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Im Jahre 1960 behauptete Yamabe folgende Aussage bewiesen zu haben: Auf jeder kompakten Riemannschen Mannigfaltigkeit (M,g) der Dimension n ≥ 3 existiert eine zu g konform äquivalente Metrik mit konstanter Skalarkrümmung. Diese Aussage ist äquivalent zur Existenz einer Lösung einer bestimmten semilinearen elliptischen Differentialgleichung, der Yamabe-Gleichung. 1968 fand Trudinger einen Fehler in seinem Beweis und infolgedessen beschäftigten sich viele Mathematiker mit diesem nach Yamabe benannten Yamabe-Problem. In den 80er Jahren konnte durch die Arbeiten von Trudinger, Aubin und Schoen gezeigt werden, dass diese Aussage tatsächlich zutrifft. Dadurch ergeben sich viele Vorteile, z.B. kann beim Analysieren von konform invarianten partiellen Differentialgleichungen auf kompakten Riemannschen Mannigfaltigkeiten die Skalarkrümmung als konstant vorausgesetzt werden.
Es stellt sich nun die Frage, ob die entsprechende Aussage auch auf Lorentz-Mannigfaltigkeiten gilt. Das Lorentz'sche Yamabe Problem lautet somit: Existiert zu einer gegebenen räumlich kompakten global-hyperbolischen Lorentz-Mannigfaltigkeit (M,g) eine zu g konform äquivalente Metrik mit konstanter Skalarkrümmung? Das Ziel dieser Arbeit ist es, dieses Problem zu untersuchen.
Bei der sich aus dieser Fragestellung ergebenden Yamabe-Gleichung handelt es sich um eine semilineare Wellengleichung, deren Lösung eine positive glatte Funktion ist und aus der sich der konforme Faktor ergibt. Um die für die Behandlung des Yamabe-Problems benötigten Grundlagen so allgemein wie möglich zu halten, wird im ersten Teil dieser Arbeit die lokale Existenztheorie für beliebige semilineare Wellengleichungen für Schnitte auf Vektorbündeln im Rahmen eines Cauchy-Problems entwickelt. Hierzu wird der Umkehrsatz für Banachräume angewendet, um mithilfe von bereits existierenden Existenzergebnissen zu linearen Wellengleichungen, Existenzaussagen zu semilinearen Wellengleichungen machen zu können. Es wird bewiesen, dass, falls die Nichtlinearität bestimmte Bedingungen erfüllt, eine fast zeitglobale Lösung des Cauchy-Problems für kleine Anfangsdaten sowie eine zeitlokale Lösung für beliebige Anfangsdaten existiert.
Der zweite Teil der Arbeit befasst sich mit der Yamabe-Gleichung auf global-hyperbolischen Lorentz-Mannigfaltigkeiten. Zuerst wird gezeigt, dass die Nichtlinearität der Yamabe-Gleichung die geforderten Bedingungen aus dem ersten Teil erfüllt, so dass, falls die Skalarkrümmung der gegebenen Metrik nahe an einer Konstanten liegt, kleine Anfangsdaten existieren, so dass die Yamabe-Gleichung eine fast zeitglobale Lösung besitzt. Mithilfe von Energieabschätzungen wird anschließend für 4-dimensionale global-hyperbolische Lorentz-Mannigfaltigkeiten gezeigt, dass unter der Annahme, dass die konstante Skalarkrümmung der konform äquivalenten Metrik nichtpositiv ist, eine zeitglobale Lösung der Yamabe-Gleichung existiert, die allerdings nicht notwendigerweise positiv ist. Außerdem wird gezeigt, dass, falls die H2-Norm der Skalarkrümmung bezüglich der gegebenen Metrik auf einem kompakten Zeitintervall auf eine bestimmte Weise beschränkt ist, die Lösung positiv auf diesem Zeitintervall ist. Hierbei wird ebenfalls angenommen, dass die konstante Skalarkrümmung der konform äquivalenten Metrik nichtpositiv ist. Falls zusätzlich hierzu gilt, dass die Skalarkrümmung bezüglich der gegebenen Metrik negativ ist und die Metrik gewisse Bedingungen erfüllt, dann ist die Lösung für alle Zeiten in einem kompakten Zeitintervall positiv, auf dem der Gradient der Skalarkrümmung auf eine bestimmte Weise beschränkt ist. In beiden Fällen folgt unter den angeführten Bedingungen die Existenz einer zeitglobalen positiven Lösung, falls M = I x Σ für ein beschränktes offenes Intervall I ist. Zum Schluss wird für M = R x Σ ein Beispiel für die Nichtexistenz einer globalen positiven Lösung angeführt.
Boolean Satisfiability (SAT) is one of the problems at the core of theoretical computer science. It was the first problem proven to be NP-complete by Cook and, independently, by Levin. Nowadays it is conjectured that SAT cannot be solved in sub-exponential time. Thus, it is generally assumed that SAT and its restricted version k-SAT are hard to solve. However, state-of-the-art SAT solvers can solve even huge practical instances of these problems in a reasonable amount of time.
Why is SAT hard in theory, but easy in practice? One approach to answering this question is investigating the average runtime of SAT. In order to analyze this average runtime the random k-SAT model was introduced. The model generates all k-SAT instances with n variables and m clauses with uniform probability. Researching random k-SAT led to a multitude of insights and tools for analyzing random structures in general. One major observation was the emergence of the so-called satisfiability threshold: A phase transition point in the number of clauses at which the generated formulas go from asymptotically almost surely satisfiable to asymptotically almost surely unsatisfiable. Additionally, instances around the threshold seem to be particularly hard to solve.
In this thesis we analyze a more general model of random k-SAT that we call non-uniform random k-SAT. In contrast to the classical model each of the n Boolean variables now has a distinct probability of being drawn. For each of the m clauses we draw k variables according to the variable distribution and choose their signs uniformly at random. Non-uniform random k-SAT gives us more control over the distribution of Boolean variables in the resulting formulas. This allows us to tailor distributions to the ones observed in practice. Notably, non-uniform random k-SAT contains the previously proposed models random k-SAT, power-law random k-SAT and geometric random k-SAT as special cases.
We analyze the satisfiability threshold in non-uniform random k-SAT depending on the variable probability distribution. Our goal is to derive conditions on this distribution under which an equivalent of the satisfiability threshold conjecture holds. We start with the arguably simpler case of non-uniform random 2-SAT. For this model we show under which conditions a threshold exists, if it is sharp or coarse, and what the leading constant of the threshold function is. These are exactly the three ingredients one needs in order to prove or disprove the satisfiability threshold conjecture. For non-uniform random k-SAT with k=3 we only prove sufficient conditions under which a threshold exists. We also show some properties of the variable probabilities under which the threshold is sharp in this case. These are the first results on the threshold behavior of non-uniform random k-SAT.
Räume, Linien, Punkte
(2018)
Schulpraktische Studien werden vermehrt als „Herzstück“ der Lehrerbildung betrachtet; zu ihren Effekten auf die Kompetenzentwicklung der Studierenden liegen bisher jedoch nur wenige Erkenntnisse vor. Auf der Grundlage des Konzepts zu Standards und Kompetenzen in Schulpraktischen Studien nimmt das PSI-Teilprojekt „Kompetenzerwerb in Schulpraktischen Studien – Spiralcurriculum“ eine erste empirische Analyse der fünf bildungswissenschaftlichen und fachdidaktischen Praktika im Potsdamer Modell der Lehrerbildung vor. Eine ausgewählte Kohorte Lehramtsstudierender wird durch alle fünf Schulpraktischen Studien in der Bachelor- und Masterphase begleitet und anhand eines Online-Fragebogens zu ihrem Kompetenzerwerb befragt. Besonders zeichnet sich die Studie durch das quer- sowie längsschnittliche Forschungsdesign aus, das im folgenden Beitrag anhand der Skizzierung des Erhebungsinstruments – einem umfassenden, mehrteiligen Online-Fragebogen – vorgestellt wird. Vor dem Hintergrund des theoretischen Projektmodells wird die Entwicklung des Fragebogens mit Angaben zur statistischen Güte unterlegt und durch Perspektiven des Forschungsprojekts ergänzt.
Von 2016 bis 2022 wurden im Rahmen des PSI-Projekts „Kompetenzerwerb in Schulpraktischen Studien – Spiralcurriculum“ N = 578 Lehramtsstudierende durch alle fünf Schulpraktischen Studien begleitet und mittels Online-Erhebung zu ihrem Kompetenzerleben in den Praxisphasen befragt. In retrospektiver Perspektive wurde der nachhaltige Einfluss der drei Bachelorpraktika auf das Kompetenzerleben der Masterstudierenden am Beginn ihres Schulpraktikums (Praxissemesters) untersucht, um konzeptionelle Schwerpunkte und intendierte Kompetenzziele des jeweiligen Praktikums im zugrundeliegenden Spiralcurriculum zu überprüfen. Die quantitativen Befunde verweisen auf die Wirkung aller drei Bachelor-Praxisphasen, wobei die Einschätzungen zum außerunterrichtlichen Praktikum in pädagogisch-psychologischen Handlungsfeldern (PppH) – hier die Skala „Erziehen“ – das Kompetenzerleben der Studierenden am stärksten aufklärt. Die qualitative Auswertung bekräftigt den Stellenwert der mit dem PppH verbundenen Handlungsfelder.
Das Orientierungspraktikum (OP)/Integrierte Eingangspraktikum (IEP) ist die erste schulpraktische Phase im Potsdamer Modell der Lehrerbildung. Mit diesem (Hospitations-)Praktikum (im 1. – 2. Fachsemester des Bachelorstudiums) soll der Perspektivwechsel von der Schüler:innen- zur Lehrer:innenrolle angestoßen und der Lehrer:innenberuf, die Institution Schule und der Unterricht durch eine beobachtende Perspektive reflektiert werden. Im Beitrag werden erste Ergebnisse der quantitativen und qualitativen Analyse zum OP/ IEP im Rahmen des PSI-Projekts „Kompetenzerwerb in Schulpraktischen Studien – Spiralcurriculum“ diskutiert. Aus den nachgewiesenen Effekten – u. a. Aktivierung der Reflexionsfähigkeit und Förderung der persönlichen Entwicklung – und den analysierten Bedürfnissen der Studierenden werden abschließend in zwei Diskussionssträngen „Konzeption und Handlungsrahmen“ sowie „Unterstützung und Begleitung“ Empfehlungen formuliert, die wichtige Impulse zur Weiterentwicklung des Praktikums und der begleitenden Lehrveranstaltungen liefern.
Die Manosphere
(2020)
Die sogenannte Manosphere – eine digitale Gemeinschaft, die sich hauptsächlich durch misogyne und antifeministische Beiträge und Ideologien auszeichnet – ist aufgrund ihrer Verbindung zu verschiedenen Terroranschlägen in der letzten Zeit verstärkt in das Blickfeld der Medien gelangt. Dieser Beitrag untersucht die bislang häufig vernachlässigte Rolle digitaler Räume und Netzwerke im Kontext regressiver, frauenfeindlicher Ideologien und daraus erwachsende gewalttätige antifeministische Handlungsrepertoires aus Perspektive der Bewegungsforschung. Am Beispiel der Manosphere auf der Plattform Reddit zeige ich, wie durch das Zusammenspiel zwischen technologischer Infrastruktur und regressiver Ideologie die Grundlage für die Mobilisierung und Sozialisierung in antifeministische Bewegungskulturen mit gewalttätigen Handlungsrepertoires on- und offline geschaffen wird.
The United Nations (UN) policy agenda on Preventing and Countering Violent Extremism (P/CVE) promotes a “holistic” approach to counterterrorism, which includes elements traditionally found in security and development programs. Advocates of the agenda increasingly emphasize the importance of gender mainstreaming for counterterrorism goals. In this article, I scrutinize the merging of the goals of gender equality, security, and development into a global agenda for counterterrorism. A critical feminist discourse-analytical reading of gender representations in P/CVE shows how problematic imageries of women as victims, economic entrepreneurs, and peacemakers from both the UN’s Sustainable Development Goals and the Women, Peace and Security agenda are reproduced in core UN documents advocating for a “holistic” P/CVE approach. By highlighting the tensions that are produced by efforts to merge the different gender discourses across the UN’s security and development institutions, the article underlines the relevance of considering the particular position of P/CVE at the security–development nexus for further gender-sensitive analysis and policies of counterterrorism.
The Other Side
(2020)
Given the current polarization of gender knowledge in the public discourse, this article investigates the "other side" of gender knowledge production. Building on feminist standpoint literature, I conduct a close reading of the affective-discursive dynamics of knowledge production in two anti-feminist online communities in the United States and India. I find that anti-feminist communities appropriate feminist practices of consciousness-raising to construct a shared sense of victimization. This appropriation is, however, incomplete. In contrast to feminist practices, anti-feminist knowledge generation is premised on the polarizing themes of "ultimate victimhood" and "ultimate other," which lead to violence and exclusion, rather than liberation.
Women's rights are a core part of a global consensus on human rights. However, we are currently experiencing an increasing popularity of anti-feminist and misogynist politics threatening to override feminist gains. In order to help explain this current revival and appeal, in this article I analyse how anti-feminist communities construct their collective identities at the intersection of local and global trends and affiliations. Through an in-depth analysis of representations in the collective identities of six popular online anti-feminist communities based in India, Russia and the United States, I shed light on how anti-feminists discursively construct their anti-feminist 'self' and the feminist 'other' between narratives of localized resistance to change and backlash against the results of broader societal developments associated with globalization. The results expose a complex set of global-local dynamics, which provide a nuanced understanding of the differences and commonalities of anti-feminist collective identity-building and mobilization processes across contexts. By explicitly focusing on the role of discursively produced locations for anti-feminist identity-building and providing new evidence on anti-feminist communities across three different continents, the article contributes to current discussions on transnational anti-feminist mobilizations in both social movement studies and feminist International Relations.
Über kaum ein Thema werden so hitzige Debatten geführt wie über Geschlechtsidentität. Das Wissen darum, dass Gender sozial konstruiert ist, wird von Anti-Gender Aktivist*innen häufig als ‚Gender-Ideologie‘ bezeichnet und ruft heftige Gegenreaktionen hervor. Dies gilt nicht nur in Deutschland – sondern länderübergreifend. Auffällig viele der transnationalen Anti- Gender Mobilisierungen der letzten 20 Jahre finden bezogen auf Bildungseinrichtungen statt. Dieser Beitrag widmet sich der besonderen Rolle der Universität und der Wissenschaft für transnationale Anti-Gender Diskurse. Anhand verschiedener Beispiele zeige ich auf, dass das Verhältnis zwischen Anti-Gender Bewegungen und Wissenschaft geprägt ist von widersprüchlichen Dynamiken, von Abgrenzung aber auch Imitation. In ihrem Zusammenspiel wirken beide Dynamiken mobilisierend und tragen zum Erstarken regressiver Rollenbilder und antidemokratischer rechter Bewegungen in der breiteren Gesellschaft bei. Der letzte Teil des Beitrags ruft daher zu mehr Selbstreflexion der wissenschaftlichen Praxis auf Grundlage feministischer und intersektionaler Ansätze auf.
Über kaum ein Thema werden so hitzige Debatten geführt wie über Geschlechtsidentität. Das Wissen darum, dass Gender sozial konstruiert ist, wird von Anti-Gender Aktivist*innen häufig als ‚Gender-Ideologie‘ bezeichnet und ruft heftige Gegenreaktionen hervor. Dies gilt nicht nur in Deutschland – sondern länderübergreifend. Auffällig viele der transnationalen Anti- Gender Mobilisierungen der letzten 20 Jahre finden bezogen auf Bildungseinrichtungen statt. Dieser Beitrag widmet sich der besonderen Rolle der Universität und der Wissenschaft für transnationale Anti-Gender Diskurse. Anhand verschiedener Beispiele zeige ich auf, dass das Verhältnis zwischen Anti-Gender Bewegungen und Wissenschaft geprägt ist von widersprüchlichen Dynamiken, von Abgrenzung aber auch Imitation. In ihrem Zusammenspiel wirken beide Dynamiken mobilisierend und tragen zum Erstarken regressiver Rollenbilder und antidemokratischer rechter Bewegungen in der breiteren Gesellschaft bei. Der letzte Teil des Beitrags ruft daher zu mehr Selbstreflexion der wissenschaftlichen Praxis auf Grundlage feministischer und intersektionaler Ansätze auf.
The politics of fear
(2022)
Introduction
(2023)
Several global governance initiatives launched in recent years have explicitly sought to integrate concern for gender equality and gendered harms into efforts to counter terrorism and violent extremism. As a result, commitments to gender-sensitivity and gender equality in international and regional counterterrorism and countering violent extremism (CT/CVE) initiatives, in national action plans, and at the level of civil society programming, have become a common aspect of the multilevel governance of terrorism and violent extremism. In light of these developments, aspects of our own research have turned in the past years to explore how concerns about gender are being incorporated in the governance of terrorism and violent extremism and how this development has affected (gendered) practices and power relations in CT policymaking and implementation. We were inspired by the growing literature on gender and CT/CVE, and critical scholarship on terrorism and political violence, to bring together a collection of new research addressing these questions.
In recent years, there have been a growing number of online and offline attacks linked to a loosely connected network of misogynist and antifeminist online communities called ‘the manosphere’. Since 2016, the ideas spread among and by groups of the manosphere have also become more closely aligned with those of other Far-Right online networks. In this commentary, I explore the role of what I term ‘evidence-based misogyny’ for mobilization and radicalization into the antifeminist and misogynist subcultures of the manosphere. Evidence-based misogyny is a discursive strategy, whereby members of the manosphere refer to (and misinterpret) knowledge in the form of statistics, studies, news items and pop-culture and mimic accepted methods of knowledge presentation to support their essentializing, polarizing views about gender relations in society. Evidence-based misogyny is a core aspect for manosphere-related mobilization as it provides a false sense of authority and forges a collective identity, which is framed as a supposed ‘alternative’ to mainstream gender knowledge. Due to its core function to justify and confirm the misogynist sentiments of users, evidence-based misogyny serves as connector between the manosphere and both mainstream conservative as well as other Far-Right and conspiratorial discourses.
„Gender-Ideologie“ und „Gender-Wahn“– diese Begriffe entstammen einem antifeministischen Diskurs, der ohne Bedrohungsszenarien nicht funktioniert. Feministische Errungenschaften – wie die Ehe für alle – werden zur Ursache persönlicher Nachteile umgedeutet. Seine Vertreter*innen verbreiten ihre (oft gewaltvollen) Narrative sowohl auf der Straße als auch im Internet. Antifeministische Bewegungen weisen zudem vielfältige Querverbindungen mit konservativen, nationalistischen, fundamentalreligiösen und faschistischen Diskursen auf.
Gender at the crossroads
(2021)
Since the early 2000s, the United Nations (UN) global counterterrorism architecture has seen significant changes towards increased multilateralism, a focus on prevention, and inter-institutional coordination across the UN’s three pillars of work. Throughout this reform process, gender aspects have increasingly become presented as a “cross-cutting” theme. In this article, I investigate the role of gender in the UN’s counterterrorism reform process at the humanitarian-development-peace nexus, or “triple nexus”, from a feminist institutionalist perspective. I conduct a feminist discourse analysis of the counterterrorism discourses of three UN entities, which represent the different UN pillars of peace and security (DPO), development (UNDP), and humanitarianism and human rights (OHCHR). The article examines the role of gender in the inter-institutional reform process by focusing on the changes, overlaps and differences in the discursive production of gender in the entities’ counterterrorism agendas over time and in two recent UN counterterrorism conferences. I find that gendered dynamics of nested newness and institutional layering have played an essential role both as a justification for the involvement of individual entities in counterterrorism and as a vehicle for inter-institutional cooperation and struggle for discursive power.
Gender at the crossroads
(2023)
Since the early 2000s, the United Nations (UN) global counterterrorism architecture has seen significant changes towards increased multilateralism, a focus on prevention, and inter-institutional coordination across the UN’s three pillars of work. Throughout this reform process, gender aspects have increasingly become presented as a “cross-cutting” theme. In this article, I investigate the role of gender in the UN’s counterterrorism reform process at the humanitarian-development-peace nexus, or “triple nexus”, from a feminist institutionalist perspective. I conduct a feminist discourse analysis of the counterterrorism discourses of three UN entities, which represent the different UN pillars of peace and security (DPO), development (UNDP), and humanitarianism and human rights (OHCHR). The article examines the role of gender in the inter-institutional reform process by focusing on the changes, overlaps and differences in the discursive production of gender in the entities’ counterterrorism agendas over time and in two recent UN counterterrorism conferences. I find that gendered dynamics of nested newness and institutional layering have played an essential role both as a justification for the involvement of individual entities in counterterrorism and as a vehicle for inter-institutional cooperation and struggle for discursive power.
From victims to activists
(2022)
Over the last few decades, a network of misogynist blogs, websites, wikis, and forums has developed, where users share their bigoted, sexist, and toxic views of society in general and masculinity and femininity in particular. This chapter outlines conceptual framework of hegemonic and hybrid masculinity. It provides a brief overview of the historical development of the manosphere and its various configurations and present our analysis of the masculinities performed by the five groups of the manosphere. The concept of hegemonic masculinity was articulated by Connell and colleagues in the 1980s as “the pattern of practice that allowed men’s dominance over women to continue.” Prior to the advent of the manosphere, an online iteration of male supremacist mobilizations, both Men’s Rights Activists and Pick-up artists developed as offline movements in the 1970s. MRAs perceive their respective societies as inherently stacked against men. This chapter analyses the masculinities of the manosphere and how they “repudiat[e] and reif[y]” hegemonic masculinity and male supremacism.
Introduction
(2022)
Several global governance initiatives launched in recent years have explicitly sought to integrate concern for gender equality and gendered harms into efforts to counter terrorism and violent extremism (CT/CVE). As a result, commitments to gender-sensitivity and gender equality in international and regional CT/CVE initiatives, in national action plans, and at the level of civil society programming, have become a common aspect of the multilevel governance of terrorism and violent extremism. In light of these developments, aspects of our own research have turned in the past years to explore how concerns about gender are being incorporated in the governance of (counter-)terrorism and violent extremism, and how this development has affected (gendered) practices and power relations in counterterrorism policymaking and implementation. We were inspired by the growing literature on gender and CT/CVE, and critical scholarship on terrorism and political violence, to bring together a collection of new research addressing these questions.
Understanding how humans move their eyes is an important part for understanding the functioning of the visual system. Analyzing eye movements from observations of natural scenes on a computer screen is a step to understand human visual behavior in the real world. When analyzing eye-movement data from scene-viewing experiments, the impor- tant questions are where (fixation locations), how long (fixation durations) and when (ordering of fixations) participants fixate on an image. By answering these questions, computational models can be developed which predict human scanpaths. Models serve as a tool to understand the underlying cognitive processes while observing an image, especially the allocation of visual attention.
The goal of this thesis is to provide new contributions to characterize and model human scanpaths on natural scenes. The results from this thesis will help to understand and describe certain systematic eye-movement tendencies, which are mostly independent of the image. One eye-movement tendency I focus on throughout this thesis is the tendency to fixate more in the center of an image than on the outer parts, called the central fixation bias. Another tendency, which I will investigate thoroughly, is the characteristic distribution of angles between successive eye movements.
The results serve to evaluate and improve a previously published model of scanpath generation from our laboratory, the SceneWalk model. Overall, six experiments were conducted for this thesis which led to the following five core results:
i) A spatial inhibition of return can be found in scene-viewing data. This means that locations which have already been fixated are afterwards avoided for a certain time interval (Chapter 2).
ii) The initial fixation position when observing an image has a long-lasting influence of up to five seconds on further scanpath progression (Chapter 2 & 3).
iii) The often described central fixation bias on images depends strongly on the duration of the initial fixation. Long-lasting initial fixations lead to a weaker central fixation bias than short fixations (Chapter 2 & 3).
iv) Human observers adjust their basic eye-movement parameters, like fixation dura- tions and saccade amplitudes, to the visual properties of a target they look for in visual search (Chapter 4).
v) The angle between two adjacent saccades is an indicator for the selectivity of the upcoming saccade target (Chapter 4).
All results emphasize the importance of systematic behavioral eye-movement tenden- cies and dynamic aspects of human scanpaths in scene viewing.
When searching a target in a natural scene, it has been shown that both the target’s visual properties and similarity to the background influence whether and how fast humans are able to find it. So far, it was unclear whether searchers adjust the dynamics of their eye movements (e.g., fixation durations, saccade amplitudes) to the target they search for. In our experiment, participants searched natural scenes for six artificial targets with different spatial frequency content throughout eight consecutive sessions. High-spatial frequency targets led to smaller saccade amplitudes and shorter fixation durations than low-spatial frequency targets if target identity was known. If a saccade was programmed in the same direction as the previous saccade, fixation durations and successive saccade amplitudes were not influenced by target type. Visual saliency and empirical fixation density at the endpoints of saccades which maintain direction were comparatively low, indicating that these saccades were less selective. Our results suggest that searchers adjust their eye movement dynamics to the search target efficiently, since previous research has shown that low-spatial frequencies are visible farther into the periphery than high-spatial frequencies. We interpret the saccade direction specificity of our effects as an underlying separation into a default scanning mechanism and a selective, target-dependent mechanism.
When watching the image of a natural scene on a computer screen, observers initially move their eyes toward the center of the image—a reliable experimental finding termed central fixation bias. This systematic tendency in eye guidance likely masks attentional selection driven by image properties and top-down cognitive processes. Here, we show that the central fixation bias can be reduced by delaying the initial saccade relative to image onset. In four scene-viewing experiments we manipulated observers' initial gaze position and delayed their first saccade by a specific time interval relative to the onset of an image. We analyzed the distance to image center over time and show that the central fixation bias of initial fixations was significantly reduced after delayed saccade onsets. We additionally show that selection of the initial saccade target strongly depended on the first saccade latency. A previously published model of saccade generation was extended with a central activation map on the initial fixation whose influence declined with increasing saccade latency. This extension was sufficient to replicate the central fixation bias from our experiments. Our results suggest that the central fixation bias is generated by default activation as a response to the sudden image onset and that this default activation pattern decreases over time. Thus, it may often be preferable to use a modified version of the scene viewing paradigm that decouples image onset from the start signal for scene exploration to explicitly reduce the central fixation bias.
This study investigates phenomena that have been claimed to be indicative of Specific Language Impairment (SLI) in German, focusing on subject-verb agreement marking. Longitudinal data from fourteen German-speaking children with SLI, seven monolingual and seven Turkish-German successive bilingual children, were examined. We found similar patterns of impairment in the two participant groups. Both the monolingual and the bilingual children with SLI had correct (present vs. preterit) tense marking and produced syntactically complex sentences such as embedded clauses and wh-questions, but were limited in reliably producing correct agreement-marked verb forms. These contrasts indicate that agreement marking is impaired in German-speaking children with SLI, without any necessary concurrent deficits in either the CP-domain or in tense marking. Our results also show that it is possible to identify SLI from an early successive bilingual child's performance in one of her two languages.
This study investigates phenomena that have been claimed to be indicative of Specific Language Impairment (SLI) in German, focusing on subject-verb agreement marking. Longitudinal data from fourteen German-speaking children with SLI, seven monolingual and seven Turkish-German successive bilingual children, were examined. We found similar patterns of impairment in the two participant groups. Both the monolingual and the bilingual children with SLI had correct (present vs. preterit) tense marking and produced syntactically complex sentences such as embedded clauses and wh-questions, but were limited in reliably producing correct agreement-marked verb forms. These contrasts indicate that agreement marking is impaired in German-speaking children with SLI, without any necessary concurrent deficits in either the CP-domain or in tense marking. Our results also show that it is possible to identify SLI from an early successive bilingual child's performance in one of her two languages.
Metabolic signatures of healthy lifestyle patterns and colorectal cancer risk in a European cohort
(2020)
BACKGROUND & AIMS: Colorectal cancer risk can be lowered by adherence to the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) guidelines. We derived metabolic signatures of adherence to these guidelines and tested their associations with colorectal cancer risk in the European Prospective Investigation into Cancer and Nutrition cohort.
METHODS: Scores reflecting adherence to the WCRF/AICR recommendations (scale, 1-5) were calculated from participant data on weight maintenance, physical activity, diet, and alcohol among a discovery set of 5738 cancer-free European Prospective Investigation into Cancer and Nutrition participants with metabolomics data. Partial least-squares regression was used to derive fatty acid and endogenous metabolite signatures of the WCRF/AICR score in this group. In an independent set of 1608 colorectal cancer cases and matched controls, odds ratios (ORs) and 95% CIs were calculated for colorectal cancer risk per unit increase in WCRF/AICR score and per the corresponding change in metabolic signatures using multivariable conditional logistic regression.
RESULTS: Higher WCRF/AICR scores were characterized by metabolic signatures of increased odd-chain fatty acids, serine, glycine, and specific phosphatidylcholines. Signatures were inversely associated more strongly with colorectal cancer risk (fatty acids: OR, 0.51 per unit increase; 95% CI, 0.29-0.90; endogenous metabolites: OR, 0.62 per unit change; 95% CI, 0.50-0.78) than the WCRF/AICR score (OR, 0.93 per unit change; 95% CI, 0.86-1.00) overall. Signature associations were stronger in male compared with female participants.
CONCLUSIONS: Metabolite profiles reflecting adherence to WCRF/AICR guidelines and additional lifestyle or biological risk factors were associated with colorectal cancer. Measuring a specific panel of metabolites representative of a healthy or unhealthy lifestyle may identify strata of the population at higher risk of colorectal cancer.
1. Migration conveys an immense challenge, especially for juvenile birds coping with enduring and risky journeys shortly after fledging. Accordingly, juveniles exhibit considerably lower survival rates compared to adults, particularly during migration. Juvenile white storks (Ciconia ciconia), which are known to rely on adults during their first fall migration presumably for navigational purposes, also display much lower annual survival than adults.
2. Using detailed GPS and body acceleration data, we examined the patterns and potential causes of age-related differences in fall migration properties of white storks by comparing first-year juveniles and adults. We compared juvenile and adult parameters of movement, behaviour and energy expenditure (estimated from overall dynamic body acceleration) and placed this in the context of the juveniles’ lower survival rate.
3. Juveniles used flapping flight vs. soaring flight 23% more than adults and were estimated to expend 14% more energy during flight. Juveniles did not compensate for their higher flight costs by increased refuelling or resting during migration. When juveniles and adults migrated together in the same flock, the juvenile flew mostly behind the adult and was left behind when they separated. Juveniles showed greater improvement in flight efficiency throughout migration compared to adults which appears crucial because juveniles exhibiting higher flight costs suffered increased mortality.
4. Our findings demonstrate the conflict between the juveniles’ inferior flight skills and their urge to keep up with mixed adult–juvenile flocks. We suggest that increased flight costs are an important proximate cause of juvenile mortality in white storks and likely in other soaring migrants and that natural selection is operating on juvenile variation in flight efficiency.
Therapie der auditiven Verarbeitungs- und Wahrnehmungsstörungen (AVWS) bei Kindern im Vorschulalter
(2016)
1. Teilleistungsbereiche der auditiven Verarbeitung und Wahrnehmung, 2. Therapie- und Fördermöglichkeiten, 3. Praxisnahe Darstellung der Therapieinhalte einzelner Teilleistungsbereiche der AVWS, 3.1 Höraufmerksamkeit (auditive Aufmerksamkeit), 3.2 Entdecken, 3.3 Lokalisation (Richtungshören), 3.4 Diskrimination, 3.5 Verstehen, 3.6 Selektion (Figur-Grund Wahrnehmung), 3.7 Auditive Merkfähigkeit, 3.8 Ergänzung zur auditiven Merkfähigkeit, 3.9 Separation (dichotisches Hören), 3.10 Lautheitsempfinden, 3.11 Auditive Ergänzung, 3.12 Auditive Analyse, 3.13 Auditive Synthese, 3.14 Qualitätsmanagment, 4. Literatur
Die vorliegende Abhandlung beschäftigt sich mit einem bisher wenig beachteten Aspekt von Humboldts Amerikanischer Reise (1799─1804). Während seine Studien der Pflanzen- und Tierwelt bis heute große Aufmerksamkeit genießen, wird Humboldts Beitrag zu der Entwicklung der modernen Landwirtschaft wenig beachtet. Während seines Aufenthalts in Lima erhielt er Proben von Guano, Vogelmist von den Chincha-Inseln vor der peruanischen Küste. Einige Proben, die er von dieser Reise zurückbrachte, wurden von Wissenschaftlern in Frankreich und Deutschland untersucht. Die Analysenergebnisse zeigten außerordentlich hohe Gehalte an Pflanzennährstoffen, insbesondere Stickstoff und Phosphor. In den folgenden Jahrzehnten wurde Guano zu einem bedeutsamen Düngemittel und Auslöser eines Booms in Europa und Peru. Die Auswirkungen dieser Entwicklung sind bis heute sichtbar und werden hier unter besonderer Beachtung von Phosphor beschrieben.
Die Rolle der plastidären APT Synthase in der Regulation des photosynthetischen Elektronenflusses
(2011)
Die acinösen Speicheldrüsen der Schabe Periplaneta americana sind reich durch serotonerge, dopaminerge und GABAerge Fasern innerviert. Die biogenen Amine Serotonin (5-HT) und Dopamin (DA) induzieren die Sekretion eines NaCl-haltigen Primärspeichels. Die physiologische Rolle der GABAergen Innervation des Drüsenkomplexes war bislang unbekannt. Weiterhin wurde vermutet, dass Tyramin (TA) und Octopamin (OA) an der Speichelbildung beteiligt sind. Mittels intrazellulärer Ableitungen von sekretorischen Acinuszellen mit und ohne Stimulierung des Speicheldrüsennervs (SDN) sollte daher die Wirkung von GABA, TA und OA im Speicheldrüsenkomplex untersucht werden. Intrazelluläre Ableitungen aus Acinuszellen zeigten, dass sowohl DA als auch 5 HT biphasische Änderungen des Membranpotentials induzierten. Diese bestanden aus einer initialen Hyperpolarisation und einer darauf folgenden transienten Depolarisation. Stimulierung des SDN mittels einer Saugelektrode verursachte ebenfalls biphasische Änderungen des Membranpotentials der Acinuszellen, die mit den DA- bzw. 5-HT-induzierten Änderungen kinetisch identisch waren. Dieses Ergebnis zeigte, dass die elektrische Stimulierung des SDN im Nerv-Speicheldrüsenpräparat eine verlässliche Methode zur Untersuchung der Wirkungen von Neuromodulatoren auf die dopaminerge und/oder sertotonerge Neurotransmission ist. Die Hyperpolarisation der DA-induzierten Potentialänderungen wurde durch eine intrazelluläre Ca2+-Freisetzung und die Öffnung basolateral lokalisierter Ca2+-gesteuerter K+-Kanäle verur-sacht. Die DA- und 5-HT-induzierte Depolarisation hing kritisch von der Aktivität eines basolateral lokalisierten Na+-K+-2Cl--Symporters ab. GABA, TA und OA potenzierten die elektrischen Antworten der Acinuszellen, wenn diese durch SDN-Stimulierung hervorgerufen wurden. Dabei war OA wirksamer als TA. Dieses Ergebnis zeigte, dass diese Substanzen als im Drüsenkomplex präsynaptisch und erregend als Neuromodulatoren wirken. Pharmakologische Untersuchungen ergaben, dass die erregende Wirkung von GABA durch einen G-Protein-gekoppelten GABAB-Rezeptor vermittelt wurde. Messungen der durch SDN-Stimulierung induzierten Flüssigkeits- und Proteinsekretionsraten zeigten, dass beide Parameter in Anwesenheit von GABA verstärkt waren. Dies ließ auf eine verstärkte serotonerge Neurotransmission schließen, da nur 5-HT die Bildung eines Protein-haltigen Speichels verursacht. Immuncytochemische Untersuchungen zeigten, dass die Drüsen tyraminerge und octopaminerge Innervation empfangen. Weiterhin wurde der erste charakterisierte TA-Rezeptor (PeaTYR1) der Schabe auf einem paarigen, lateral zur Drüse ziehenden Nerv markiert, der auch tyraminerge Fasern enthielt. Die vorliegende Arbeit trug zum Verständnis der komplexen Funktionsweise der Speicheldrüse der Schabe bei und erweiterte das lückenhafte Wissen über die neuronale Kontrolle exokriner Drüsen in Insekten.
A thermoresponsive NIPAAm-based polymer is combined with the selective acetylcholinesterase inhibitor tacrine in order to create a strict in sense on/off switch for enzymatic activity. This polymer-inhibitor conjugate inhibits AChE at room temperature and enables reactivation of AChE by heating above the cloud point of the conjugate.
An ellipsometric approach towards the description of inhomogeneous polymer-based Langmuir layers
(2016)
The applicability of nulling-based ellipsometric mapping as a complementary method next to Brewster angle microscopy (BAM) and imaging ellipsometry (IE) is presented for the characterization of ultrathin films at the air-water interface. First, the methodology is demonstrated for a vertically nonmoving Langmuir layer of star-shaped, 4-arm poly(omega-pentadecalactone) (PPDL-D4). Using nulling-based ellipsometric mapping, PPDL-D4-based inhomogeneously structured morphologies with a vertical dimension in the lower nm range could be mapped. In addition to the identification of these structures, the differentiation between a monolayer and bare water was possible. Second, the potential and limitations of this method were verified by applying it to more versatile Langmuir layers of telechelic poly[(rac-lactide)-co-glycolide]-diol (PLGA). All ellipsometric maps were converted into thickness maps by introduction of the refractive index that was derived from independent ellipsometric experiments, and the result was additionally evaluated in terms of the root mean square roughness, R-q. Thereby, a three-dimensional view into the layers was enabled and morphological inhomogeneity could be quantified.
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.
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.
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.
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.
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.
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.
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.
Hydro Explorer
(2021)
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.
Elevation-dependent compensation effects in snowmelt in the Rhine River Basin upstream gauge Basel
(2021)
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.