Although the capability of computational fluid dynamics (CFD) in modeling ship hydrodynamics is well explored in many studies, they still have two main limitations. First, those studies ignore the effect of non-uniform shear current which exists in realistic situation. Second, the focus of most studies was laid more on the seakeeping/maneuvering performance and less attention was paid to survivability of ships due to extreme ship response events in waves, which are considered rare events but influential. In this thesis, we explore the capability of CFD in those two areas. In the first part of the thesis, the hydrodynamic performance of KCS in the presence of a non-uniform shear current is investigated for the first time using high-fidelity CFD simulations. Various shear current conditions with different directions were considered and results were compared with the ones with no shear current. The second part of the thesis focuses on study of rare events of ship responses by development of extreme response conditioning techniques to design the wave trail. Two conditioned techniques based on Gaussian and non-Gaussian processes are considered.

<p>The thesis aims to investigate the impact of climate change on the hydrology of four semi-urban watersheds in southern Ontario. The study is mainly concerned with future changes in climate variables and flow regimes. The study also assesses future changes in the frequency and magnitude of peak and low flows. The hydrologic effects of climate change were assessed using a couple of climate and hydrological models. Three regional climate models (RCMs), namely, Canadian Regional Climate Model (CRCM), United States Regional Climate Model 3 (RCM3), United Kingdom Hadley Regional Model 3 (HRM3) were used to extract raw climate variables. The raw RCM data were corrected using a bias correction method. The method performance statistics and the nonparametric test results revealed that the bias corrected climate variables followed the patterns of the observed climate variables for all weather stations. Future climate scenario was then simulated and analyses show increases in annual precipitation about 5-8% and increases in mean annual daily mean temperature about 2.6-3.2 oC. Three hydrological models (namely HBV, MAC-HBV, and SAC-SMA) were used for flow simulation. The models' validation results show a good agreement with the observed flow with a Nash Sutcliffe efficiency around 0.49-0.75 and a correlation coefficient of around 0.7-0.8 for all sub-basins. The three hydrologic models coupled with the bias corrected RCMs data were used to simulate current and future flow. For future period (2050s), the models predicted increasing winter flow and decreasing spring, summer and autumn flows. Mean annual flow shows slight to moderate changes. Significant increases in peak and low flow magnitude are predicted for higher return periods (20-100 years). Overall, the effects of projected future changes in precipitation and temperature clearly govern the significant changes in seasonal and annual flows, peak and low flow magnitudes and frequencies. Using three hydrologic and three climate models projections, a comprehensive picture of probable hydrologic impact of climate change was assessed in the study area. The wide range of predicted changes will have significant implications for future water resources development in the selected semi-urban watersheds.</p> / Master of Applied Science (MASc)

Cette thèse sur travaux vise à rassembler et unifier les travaux réalisés sur le sujet des évènements météo-océaniques extrêmes depuis 2009, dans le cadre de mon travail à SOGREAH, devenu depuis ARTELIA. À mesure que progressaient ces travaux, un thème central a progressivement apparu : la notion d'évènement, tel qu'une tempête. Ce concept fournit un cadre robuste et pertinent, en particulier dans le cas des extrêmes multivariés (par exemple, la probabilité d'occurrence conjointe des vagues et des niveaux marins), ainsi qu'une meilleure compréhension de la notion de période de retour, très utilisée dans le domaine de l'ingénierie.Les principaux résultats des travaux réalisés au cours de la décennie écoulée sont les suivants :- mise à jour de la méthodologie de détermination des houles ou vents extrêmes :- développement et justification d'un cadre en deux étapes pour la modélisation sup-seuil des extrêmes univariés (méthode du renouvellement), introduisant la notion d'évènement et la séparation des seuils physique et statistique,- proposition d'outils pratiques pour le choix du seuil statistique,- introduction de la méthode du bootstrap paramétrique pour le calcul des intervalles de confiance,- identification d'un comportement problématique de l'Estimateur du Maximum de Vraisemblance et proposition d'une solution : utilisation de distributions à trois paramètres avec l'estimateur des L-moments,- application du cadre POT (Peaks-Over-Threshold) à la Méthode des Probabilités Jointes (JPM) pour la détermination des niveaux marins extrêmes :- distinction entre les valeurs séquentielles et les pics des évènements à l'aide d'indices extrémaux pour les surcotes et les niveaux marins,- construction d'un modèle mixte pour la distribution des surcotes,- raffinements pour le traitement de la dépendance marée-surcote,- application du cadre POT-JPM pour l'analyse conjointe des hauteurs de vagues et des niveaux marins :- proposition d'une procédure alternative d'échantillonnage,- analyse séparée de la marée et de la surcote dans le but de modéliser la dépendance entre la hauteur de vagues et la surcote ; avec incorporation dans la distribution conjointe de la hauteur de vagues et du niveau marin à l'aide d'une opération de convolution 2D1D,- utilisation de copules des valeurs extrêmes,- présentation améliorée du chi-plot,- introduction d'une nouvelle classification pour les analyses multivariées :- Type A : un phénomène unique décrit par différentes grandeurs physiques qui ne sont pas du même type,- Type B : un phénomène fait de différentes composantes, décrits par des grandeurs physiques du même type d'un composant à l'autre,- Type C : plusieurs phénomènes décrits par des grandeurs physiques qui ne sont pas du même type,- interprétation de la signification des évènements multivariés :- lien avec l'échantillonnage,- lien avec les différentes définitions de la période de retour,- dans le cas bivarié : transformation d'une distribution conjointe de variables descriptives de l'évènement vers la distribution des couples de variables séquentielles,- génération de graphes de srotie alternatifs tels que les contours d'iso-densité pour les couples de variables séquentielles,- un package R dédié, artextreme, pour l'implémentation des méthodes ci-dessus / This PhD on published works aims at unifying the works carried out on the topic of extreme metocean events since 2009, while working for SOGREAH then ARTELIA.As these works went along, a leading theme progressively appeared: the notion of event, such as a storm. This concept provides a sound and relevant framework in particular in the case of multivariate extremes (such as joint probabilities of waves and sea levels), as well as a better understanding of the notion of return period, much used for design in the field of engineering.The main results of the works carried out in the last decade are as follows:- updating of the methodology for determining extreme wave heights or wind speeds:- development and justification of a two-step framework for extreme univariate over-threshold modelling introducing the concept of event and the separation of the physical and statistical thresholds,- proposal of practical tools for choosing the statistical threshold,- introduction of the parametric bootstrap approach for computing confidence intervals,- identification of a problematic issue in the behaviour of the Maximum Likelihood Estimator and proposal of a solution: use of 3-parameter distributions along with the L-moments estimator,- application of the POT framework to the Joint Probability Method for determining extreme sea levels:- distinction between sequential values and event peaks through extremal indexes for surge and sea level,- construction of a mixture model for the surge distribution,- refinements for handling tide-surge dependence,- application of the POT-JPM framework for the joint analysis of wave height and sea level:- proposal of an alternative sampling procedure,- separate analysis of tide and surge in order to model the dependence between wave height and surge to be incorporated in the joint distribution of wave height and sea level thanks to a 2D1D convolution operation,- use of extreme-value copulas,- improved presentation of the chi-plot,- introduction of a new classification for multivariate analyses:- Type A: a single phenomenon described by different physical quantities that are not of the same kind,- Type B: a phenomenon made of different components, described by physical quantities of the same kind between one component and another,- Type C: several phenomena described by physical quantities that are not of the same kind,- interpretation of the meaning of multivariate events:- link with the sampling procedure,- link with the different definitions of the return period,- in the bivariate case: transformation of the joint distribution of event-describing variables into the joint distribution of sequential pairs,- generation of alternative output plots such as contours of density for sequential pairs;- a dedicated R package, artextreme, for implementing the methodologies presented above

As ondas de calor constituem sequências extremas de elevadas temperaturas que podem causar prejuízos biológicos, econômicos e sociais, desta forma demandando discussões em planejamentos estratégicos para a manutenção do funcionamento social. No entanto, inexistem trabalhos que as abordem historicamente em suas complexidades estatísticas, sinóticas e termodinâmicas em toda a extensão da América do Sul (AS), sendo os estudos ora restritivos no tempo, ora restritivos no espaço. Esta dissertação identifica e analisa as ondas de calor sobre a AS em suas distintas áreas de atuação regional, para um período de 30 anos, fazendo uso dos dados diários de reanálise do European Centre for Medium-Range Weather Forecasts (ECMWF), com resolução de 0,75° na área delimitadas pelas coordenadas (60°S15°N) e (8530°W). Para isto adota um critério de identificação objetivo e consistente com a variabilidade da extensão temporal e da intensidade das anomalias positivas de temperaturas, discutindo os aspectos metodológicos não consensuais presentes na literatura. As ondas de calor foram agrupadas segundo os padrões de variabilidade guiados por fenômenos atmosféricos específicos, em uma nova técnica alternativa ao uso das Funções Ortogonais Empíricas, derivada dos mapas de correlações espaciais. Os resultados mostram que as ondas de calor acontecem em qualquer época do ano, preferencialmente no período climatológico de maiores temperaturas; além disso, sua frequência está aumentando com o passar dos anos na AS. Para completar, os mapas de composições das climatologias sinóticas permitem identificar sistemas meteorológicos específicos para cada uma das dez regiões homogêneas identificadas, alguns deles relacionados ao fenômeno El Niño Oscilação-Sul e a padrões determinados de circulação atmosférica, precipitação e Temperatura da Superfície do Mar. Tendo em vista a possibilidade de inclusão da mesma técnica aos estudos globais e para as ondas de frio, este trabalho se insere no início de uma vasta gama de estudos inter-relacionados, dentro do contexto das mudanças climáticas e de considerável interesse socioeconômico envolvido. / Heat waves constitute extreme sequences of high temperatures that can cause biological, economic, and social damages, thus requiring strategic planning discussion for social functioning maintenance. However, there are no papers addressing them from a historical point of view in their statistical, synoptic, and thermodynamic complexities throughout South America (SA), being the studies sometimes restrictive in time, and sometimes restrictive in space. This dissertation identifies and analyses the SA heat waves over their regional areas, for a period of 30 years, making use of reanalysis daily data of European Centre for Medium-Range Weather Forecasts (ECMWF), with 0.75° resolution over the area delimited by the coordinates ranges (60°S15°N) and (8530°W). To do that, it adopts an objective identification criterion consistent with the variability of the temporal extension and the intensity of the positive anomalies of temperatures, discussing the nonconsensual methodological aspects present in the literature. The heat waves were grouped according to the variability patterns guided by specific atmospheric phenomena, in a new alternative technique to the use of the Empirical Orthogonal Functions, derived from the maps of spatial correlations. The results show that the heat waves happen at any time of the year, preferably in the climatic period of higher temperatures; in addition, its frequency is increasing over the years in AS. To complete, the correlation maps of synoptic climatology allow the identification of specific meteorological systems in each of the ten identified homogeneous region, some of them related with El Niño Southern Oscillation and with determined patterns of atmospheric circulation, precipitation, and Sea Surface Temperature. Considering the possibility of including the same technique in global studies and in the case of cold waves, this work is part of a wide range of interrelated studies within the context of climate change and considerable socioeconomic interest involved.

As ondas de calor constituem sequências extremas de elevadas temperaturas que podem causar prejuízos biológicos, econômicos e sociais, desta forma demandando discussões em planejamentos estratégicos para a manutenção do funcionamento social. No entanto, inexistem trabalhos que as abordem historicamente em suas complexidades estatísticas, sinóticas e termodinâmicas em toda a extensão da América do Sul (AS), sendo os estudos ora restritivos no tempo, ora restritivos no espaço. Esta dissertação identifica e analisa as ondas de calor sobre a AS em suas distintas áreas de atuação regional, para um período de 30 anos, fazendo uso dos dados diários de reanálise do European Centre for Medium-Range Weather Forecasts (ECMWF), com resolução de 0,75° na área delimitadas pelas coordenadas (60°S15°N) e (8530°W). Para isto adota um critério de identificação objetivo e consistente com a variabilidade da extensão temporal e da intensidade das anomalias positivas de temperaturas, discutindo os aspectos metodológicos não consensuais presentes na literatura. As ondas de calor foram agrupadas segundo os padrões de variabilidade guiados por fenômenos atmosféricos específicos, em uma nova técnica alternativa ao uso das Funções Ortogonais Empíricas, derivada dos mapas de correlações espaciais. Os resultados mostram que as ondas de calor acontecem em qualquer época do ano, preferencialmente no período climatológico de maiores temperaturas; além disso, sua frequência está aumentando com o passar dos anos na AS. Para completar, os mapas de composições das climatologias sinóticas permitem identificar sistemas meteorológicos específicos para cada uma das dez regiões homogêneas identificadas, alguns deles relacionados ao fenômeno El Niño Oscilação-Sul e a padrões determinados de circulação atmosférica, precipitação e Temperatura da Superfície do Mar. Tendo em vista a possibilidade de inclusão da mesma técnica aos estudos globais e para as ondas de frio, este trabalho se insere no início de uma vasta gama de estudos inter-relacionados, dentro do contexto das mudanças climáticas e de considerável interesse socioeconômico envolvido. / Heat waves constitute extreme sequences of high temperatures that can cause biological, economic, and social damages, thus requiring strategic planning discussion for social functioning maintenance. However, there are no papers addressing them from a historical point of view in their statistical, synoptic, and thermodynamic complexities throughout South America (SA), being the studies sometimes restrictive in time, and sometimes restrictive in space. This dissertation identifies and analyses the SA heat waves over their regional areas, for a period of 30 years, making use of reanalysis daily data of European Centre for Medium-Range Weather Forecasts (ECMWF), with 0.75° resolution over the area delimited by the coordinates ranges (60°S15°N) and (8530°W). To do that, it adopts an objective identification criterion consistent with the variability of the temporal extension and the intensity of the positive anomalies of temperatures, discussing the nonconsensual methodological aspects present in the literature. The heat waves were grouped according to the variability patterns guided by specific atmospheric phenomena, in a new alternative technique to the use of the Empirical Orthogonal Functions, derived from the maps of spatial correlations. The results show that the heat waves happen at any time of the year, preferably in the climatic period of higher temperatures; in addition, its frequency is increasing over the years in AS. To complete, the correlation maps of synoptic climatology allow the identification of specific meteorological systems in each of the ten identified homogeneous region, some of them related with El Niño Southern Oscillation and with determined patterns of atmospheric circulation, precipitation, and Sea Surface Temperature. Considering the possibility of including the same technique in global studies and in the case of cold waves, this work is part of a wide range of interrelated studies within the context of climate change and considerable socioeconomic interest involved.

Made available in DSpace on 2017-07-21T19:26:05Z (GMT). No. of bitstreams: 1 Rafael Ribaski Borges.pdf: 2504879 bytes, checksum: b87dbb16266c955866bfc47eef34de30 (MD5) Previous issue date: 2013-03-05 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The extreme value theory is a branch of statistics and probability. It deals with the asymptotic distributions of extreme values (maximum or minimum) temporal series. The events which takes the average values removed are classified as extreme events. Examples include natural disasters such as goods, earthquakes or an event that causes a strong impact on society. Considering the scenario of complex networks, some examples of extreme events are congestion in networks of roads, power outages in power transmission networks and web servers congested. Thus, understanding the mechanisms that occur in such events is of great interest, because the prediction of these occurrences can minimize its efects, or even avoid them. Thus, the objectives of this study were: 1) to describe the asymptotic behavior of exceedances of a threshold specified by the generalized extreme value distribution, 2) extend the study to the probability of extreme events in complex networks with random topology, small world and scale free. This work was carried out by simulations of random walk pattern and shorter paths. The results shows that for the nodes, also called vertices or sites with low connectivity (lesser degree) in the networks analyzed, the distribution of excesses is not of exponential type. This implies that this distribution is bounded above. The results for the nodes with higher degree were similar, but only for the scale-free network this behavior does not occur. This is due to the fact that the number of exceedances observed in this case is signicantly smaller than the other. It was checked analytically and numerically simulated by random walk pattern, the probability of extreme event is larger and the average time between them is smaller for nodes with lower degree when compared with nodes with higher degree. The spectrum of eigenvalues of the adjacency matrix of the network, which describes the links between nodes, provides conditions for a good agreement between the analytical results and the simulations. For simulations of random walk for shorter paths it was found that nodes with lower betweenness centralities are more likely to have extreme events. / A teoria de valores extremos é um ramo da estatística e probabilidade. Ela trata das distribuições assintóticas de valores extremos (máximos ou mínimos) de séries temporais. Os eventos que assumem valores afastados da média são classificados como eventos extremos. Alguns exemplos são desastres naturais, tais como enchentes, terremotos ou um evento que cause um forte impacto na sociedade. Considerando o cenário de redes complexas, alguns exemplos de eventos extremos são congestionamentos em redes de rodovias, quedas de energia em redes de transmissão e servidores de internet congestionados. Assim, a compreensão dos mecanismos que regem tais eventos é de grande interesse, pois com a previsão de ocorrências destes pode-se minimizar seus efeitos ou até mesmo evitá-los. Com isso, os objetivos deste trabalho foram: 1) descrever o comportamento assintótico das excedências de um valor limite especicado por meio da distribuição de valores extremos generalizada; 2) estender o estudo para a probabilidade de eventos extremos em redes complexas com topologia aleatória, mundo pequeno e escala livre. Este trabalho foi realizado por meio de simulações de caminhada aleatória padrão e por menores caminhos. Os resultados obtidos mostram que para os nós, também denominados vértices ou sítios, com menor conectividade (menor grau) nas redes analisadas, a distribuição dos excessos não é do tipo exponencial. Isto implica que esta distribuição é limitada superiormente. Os resultados para os nós com maior grau foram semelhantes, porém, somente para a rede de escala livre este comportamento não ocorre. Isto se deve ao fato de que o número de excedências observadas neste caso são menores do que nos demais. Foi vericado analiticamente e numericamente por meio de simulações de caminhada aleatória padrão, que a probabilidade de evento extremo é maior e que o tempo médio entre eles é menor para os nós com grau menor, quando comparados com nós com grau maior. O espectro de autovalores da matriz adjacência da rede, a qual descreve as ligações entre os nós, fornece condições para uma boa concordância entre os resultados analíticos e das simulações.Para simulações de caminhada aleatória por menores caminhos verificou-se que os nós com menores centralidades de intermediação são mais propensos a ter eventos extremos.

La presente tesis estudia la correlación negativa entre inflación y precios reales de las acciones. En primer lugar, muestro evidencia de que la inflación impone costos reales en la economía, en particular al disminuir los beneficios de las empresas, tal como sugiriera originalmente Miton Friedman. Segundo, sugiero que la inflación decrece los precios reales de las acciones dado que la probabilidad de sufrir estanflación en el futuro crece con la tasa de inflación (premio evento-extremo). Tercero, testeo si la evidencia macroeconómica respalda la relación positiva entre inflación e incertidumbre, y la relación entre inflación y el precio del riesgo (avesión relativa al riesgo). Cuarto, presento un estudio histórico, Alemania entre 1870 y 1935, para mostrar que es el premio por evento-extremo, y no illusion monetaria, lo que conlleva la correlación negativa entre inflación y precios reales de acciones. El último capítulo discute contagio en países emergentes.

abstract: Earth-system models describe the interacting components of the climate system and technological systems that affect society, such as communication infrastructures. Data assimilation addresses the challenge of state specification by incorporating system observations into the model estimates. In this research, a particular data assimilation technique called the Local Ensemble Transform Kalman Filter (LETKF) is applied to the ionosphere, which is a domain of practical interest due to its effects on infrastructures that depend on satellite communication and remote sensing. This dissertation consists of three main studies that propose strategies to improve space- weather specification during ionospheric extreme events, but are generally applicable to Earth-system models: Topic I applies the LETKF to estimate ion density with an idealized model of the ionosphere, given noisy synthetic observations of varying sparsity. Results show that the LETKF yields accurate estimates of the ion density field and unobserved components of neutral winds even when the observation density is spatially sparse (2% of grid points) and there is large levels (40%) of Gaussian observation noise. Topic II proposes a targeted observing strategy for data assimilation, which uses the influence matrix diagnostic to target errors in chosen state variables. This strategy is applied in observing system experiments, in which synthetic electron density observations are assimilated with the LETKF into the Thermosphere-Ionosphere- Electrodynamics Global Circulation Model (TIEGCM) during a geomagnetic storm. Results show that assimilating targeted electron density observations yields on average about 60%–80% reduction in electron density error within a 600 km radius of the observed location, compared to 15% reduction obtained with randomly placed vertical profiles. Topic III proposes a methodology to account for systematic model bias arising ifrom errors in parametrized solar and magnetospheric inputs. This strategy is ap- plied with the TIEGCM during a geomagnetic storm, and is used to estimate the spatiotemporal variations of bias in electron density predictions during the transitionary phases of the geomagnetic storm. Results show that this strategy reduces error in 1-hour predictions of electron density by about 35% and 30% in polar regions during the main and relaxation phases of the geomagnetic storm, respectively. / Dissertation/Thesis / Doctoral Dissertation Applied Mathematics 2018

A Water Safety Plan for Extreme Events - PSAEE, has the purpose of description the procedures in potentially critical situations due to the occurrence of extreme weather events (droughts and floods). Provides the developing of preventive actions and contingency plan as a way to mitigate the effects of these phenomena. Will be developed in different and complementary steps, aiming anticipation, recognition and risk assessment, identification and monitoring of vulnerable regions and the implementation of a warning network against Floods and Droughts. The present document describes guidelines for structuring a Water Safety Plan for Extreme Events, Floods and Droughts, structured in five (05) steps; 1. Preliminary Steps, 2 Diagnostic System; 3 Operational Monitoring; 4. Management Plans and 5.Validation and Verification. As a case study, the document analyzed the process of implementing the Situation Room of the Water Resources Management Company of Cearà - COGERH , also presenting some suggestion of a Work Plan for the Situation Room, which will serve as a Management Center of Extreme Hydrological Events for the State of CearÃ, Brazil. / Um Plano de SeguranÃa de Ãgua para Eventos Extremos â PSAEE, tem como objetivo a descriÃÃo de procedimentos em situaÃÃes potencialmente criticas devido a ocorrÃncia de eventos climÃticos extremos (Secas e Cheias). Prevà o desenvolvendo de aÃÃes preventivas e plano de contingÃncia como forma de mitigar os efeitos destes fenÃmenos. Serà desenvolvido em etapas distintas e complementares, visando a antecipaÃÃo, reconhecimento e avaliaÃÃo de riscos, a identificaÃÃo e monitoramento de regiÃes vulnerÃveis, a implementaÃÃo de rede de alerta contra Cheias e Secas. O presente trabalho descreve diretrizes para estruturaÃÃo de um Plano de SeguranÃa de Ãgua para Eventos Extremos, Cheias e Secas, estruturado em 05 (cinco) etapas; 1. Etapas Preliminares, 2. DiagnÃstico do Sistema; 3. Monitoramento Operacional; 4. Planos de GestÃo e 5. ValidaÃÃo e VerificaÃÃo. Como estudo de caso, o trabalho analisou o processo de implantaÃÃo da Sala de SituaÃÃo da Companhia de GestÃo dos Recursos HÃdricos do Cearà â COGERH, apresentando, tambÃm, sugestÃo de um Plano de Trabalho para a Sala de SituaÃÃo, a qual servirà de Centro de GestÃo de Eventos Extremos HidrolÃgicos para o Estado do CearÃ, Brasil.

There is growing concern for increased frequency of extreme events due to several severe floods and droughts occurring globally in recent years. Improving knowledge on the complexity of hydrological systems and interactions with climate is essential to be able to determine drivers and predict changes in the future. This is especially true in cold regions such as the Swedish Subarctic. This thesis explored changes in high peak flows and linked trends to climate. Trend analyses were applied on 18 catchments in the Swedish Subarctic over their entire periods of record and a common period (1990-2013) among the data to explore changes in flood magnitude, flood occurrence, mean summer flow, snowmelt onset and center of mass. Further, a flood frequency analysis was applied using the extreme value type I (Gumbel) distribution and selected flood percentiles were tested for stationarity. The results show the complexity of the hydrological system and interactions with climate. No clear overall pattern could be determined suggesting that changes are happening at catchment scale. Indications for a shift in flow regime from snowmelt-dominated to rainfall-dominated are evident with all significant trends pointing towards lower flood magnitudes in the spring flood, earlier flood occurrence and snowmelt onset, and decreasing mean summer flows. The shift in flow regime suggests that air temperature is more clearly reflected in streamflow than precipitation in the Swedish Subarctic. Decreasing trends in flood magnitude and mean summer flows are suggestive of permafrost thawing, which agrees with the increasing trends in the annual minimum flow. Long streamflow records can further link variability in streamflow to multidecadal atmospheric circulations over the North Atlantic. Most evident are changes towards lower mean summer flows (ten catchments significant at a 95% confidence interval) and earlier snowmelt onset (eight catchments significant). Trends in the selected flood percentiles show indications towards an increase in extreme events over the entire period (significant for four catchments), with all significant trends being positive. Over the common period, no pattern is notable and the sensitivity of trend analyses is evident.