@phdthesis{Carus2017,
  author    = {Carus, Jana},
  title     = {Plant-habitat interactions in brackish marshes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-404966},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VII, 103},
  year      = {2017},
  abstract  = {Estuarine marshes are ecosystems that are situated at the transition zone between land and water and are thus controlled by physical and biological interactions. Marsh vegetation offers important ecosystem services by filtrating solid and dissolved substances from the water and providing habitat. By buffering a large part of the arriving flow velocity, attenuating wave energy and serving as erosion control for riverbanks, tidal marshes furthermore reduce the destructive effects of storm surges and storm waves and thus contribute to ecosystem-based shore protection. However, in many estuaries, extensive embankments, artificial bank protection, river dredging and agriculture threaten tidal marshes. Global warming might entail additional risks, such as changes in water levels, an increase of the tidal amplitude and a resulting shift of the salinity zones. This can affect the dynamics of the shore and foreland vegetation, and vegetation belts can be narrowed or fragmented. Against this background, it is crucial to gain a better understanding of the processes underlying the spatio temporal vegetation dynamics in brackish marshes. Furthermore, a better understanding of how plant-habitat relationships generate patterns in tidal marsh vegetation is vital to maintain ecosystem functions and assess the response of marshes to environmental change as well as the success of engineering and restoration projects. For this purpose, three research objectives were addressed within this thesis: (1) to explore the possibility of vegetation serving as self-adaptive shore protection by quantifying the reduction of current velocity in the vegetation belt and the morphologic plasticity of a brackish marsh pioneer, (2) to disentangle the roles of abiotic factors and interspecific competition on species distribution and stand characteristics in brackish marshes, and (3) to develop a mechanistic vegetation model that helps analysing the influence of habitat conditions on the spatio-temporal dynamic of tidal marsh vegetation. These aspects were investigated using a combination of field studies and statistical as well as process-based modelling. To explore the possibility of vegetation serving as self-adaptive coastal protection, in the first study, we measured current velocity with and without living vegetation, recorded ramet density and plant thickness during two growing periods at two locations in the Elbe estuary and assessed the adaptive value of a larger stem diameter of plants at locations with higher mechanical stress by biomechanical measurements. The results of this study show that under non-storm conditions, the vegetation belt of the marsh pioneer Bolboschoenus maritimus is able to buffer a large proportion of the flow velocity. We were furthermore able to show that morphological traits of plant species are adapted to hydrodynamic forces by demonstrating a positive correlation between ramet thickness and cross-shore current. In addition, our measurements revealed that thicker ramets growing at the front of the vegetation belt have a significantly higher stability than ramets inside the vegetation belt. This self-adaptive effect improves the ability of B. maritimus to grow and persist in the pioneer zone and could provide an adaptive value in habitats with high mechanical stress. In the second study, we assessed the distribution of the two marsh species and a set of stand characteristics, namely aboveground and belowground biomass, ramet density, ramet height and the percentage of flowering ramets. Furthermore, we collected information on several abiotic habitat factors to test their effect on plant growth and zonation with generalised linear models (GLMs). Our results demonstrate that flow velocity is the main factor controlling the distribution of Bolboschoenus maritimus and Phragmites australis. Additionally, inundation height and duration, as well as intraspecific competition affect distribution patterns. This study furthermore shows that cross-shore flow velocity does not only directly influence the distribution of the two marsh species, but also alters the plants' occurrence relative to inun-dation height and duration. This suggests an effect of cross-shore flow velocity on their tolerance to inundation. The analysis of the measured stand characteristics revealed a negative effect of total flow velocity on all measured parameters of B. maritimus and thus confirmed our expectation that flow velocity is a decisive stressor which influences the growth of this species. To gain a better understanding of the processes and habitat factors influencing the spatio-temporal vegetation dynamics in brackish marshes, I built a spatially explicit, mechanistic model applying a pattern-oriented modelling approach. A sensitivity analysis of the para-meters of this dynamic habitat-macrophyte model HaMac suggests that rhizome growth is the key process for the lateral dynamics of brackish marshes. From the analysed habitat factors, P. australis patterns were mainly influenced by flow velocity. The competition with P. australis was of key importance for the belowground biomass of B. maritimus. Concerning vegetation dynamics, the model results emphasise that without the effect of flow velocity the B. maritimus vegetation belt would expand into the tidal flat at locations with present vegetation recession, suggesting that flow velocity is the main reason for vegetation recession at exposed locations. Overall, the results of this thesis demonstrate that brackish marsh vegetation considerably contributes to flow reduction under average flow conditions and can hence be a valuable component of shore-protection schemes. At the same time, the distribution, growth and expansion of tidal marsh vegetation is substantially influenced by flow. Altogether, this thesis provides a clear step forward in understanding plant-habitat interactions in tidal marshes. Future research should integrate studies of vertical marsh accretion with research on the factors that control the lateral position of marshes.},
  language  = {en}
}
@phdthesis{Schmidt2017,
  author    = {Schmidt, Silke Regina},
  title     = {Analyzing lakes in the time frequency domain},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-406955},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VIII, 126},
  year      = {2017},
  abstract  = {The central aim of this thesis is to demonstrate the benefits of innovative frequency-based methods to better explain the variability observed in lake ecosystems. Freshwater ecosystems may be the most threatened part of the hydrosphere. Lake ecosystems are particularly sensitive to changes in climate and land use because they integrate disturbances across their entire catchment. This makes understanding the dynamics of lake ecosystems an intriguing and important research priority. This thesis adds new findings to the baseline knowledge regarding variability in lake ecosystems. It provides a literature-based, data-driven and methodological framework for the investigation of variability and patterns in environmental parameters in the time frequency domain. Observational data often show considerable variability in the environmental parameters of lake ecosystems. This variability is mostly driven by a plethora of periodic and stochastic processes inside and outside the ecosystems. These run in parallel and may operate at vastly different time scales, ranging from seconds to decades. In measured data, all of these signals are superimposed, and dominant processes may obscure the signals of other processes, particularly when analyzing mean values over long time scales. Dominant signals are often caused by phenomena at long time scales like seasonal cycles, and most of these are well understood in the limnological literature. The variability injected by biological, chemical and physical processes operating at smaller time scales is less well understood. However, variability affects the state and health of lake ecosystems at all time scales. Besides measuring time series at sufficiently high temporal resolution, the investigation of the full spectrum of variability requires innovative methods of analysis. Analyzing observational data in the time frequency domain allows to identify variability at different time scales and facilitates their attribution to specific processes. The merit of this approach is subsequently demonstrated in three case studies. The first study uses a conceptual analysis to demonstrate the importance of time scales for the detection of ecosystem responses to climate change. These responses often occur during critical time windows in the year, may exhibit a time lag and can be driven by the exceedance of thresholds in their drivers. This can only be detected if the temporal resolution of the data is high enough. The second study applies Fast Fourier Transform spectral analysis to two decades of daily water temperature measurements to show how temporal and spatial scales of water temperature variability can serve as an indicator for mixing in a shallow, polymictic lake. The final study uses wavelet coherence as a diagnostic tool for limnology on a multivariate high-frequency data set recorded between the onset of ice cover and a cyanobacteria summer bloom in the year 2009 in a polymictic lake. Synchronicities among limnological and meteorological time series in narrow frequency bands were used to identify and disentangle prevailing limnological processes. Beyond the novel empirical findings reported in the three case studies, this thesis aims to more generally be of interest to researchers dealing with now increasingly available time series data at high temporal resolution. A set of innovative methods to attribute patterns to processes, their drivers and constraints is provided to help make more efficient use of this kind of data.},
  language  = {en}
}
@phdthesis{Siddiqui2017,
  author    = {Siddiqui, Tarique Adnan},
  title     = {Long-term investigation of the lunar tide in the equatorial electrojet during stratospheric sudden warmings},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-406384},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xvii, 116},
  year      = {2017},
  abstract  = {The ionosphere, which is strongly influenced by the Sun, is known to be also affected by meteorological processes. These processes, despite having their origin in the troposphere and stratosphere, interact with the upper atmosphere. Such an interaction between atmospheric layers is known as vertical coupling. During geomagnetically quiet times, when near-Earth space is not under the influence of solar storms, these processes become important drivers for ionospheric variability. Studying the link between these processes in the lower atmosphere and the ionospheric variability is important for our understanding of fundamental mechanisms in ionospheric and meteorological research. A prominent example of vertical coupling between the stratosphere and the ionosphere are the so-called stratospheric sudden warming (SSW) events that occur usually during northern winters and result in an increase in the polar stratospheric temperature and a reversal of the circumpolar winds. While the phenomenon of SSW is confined to the northern polar stratosphere, its influence on the ionosphere can be observed even at equatorial latitudes. During SSW events, the connection between the polar stratosphere and the equatorial ionosphere is believed to be through the modulation of global atmospheric tides. These tides are fundamental for the ionospheric E-region wind dynamo that generates electric fields and currents in the ionosphere. Observations of ionospheric currents indicate a large enhancement of the semidiurnal lunar tide in response to SSW events. Thus, the semidiurnal lunar tide becomes an important driver of ionospheric variability during SSW events. In this thesis, the ionospheric effect of SSW events is investigated in the equatorial region, where a narrow but an intense E-region current known as the equatorial electrojet (EEJ) flows above the dip equator during the daytime. The day-to-day variability of the EEJ can be determined from magnetic field records at geomagnetic observatories close to the dip equator. Such magnetic data are available for several decades and allows to investigate the impact of SSW events on the EEJ and, even more importantly, helps in understanding the effects of SSW events on the equatorial ionosphere. An excellent long-term record of the geomagnetic field at the equator from 1922 onwards is available for the observatory Huancayo in Peru and is extensively utilized in this study. The central subject of this thesis is the investigation of lunar tides in the EEJ during SSW events by analyzing long time series. This is done by estimating the lunar tidal amplitude in the EEJ from the magnetic records at Huancayo and by comparing them to measurements of the polar stratospheric wind and temperature, which led to the identification of the known SSW events from 1952 onwards. One goal of this thesis is to identify SSW events that predate 1952. To this end, superposed epoch analysis (SEA) is employed to establish a relationship between the lunar tidal power and the wind and temperature conditions in the lower atmosphere. A threshold value for the lunar tidal power is identified that is discriminative for the known SSW events. This threshold is then used to identify lunar tidal enhancements, which are indicative for any historic SSW events prior to 1952. It can be shown, that the number of lunar tidal enhancements and thus the occurrence frequency of historic SSW events between 1926 and 1952 is similar to the occurrence frequency of the known SSW events from 1952 onwards. Next to the classic SSW definition, the concept of polar vortex weakening (PVW) is utilized in this thesis. PVW is defined for higher latitudes and altitudes (≈ 40km) than the classical SSW definition (≈ 32km). The correlation between the timing and magnitude of lunar tidal enhancements in the EEJ and the timing and magnitude of PVW is found to be better than for the classic SSW definition. This suggests that the lunar tidal enhancements in the EEJ are closely linked to the state of the middle atmosphere. Geomagnetic observatories located in different longitudes at the dip equator allow investigating the longitudinally dependent variability of the EEJ during SSW events. For this purpose, the lunar tidal enhancements in the EEJ are determined for the Peruvian and Indian sectors during the major SSW events of the years 2006 and 2009. It is found that the lunar tidal amplitude shows similar enhancements in the Peruvian sector during both SSW events, while the enhancements are notably different for the two events in the Indian sector. In summary, this thesis shows that lunar tidal enhancements in the EEJ are indeed correlated to the occurrence of SSW events and they should be considered a prominent driver of low latitude ionospheric variability. Secondly, lunar tidal enhancements are found to be longitudinally variable. This suggests that regional effects, such as ionospheric conductivity and the geometry and strength of the geomagnetic field, also play an important role and have to be considered when investigating the mechanisms behind vertical coupling.},
  language  = {en}
}
@phdthesis{Herbrich2017,
  author    = {Herbrich, Marcus},
  title     = {Einfluss der erosionsbedingten Pedogenese auf den Wasserund Stoffhaushalt ackerbaulich genutzter B{\"o}den der Grundmor{\"a}nenbodenlandschaft NO-Deutschlands - hydropedologische Untersuchungen mittels w{\"a}gbarer Pr{\"a}zisionslysimeter},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-408561},
  school      = {Universit{\"a}t Potsdam},
  pages     = {186},
  year      = {2017},
  abstract  = {In the arable soil landscape of hummocky ground moraines, an erosion-affected spatial differentiation of soils can be observed. Man-made erosion leads to soil profile modifications along slopes with changed solum thickness and modified properties of soil horizons due to water erosion in combination with tillage operations. Soil erosion creates, thereby, spatial patterns of soil properties (e.g., texture and organic matter content) and differences in crop development. However, little is known about the manner in which water fluxes are affected by soil-crop interactions depending on contrasting properties of differently-developed soil horizons and how water fluxes influence the carbon transport in an eroded landscape. To identify such feedbacks between erosion-induced soil profile modifications and the 1D-water and solute balance, high-precision weighing lysimeters equipped with a wide range of sensor technique were filled with undisturbed soil monoliths that differed in the degree of past soil erosion. Furthermore, lysimeter effluent concentrations were analyzed for dissolved carbon fractions in bi-weekly intervals. The water balance components measured by high precision lysimeters varied from the most eroded to the less eroded monolith up to 83 \% (deep drainage) primarily caused due to varying amounts of precipitation and evapotranspiration for a 3-years period. Here, interactions between crop development and contrasting rainfall interception by above ground biomass could explain differences in water balance components. Concentrations of dissolved carbon in soil water samples were relatively constant in time, suggesting carbon leaching was mainly affected by water fluxes in this observation period. For the lysimeter-based water balance analysis, a filtering scheme was developed considering temporal autocorrelation. The minute-based autocorrelation analysis of mass changes from lysimeter time series revealed characteristic autocorrelation lengths ranging from 23 to 76 minutes. Thereby, temporal autocorrelation provided an optimal approximation of precipitation quantities. However, the high temporal resolution in lysimeter time series is restricted by the lengths of autocorrelation. Erosion-induced but also gradual changes in soil properties were reflected by dynamics of soil water retention properties in the lysimeter soils. Short-term and long-term hysteretic water retention data suggested seasonal wettability problems of soils increasingly limited rewetting of previously dried pore regions. Differences in water retention were assigned to soil tillage operations and the erosion history at different slope positions. The threedimensional spatial pattern of soil types that result from erosional soil profile modifications were also reflected in differences of crop root development at different landscape positions. Contrasting root densities revealed positive relations of root and aboveground plant characteristics. Differences in the spatially-distributed root growth between different eroded soil types provided indications that root development was affected by the erosion-induced soil evolution processes. Overall, the current thesis corroborated the hypothesis that erosion-induced soil profile modifications affect the soil water balance, carbon leaching and soil hydraulic properties, but also the crop root system is influenced by erosion-induced spatial patterns of soil properties in the arable hummocky post glacial soil landscape. The results will help to improve model predictions of water and solute movement in arable soils and to understand interactions between soil erosion and carbon pathways regarding sink-or-source terms in landscapes.},
  language  = {en}
}
@phdthesis{Zhou2017,
  author    = {Zhou, Bin},
  title     = {On the assessment of surface urban heat island},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-404383},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiii, 119},
  year      = {2017},
  abstract  = {Inwiefern St{\"a}dte unter den Megatrends der Urbanisierung und des Klimawandels nachhaltig gestaltet werden k{\"o}nnen, bleibt umstritten. Dies ist zum Teil auf unzureichende Kenntnisse der Mensch-Umwelt-Interaktionen zur{\"u}ckzuf{\"u}hren. Als die am vollst{\"a}ndigsten dokumentierte anthropogene Klimamodifikation ruft der Urbane Hitzeinsel (UHI) Effekt weltweit Sorgen hinsichtlich der Gesundheit der Bev{\"o}lkerung hervor. Dazu kommt noch ein immer h{\"a}ufigeres und intensiveres Auftreten von Hitzewellen, wodurch das Wohlbefinden der Stadtbewohner weiter beeintr{\"a}chtigt wird. Trotz eines deutlichen Anstiegs der Zahl der UHI-bezogenen Ver{\"o}ffentlichungen in den letzten Jahrzehnten haben die unterschiedlichen Definitionen von st{\"a}dtischen und l{\"a}ndlichen Gebieten in bisherigen Studien die allgemeine Vergleichbarkeit der Resultate stark erschwert. Dar{\"u}ber hinaus haben nur wenige Studien den UHI-Effekt und seine Einflussfaktoren anhand einer Kombination der Landnutzungsdaten und der thermischen Fernerkundung systematisch untersucht. Diese Arbeit stellt einen allgemeinen Rahmen zur Quantifizierung von UHI-Intensit{\"a}ten mittels eines automatisierten Algorithmus vor, wobei St{\"a}dte als Agglomerationen maximal r{\"a}umlicher Kontinuit{\"a}t basierend auf Landnutzungsdaten identifiziert, sowie deren l{\"a}ndliche Umfelder analog definiert werden. Durch Verkn{\"u}pfung der Landnutzungsdaten mit Landoberfl{\"a}chentemperaturen von Satelliten kann die UHI-Intensit{\"a}t robust und konsistent berechnet werden. Anhand dieser Innovation wurde nicht nur der Zusammenhang zwischen Stadtgr{\"o}ße und UHI-Intensit{\"a}t erneut untersucht, sondern auch die Auswirkungen der Stadtform auf die UHI-Intensit{\"a}t quantifiziert. Diese Arbeit leistet vielf{\"a}ltige Beitr{\"a}ge zum tieferen Verst{\"a}ndnis des UHI-Ph{\"a}nomens. Erstens wurde eine log-lineare Beziehung zwischen UHI-Intensit{\"a}t und Stadtgr{\"o}ße unter Ber{\"u}cksichtigung der 5,000 europ{\"a}ischen St{\"a}dte best{\"a}tigt. Werden kleinere St{\"a}dte auch ber{\"u}cksichtigt, ergibt sich eine log-logistische Beziehung. Zweitens besteht ein komplexes Zusammenspiel zwischen der Stadtform und der UHI-Intensit{\"a}t: die Stadtgr{\"o}ße stellt den st{\"a}rksten Einfluss auf die UHI-Intensit{\"a}t dar, gefolgt von der fraktalen Dimension und der Anisometrie. Allerdings zeigen ihre relativen Beitr{\"a}ge zur UHI-Intensit{\"a}t eine regionale Heterogenit{\"a}t, welche die Bedeutung r{\"a}umlicher Muster w{\"a}hrend der Umsetzung von UHI-Anpassungsmaßnahmen hervorhebt. Des Weiteren ergibt sich eine neue Saisonalit{\"a}t der UHI-Intensit{\"a}t f{\"u}r individuelle St{\"a}dte in Form von Hysteresekurven, die eine Phasenverschiebung zwischen den Zeitreihen der UHI-Intensit{\"a}t und der Hintergrundtemperatur andeutet. Diese Saisonalit{\"a}t wurde anhand von Luft- und Landoberfl{\"a}chentemperaturen untersucht, indem die Satellitenbeobachtung und die Modellierung der urbanen Grenzschicht mittels des UrbClim-Modells kombiniert wurden. Am Beispiel von London ist die Diskrepanz der Saisonalit{\"a}ten zwischen den beiden Temperaturen vor allem auf die mit der einfallenden Sonnenstrahlung verbundene Besonderheit der Landoberfl{\"a}chentemperatur zur{\"u}ckzuf{\"u}hren. Dar{\"u}ber hinaus spielt das regionale Klima eine wichtige Rolle bei der Entwicklung der UHI. Diese Arbeit ist eine der ersten Studien dieser Art, die eine systematische und statistische Untersuchung des UHI-Effektes erm{\"o}glicht. Die Ergebnisse sind von besonderer Bedeutung f{\"u}r die allgemeine r{\"a}umliche Planung und Regulierung auf Meso- und Makroebenen, damit sich Vorteile der rapiden Urbanisierung nutzbar machen und zeitgleich die folgende Hitzebelastung proaktiv vermindern lassen.},
  language  = {en}
}
@phdthesis{Kellermann2017,
  author    = {Kellermann, Patric},
  title     = {Assessing natural risks for railway infrastructure and transportation in Austria},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-103877},
  school      = {Universit{\"a}t Potsdam},
  pages     = {x, 113},
  year      = {2017},
  abstract  = {Natural hazards can have serious societal and economic impacts. Worldwide, around one third of economic losses due to natural hazards are attributable to floods. The majority of natural hazards are triggered by weather-related extremes such as heavy precipitation, rapid snow melt, or extreme temperatures. Some of them, and in particular floods, are expected to further increase in terms of frequency and/or intensity in the coming decades due to the impacts of climate change. In this context, the European Alps areas are constantly disclosed as being particularly sensitive. In order to enhance the resilience of societies to natural hazards, risk assessments are substantial as they can deliver comprehensive risk information to be used as a basis for effective and sustainable decision-making in natural hazards management. So far, current assessment approaches mostly focus on single societal or economic sectors - e.g. flood damage models largely concentrate on private-sector housing - and other important sectors, such as the transport infrastructure sector, are widely neglected. However, transport infrastructure considerably contributes to economic and societal welfare, e.g. by ensuring mobility of people and goods. In Austria, for example, the national railway network is essential for the European transit of passengers and freights as well as for the development of the complex Alpine topography. Moreover, a number of recent experiences show that railway infrastructure and transportation is highly vulnerable to natural hazards. As a consequence, the Austrian Federal Railways had to cope with economic losses on the scale of several million euros as a result of flooding and other alpine hazards. The motivation of this thesis is to contribute to filling the gap of knowledge about damage to railway infrastructure caused by natural hazards by providing new risk information for actors and stakeholders involved in the risk management of railway transportation. Hence, in order to support the decision-making towards a more effective and sustainable risk management, the following two shortcomings in natural risks research are approached: i) the lack of dedicated models to estimate flood damage to railway infrastructure, and ii) the scarcity of insights into possible climate change impacts on the frequency of extreme weather events with focus on future implications for railway transportation in Austria. With regard to flood impacts to railway infrastructure, the empirically derived damage model Railway Infrastructure Loss (RAIL) proved expedient to reliably estimate both structural flood damage at exposed track sections of the Northern Railway and resulting repair cost. The results show that the RAIL model is capable of identifying flood risk hot spots along the railway network and, thus, facilitates the targeted planning and implementation of (technical) risk reduction measures. However, the findings of this study also show that the development and validation of flood damage models for railway infrastructure is generally constrained by the continuing lack of detailed event and damage data. In order to provide flood risk information on the large scale to support strategic flood risk management, the RAIL model was applied for the Austrian Mur River catchment using three different hydraulic scenarios as input as well as considering an increased risk aversion of the railway operator. Results indicate that the model is able to deliver comprehensive risk information also on the catchment level. It is furthermore demonstrated that the aspect of risk aversion can have marked influence on flood damage estimates for the study area and, hence, should be considered with regard to the development of risk management strategies. Looking at the results of the investigation on future frequencies of extreme weather events jeopardizing railway infrastructure and transportation in Austria, it appears that an increase in intense rainfall events and heat waves has to be expected, whereas heavy snowfall and cold days are likely to decrease. Furthermore, results indicate that frequencies of extremes are rather sensitive to changes of the underlying thresholds. It thus emphasizes the importance to carefully define, validate, and — if needed — to adapt the thresholds that are used to detect and forecast meteorological extremes. For this, continuous and standardized documentation of damaging events and near-misses is a prerequisite. Overall, the findings of the research presented in this thesis agree on the necessity to improve event and damage documentation procedures in order to enable the acquisition of comprehensive and reliable risk information via risk assessments and, thus, support strategic natural hazards management of railway infrastructure and transportation.},
  language  = {en}
}
@phdthesis{Gudipudi2017,
  author    = {Gudipudi, Venkata Ramana},
  title     = {Cities and global sustainability},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-407113},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxii, 101},
  year      = {2017},
  abstract  = {In the wake of 21st century, humanity witnessed a phenomenal raise of urban agglomerations as powerhouses for innovation and socioeconomic growth. Driving much of national (and in few instances even global) economy, such a gargantuan raise of cities is also accompanied by subsequent increase in energy, resource consumption and waste generation. Much of anthropogenic transformation of Earth's environment in terms of environmental pollution at local level to planetary scale in the form of climate change is currently taking place in cities. Projected to be crucibles for entire humanity by the end of this century, the ultimate fate of humanity predominantly lies in the hands of technological innovation, urbanites' attitudes towards energy/resource consumption and development pathways undertaken by current and future cities. Considering the unparalleled energy, resource consumption and emissions currently attributed to global cities, this thesis addresses these issues from an efficiency point of view. More specifically, this thesis addresses the influence of population size, density, economic geography and technology in improving urban greenhouse gas (GHG) emission efficiency and identifies the factors leading to improved eco-efficiency in cities. In order to investigate the in uence of these factors in improving emission and resource efficiency in cities, a multitude of freely available datasets were coupled with some novel methodologies and analytical approaches in this thesis. Merging the well-established Kaya Identity to the recently developed urban scaling laws, an Urban Kaya Relation is developed to identify whether large cities are more emission efficient and the intrinsic factors leading to such (in)efficiency. Applying Urban Kaya Relation to a global dataset of 61 cities in 12 countries, this thesis identifed that large cities in developed regions of the world will bring emission efficiency gains because of the better technologies implemented in these cities to produce and utilize energy consumption while the opposite is the case for cities in developing regions. Large cities in developing countries are less efficient mainly because of their affluence and lack of efficient technologies. Apart from the in uence of population size on emission efficiency, this thesis identified the crucial role played by population density in improving building and on-road transport sector related emission efficiency in cities. This is achieved by applying the City Clustering Algorithm (CCA) on two different gridded land use datasets and a standard emission inventory to attribute these sectoral emissions to all inhabited settlements in the USA. Results show that doubling the population density would entail a reduction in the total CO2 emissions in buildings and on-road sectors typically by at least 42 \%. Irrespective of their population size and density, cities are often blamed for their intensive resource consumption that threatens not only local but also global sustainability. This thesis merged the concept of urban metabolism with benchmarking and identified cities which are eco-efficient. These cities enable better socioeconomic conditions while being less burden to the environment. Three environmental burden indicators (annual average NO2 concentration, per capita waste generation and water consumption) and two socioeconomic indicators (GDP per capita and employment ratio) for 88 most populous European cities are considered in this study. Using two different non-parametric ranking methods namely regression residual ranking and Data Envelopment Analysis (DEA), eco-efficient cities and their determining factors are identified. This in-depth analysis revealed that mature cities with well-established economic structures such as Munich, Stockholm and Oslo are eco-efficient. Further, correlations between objective eco-efficiency ranking with each of the indicator rankings and the ranking of urbanites' subjective perception about quality of life are analyzed. This analysis revealed that urbanites' perception about quality of life is not merely confined to the socioeconomic well-being but rather to their combination with lower environmental burden. In summary, the findings of this dissertation has three general conclusions for improving emission and ecological efficiency in cities. Firstly, large cities in emerging nations face a huge challenge with respect to improving their emission efficiency. The task in front of these cities is threefold: (1) deploying efficient technologies for the generation of electricity and improvement of public transportation to unlock their leap frogging potential, (2) addressing the issue of energy poverty and (3) ensuring that these cities do not develop similar energy consumption patterns with infrastructure lock-in behavior similar to those of cities in developed regions. Secondly, the on-going urban sprawl as a global phenomenon will decrease the emission efficiency within the building and transportation sector. Therefore, local policy makers should identify adequate fiscal and land use policies to curb urban sprawl. Lastly, since mature cities with well-established economic structures are more eco-efficient and urbanites' perception re ects its combination with decreasing environmental burden; there is a need to adopt and implement strategies which enable socioeconomic growth in cities whilst decreasing their environment burden.},
  language  = {en}
}
@phdthesis{Murawski2017,
  author    = {Murawski, Aline},
  title     = {Trends in precipitation over Germany and the Rhine basin related to changes in weather patterns},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-412725},
  school      = {Universit{\"a}t Potsdam},
  pages     = {112},
  year      = {2017},
  abstract  = {Niederschlag als eine der wichtigsten meteorologischen Gr{\"o}ßen f{\"u}r Landwirtschaft, Wasserversorgung und menschliches Wohlbefinden hat schon immer erh{\"o}hte Aufmerksamkeit erfahren. Niederschlagsmangel kann verheerende Auswirkungen haben, wie z.B. Missernten und Wasserknappheit. {\"U}berm{\"a}ßige Niederschl{\"a}ge andererseits bergen jedoch ebenfalls Gefahren in Form von Hochwasser oder Sturzfluten und wiederum Missernten. Daher wurde viel Arbeit in die Detektion von Niederschlags{\"a}nderungen und deren zugrundeliegende Prozesse gesteckt. Insbesondere angesichts von Klimawandel und unter Ber{\"u}cksichtigung des Zusammenhangs zwischen Temperatur und atmosph{\"a}rischer Wasserhaltekapazit{\"a}t, ist großer Bedarf an Forschung zum Verst{\"a}ndnis der Auswirkungen von Klimawandel auf Niederschlags{\"a}nderungen gegeben. Die vorliegende Arbeit hat das Ziel, vergangene Ver{\"a}nderungen in Niederschlag und anderen meteorologischen Variablen zu verstehen. F{\"u}r verschiedene Zeitr{\"a}ume wurden Tendenzen gefunden und mit entsprechenden Ver{\"a}nderungen in der großskaligen atmosph{\"a}rischen Zirkulation in Zusammenhang gebracht. Die Ergebnisse dieser Arbeit k{\"o}nnen als Grundlage f{\"u}r die Attributierung von Hochwasserver{\"a}nderungen zu Klimawandel genutzt werden. Die Annahmen f{\"u}r die Maßstabsverkleinerung („Downscaling") der Daten von großskaligen Zirkulationsmodellen auf die lokale Skala wurden hier getestet und verifziert. In einem ersten Schritt wurden Niederschlagsver{\"a}nderungen in Deutschland analysiert. Dabei lag der Fokus nicht nur auf Niederschlagssummen, sondern auch auf Eigenschaften der statistischen Verteilung, {\"U}bergangswahrscheinlichkeiten als Maß f{\"u}r Trocken- und Niederschlagsperioden und Extremniederschlagsereignissen. Den r{\"a}umlichen Fokus auf das Rheineinzugsgebiet, das gr{\"o}ßte Flusseinzugsgebiet Deutschlands und einer der Hauptwasserwege Europas, verlagernd, wurden nachgewiesene Ver{\"a}nderungen in Niederschlag und anderen meteorologischen Gr{\"o}ßen in Bezug zu einer „optimierten" Wetterlagenklassifikation analysiert. Die Wetterlagenklassifikation wurde unter der Maßgabe entwickelt, die Varianz des lokalen Klimas bestm{\"o}glich zu erkl{\"a}ren. Die letzte hier behandelte Frage dreht sich darum, ob die beobachteten Ver{\"a}nderungen im lokalen Klima eher H{\"a}ufigkeits{\"a}nderungen der Wetterlagen zuzuordnen sind oder einer Ver{\"a}nderung der Wetterlagen selbst. Eine gebr{\"a}uchliche Annahme f{\"u}r einen Downscaling-Ansatz mit Hilfe von Wetterlagen und einem stochastischen Wettergenerator ist, dass Klimawandel sich allein durch eine Ver{\"a}nderung der H{\"a}ufigkeit von Wetterlagen ausdr{\"u}ckt, die Eigenschaften der Wetterlagen dabei jedoch konstant bleiben. Diese Annahme wurde {\"u}berpr{\"u}ft und die F{\"a}higkeit der neuesten Generation von Zirkulationsmodellen, diese Wetterlagen zu reproduzieren, getestet. Niederschlagsver{\"a}nderungen in Deutschland im Zeitraum 1951-2006 lassen sich zusammenfassen als negativ im Sommer und positiv in allen anderen Jahreszeiten. Verschiedene Niederschlagscharakteristika best{\"a}tigen die Tendenz in den Niederschlagssummen: w{\"a}hrend mittlere und extreme Niederschlagstageswerte im Winter zugenommen haben, sind auch zusammenh{\"a}ngende Niederschlagsperioden l{\"a}nger geworden (ausgedr{\"u}ckt als eine gestiegene Wahrscheinlichkeit f{\"u}r einen Tag mit Niederschlag gefolgt von einem weiteren nassen Tag). Im Sommer wurde das Gegenteil beobachtet: gesunkene Niederschlagssummen, untermauert von verringerten Mittel- und Extremwerten und l{\"a}ngeren Trockenperioden. Abseits dieser allgemeinen Zusammenfassung f{\"u}r das gesamte Gebiet Deutschlands, ist die r{\"a}umliche Verteilung von Niederschlagsver{\"a}nderungen deutlich heterogener. Vermehrter Niederschlag im Winter wurde haupts{\"a}chlich im Nordwesten und S{\"u}dosten Deutschlands beobachtet, w{\"a}hrend im Fr{\"u}hling die st{\"a}rksten Ver{\"a}nderungen im Westen und im Herbst im S{\"u}den aufgetreten sind. Das saisonale Bild wiederum l{\"o}st sich f{\"u}r die zugeh{\"o}rigen Monate auf, z.B. setzt sich der Anstieg im Herbstniederschlag aus deutlich vermehrtem Niederschlag im S{\"u}dwesten im Oktober und im S{\"u}dosten im November zusammen. Diese Ergebnisse betonen die starken r{\"a}umlichen Zusammenh{\"a}nge der Niederschlags{\"a}nderungen. Der n{\"a}chste Schritt hinsichtlich einer Zuordnung von Niederschlagsver{\"a}nderungen zu {\"A}nderungen in großskaligen Zirkulationsmustern, war die Ableitung einer Wetterlagenklassifikation, die die betrachteten lokalen Klimavariablen hinreichend stratifizieren kann. Fokussierend auf Temperatur, Globalstrahlung und Luftfeuchte zus{\"a}tzlich zu Niederschlag, wurde eine Klassifikation basierend auf Luftdruck, Temperatur und spezifischer Luftfeuchtigkeit als am besten geeignet erachtet, die Varianz der lokalen Variablen zu erkl{\"a}ren. Eine vergleichsweise hohe Anzahl von 40 Wetterlagen wurde ausgew{\"a}hlt, die es erlaubt, typische Druckmuster durch die zus{\"a}tzlich verwendete Temperaturinformation einzelnen Jahreszeiten zuzuordnen. W{\"a}hrend die F{\"a}higkeit, Varianz im Niederschlag zu erkl{\"a}ren, relativ gering ist, ist diese deutlich besser f{\"u}r Globalstrahlung und nat{\"u}rlich Temperatur. Die meisten der aktuellen Zirkulationsmodelle des CMIP5-Ensembles sind in der Lage, die Wetterlagen hinsichtlich H{\"a}ufigkeit, Saisonalit{\"a}t und Persistenz hinreichend gut zu reproduzieren. Schließlich wurden dieWetterlagen bez{\"u}glich Ver{\"a}nderungen in ihrer H{\"a}ufigkeit, Saisonalit{\"a}t und Persistenz, sowie der Wetterlagen-spezifischen Niederschl{\"a}ge und Temperatur, untersucht. Um Unsicherheiten durch die Wahl eines bestimmten Analysezeitraums auszuschließen, wurden alle m{\"o}glichen Zeitr{\"a}ume mit mindestens 31 Jahren im Zeitraum 1901-2010 untersucht. Dadurch konnte die Annahme eines konstanten Zusammenhangs zwischen Wetterlagen und lokalem Wetter gr{\"u}ndlich {\"u}berpr{\"u}ft werden. Es wurde herausgefunden, dass diese Annahme nur zum Teil haltbar ist. W{\"a}hrend Ver{\"a}nderungen in der Temperatur haupts{\"a}chlich auf Ver{\"a}nderungen in der Wetterlagenh{\"a}ufigkeit zur{\"u}ckzuf{\"u}hren sind, wurde f{\"u}r Niederschlag ein erheblicher Teil von Ver{\"a}nderungen innerhalb einzelner Wetterlagen gefunden. Das Ausmaß und sogar das Vorzeichen der Ver{\"a}nderungen h{\"a}ngt hochgradig vom untersuchten Zeitraum ab. Die H{\"a}ufigkeit einiger Wetterlagen steht in direkter Beziehung zur langfristigen Variabilit{\"a}t großskaliger Zirkulationsmuster. Niederschlagsver{\"a}nderungen variieren nicht nur r{\"a}umlich, sondern auch zeitlich - Aussagen {\"u}ber Tendenzen sind nur in Bezug zum jeweils untersuchten Zeitraum g{\"u}ltig. W{\"a}hrend ein Teil der Ver{\"a}nderungen auf {\"A}nderungen der großskaligen Zirkulation zur{\"u}ckzuf{\"u}hren ist, gibt es auch deutliche Ver{\"a}nderungen innerhalb einzelner Wetterlagen. Die Ergebnisse betonen die Notwendigkeit f{\"u}r einen sorgf{\"a}ltigen Nachweis von Ver{\"a}nderungen m{\"o}glichst verschiedene Zeitr{\"a}ume zu untersuchen und mahnen zur Vorsicht bei der Anwendung von Downscaling-Ans{\"a}tzen mit Hilfe von Wetterlagen, da diese die Auswirkungen von Klimaver{\"a}nderungen durch das Vernachl{\"a}ssigen von Wetterlagen-internen Ver{\"a}nderungen falsch einsch{\"a}tzen k{\"o}nnten.},
  language  = {en}
}
@phdthesis{Golly2017,
  author    = {Golly, Antonius},
  title     = {Formation and evolution of channel steps and their role for sediment dynamics in a steep mountain stream},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-411728},
  school      = {Universit{\"a}t Potsdam},
  pages     = {180},
  year      = {2017},
  abstract  = {Steep mountain channels are an important component of the fluvial system. On geological timescales, they shape mountain belts and counteract tectonic uplift by erosion. Their channels are strongly coupled to hillslopes and they are often the main source of sediment transported downstream to low-gradient rivers and to alluvial fans, where commonly settlements in mountainous areas are located. Hence, mountain streams are the cause for one of the main natural hazards in these regions. Due to climate change and a pronounced populating of mountainous regions the attention given to this threat is even growing. Although quantitative studies on sediment transport have significantly advanced our knowledge on measuring and calibration techniques we still lack studies of the processes within mountain catchments. Studies examining the mechanisms of energy and mass exchange on small temporal and spatial scales in steep streams remain sparse in comparison to low-gradient alluvial channels. In the beginning of this doctoral project, a vast amount of experience and knowledge of a steep stream in the Swiss Prealps had to be consolidated in order to shape the principal aim of this research effort. It became obvious, that observations from within the catchment are underrepresented in comparison to experiments performed at the catchment's outlet measuring fluxes and the effects of the transported material. To counteract this imbalance, an examination of mass fluxes within the catchment on the process scale was intended. Hence, this thesis is heavily based on direct field observations, which are generally rare in these environments in quantity and quality. The first objective was to investigate the coupling of the channel with surrounding hillslopes, the major sources of sediment. This research, which involved the monitoring of the channel and adjacent hillslopes, revealed that alluvial channel steps play a key role in coupling of channel and hillslopes. The observations showed that hillslope stability is strongly associated with the step presence and an understanding of step morphology and stability is therefore crucial in understanding sediment mobilization. This finding refined the way we think about the sediment dynamics in steep channels and motivated continued research of the step dynamics. However, soon it became obvious that the technological basis for developing field tests and analyzing the high resolution geometry measured in the field was not available. Moreover, for many geometrical quantities in mountain channels definitions and a clear scientific standard was not available. For example, these streams are characterized by a high spatial variability of the channel banks, preventing straightforward calculations of the channel width without a defined reference. Thus, the second and inevitable part of this thesis became the development and evaluation of scientific tools in order to investigate the geometrical content of the study reach thoroughly. The developed framework allowed the derivation of various metrics of step and channel geometry which facilitated research on the a large data set of observations of channel steps. In the third part, innovative, physically-based metrics have been developed and compared to current knowledge on step formation, suggested in the literature. With this analyses it could be demonstrated that the formation of channel steps follow a wide range of hydraulic controls. Due to the wide range of tested parameters channel steps observed in a natural stream were attributed to different mechanisms of step formation, including those based on jamming and those based on key-stones. This study extended our knowledge on step formation in a steep stream and harmonized different, often time seen as competing, processes of step formation. This study was based on observations collected at one point in time. In the fourth part of this project, the findings of the snap-shot observations were extended in the temporal dimension and the derived concepts have been utilized to investigate reach-scale step patterns in response to large, exceptional flood events. The preliminary results of this work based on the long-term analyses of 7 years of long profile surveys showed that the previously observed channel-hillslope mechanism is the responsible for the short-term response of step formation. The findings of the long-term analyses of step patterns drew a bow to the initial observations of a channel-hillslope system which allowed to join the dots in the dynamics of steep stream. Thus, in this thesis a broad approach has been chosen to gain insights into the complex system of steep mountain rivers. The effort includes in situ field observations (article I), the development of quantitative scientific tools (article II), the reach-scale analyses of step-pool morphology (article III) and its temporal evolution (article IV). With this work our view on the processes within the catchment has been advanced towards a better mechanistic understanding of these fluvial system relevant to improve applied scientific work.},
  language  = {en}
}
@phdthesis{Theuring2017,
  author    = {Theuring, Philipp Christian},
  title     = {Suspended sediments in the Kharaa River, sources and impacts},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-410550},
  school      = {Universit{\"a}t Potsdam},
  pages     = {135},
  year      = {2017},
  abstract  = {Anthropogenically amplified erosion leads to increased fine-grained sediment input into the fluvial system in the 15.000 km2 Kharaa River catchment in northern Mongolia and constitutes a major stressing factor for the aquatic ecosystem. This study uniquely combines the application of intensive monitoring, source fingerprinting and catchment modelling techniques to allow for the comparison of the credibility and accuracy of each single method. High-resolution discharge data were used in combination with daily suspended solid measurements to calculate the suspended sediment budget and compare it with estimations of the sediment budget model SedNet. The comparison of both techniques showed that the development of an overall sediment budget with SedNet was possible, yielding results in the same order of magnitude (20.3 kt a- 1 and 16.2 kt a- 1). Radionuclide sediment tracing, using Be-7, Cs-137 and Pb-210 was applied to differentiate sediment sources for particles < 10μm from hillslope and riverbank erosion and showed that riverbank erosion generates 74.5\% of the suspended sediment load, whereas surface erosion contributes 21.7\% and gully erosion only 3.8\%. The contribution of the single subcatchments of the Kharaa to the suspended sediment load was assessed based on their variation in geochemical composition (e.g. in Ti, Sn, Mo, Mn, As, Sr, B, U, Ca and Sb). These variations were used for sediment source discrimination with geochemical composite fingerprints based on Genetic Algorithm driven Discriminant Function Analysis, the Kruskal-Wallis H-test and Principal Component Analysis. The contributions of the individual sub-catchment varied from 6.4\% to 36.2\%, generally showing higher contributions from the sub-catchments in the middle, rather than the upstream portions of the study area. The results indicate that river bank erosion generated by existing grazing practices of livestock is the main cause for elevated fine sediment input. Actions towards the protection of the headwaters and the stabilization of the river banks within the middle reaches were identified as the highest priority. Deforestation and by lodging and forest fires should be prevented to avoid increased hillslope erosion in the mountainous areas. Mining activities are of minor importance for the overall catchment sediment load but can constitute locally important point sources for particular heavy metals in the fluvial system.},
  language  = {en}
}