No description available.

Flood hazard estimations are conducted with a variety of methods. These include flood frequency analysis (FFA), hydrologic and hydraulic modelling, probable maximum discharges as well as climate scenarios. However, most of these methods assume stationarity of the used time series, i.e., the series must not exhibit trends. Against the background of climate change and proven significant trends in atmospheric circulation patterns, it is questionable whether these changes are also reflected in the discharge data. The aim of this PhD thesis is therefore to clarify, in a spatially-explicit manner, whether the available discharge data derived from selected German catchments exhibit trends. Concerning the flood hazard, the suitability of the currently used stationary FFA approaches is evaluated for the discharge data. Moreover, dynamics in atmospheric circulation patterns are studied and the link between trends in these patterns and discharges is investigated. To tackle this research topic, a number of different analyses are conducted. The first part of the PhD thesis comprises the study and trend test of 145 discharge series from catchments, which cover most of Germany for the period 1951–2002. The seasonality and trend pattern of eight flood indicators, such as maximum series and peak-over-threshold series, are analyzed in a spatially-explicit manner. Analyses are performed on different spatial scales: at the local scale, through gauge-specific analyses, and on the catchment-wide and basin scales. Besides the analysis of discharge series, data on atmospheric circulation patterns (CP) are an important source of information, upon which conclusions about the flood hazard can be drawn. The analyses of these circulation patterns (after Hess und Brezowsky) and the study of the link to peak discharges form the second part of the thesis. For this, daily data on the dominant CP across Europe are studied; these are represented by different indicators, which are tested for trend. Moreover, analyses are performed to extract flood triggering circulation patterns and to estimate the flood potential of CPs. Correlations between discharge series and CP indicators are calculated to assess a possible link between them. For this research topic, data from 122 meso-scale catchments in the period 1951–2002 are used. In a third part, the Mulde catchment, a mesoscale sub-catchment of the Elbe basin, is studied in more detail. Fifteen discharge series of different lengths in the period 1910–2002 are available for the seasonally differentiated analysis of the flood potential of CPs and flood influencing landscape parameters. For trend tests of discharge and CP data, different methods are used. The Mann-Kendall test is applied with a significance level of 10%, ensuring statistically sound results. Besides the test of the entire series for trend, multiple time-varying trend tests are performed with the help of a resampling approach in order to better differentiate short-term fluctuations from long-lasting trends. Calculations of the field significance complement the flood hazard assessment for the studied regions. The present thesis shows that the flood hazard is indeed significantly increasing for selected regions in Germany during the winter season. Especially affected are the middle mountain ranges in Central Germany. This increase of the flood hazard is attributed to a longer persistence of selected CPs during winter. Increasing trends in summer floods are found in the Rhine and Danube catchments, decreasing trends in the Elbe and Weser catchments. Finally, a significant trend towards a reduced diversity of CPs is found causing fewer patterns with longer persistence to dominate the weather over Europe. The detailed study of the Mulde catchment reveals a flood regime with frequent low winter floods and fewer summer floods, which bear, however, the potential of becoming extreme. Based on the results, the use of instationary approaches for flood hazard estimation is recommended in order to account for the detected trends in many of the series. Through this methodology it is possible to directly consider temporal changes in flood series, which in turn reduces the possibility of large under- or overestimations of the extreme discharges, respectively. / Hochwasserabschätzungen werden mit Hilfe einer Vielzahl von Methoden ermittelt. Zu diesen zählen Hochwasserhäufigkeitsanalysen, die hydrologische und hydraulische Modellierung, Abschätzungen zu maximal möglichen Abflüssen wie auch Langzeitstudien und Klimaszenarien. Den meisten Methoden ist jedoch gemein, dass sie stationäre Bedingungen der beobachteten Abflussdaten annehmen. Das heißt, in den genutzten Zeitreihen dürfen keine Trends vorliegen. Vor dem Hintergrund des Klimawandels und nachgewiesener Trends in atmosphärischen Zirkulationsmustern, stellt sich jedoch die Frage, ob sich diese Veränderungen nicht auch in den Abflussdaten widerspiegeln. Ziel der Dissertation ist daher die Überprüfung der Annahme von Trendfreiheit in Abflüssen und Großwetterlagen, um zu klären, ob die aktuell genutzten stationären Verfahren zur Hochwasserbemessung für die vorhandenen Daten in Deutschland geeignet sind. Zu prüfen ist des Weiteren, inwiefern regional und saisonal eine Verschärfung bzw. Abschwächung der Hochwassergefahr beobachtet werden kann und ob eindeutige Korrelationen zwischen Abflüssen und Großwetterlagen bestehen. Den ersten Schwerpunkt der vorliegenden Dissertation bildet die deutschlandweite Analyse von 145 Abflusszeitreihen für den Zeitraum 1951–2002. Acht Hochwasserindikatoren, die verschiedene Aspekte der Hochwasser-Charakteristik beleuchten, werden analysiert und bezüglich möglicher Trends getestet. Um saisonalen Unterschieden in der Hochwassercharakteristik der einzelnen Regionen gerecht zu werden, werden neben jährlichen auch saisonale Reihen untersucht. Die Analyse von Maximalreihen wird durch Schwellenwertanalysen ergänzt, die die Hochwasserdynamik bzgl. Frequenz und Magnitude detaillierter erfassen. Die Daten werden auf verschiedenen Skalen untersucht: sowohl für jeden einzelnen Pegel wie auch für ganze Regionen und Einzugsgebiete. Nicht nur die Analyse der Abflussdaten bietet die Möglichkeit, Bewertungen für die zukünftige Hochwasserabschätzung abzuleiten. Auch Großwetterlagen bilden eine bedeutende Informationsquelle über die Hochwassergefahr, da in der Regel nur ausgewählte Zirkulationsmuster die Entstehung von Hochwasser begünstigen. Die saisonal differenzierte Untersuchung der Großwetterlagen und die Prüfung einer Korrelation zu den Abflüssen an 122 mesoskaligen Einzugsgebieten bilden deshalb den zweiten Schwerpunkt der Arbeit. Hierzu werden tägliche Daten der über Europa dominierenden Großwetterlage (nach Hess und Brezowsky) mit Hilfe verschiedener Indikatoren untersucht. Analysen zum Hochwasserpotential der einzelnen Wetterlagen und weiterer Einflussfaktoren werden für das mesoskalige Einzugsgebiet der Mulde in einer separaten Studie durchgeführt. Für diese Detail-Studie stehen 15 Abflusszeitreihen verschiedener Länge im Zeitraum 1909–2002 zur Verfügung. Um die Daten von Abflüssen und Großwetterlagen bezüglich vorhandener Trends zu testen, werden verschiedene Methoden genutzt. Der Mann-Kendall Test wird mit einem Signifikanzniveau von 10% (zweiseitiger Test) angewendet, was statistisch sichere Bewertungen ermöglicht. Neben der Prüfung der gesamten Datenreihe werden multiple zeitlich-variable Trendanalysen mit Hilfe eines Resampling-Ansatzes durchgeführt. Darüber hinaus werden räumlich differenzierte Analysen durchgeführt, um die saisonale Hochwassercharakteristik einzelner Regionen besser zu verstehen. Diese werden durch Tests zur Feldsignifikanz der Trends ergänzt. Mit der vorliegenden Arbeit kann gezeigt werden, dass die Hochwassergefahr für einzelne Regionen im Winterhalbjahr signifikant steigt. Davon sind insbesondere Gebiete in Mitteldeutschland betroffen. Die Verschärfung der Hochwassergefahr durch eine längere Persistenz ausgewählter Großwetterlagen konnte ebenfalls für das Winterhalbjahr nachgewiesen werden. Sommerhochwasser zeigen zwar ebenfalls steigende, aber auch fallende Trends, die räumlich geclustert sind. Im Elbe- und Weser-Einzugsgebiet sinken die Abflüsse signifikant, im Donau- und Rheineinzugsgebiet steigen sie nachweisbar. Darüber hinaus ist eine signifikante Abnahme der Anzahl verschiedener Großwetterlagen sowohl im Sommer als auch im Winter zu verzeichnen. Bzgl. der Studie zum Mulde-Einzugsgebiet konnte ein zweigeteiltes Hochwasserregime nachgewiesen werden. In den Wintermonaten treten häufig kleine Hochwasser auf, die auch die Mehrheit der jährlichen Maximalwerte bilden. Sommerhochwasser sind seltener, können aber extreme Ausmaße annehmen. Ein Vergleich der geschätzten Jährlichkeiten mit verschiedenen Zeitreihen zeigt die Notwendigkeit der Berücksichtigung saisonaler Aspekte für die Bemessung von Hochwassern. Aufgrund der Ergebnisse müssen die bisher genutzten stationären Verfahren als nicht mehr geeignet bewertet werden. Es wird daher die Nutzung instationärer Verfahren zur Abschätzung von Extremhochwasser und der damit verbundenen Bemessung von Schutzmaßnahmen empfohlen, um den teilweise vorliegenden Trends in den Daten Rechnung zu tragen. Durch diesen Ansatz ist es möglich, zeitlich dynamische Veränderungen im Hochwassergeschehen stärker zu berücksichtigen. Darüber hinaus sollten saisonale Aspekte des Einzugsgebietes Eingang in die Gefahrenabschätzung finden.

A pesquisa teve como objetivo central investigar se os furacões do Oceano Atlântico Tropical Norte são capazes de influenciar a América do Sul (AS), principalmente no que se refere aos padrões de precipitação e circulação atmosférica. No entanto, como os furacões possuem uma gama de variedades de trajetórias, gêneses e decaimento, a pesquisa se restringiu apenas a avaliação dos furacões que poderiam causar maiores impactos na atmosfera da AS, sobretudo no norte do continente. Nesse sentido duas hipóteses foram estabelecidas concernente a trajetória e intensidades dos furacões. Para a trajetória a hipótese era de que quanto mais próximo da AS os furacões transitassem maior seria seu grau de interação com o continente ao passo que os furacões que atingissem a categoria 5 na escala de intensidade Saffir-Simpson também poderiam exercer maiores influências. Assim, através desses critérios, 6 furacões foram selecionados entre os anos de 1988-2017 e estes foram avaliados com base nos dados do CHIRPS e da reanálise ERA Interim, além de simulações numéricas com o modelo dinâmico GCM DREAM. Os resultados mostraram que, de fato, os furacões conseguiam impactar a atmosfera da AS uma vez que nos baixos níveis da troposfera foram observados modificações nos alísios, interferência na posição da Zona de Convergência Intertropical (ZCIT) e influência na nebulosidade, pressão, temperatura e umidade do norte da AS. Além disso, foram constatadas interações entre os furacões e a Alta Subtropical do Atlântico Sul (ASAS), onde essa última canalizava parte dos seus escoamentos para os furacões que, por sua vez, se intensificavam. Já para os altos níveis da troposfera, foram observados o surgimento de um anticiclone no Noroeste (NO) da AS como resposta a existência dos furacões, sendo que após formado esse anticiclone sugere uma possível interação com os furacões uma vez que ele se deslocava segundo o movimento dos mesmos. Além dessas duas abordagens a pesquisa também se utilizou das Funções dos Modos Normais no sentido de reconstituir o campo de vento horizontal através da contribuição individual de cada onda atmosférica excitada a partir de um furacão. Nessa etapa escolheu-se um dos furacões selecionados e os resultados indicaram que as principais ondas envolvidas nas características observadas nos baixos níveis da troposfera como, por exemplo, ciclones ou sistemas frontais, vinham das ondas de Rossby e Gravidade-Inercial (GI). Já para os altos níveis as ondas atmosféricas envolvidas no processo de formação do anticiclone no NO da AS foram as ondas de Rossby, GI e as ondas Mistas de Rossby-Gravidade (MRG), sendo que essa última indicava justamente uma comunicação entre os dois hemisférios. No que se refere as ondas de Rossby elas se sobressaíram em todos nos níveis atmosféricos devido a relação delas com a geostrofia ao passo que as ondas GI ficaram restritas em mostrar apenas processos de divergência, logo elas foram úteis para identificar regiões ligadas a precipitação. Com relação aos resultados para os padrões de precipitação foram observadas durante a passagem dos furacões anomalias positivas no norte da AS e anomalias negativas no Brasil Central, sendo que esse resultado foi interpretado como sendo um reflexo do aumento das concentrações de momento e umidade na região norte da AS por onde os furacões transitavam. Por fim, foi avaliado o caso do furacão Irma que teve uma trajetória distante da AS. Esse furacão foi avaliado no sentindo de testar as hipóteses feitas anteriormente e os resultados mostraram que esse furacão não conseguiu exercer impacto na atmosfera da AS. Desse modo, concluiu-se que os furacões do Oceano Atlântico conseguem impactar a atmosfera da AS como indicou os resultados, porém que isso só ocorrerá se eles descreverem uma trajetória muito próxima ao continente sul-americano. / The main objective of this research is to investigate whether hurricanes from the North Tropical Atlantic Ocean can influence the South Americans atmosphere, especially in terms of circulation and precipitation patterns. However, since hurricanes have a great range of trajectories, genesis and decay this research only focused the study of hurricanes that may impact the South American, particularly in the northern continental region. In this sense, two hypotheses were established about the trajectory and intensities of hurricanes. For the trajectory, the hypothesis is that the closer the hurricanes pass by South America the greater would be their degree of interaction with the South American atmosphere variability. Also, the higher the Hurricanes classification, for instance, category 5 on the Saffir-Simpson Scale, the influence could be increased. Following this criteria 6 hurricanes were selected between the years 1988-2017 and they were evaluated based on ERA Interim reanalysis and CHIRPS data, as well as numerical simulations using the dynamic GCM DREAM model. The results showed that these hurricanes really impacted the atmosphere of the South America. At lower levels of the troposphere, the passage of hurricanes caused trade winds deformation, interference in the Intertropical Convergence Zones (ITCZ) position, besides of the influence on the cloudiness, pressure, temperature and moist in the north of the continent. In addition, it was detected interactions between hurricanes and the South Atlantic Subtropical High (SASH), where the SASH sustained the wind flows towards the hurricanes, supporting their intensification. Regarding the results for the upper levels of the troposphere it was observed the development of an anticyclone in the Northwest of South America as a response to the hurricane presence. It was noticed that this anticyclone interacts with the hurricanes once it moves according to their movement. In addition to these two approaches, it was also used the Normal Mode Functions in order to reconstruct the horizontal wind field through the individual contribution of each atmospheric waves excited from a hurricane. One of the selected hurricanes was chosen and the results indicated the main waves related to the characteristics observed at lower levels of the troposphere are the Rossby and Gravity-Inertial (GI) waves. For the upper levels, the atmospheric waves related with the formation of the anticyclone in northwestern South Americas were the Rossby, GI and the Mixed Rossby-Gravity (MRG) modes, where the MRG waves clearly show the interaction between the two hemispheres. The Rossby waves excelled at all atmospheric levels due to their relationship to the geostrophic approach, while the GI waves only showed divergence processes, being useful to identify regions linked to precipitation. The precipitation patterns during the hurricanes passage generates positive anomalies in the north of the South America and negative anomalies in central Brazil. This result was interpreted as an increase of momentum and moist concentrations in the South Americas northern region due to the interaction with the hurricanes. As a case study the hurricane Irma was investigated. This hurricane was intense but its track was distant of the South America being evaluated in the order to test the hypotheses previously assumed. The results indicated that the hurricane Irma did not have any impact in the South Americans atmosphere, where not interations with SASH, temperature or moist were observed. In summary, it was observed that North Atlantic Ocean hurricanes can influence the South Americas atmosphere when their trajectories are close to the South American continent.

Connection between upper tropospheric cyclonic vortex (UTCV) and jet stream in the Northeastern region of Brazil (JSNEB) were analyzed for 10 years (1998-2007). These studies are necessary for short term weather forecasting improvement in the Alagoas State of Brazil. The National Centers for Environmental Prediction/ National Center for Atmospheric Research (NCEP/NCAR) reanalysis data were used for elaborate 200 hPa streamlines fields at 00:00 UTC. The 3.652 streamlines fields were analyzed. All events of UTCV with and without JSNEB were identified. During study period 214 UTCVs near NEB were observed and 147 of them above the Alagoas State. 63% UTCV events near Alagoas were associated with JSNEB. The durations of UTCVs and UTCV with JSNEB were on an average 3.8 and 3.0 days, respectively. The UTCVs were observed throughout the year, excluding July. UTCV with JSNEB were registered throughout the year except July and September and were stronger in the warm period (November - March). All JSNEB were weak, wind velocity at the nucleus center was at an average 32(verificar valor) ms-1 and value maximum reached 44m/s. The predominant velocity was 20-28ms-1 and was registered in 78% of events. The CJNEB direction from South, West, Nortwest and Southeast were observed more frequently. Three circulation pattern Zonal, Meridional and Transversal were obtained. For example, each circulation pattern was described in details. The precipitation in Alagoas State, associated with the Zonal, Meridional and Transversal events, were studied. / Fundação de Amparo a Pesquisa do Estado de Alagoas / A ligação entre os Vórtices Ciclônicos em Altos Nivéis (VCAN) e a Corrente de Jato na região Nordeste do Brasil (CJNEB) foram analisados por 10 anos (1998-2007). Estes estudos são necessários para a melhoria da previsão meteorológica de curto prazo no Estado de Alagoas, Brasil. O Centro Nacional de Previsão Ambiental / National Center for Atmospheric Research (NCEP / NCAR) , disponibiliza dados de reanálise para elaborar campos de linhas de corrente em conjunto com magnitude do vento em 200 hPa nos quatros horarios sinóticos (UTC). A analise foi feita em 3.652 campos que foram gerados respresentando os dias de cada ano. Todos os eventos de vórtices com e sem CJNEB foram identificados. Durante o período de estudo 214 VCAN próximo ao NEB foram observados e 147 deles acima do Estado de Alagoas. Em 63% dos eventos de VCAN próximo a Alagoas foram associados com CJNEB. As durações de VCAN e VCAN associado a CJNEB foram, em média, 3,8 e 3,0 dias, respectivamente. Os VCAN foram observados durante todo o ano, exceto em julho. O VCAN com CJNEB foram registrados durante todo o ano excluindo julho e setembro, e foram mais fortes do período mais quente (novembro-março). Todos CJNEB eram fracas, com velocidade do vento no centro do núcleo em média 32ms-1. E o valor máximo alcançou 44ms-1. A velocidade predominante foi entre 20 e 28ms-1 , e foi registrada em 78% dos eventos. A direção da CJNEB foram observados com maior frequência com sentidos de sul, oeste e sudeste. Três padrões de circulação zonal, meridional e transversal foram obtidos. Por exemplo, cada padrão de circulação foi descrito em detalhes. A precipitação no Estado de Alagoas, associada ao aos eventos de Padrão zonal, meridional e transversal, foram estudados.

No description available.