TY - THES A1 - Murawski, Aline T1 - Trends in precipitation over Germany and the Rhine basin related to changes in weather patterns T1 - Zeitliche Veränderungen im Niederschlag über Deutschland und dem Rheineinzugsgebiet in Zusammenhang mit Wetterlagen N2 - Niederschlag als eine der wichtigsten meteorologischen Größen für Landwirtschaft, Wasserversorgung und menschliches Wohlbefinden hat schon immer erhöhte Aufmerksamkeit erfahren. Niederschlagsmangel kann verheerende Auswirkungen haben, wie z.B. Missernten und Wasserknappheit. Übermäßige Niederschläge andererseits bergen jedoch ebenfalls Gefahren in Form von Hochwasser oder Sturzfluten und wiederum Missernten. Daher wurde viel Arbeit in die Detektion von Niederschlagsänderungen und deren zugrundeliegende Prozesse gesteckt. Insbesondere angesichts von Klimawandel und unter Berücksichtigung des Zusammenhangs zwischen Temperatur und atmosphärischer Wasserhaltekapazität, ist großer Bedarf an Forschung zum Verständnis der Auswirkungen von Klimawandel auf Niederschlagsänderungen gegeben. Die vorliegende Arbeit hat das Ziel, vergangene Veränderungen in Niederschlag und anderen meteorologischen Variablen zu verstehen. Für verschiedene Zeiträume wurden Tendenzen gefunden und mit entsprechenden Veränderungen in der großskaligen atmosphärischen Zirkulation in Zusammenhang gebracht. Die Ergebnisse dieser Arbeit können als Grundlage für die Attributierung von Hochwasserveränderungen zu Klimawandel genutzt werden. Die Annahmen für die Maßstabsverkleinerung („Downscaling“) der Daten von großskaligen Zirkulationsmodellen auf die lokale Skala wurden hier getestet und verifziert. In einem ersten Schritt wurden Niederschlagsveränderungen in Deutschland analysiert. Dabei lag der Fokus nicht nur auf Niederschlagssummen, sondern auch auf Eigenschaften der statistischen Verteilung, Übergangswahrscheinlichkeiten als Maß für Trocken- und Niederschlagsperioden und Extremniederschlagsereignissen. Den räumlichen Fokus auf das Rheineinzugsgebiet, das größte Flusseinzugsgebiet Deutschlands und einer der Hauptwasserwege Europas, verlagernd, wurden nachgewiesene Veränderungen in Niederschlag und anderen meteorologischen Größen in Bezug zu einer „optimierten“ Wetterlagenklassifikation analysiert. Die Wetterlagenklassifikation wurde unter der Maßgabe entwickelt, die Varianz des lokalen Klimas bestmöglich zu erklären. Die letzte hier behandelte Frage dreht sich darum, ob die beobachteten Veränderungen im lokalen Klima eher Häufigkeitsänderungen der Wetterlagen zuzuordnen sind oder einer Veränderung der Wetterlagen selbst. Eine gebräuchliche Annahme für einen Downscaling-Ansatz mit Hilfe von Wetterlagen und einem stochastischen Wettergenerator ist, dass Klimawandel sich allein durch eine Veränderung der Häufigkeit von Wetterlagen ausdrückt, die Eigenschaften der Wetterlagen dabei jedoch konstant bleiben. Diese Annahme wurde überprüft und die Fähigkeit der neuesten Generation von Zirkulationsmodellen, diese Wetterlagen zu reproduzieren, getestet. Niederschlagsveränderungen in Deutschland im Zeitraum 1951–2006 lassen sich zusammenfassen als negativ im Sommer und positiv in allen anderen Jahreszeiten. Verschiedene Niederschlagscharakteristika bestätigen die Tendenz in den Niederschlagssummen: während mittlere und extreme Niederschlagstageswerte im Winter zugenommen haben, sind auch zusammenhängende Niederschlagsperioden länger geworden (ausgedrückt als eine gestiegene Wahrscheinlichkeit für 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 längeren Trockenperioden. Abseits dieser allgemeinen Zusammenfassung für das gesamte Gebiet Deutschlands, ist die räumliche Verteilung von Niederschlagsveränderungen deutlich heterogener. Vermehrter Niederschlag im Winter wurde hauptsächlich im Nordwesten und Südosten Deutschlands beobachtet, während im Frühling die stärksten Veränderungen im Westen und im Herbst im Süden aufgetreten sind. Das saisonale Bild wiederum löst sich für die zugehörigen Monate auf, z.B. setzt sich der Anstieg im Herbstniederschlag aus deutlich vermehrtem Niederschlag im Südwesten im Oktober und im Südosten im November zusammen. Diese Ergebnisse betonen die starken räumlichen Zusammenhänge der Niederschlagsänderungen. Der nächste Schritt hinsichtlich einer Zuordnung von Niederschlagsveränderungen zu Änderungen in großskaligen Zirkulationsmustern, war die Ableitung einer Wetterlagenklassifikation, die die betrachteten lokalen Klimavariablen hinreichend stratifizieren kann. Fokussierend auf Temperatur, Globalstrahlung und Luftfeuchte zusätzlich zu Niederschlag, wurde eine Klassifikation basierend auf Luftdruck, Temperatur und spezifischer Luftfeuchtigkeit als am besten geeignet erachtet, die Varianz der lokalen Variablen zu erklären. Eine vergleichsweise hohe Anzahl von 40 Wetterlagen wurde ausgewählt, die es erlaubt, typische Druckmuster durch die zusätzlich verwendete Temperaturinformation einzelnen Jahreszeiten zuzuordnen. Während die Fähigkeit, Varianz im Niederschlag zu erklären, relativ gering ist, ist diese deutlich besser für Globalstrahlung und natürlich Temperatur. Die meisten der aktuellen Zirkulationsmodelle des CMIP5-Ensembles sind in der Lage, die Wetterlagen hinsichtlich Häufigkeit, Saisonalität und Persistenz hinreichend gut zu reproduzieren. Schließlich wurden dieWetterlagen bezüglich Veränderungen in ihrer Häufigkeit, Saisonalität und Persistenz, sowie der Wetterlagen-spezifischen Niederschläge und Temperatur, untersucht. Um Unsicherheiten durch die Wahl eines bestimmten Analysezeitraums auszuschließen, wurden alle möglichen Zeiträume mit mindestens 31 Jahren im Zeitraum 1901–2010 untersucht. Dadurch konnte die Annahme eines konstanten Zusammenhangs zwischen Wetterlagen und lokalem Wetter gründlich überprüft werden. Es wurde herausgefunden, dass diese Annahme nur zum Teil haltbar ist. Während Veränderungen in der Temperatur hauptsächlich auf Veränderungen in der Wetterlagenhäufigkeit zurückzuführen sind, wurde für Niederschlag ein erheblicher Teil von Veränderungen innerhalb einzelner Wetterlagen gefunden. Das Ausmaß und sogar das Vorzeichen der Veränderungen hängt hochgradig vom untersuchten Zeitraum ab. Die Häufigkeit einiger Wetterlagen steht in direkter Beziehung zur langfristigen Variabilität großskaliger Zirkulationsmuster. Niederschlagsveränderungen variieren nicht nur räumlich, sondern auch zeitlich – Aussagen über Tendenzen sind nur in Bezug zum jeweils untersuchten Zeitraum gültig. Während ein Teil der Veränderungen auf Änderungen der großskaligen Zirkulation zurückzuführen ist, gibt es auch deutliche Veränderungen innerhalb einzelner Wetterlagen. Die Ergebnisse betonen die Notwendigkeit für einen sorgfältigen Nachweis von Veränderungen möglichst verschiedene Zeiträume zu untersuchen und mahnen zur Vorsicht bei der Anwendung von Downscaling-Ansätzen mit Hilfe von Wetterlagen, da diese die Auswirkungen von Klimaveränderungen durch das Vernachlässigen von Wetterlagen-internen Veränderungen falsch einschätzen könnten. N2 - Precipitation as the central meteorological feature for agriculture, water security, and human well-being amongst others, has gained special attention ever since. Lack of precipitation may have devastating effects such as crop failure and water scarcity. Abundance of precipitation, on the other hand, may as well result in hazardous events such as flooding and again crop failure. Thus, great effort has been spent on tracking changes in precipitation and relating them to underlying processes. Particularly in the face of global warming and given the link between temperature and atmospheric water holding capacity, research is needed to understand the effect of climate change on precipitation. The present work aims at understanding past changes in precipitation and other meteorological variables. Trends were detected for various time periods and related to associated changes in large-scale atmospheric circulation. The results derived in this thesis may be used as the foundation for attributing changes in floods to climate change. Assumptions needed for the downscaling of large-scale circulation model output to local climate stations are tested and verified here. In a first step, changes in precipitation over Germany were detected, focussing not only on precipitation totals, but also on properties of the statistical distribution, transition probabilities as a measure for wet/dry spells, and extreme precipitation events. Shifting the spatial focus to the Rhine catchment as one of the major water lifelines of Europe and the largest river basin in Germany, detected trends in precipitation and other meteorological variables were analysed in relation to states of an ``optimal'' weather pattern classification. The weather pattern classification was developed seeking the best skill in explaining the variance of local climate variables. The last question addressed whether observed changes in local climate variables are attributable to changes in the frequency of weather patterns or rather to changes within the patterns itself. A common assumption for a downscaling approach using weather patterns and a stochastic weather generator is that climate change is expressed only as a changed occurrence of patterns with the pattern properties remaining constant. This assumption was validated and the ability of the latest generation of general circulation models to reproduce the weather patterns was evaluated. % Paper 1 Precipitation changes in Germany in the period 1951-2006 can be summarised briefly as negative in summer and positive in all other seasons. Different precipitation characteristics confirm the trends in total precipitation: while winter mean and extreme precipitation have increased, wet spells tend to be longer as well (expressed as increased probability for a wet day followed by another wet day). For summer the opposite was observed: reduced total precipitation, supported by decreasing mean and extreme precipitation and reflected in an increasing length of dry spells. Apart from this general summary for the whole of Germany, the spatial distribution within the country is much more differentiated. Increases in winter precipitation are most pronounced in the north-west and south-east of Germany, while precipitation increases are highest in the west for spring and in the south for autumn. Decreasing summer precipitation was observed in most regions of Germany, with particular focus on the south and west. The seasonal picture, however, was again differently represented in the contributing months, e.g.\ increasing autumn precipitation in the south of Germany is formed by strong trends in the south-west in October and in the south-east in November. These results emphasise the high spatial and temporal organisation of precipitation changes. % Paper 2 The next step towards attributing precipitation trends to changes in large-scale atmospheric patterns was the derivation of a weather pattern classification that sufficiently stratifies the local climate variables under investigation. Focussing on temperature, radiation, and humidity in addition to precipitation, a classification based on mean sea level pressure, near-surface temperature, and specific humidity was found to have the best skill in explaining the variance of the local variables. A rather high number of 40 patterns was selected, allowing typical pressure patterns being assigned to specific seasons by the associated temperature patterns. While the skill in explaining precipitation variance is rather low, better skill was achieved for radiation and, of course, temperature. Most of the recent GCMs from the CMIP5 ensemble were found to reproduce these weather patterns sufficiently well in terms of frequency, seasonality, and persistence. % Paper 3 Finally, the weather patterns were analysed for trends in pattern frequency, seasonality, persistence, and trends in pattern-specific precipitation and temperature. To overcome uncertainties in trend detection resulting from the selected time period, all possible periods in 1901-2010 with a minimum length of 31 years were considered. Thus, the assumption of a constant link between patterns and local weather was tested rigorously. This assumption was found to hold true only partly. While changes in temperature are mainly attributable to changes in pattern frequency, for precipitation a substantial amount of change was detected within individual patterns. Magnitude and even sign of trends depend highly on the selected time period. The frequency of certain patterns is related to the long-term variability of large-scale circulation modes. Changes in precipitation were found to be heterogeneous not only in space, but also in time - statements on trends are only valid for the specific time period under investigation. While some part of the trends can be attributed to changes in the large-scale circulation, distinct changes were found within single weather patterns as well. The results emphasise the need to analyse multiple periods for thorough trend detection wherever possible and add some note of caution to the application of downscaling approaches based on weather patterns, as they might misinterpret the effect of climate change due to neglecting within-type trends. KW - precipitation KW - weather pattern KW - trend analyses KW - Niederschlag KW - Wetterlagen KW - Trendanalysen Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-412725 ER - TY - GEN A1 - Dallmeyer, Anne A1 - Claussen, M. A1 - Fischer, N. A1 - Haberkorn, K. A1 - Wagner, S. A1 - Pfeiffer, M. A1 - Jin, L. A1 - Khon, Vyacheslav A1 - Wang, Y. A1 - Herzschuh, Ulrike T1 - The evolution of sub-monsoon systems in the Afro-Asian monsoon region during the Holocene BT - comparison of different transient climate model simulations T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The recently proposed global monsoon hypothesis interprets monsoon systems as part of one global-scale atmospheric overturning circulation, implying a connection between the regional monsoon systems and an in-phase behaviour of all northern hemispheric monsoons on annual timescales (Trenberth et al., 2000). Whether this concept can be applied to past climates and variability on longer timescales is still under debate, because the monsoon systems exhibit different regional characteristics such as different seasonality (i. e. onset, peak and withdrawal). To investigate the interconnection of different monsoon systems during the pre-industrial Holocene, five transient global climate model simulations have been analysed with respect to the rainfall trend and variability in different sub-domains of the Afro-Asian monsoon region. Our analysis suggests that on millennial timescales with varying orbital forcing, the monsoons do not behave as a tightly connected global system. According to the models, the Indian and North African monsoons are coupled, showing similar rainfall trend and moderate correlation in centennial rainfall variability in all models. The East Asian monsoon changes independently during the Holocene. The dissimilarities in the seasonality of the monsoon sub-systems lead to a stronger response of the North African and Indian monsoon systems to the Holocene insolation forcing than of the East Asian monsoon and affect the seasonal distribution of Holocene rainfall variations. Within the Indian and North African monsoon domain, precipitation solely changes during the summer months, showing a decreasing Holocene precipitation trend. In the East Asian monsoon region, the precipitation signal is determined by an increasing precipitation trend during spring and a decreasing precipitation change during summer, partly balancing each other. A synthesis of reconstructions and the model results do not reveal an impact of the different seasonality on the timing of the Holocene rainfall optimum in the different sub-monsoon systems. Rather they indicate locally inhomogeneous rainfall changes and show that single palaeo-records should not be used to characterise the rainfall change and monsoon evolution for entire monsoon sub-systems. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 587 KW - summer monsoon KW - global monsoon KW - indian monsoon KW - high-resolution KW - cave records KW - variability KW - precipitation KW - circulation KW - insolation KW - rainfall Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-409727 SN - 1866-8372 IS - 587 ER - TY - GEN A1 - Dallmeyer, Anne A1 - Claussen, Martin A1 - Wang, Yongbo A1 - Herzschuh, Ulrike T1 - Spatial variability of Holocene changes in the annual precipitation pattern BT - a model-data synthesis for the Asian monsoon region T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - This study provides a detailed analysis of the mid-Holocene to present-day precipitation change in the Asian monsoon region. We compare for the first time results of high resolution climate model simulations with a standardised set of mid-Holocene moisture reconstructions. Changes in the simulated summer monsoon characteristics (onset, withdrawal, length and associated rainfall) and the mechanisms causing the Holocene precipitation changes are investigated. According to the model, most parts of the Indian subcontinent received more precipitation (up to 5 mm/day) at mid-Holocene than at present-day. This is related to a stronger Indian summer monsoon accompanied by an intensified vertically integrated moisture flux convergence. The East Asian monsoon region exhibits local inhomogeneities in the simulated annual precipitation signal. The sign of this signal depends on the balance of decreased pre-monsoon and increased monsoon precipitation at mid-Holocene compared to present-day. Hence, rainfall changes in the East Asian monsoon domain are not solely associated with modifications in the summer monsoon circulation but also depend on changes in the mid-latitudinal westerly wind system that dominates the circulation during the pre-monsoon season. The proxy-based climate reconstructions confirm the regional dissimilarities in the annual precipitation signal and agree well with the model results. Our results highlight the importance of including the pre-monsoon season in climate studies of the Asian monsoon system and point out the complex response of this system to the Holocene insolation forcing. The comparison with a coarse climate model simulation reveals that this complex response can only be resolved in high resolution simulations. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 905 KW - Asian monsoon KW - holocene KW - precipitation KW - climate modelling KW - moisture reconstructions Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-432771 SN - 1866-8372 IS - 905 ER - TY - GEN A1 - Agarwal, Ankit A1 - Marwan, Norbert A1 - Maheswaran, Rathinasamy A1 - Öztürk, Ugur A1 - Kurths, Jürgen A1 - Merz, Bruno T1 - Optimal design of hydrometric station networks based on complex network analysis T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Hydrometric networks play a vital role in providing information for decision-making in water resource management. They should be set up optimally to provide as much information as possible that is as accurate as possible and, at the same time, be cost-effective. Although the design of hydrometric networks is a well-identified problem in hydrometeorology and has received considerable attention, there is still scope for further advancement. In this study, we use complex network analysis, defined as a collection of nodes interconnected by links, to propose a new measure that identifies critical nodes of station networks. The approach can support the design and redesign of hydrometric station networks. The science of complex networks is a relatively young field and has gained significant momentum over the last few years in different areas such as brain networks, social networks, technological networks, or climate networks. The identification of influential nodes in complex networks is an important field of research. We propose a new node-ranking measure – the weighted degree–betweenness (WDB) measure – to evaluate the importance of nodes in a network. It is compared to previously proposed measures used on synthetic sample networks and then applied to a real-world rain gauge network comprising 1229 stations across Germany to demonstrate its applicability. The proposed measure is evaluated using the decline rate of the network efficiency and the kriging error. The results suggest that WDB effectively quantifies the importance of rain gauges, although the benefits of the method need to be investigated in more detail. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 951 KW - identifying influential nodes KW - climate networks KW - rainfall KW - streamflow KW - synchronization KW - precipitation KW - classification KW - events Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-471006 SN - 1866-8372 IS - 951 ER - TY - GEN A1 - Agarwal, Ankit A1 - Marwan, Norbert A1 - Maheswaran, Rathinasamy A1 - Merz, Bruno A1 - Kurths, Jürgen T1 - Multi-scale event synchronization analysis for unravelling climate processes BT - a wavelet-based approach T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The temporal dynamics of climate processes are spread across different timescales and, as such, the study of these processes at only one selected timescale might not reveal the complete mechanisms and interactions within and between the (sub-) processes. To capture the non-linear interactions between climatic events, the method of event synchronization has found increasing attention recently. The main drawback with the present estimation of event synchronization is its restriction to analysing the time series at one reference timescale only. The study of event synchronization at multiple scales would be of great interest to comprehend the dynamics of the investigated climate processes. In this paper, the wavelet-based multi-scale event synchronization (MSES) method is proposed by combining the wavelet transform and event synchronization. Wavelets are used extensively to comprehend multi-scale processes and the dynamics of processes across various timescales. The proposed method allows the study of spatio-temporal patterns across different timescales. The method is tested on synthetic and real-world time series in order to check its replicability and applicability. The results indicate that MSES is able to capture relationships that exist between processes at different timescales. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 661 KW - precipitation KW - phase KW - EEG KW - desynchronization KW - interdependences KW - coherence KW - networks KW - monsoon KW - models KW - time Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-418274 SN - 1866-8372 IS - 661 ER - TY - GEN A1 - Marc, Odin A1 - Behling, Robert A1 - Andermann, Christoff A1 - Turowski, Jens M. A1 - Illien, Luc A1 - Roessner, Sigrid A1 - Hovius, Niels T1 - Long-term erosion of the Nepal Himalayas by bedrock landsliding BT - the role of monsoons, earthquakes and giant landslides T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - In active mountain belts with steep terrain, bedrock landsliding is a major erosional agent. In the Himalayas, landsliding is driven by annual hydro-meteorological forcing due to the summer monsoon and by rarer, exceptional events, such as earthquakes. Independent methods yield erosion rate estimates that appear to increase with sampling time, suggesting that rare, high-magnitude erosion events dominate the erosional budget. Nevertheless, until now, neither the contribution of monsoon and earthquakes to landslide erosion nor the proportion of erosion due to rare, giant landslides have been quantified in the Himalayas. We address these challenges by combining and analysing earthquake- and monsoon-induced landslide inventories across different timescales. With time series of 5 m satellite images over four main valleys in central Nepal, we comprehensively mapped landslides caused by the monsoon from 2010 to 2018. We found no clear correlation between monsoon properties and landsliding and a similar mean landsliding rate for all valleys, except in 2015, where the valleys affected by the earthquake featured ∼ 5–8 times more landsliding than the pre-earthquake mean rate. The longterm size–frequency distribution of monsoon-induced landsliding (MIL) was derived from these inventories and from an inventory of landslides larger than ∼ 0.1 km 2 that occurred between 1972 and 2014. Using a published landslide inventory for the Gorkha 2015 earthquake, we derive the size–frequency distribution for earthquake-induced landsliding (EQIL). These two distributions are dominated by infrequent, large and giant landslides but under-predict an estimated Holocene frequency of giant landslides (> 1 km 3 ) which we derived from a literature compilation. This discrepancy can be resolved when modelling the effect of a full distribution of earthquakes of variable magnitude and when considering that a shallower earthquake may cause larger landslides. In this case, EQIL and MIL contribute about equally to a total long-term erosion of ∼ 2 ± 0.75 mm yr −1 in agreement with most thermo-chronological data. Independently of the specific total and relative erosion rates, the heavy-tailed size–frequency distribution from MIL and EQIL and the very large maximal landslide size in the Himalayas indicate that mean landslide erosion rates increase with sampling time, as has been observed for independent erosion estimates. Further, we find that the sampling timescale required to adequately capture the frequency of the largest landslides, which is necessary for deriving long-term mean erosion rates, is often much longer than the averaging time of cosmogenic 10 Be methods. This observation presents a strong caveat when interpreting spatial or temporal variability in erosion rates from this method. Thus, in areas where a very large, rare landslide contributes heavily to long-term erosion (as the Himalayas), we recommend 10 Be sample in catchments with source areas > 10 000 km 2 to reduce the method mean bias to below ∼ 20 % of the long-term erosion. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 646 KW - rainfall thresholds KW - global database KW - sediment flux KW - mountain belt KW - rates KW - river KW - size KW - exhumation KW - precipitation KW - inventories Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-425022 SN - 1866-8372 IS - 646 ER - TY - GEN A1 - Hentrich, Doreen A1 - Tauer, Klaus A1 - Espanol, Montserrat A1 - Ginebra, Maria-Pau A1 - Taubert, Andreas T1 - EDTA and NTA effectively tune the mineralization of calcium phosphate from bulk aqueous solution T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - This study describes the effects of nitrilotriacetic acid (NTA) and ethylenediaminotetraacetic acid (EDTA) on themineralization of calciumphosphate from bulk aqueous solution. Mineralization was performed between pH 6 and 9 and with NTA or EDTA concentrations of 0, 5, 10, and 15 mM. X-ray diffraction and infrared spectroscopy show that at low pH, mainly brushite precipitates and at higher pH, mostly hydroxyapatite forms. Both additives alter the morphology of the precipitates. Without additive, brushite precipitates as large plates. With NTA, the morphology changes to an unusual rod-like shape. With EDTA, the edges of the particles are rounded and disk-like particles form. Conductivity and pH measurements suggest that the final products form through several intermediate steps. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1095 KW - biomineralization KW - biomimetic mineralization KW - calcium phosphate KW - NTA KW - EDTA KW - precipitation KW - brushite KW - hydroxyapatite Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-469186 SN - 1866-8372 IS - 1095 ER - TY - GEN A1 - Münch, Thomas A1 - Kipfstuhl, Sepp A1 - Freitag, Johannes A1 - Meyer, Hanno A1 - Laepple, Thomas T1 - Constraints on post-depositional isotope modifications in East Antarctic firn from analysing temporal changes of isotope profiles T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The isotopic composition of water in ice sheets is extensively used to infer past climate changes. In low-accumulation regions their interpretation is, however, challenged by poorly constrained effects that may influence the initial isotope signal during and after deposition of the snow. This is reflected in snow-pit isotope data from Kohnen Station, Antarctica, which exhibit a seasonal cycle but also strong interannual variations that contradict local temperature observations. These inconsistencies persist even after averaging many profiles and are thus not explained by local stratigraphic noise. Previous studies have suggested that post-depositional processes may significantly influence the isotopic composition of East Antarctic firn. Here, we investigate the importance of post-depositional processes within the open-porous firn (greater than or similar to 10 cm depth) at Kohnen Station by separating spatial from temporal variability. To this end, we analyse 22 isotope profiles obtained from two snow trenches and examine the temporal isotope modifications by comparing the new data with published trench data extracted 2 years earlier. The initial isotope profiles undergo changes over time due to downward advection, firn diffusion and densification in magnitudes consistent with independent estimates. Beyond that, we find further modifications of the original isotope record to be unlikely or small in magnitude (<< 1 parts per thousand RMSD). These results show that the discrepancy between local temperatures and isotopes most likely originates from spatially coherent processes prior to or during deposition, such as precipitation intermittency or systematic isotope modifications acting on drifting or loose surface snow. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 662 KW - Dronning Maud Land KW - near-surface snow KW - Ice core records KW - Kohnen Station KW - stable isotopes KW - water isotopes KW - polar firn KW - climate KW - diffusion KW - precipitation Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-418763 SN - 1866-8372 IS - 662 ER - TY - GEN A1 - Murawski, Aline A1 - Bürger, Gerd A1 - Vorogushyn, Sergiy A1 - Merz, Bruno T1 - Can local climate variability be explained by weather patterns? BT - a multi-station evaluation for the Rhine basin T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - To understand past flood changes in the Rhine catchment and in particular the role of anthropogenic climate change in extreme flows, an attribution study relying on a proper GCM (general circulation model) downscaling is needed. A downscaling based on conditioning a stochastic weather generator on weather patterns is a promising approach. This approach assumes a strong link between weather patterns and local climate, and sufficient GCM skill in reproducing weather pattern climatology. These presuppositions are unprecedentedly evaluated here using 111 years of daily climate data from 490 stations in the Rhine basin and comprehensively testing the number of classification parameters and GCM weather pattern characteristics. A classification based on a combination of mean sea level pressure, temperature, and humidity from the ERA20C reanalysis of atmospheric fields over central Europe with 40 weather types was found to be the most appropriate for stratifying six local climate variables. The corresponding skill is quite diverse though, ranging from good for radiation to poor for precipitation. Especially for the latter it was apparent that pressure fields alone cannot sufficiently stratify local variability. To test the skill of the latest generation of GCMs from the CMIP5 ensemble in reproducing the frequency, seasonality, and persistence of the derived weather patterns, output from 15 GCMs is evaluated. Most GCMs are able to capture these characteristics well, but some models showed consistent deviations in all three evaluation criteria and should be excluded from further attribution analysis. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 525 KW - athmospheric circulation patterns KW - stochastic rainfall model KW - within-type variability KW - river Rhine KW - precipitation KW - temperature KW - trends KW - classification KW - Europe KW - scenarios Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-410155 SN - 1866-8372 IS - 525 ER - TY - GEN A1 - Hargis, Hailey A1 - Gotsch, Sybil G. A1 - Porada, Philipp A1 - Moore, Georgianne W. A1 - Ferguson, Briana A1 - Van Stan II, John T. T1 - Arboreal epiphytes in the soil-atmosphere interface BT - how often are the biggest “buckets” in the canopy empty? T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Arboreal epiphytes (plants residing in forest canopies) are present across all major climate zones and play important roles in forest biogeochemistry. The substantial water storage capacity per unit area of the epiphyte “bucket” is a key attribute underlying their capability to influence forest hydrological processes and their related mass and energy flows. It is commonly assumed that the epiphyte bucket remains saturated, or near-saturated, most of the time; thus, epiphytes (particularly vascular epiphytes) can store little precipitation, limiting their impact on the forest canopy water budget. We present evidence that contradicts this common assumption from (i) an examination of past research; (ii) new datasets on vascular epiphyte and epi-soil water relations at a tropical montane cloud forest (Monteverde, Costa Rica); and (iii) a global evaluation of non-vascular epiphyte saturation state using a process-based vegetation model, LiBry. All analyses found that the external and internal water storage capacity of epiphyte communities is highly dynamic and frequently available to intercept precipitation. Globally, non-vascular epiphytes spend <20% of their time near saturation and regionally, including the humid tropics, model results found that non-vascular epiphytes spend ~1/3 of their time in the dry state (0–10% of water storage capacity). Even data from Costa Rican cloud forest sites found the epiphyte community was saturated only 1/3 of the time and that internal leaf water storage was temporally dynamic enough to aid in precipitation interception. Analysis of the epi-soils associated with epiphytes further revealed the extent to which the epiphyte bucket emptied—as even the canopy soils were often <50% saturated (29–53% of all days observed). Results clearly show that the epiphyte bucket is more dynamic than currently assumed, meriting further research on epiphyte roles in precipitation interception, redistribution to the surface and chemical composition of “net” precipitation waters reaching the surface. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 928 KW - precipitation KW - interception KW - bromeliad KW - vascular epiphyte KW - non-vascular epiphyte KW - lichens KW - bryophytes KW - water storage capacity Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-441993 SN - 1866-8372 IS - 928 ER -