- and long-wave radiation. Temperature signals arising from snow/ice albedo feedback mechanisms are probably small and might be hidden by other effects. KW - cloud cover KW - elevation dependency KW - mountain climate KW - snow KW - ice-albedo feedback KW - Swiss Alps KW - temperature trend KW - weather types Y1 - 2018 U6 - https://doi.org/10.1002/joc.5970 SN - 0899-8418 SN - 1097-0088 VL - 39 IS - 5 SP - 2556 EP - 2568 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Rottler, Erwin A1 - Francke, Till A1 - Bürger, Gerd A1 - Bronstert, Axel T1 - Long-term changes in central European river discharge for 1869–2016 BT - impact of changing snow covers, reservoir constructions and an intensified hydrological cycle JF - Hydrology and Earth System Sciences N2 - Recent climatic changes have the potential to severely alter river runoff, particularly in snow-dominated river basins. Effects of changing snow covers superimpose with changes in precipitation and anthropogenic modifications of the watershed and river network. In the attempt to identify and disentangle long-term effects of different mechanisms, we employ a set of analytical tools to extract long-term changes in river runoff at high resolution. We combine quantile sampling with moving average trend statistics and empirical mode decomposition and apply these tools to discharge data recorded along rivers with nival, pluvial and mixed flow regimes as well as temperature and precipitation data covering the time frame 1869-2016. With a focus on central Europe, we analyse the long-term impact of snow cover and precipitation changes along with their interaction with reservoir constructions. Our results show that runoff seasonality of snow-dominated rivers decreases. Runoff increases in winter and spring, while discharge decreases in summer and at the beginning of autumn. We attribute this redistribution of annual flow mainly to reservoir constructions in the Alpine ridge. During the course of the last century, large fractions of the Alpine rivers were dammed to produce hydropower. In recent decades, runoff changes induced by reservoir constructions seem to overlap with changes in snow cover. We suggest that Alpine signals propagate downstream and affect runoff far outside the Alpine area in river segments with mixed flow regimes. Furthermore, our results hint at more (intense) rain-fall in recent decades. Detected increases in high discharge can be traced back to corresponding changes in precipitation. KW - empirical mode decomposition KW - atmospheric blocking KW - heavy precipitation KW - streamflow trends KW - climate-change KW - rhine basin KW - time-series KW - events KW - Switzerland KW - variability Y1 - 2020 U6 - https://doi.org/10.5194/hess-24-1721-2020 SN - 1027-5606 SN - 1607-7938 VL - 24 IS - 4 SP - 1721 EP - 1740 PB - Copernicus CY - Göttingen ER - TY - GEN A1 - Rottler, Erwin A1 - Francke, Till A1 - Bürger, Gerd A1 - Bronstert, Axel T1 - Long-term changes in central European river discharge for 1869–2016 BT - Impact of changing snow covers, reservoir constructions and an intensified hydrological cycle T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Recent climatic changes have the potential to severely alter river runoff, particularly in snow-dominated river basins. Effects of changing snow covers superimpose with changes in precipitation and anthropogenic modifications of the watershed and river network. In the attempt to identify and disentangle long-term effects of different mechanisms, we employ a set of analytical tools to extract long-term changes in river runoff at high resolution. We combine quantile sampling with moving average trend statistics and empirical mode decomposition and apply these tools to discharge data recorded along rivers with nival, pluvial and mixed flow regimes as well as temperature and precipitation data covering the time frame 1869-2016. With a focus on central Europe, we analyse the long-term impact of snow cover and precipitation changes along with their interaction with reservoir constructions. Our results show that runoff seasonality of snow-dominated rivers decreases. Runoff increases in winter and spring, while discharge decreases in summer and at the beginning of autumn. We attribute this redistribution of annual flow mainly to reservoir constructions in the Alpine ridge. During the course of the last century, large fractions of the Alpine rivers were dammed to produce hydropower. In recent decades, runoff changes induced by reservoir constructions seem to overlap with changes in snow cover. We suggest that Alpine signals propagate downstream and affect runoff far outside the Alpine area in river segments with mixed flow regimes. Furthermore, our results hint at more (intense) rain-fall in recent decades. Detected increases in high discharge can be traced back to corresponding changes in precipitation. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1412 KW - empirical mode decomposition KW - atmospheric blocking KW - heavy precipitation KW - streamflow trends KW - climate-change KW - rhine basin KW - time-series KW - events KW - Switzerland KW - variability Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-517763 SN - 1866-8372 IS - 4 ER - TY - GEN A1 - Rottler, Erwin A1 - Bronstert, Axel A1 - Bürger, Gerd A1 - Rakovec, Oldrich T1 - Projected changes in Rhine River flood seasonality under global warming T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Climatic change alters the frequency and intensity of natural hazards. In order to assess potential future changes in flood seasonality in the Rhine River Basin, we analyse changes in streamflow, snowmelt, precipitation, and evapotranspiration at 1.5, 2.0 and 3.0 ◦C global warming levels. The mesoscale Hydrological Model (mHM) forced with an ensemble of climate projection scenarios (five general circulation models under three representative concentration pathways) is used to simulate the present and future climate conditions of both, pluvial and nival hydrological regimes. Our results indicate that the interplay between changes in snowmelt- and rainfall-driven runoff is crucial to understand changes in streamflow maxima in the Rhine River. Climate projections suggest that future changes in flood characteristics in the entire Rhine River are controlled by both, more intense precipitation events and diminishing snow packs. The nature of this interplay defines the type of change in runoff peaks. On the sub-basin level (the Moselle River), more intense rainfall during winter is mostly counterbalanced by reduced snowmelt contribution to the streamflow. In the High Rhine (gauge at Basel), the strongest increases in streamflow maxima show up during winter, when strong increases in liquid precipitation intensity encounter almost unchanged snowmelt-driven runoff. The analysis of snowmelt events suggests that at no point in time during the snowmelt season, a warming climate results in an increase in the risk of snowmelt-driven flooding. We do not find indications of a transient merging of pluvial and nival floods due to climate warming. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1164 Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-522962 SN - 1866-8372 ER - TY - JOUR A1 - Rottler, Erwin A1 - Bronstert, Axel A1 - Bürger, Gerd A1 - Rakovec, Oldrich T1 - Projected changes in Rhine River flood seasonality under global warming JF - Hydrology and earth system sciences : HESS / European Geosciences Union N2 - Climatic change alters the frequency and intensity of natural hazards. In order to assess potential future changes in flood seasonality in the Rhine River Basin, we analyse changes in streamflow, snowmelt, precipitation, and evapotranspiration at 1.5, 2.0 and 3.0 ◦C global warming levels. The mesoscale Hydrological Model (mHM) forced with an ensemble of climate projection scenarios (five general circulation models under three representative concentration pathways) is used to simulate the present and future climate conditions of both, pluvial and nival hydrological regimes. Our results indicate that the interplay between changes in snowmelt- and rainfall-driven runoff is crucial to understand changes in streamflow maxima in the Rhine River. Climate projections suggest that future changes in flood characteristics in the entire Rhine River are controlled by both, more intense precipitation events and diminishing snow packs. The nature of this interplay defines the type of change in runoff peaks. On the sub-basin level (the Moselle River), more intense rainfall during winter is mostly counterbalanced by reduced snowmelt contribution to the streamflow. In the High Rhine (gauge at Basel), the strongest increases in streamflow maxima show up during winter, when strong increases in liquid precipitation intensity encounter almost unchanged snowmelt-driven runoff. The analysis of snowmelt events suggests that at no point in time during the snowmelt season, a warming climate results in an increase in the risk of snowmelt-driven flooding. We do not find indications of a transient merging of pluvial and nival floods due to climate warming. Y1 - 2020 U6 - https://doi.org/10.5194/hess-25-2353-2021 SN - 1607-7938 SN - 1027-5606 VL - 25 IS - 5 SP - 2353 EP - 2371 PB - Copernicus Publications CY - Göttingen ER - TY - THES A1 - Rottler, Erwin T1 - Implementation of a snow routine into the hydrological model WASA-SED and its validation in a mountainous catchment T1 - Einbau einer Schneeroutine in das hydrologische Modell WASA-SED und deren Validierung in einem gebirgigen Einzugsgebiet N2 - In many regions of the world, snow accumulation and melt constitute important components of the hydrologic cycle. With the objective to improve model performance of the hydrological model WASA-SED (Water Availability in Semi-Arid environments - SEDiments) in catchments affected by snow and ice, a physically-based snow routine has been implemented into the model. The snow routine bases on the energy-balance method of the ECHSE (Eco-hydrological Simulation Environment) software. A first test application has been conducted in two sub-basins of the Isábena river catchment (Central Spanish Pre-Pyrenees). Results were validated using satellite-derived snow cover data. Furthermore, a rainfall gauge correction algorithm to restore the liquid precipitation signal of measurements affected by solid precipitation was applied. The snow module proved to be able to capture the dynamics of the snow cover forming during the cold months of the year. The temporary storage of water in the snow cover is able to improve simulations of river discharge. General patterns of the temporal evolution of observed and simulated snow cover fractions coincide. The work conducted only represents a first step in the process of implementation and evaluation of a physically-based snow routine into WASA-SED. Future work is necessary to further improve and test the snow routine and to resolve difficulties that occurred during model applications in the catchment. N2 - In vielen Gebieten der Erde stellen die Prozesse Schneeakkumulation und -schmelze einen wichtigen Bestandteil des Wasserkreislaufs dar. Im Bestreben, Simulationen des hydrologischen Modells WASA-SED (Water Availability in Semi-Arid environments - SEDiments) in Gebieten mit Schnee und Eis zu verbessern, wurde eine physikalisch basierte Schneeroutine in die Modellstruktur implementiert. Die Schneeroutine beruht auf der Energiebilanz-Methode der ECHSE-Software (Ecohydrological Simulation Environment). Eine erste Anwendung wurde in zwei Teileinzugsgebieten des Flusses Isábena (zentrale, spanische Pre-Pyrenäen) durchgeführt. Die Validierung der Ergebnisse erfolgte anhand satellitengestützter Schneebedeckungsdaten. Außerdem wurde ein Korrekturalgorithmus zur Wiederherestellung des Signals flüssigen Niederschlags angewendet. Die Schneeroutine konnte die Dynamik der winterlichen Schneedecke erfassen. Die temporäre Speicherung des Niederschlags in der Schneedecken konnte Simulationen des Abflusses im Gebiet verbessern. Das generelle Muster der zeitlichen Entwicklung simulierter und beobachteter Schneebedeckungsgrade stimmt überein. Die durchgeführte Arbeit ist nur ein erster Schritt im Prozess der Implementierung und Validierung einer physikalisch begründeten WASA-SED Schneeroutine. Zukünftige Forschungsarbeit ist nötig, um die Schneeroutine weiter zu verbessern, zu testen und aufgetretene Schwierigkeiten bei der Modellanwendung im Gebiet zu lösen. KW - WASA-SED KW - snow routine KW - energy balance KW - MODIS snow cover KW - Pyrenees KW - WASA-SED KW - Schneeroutine KW - Energiebilanz KW - MODIS Schneebedeckung KW - Pyrenäen Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-504963 ER - TY - THES A1 - Rottler, Erwin T1 - Transient merging of two Rhine flow regimes from climate change T1 - Vorübergehende Überlagerung von zwei Abflussregimen im Rhein durch den Klimawandel N2 - River flooding poses a threat to numerous cities and communities all over the world. The detection, quantification and attribution of changes in flood characteristics is key to assess changes in flood hazard and help affected societies to timely mitigate and adapt to emerging risks. The Rhine River is one of the major European rivers and numerous large cities reside at its shores. Runoff from several large tributaries superimposes in the main channel shaping the complex from regime. Rainfall, snowmelt as well as ice-melt are important runoff components. The main objective of this thesis is the investigation of a possible transient merging of nival and pluvial Rhine flood regimes under global warming. Rising temperatures cause snowmelt to occur earlier in the year and rainfall to be more intense. The superposition of snowmelt-induced floods originating from the Alps with more intense rainfall-induced runoff from pluvial-type tributaries might create a new flood type with potentially disastrous consequences. To introduce the topic of changing hydrological flow regimes, an interactive web application that enables the investigation of runoff timing and runoff season- ality observed at river gauges all over the world is presented. The exploration and comparison of a great diversity of river gauges in the Rhine River Basin and beyond indicates that river systems around the world undergo fundamental changes. In hazard and risk research, the provision of background as well as real-time information to residents and decision-makers in an easy accessible way is of great importance. Future studies need to further harness the potential of scientifically engineered online tools to improve the communication of information related to hazards and risks. A next step is the development of a cascading sequence of analytical tools to investigate long-term changes in hydro-climatic time series. The combination of quantile sampling with moving average trend statistics and empirical mode decomposition allows for the extraction of high resolution signals and the identification of mechanisms driving changes in river runoff. Results point out that the construction and operation of large reservoirs in the Alps is an important factor redistributing runoff from summer to winter and hint at more (intense) rainfall in recent decades, particularly during winter, in turn increasing high runoff quantiles. The development and application of the analytical sequence represents a further step in the scientific quest to disentangling natural variability, climate change signals and direct human impacts. The in-depth analysis of in situ snow measurements and the simulations of the Alpine snow cover using a physically-based snow model enable the quantification of changes in snowmelt in the sub-basin upstream gauge Basel. Results confirm previous investigations indicating that rising temperatures result in a decrease in maximum melt rates. Extending these findings to a catchment perspective, a threefold effect of rising temperatures can be identified: snowmelt becomes weaker, occurs earlier and forms at higher elevations. Furthermore, results indicate that due to the wide range of elevations in the basin, snowmelt does not occur simultaneously at all elevation, but elevation bands melt together in blocks. The beginning and end of the release of meltwater seem to be determined by the passage of warm air masses, and the respective elevation range affected by accompanying temperatures and snow availability. Following those findings, a hypothesis describing elevation-dependent compensation effects in snowmelt is introduced: In a warmer world with similar sequences of weather conditions, snowmelt is moved upward to higher elevations, i.e., the block of elevation bands providing most water to the snowmelt-induced runoff is located at higher elevations. The movement upward the elevation range makes snowmelt in individual elevation bands occur earlier. The timing of the snowmelt-induced runoff, however, stays the same. Meltwater from higher elevations, at least partly, replaces meltwater from elevations below. The insights on past and present changes in river runoff, snow covers and underlying mechanisms form the basis of investigations of potential future changes in Rhine River runoff. The mesoscale Hydrological Model (mHM) forced with an ensemble of climate projection scenarios is used to analyse future changes in streamflow, snowmelt, precipitation and evapotranspiration at 1.5, 2.0 and 3.0 ◦ C global warming. Simulation results suggest that future changes in flood characteristics in the Rhine River Basin are controlled by increased precipitation amounts on the one hand, and reduced snowmelt on the other hand. Rising temperatures deplete seasonal snowpacks. At no time during the year, a warming climate results in an increase in the risk of snowmelt-driven flooding. Counterbalancing effects between snowmelt and precipitation often result in only little and transient changes in streamflow peaks. Although, investigations point at changes in both rainfall and snowmelt-driven runoff, there are no indications of a transient merging of nival and pluvial Rhine flood regimes due to climate warming. Flooding in the main tributaries of the Rhine, such as the Moselle River, as well as the High Rhine is controlled by both precipitation and snowmelt. Caution has to be exercised labelling sub-basins such as the Moselle catchment as purely pluvial-type or the Rhine River Basin at Basel as purely nival-type. Results indicate that this (over-) simplifications can entail misleading assumptions with regard to flood-generating mechanisms and changes in flood hazard. In the framework of this thesis, some progress has been made in detecting, quantifying and attributing past, present and future changes in Rhine flow/flood characteristics. However, further studies are necessary to pin down future changes in the flood genesis of Rhine floods, particularly very rare events. N2 - Überflutungen durch Flusshochwasser stellen für zahlreiche Städte und Gemeinden auf der ganzen Welt eine große Gefahr dar. Die Detektion, Quantifizierung und Attribuierung sich verändernder Hochwassereigenschaften ist wichtig, um Änderungen in der Gefahrenlage zu bewerten und Anrainerstaaten die Möglichkeit zur Abschwächung und Anpassung an das Hochwasserrisiko zu geben. Der Rhein ist einer der großen Flüsse Europas und zahlreiche Städte liegen an seinen Ufern. Sich überlagernde Abflüsse aus den großen Zuflüssen prägen das komplexe Abflussregime des Rheins. Sowohl Regen, Schneeschmelze als auch Eisschmelze sind wichtige Abflusskomponenten. Vorrangiges Ziel dieser Arbeit ist die Untersuchung der Möglichkeit einer durch den Klimawandel verursachten vorübergehenden Überlagerung von nivalen und pluvial Hochwasserereignissen im Rheingebiet. Steigende Temperaturen können zu einer früheren Schneeschmelze und intensivieren Niederschlägen führen. Die Überlagerung von durch Schneeschmelze angetriebenen Spitzenabflüssen aus den Alpen mit intensiveren Hochwasserereignissen aus den pluvialen Zuflüssen, könnte zur Bildung eines neuen Hochwassertyps mit möglicherweise katastrophalen Folgen führen. Eine interaktive Web-Anwendung, die es ermöglicht, Zeitpunkt und Saisonalität von Abfluss auf der ganzen Welt zu untersuchen, führt in die Thematik sich verändernder hydrologischer Abflussregime ein. Die Untersuchungen und der Vergleich von unterschiedlichsten Abflusspegeln im Rheingebiet und darüber hinaus weißen darauf hin, dass sich Flusssysteme auf der ganzen Welt im Wandel befinden. In der Gefahren- und Risikoforschung ist die Bereitstellung von Hintergrundinformationen und Informationen zu aktuellen Entwicklungen für Anwohner und Entscheidungsträger auf leicht zugängliche Weise von großer Bedeutung. Zukünftige Studien sollten sich das Potential wissenschaftlicher Web-Anwendungen, um die Kommunikation in Bezug auf Naturgefahren und -risiken zu verbessern, verstärkt zu Nutze machen. Nächster Schritt ist die Entwicklung einer kaskadierenden Sequenz analytischer Methoden, um langfristige Änderungen in hydro-klimatoligischen Zeitreihen zu detektieren. Eine Kombination aus Quantil-Berechnungen, Statistiken basierend auf gleitenden Mittelwerten und empirischer Bandzerlegung ermöglicht die Extraktion hochaufgelöster Signale und die Identifizierungen zu Grunde liegender Antriebsmechanismen. Die Ergebnisse der Analysen zeigen, dass der Bau und Betrieb von großen Stauseen zur Gewinnung von Wasserkraft zu einer Umverteilung von Wasser vom Sommer in den Winter führt. Zudem weisen die Ergebnisse auf (mehr) intensivere Niederschläge hin, die wiederum hohe Abflussquantile intensivieren. Die Entwicklung und Anwendung der analytischen Sequenz stellt einen weiteren Schritt in dem wissenschaftlichen Bestreben, natürliche Klimavariabilität, Signale des Klimawandels und direkte anthropogene Einflüsse zu entwirren, dar. Die detaillierte Untersuchung von Schneemessungen und die Simulation der alpinen Schneedecke mittels physikalisch-basiertem Schneemodell, ermöglicht die Quantifizierung von Änderungen in der Schneeschmelze im Rheingebiet oberhalb von Basel. Steigenden Temperaturen verringern nicht nur hohe Schmelzraten, ein Dreifach-Effekt kann identifiziert werden: Schneeschmelze wird schwächer, findet früher statt und formiert sich in höhere Lagen. Auf Grund der großen Höhenunterschiede im Gebiet, findet die Schneeschmelze nicht gleichzeitig in allen Höhenlagen statt. Simulationen weisen darauf hin, dass Höhenbänder zusammen in Blöcken schmelzen. Der Beginn und das Ende eines Schmelzereignisses scheint durch vorbeiziehende warme Luftmassen und die betroffenen Höhenlagen durch zugehörige Temperaturen und die Schneeverfügbarkeit bestimmt zu werden. Basieren auf diesen Erkenntnissen, wird eine Hypothese, die höhenabhängige Kompensationseffekte in der Schneeschmelze beschreibt, vorgestellt: In einem wärmeren Klima mit einer gleichbleibenden Abfolge von Witterungsbedingungen, findet die Schneeschmelze in höheren Lagen statt, d.h., der Block an Höhenbändern, der den Hauptbestandteil des Schmelzwassers freigibt, ist nach oben verschoben. Die Verschiebung in höhere Lagen führt dazu, dass die Schneeschmelze in einzelnen Höhenbändern früher kommt, der Zeitpunkt des Schmelzereignisses jedoch unverändert bleibt. Schmelzwasser aus höheren Lagen ersetzt, zumindest teilweise, Schmelzwasser aus tieferen Lagen. Die Erkenntnisse über historische und gegenwärtige Änderungen im Abfluss, der Schneedecke und zu Grunde liegenden Mechanismen bilden die Grundlage der Untersuchungen möglicher zukünftiger Änderungen im Abfluss des Rheins. Das für die Mesoskala entwickelte hydrologisiche Modell mHM wird mit einem Ensemble aus Klimaszenarien angetrieben und projizierte Änderungen im Abfluss, der Schneeschmelze, im Niederschlag und der Evapotranspiration bei 1.5, 2.0 und 3.0 ◦ C Erwärmung untersucht. Ergebnisse der hydrologischen Simulationen zeigen, dass künftige Änderungen der Hochwassereigenschaften im Rheingebiet durch zunehmenden Niederschlagsmengen und abnehmende Schneeschmelze bestimmt werden. Steigende Temperaturen verringern saisonale Schneedecken. Zu keinem Zeitpunkt im Jahr führen höhere Temperaturen zu einer Zunahme des Hochwasserrisikos durch die Schneeschmelze. Kompensationseffekte zwischen Schneeschmelze und Niederschlag resultieren oftmals in geringe und nur vorübergehende Erhöhungen von Spitzenabflüssen. Obwohl Untersuchungen auf Veränderungen sowohl in der Schneeschmelze als auch im Niederschlag hinweisen, finden sich keine Hinweise auf eine durch den Klimawandel verursachte vorübergehende Überlagerung von nivalen und pluvialen Hochwasserregimen im Rheingebiet. Hochwasserereignisse in den Hauptzuflüssen, wie zu Beispiel der Mosel, und dem Hochrhein werden sowohl durch Niederschläge als auch Schneeschmelze kontrolliert. Vorsicht muss geübt werden, wenn Teilgebiete, wie das Einzugsgebiet der Mosel als rein pluvial oder das Rheingebiet oberhalb von Basel als rein nival gesehen werden. Die Ergebnisse zeigen, dass diese (zu starke) Vereinfachung zu irreführenden Annahmen bezüglich möglicher Änderungen von Hochwasser verursachender Mechanismen und Hochwassergefahr führen können. Diese Doktorarbeit ist ein Schritt vorwärts im wissenschaftlichen Streben die Detektion, Quantifizierung und Attribuierung vergangener und zukünftiger Veränderungen in den Abfluss- und Hochwasserregimen des Rheins zu verbessern. Weitere Untersuchungen sind nötig, um zukünftige Veränderungen in der Hochwassergenese sehr seltener Hochwasserereignisse einzuschätzen. KW - runoff seasonality KW - Rhine River KW - flooding KW - snowmelt KW - Abflusssaisonalität KW - Rhein KW - Hochwasser KW - Schneeschmelze Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-517665 ER - TY - JOUR A1 - Reza, M. Toufiq A1 - Rottler, Erwin A1 - Tölle, Rainer A1 - Werner, Maja A1 - Ramm, Patrice A1 - Mumme, Jan T1 - Production, characterization, and biogas application of magnetic hydrochar from cellulose JF - Bioresource technology : biomass, bioenergy, biowastes, conversion technologies, biotransformation, production technologies N2 - Hydrothermal carbonization (HTC) produces carbon-rich nano-micro size particles. In this study, magnetic hydrochar (MHC) was prepared from model compound cellulose by simply adding ferrites during HTC. The effects of ferrites on HTC were evaluated by characterizing solid MHC and corresponding process liquid. Additionally, magnetic stability of MHC was tested by magnetic susceptibility method. Finally, MHC was used as support media for anaerobic films in anaerobic digestion (AD). Ash-free mass yield was around 50% less in MHC than hydrochar produced without ferrites at any certain HTC reaction condition, where organic part of MHC is mainly carbon. In fact, amorphous hydrochar was growing on the surface of inorganic ferrites. MHC maintained magnetic susceptibility regardless of reaction time at reaction temperature 250 degrees C. Pronounced inhibitory effects of magnetic hydrochar occurred during start-up of AD but diminished with prolong AD times. Visible biofilms were observed on the MHC by laser scanning microscope after AD. (C) 2015 Elsevier Ltd. All rights reserved. KW - Cellulose KW - Hydrothermal carbonization KW - Magnetic hydrochar KW - Magnetic susceptibility KW - Anaerobic digestion Y1 - 2015 U6 - https://doi.org/10.1016/j.biortech.2015.03.044 SN - 0960-8524 SN - 1873-2976 VL - 186 SP - 34 EP - 43 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Reza, M. Toufiq A1 - Rottler, Erwin A1 - Herklotz, Laureen A1 - Wirth, Benjamin T1 - Hydrothermal carbonization (HTC) of wheat straw: Influence of feedwater pH prepared by acetic acid and potassium hydroxide JF - Bioresource technology : biomass, bioenergy, biowastes, conversion technologies, biotransformation, production technologies N2 - In this study, influence of feedwater pH (2-12) was studied for hydrothermal carbonization (HTC) of wheat straw at 200 and 260 degrees C. Acetic acid and KOH were used as acidic and basic medium, respectively. Hydrochars were characterized by elemental and fiber analyses, SEM, surface area, pore volume and size, and ATR-FTIR, while HTC process liquids were analyzed by HPLC and GC. Both hydrochar and HTC process liquid qualities vary with feedwater pH. At acidic pH, cellulose and elemental carbon increase in hydrochar, while hemicellulose and pseudo-lignin decrease. Hydrochars produced at pH 2 feedwater has 2.7 times larger surface area than that produced at pH 12. It also has the largest pore volume (1.1 x 10(-1) ml g(-1)) and pore size (20.2 nm). Organic acids were increasing, while sugars were decreasing in case of basic feedwater, however, phenolic compounds were present only at 260 degrees C and their concentrations were increasing in basic feedwater. (C) 2015 Elsevier Ltd. All rights reserved. KW - Hydrothermal carbonization KW - HTC biochar KW - pH KW - Fiber analysis KW - Pore analysis Y1 - 2015 U6 - https://doi.org/10.1016/j.biortech.2015.02.024 SN - 0960-8524 SN - 1873-2976 VL - 182 SP - 336 EP - 344 PB - Elsevier CY - Oxford ER -