Thesis (MSc)--Stellenbosch University, 2012. / Severe floods in the Western Cape have caused significant damage to hydraulic structures, roads and other infrastructure over the past decade. The current design criteria for these structures and flood return level calculations are based on the concept of stationarity, which assumes that natural systems vary within an envelope of variability that does not change with time. In the context of regional climate change and projected changes in rainfall intensity, the basis for these calculations may become unrealistic with the passage of time. Hydraulic structures and other infrastructure may become more vulnerable to damaging floods because of changing hydroclimatic conditions. This project assesses the changes in extreme rainfall values over time across the Western Cape, South Africa. Using a Generalised Pareto Distribution, this study examines the changes in return levels across the Western Cape region for the periods 1900-1954 and 1955-2010. Of the 137 rainfall stations used in this research, 85 (62%) showed an increase in 50-year return level, 30 (22%) a decrease in 50-year return level and 22 (16%) stations displayed little change in rainfall intensity over time. While there were no clear spatial patterns to the results, they clearly indicate an increase in frequency of intense rainfalls in the latter half of the 20th and early 21st century. The changes in return level are also accompanied by a change in the frequency of high intensity 2-3 day long storms. 115 (84%) of the 137 rainfall stations showed an increase in the frequency of long duration, high intensity storms over the data record. This change generates a shifting risk profile of extreme rainfalls, which, in turn, creates challenges for the design of hydraulic structures and any infrastructure exposed to the resulting damaging floods. It can therefore be argued that it is inappropriate to design structures or manage water resources assuming stationarity of climate and that these principles should be assessed in order to reduce the risk of flood damage owing to increasing storm intensity. KEY WORDS Flood Risk, Stationarity, Disaster Risk, Hazard, Extreme Rainfall, Generalized Pareto Distribution, Climate

This study aimed at describing the characteristics of daily precipitation and discharge extremes in the Adige river basin at the city of Trento. Annual maximum series for the period 1975−2014 were analyzed in terms of trends, seasonality indices and L-moments. A Mann-Kendall trend analysis showed a weak but significant signal of decreasing ex-tremes; the percentages of sites with significant negative trends were overall larger than the significance levels. Precipitation extremes were characterized primarily by autumn storms, while floods had a stronger seasonality with peaks occurring predominantly in June and July which indicated that the timing not solely explained by rainfall maxima. The Adige basin was found to be a homogenous region with respect to precipitation, but the results did not support a corresponding assumption for discharge. A regional fre-quency analysis was performed for precipitation data and found both the Pearson type III and generalized normal distributions to be adequate regional frequency distributions. The extreme daily precipitation at Trento with a 100-year return period was estimated to be between 114 and 148 mm/d. / Egenskaperna hos extremvärden av dygnsnederbörd och -vattenföring i Adigeflodens av-rinningsområde vid staden Trento undersöktes. Serier med årsmaxima för perioden 1975–2014 analyserades med avseende på trender, säsongsindex och L-moment. Trendanalys med Mann-Kendallmetod antydde en svag men signifikant signal om minskande extrem-värden, då andelen mätstationer med signifikant negativa trender överlag var större än signifikansnivån. Den extrema nederbörden karakteriserades huvudsakligen av höststor-mar, medan vattenföringen hade en starkare säsongsbundenhet då maxima inträffade främst under juni och juli. Vattenföringens extremvärden kunde därmed inte enbart för-klaras av nederbördsmaxima. Avrinningsområdet kunde betraktas som en homogen reg-ion för nederbörd, men resultaten gav inte stöd åt ett motsvarande antagande för vatten-föring. En regional frekvensanalys genomfördes för nederbördsdata och visade att Pear-son typ III och den generaliserade normalfördelningen var lämpliga regionala sannolik-hetsfördelningar. Över Trento uppskattades den extrema dygnsnederbörden med en åter-komstperiod på 100 år till mellan 114 och 148 mm/d.

En Europe, l'augmentation des températures moyennes de surface de l'air projetée au cours du 21ème siècle s'accompagne d'une augmentation des extrêmes chauds et d'une diminution des extrêmes froids. Dans les dernières décennies, des indices témoignent déjà de ces changements, comme l'établissement récurrent de nouveaux records de chaleur ou l'augmentation des canicules. Nous étudions l'évolution des extrêmes journaliers de température au cours du 20ème et du 21ème siècle en France et en Europe, et ce en termes d'occurrence et d'intensité. Un intérêt particulier est aussi porté aux mécanismes responsables de ces futurs extrêmes climatiques, ainsi qu'aux futures températures maximales. Nous nous intéressons tout d'abord à l'évolution des records journaliers de température à partir d'observations et de modèles de climat. Entre 1950 et 1980, l'évolution théorique des records dans le cadre d'un climat stationnaire représente correctement l'évolution observée des records chauds et froids. Depuis les années 1980, un écart à ce climat stationnaire est observé, avec respectivement une augmentation et une diminution de l'occurrence des records chauds et froids. Les modèles climatiques suggèrent une accentuation de ces changements au cours du siècle. L'occurrence moyenne des records chauds à la fin du siècle présente une forte augmentation par rapport aux premières décennies de la période observée. L'augmentation la plus importante des records chauds est projetée en été, en particulier dans la région méditerranéenne. Quant aux records froids, les modèles indiquent une diminution très importante de leur occurrence, avec une occurrence quasi-nulle dans les dernières décennies. Les variations observées d'occurrence de records sont, au début du 21ème siècle, toujours dans l'éventail des fluctuations de la variabilité interne du climat. Au cours du siècle, l'émergence de l'influence anthropique de ces fluctuations est détectable dans l'évolution des records chauds et froids en été, et ce respectivement autour des décennies 2030 et 2020. À l'horizon de la fin du siècle, les changements moyens d'occurrence de records ne peuvent pas être uniquement expliqués par des fluctuations naturelles. Nous nous sommes ensuite intéressés aux futures températures estivales extrêmes, ainsi qu'aux canicules intenses qui peuvent être à l'origine de ces extrêmes. Pour cela, l'utilisation de modèles climatiques globaux est associée à la modélisation climatique régionale et à des stations d'observations en France. Tout d'abord, l'augmentation maximale des valeurs maximales des records journaliers de température en été en France est estimée à partir d'une simulation régionale à haute résolution spatiale. À l'horizon 2100, les projections indiquent une augmentation maximale de ces valeurs extrêmes en été comprise entre de 6.6°C et 9.9°C selon les régions de la France. La comparaison de ces projections avec un ensemble de modèles climatiques indique que ces augmentations maximales pourraient être plus importantes. La médiane de la distribution des modèles indique en effet une augmentation maximale de ces valeurs maximales des records journaliers de température de 11.8°C en été et en France. Puis, des expériences de modélisation de canicules intenses du climat européen de la fin du 21ème siècle ont été réalisées à partir d'événements particuliers d'un modèle de climat. Ces expériences ont mis en évidence le rôle des interactions entre le sol et l'atmosphère dans l'amplification des températures extrêmes lors de futurs évènements caniculaire intenses. L'occurrence de telles canicules est d'abord dépendante de la circulation atmosphérique, mais l'intensité des températures peut ensuite être fortement amplifiée en fonction du contenu en humidité des sols avant la canicule, et donc des conditions climatiques des semaines et des mois précédents. / Over the 21st century, the mean increase in surface air temperatures is projected to be associated with an increase in warm temperature extremes and a decrease in the cold ones. Over the last decades, evidence already suggests these changes, as for example recurrent warm record-breaking temperatures or the increase in heatwave occurrence. We investigate the evolution of daily temperature extremes over the 20th and the 21st centuries in France and in Europe, their possible changes in frequency and intensity. We also focus on the mechanisms responsible for these projected climate extremes, as well as the maximum values of temperature extremes at the end of the century. First, we investigate the evolution of daily record-breaking temperatures in Europe based on the observations and an ensemble of climate models. From the 1950s to the 1980s, the theoretical evolution of the records in a stationary climate correctly reproduce the observed one, for both cold and warm records. From 1980, a shift from that theoretical evolution is observed, with an increase in the occurrence of warm records and a decrease in the occurrence of the cold ones. Climate models suggest an amplification of these changes over the century. At the end of the 21st century, the mean number of warm records shows a strong increase compared to the first decades of the observed period. The strongest increase in warm record-breaking temperatures is found in summer, and particularly over the Mediterranean edge. On the contrary, the occurrence of cold record-breaking temperatures is projected to strongly decrease, with almost no new records in the last decades of the century, for all seasons and over the entire European domain. Observed variations of daily record-breaking temperatures are still, at the beginning of the 21st century, consistent with internal climate variability only. Over the century, the anthropogenic influence emerge from these fluctuations in the summer record evolutions, around the 2030 and the 2020 for the warm and cold records respectively. By 2100, the mean changes in record occurrences cannot be explained by the internal climate variability solely, for all seasons and over the entire European domain. Then, we investigate future extreme temperatures at the end of the 21st century, as well as severe heatwaves leading to these extremes. Climate models analyses are associated with regional climate modeling and a French station-based dataset of observations. The summer 21st century evolution of the maximum values of daily warm record-breaking temperatures is first examined in the observations and the high resolution simulation of the regional model. By 2100, an increase of these values is projected, with maximum changes between +6.6°C and +9.9°C in summer among the French regions. These projections assessed from a regional model may underestimate the changes. The multi-model mean estimate of the maximum increase of these values is indeed around +11.8°C in summer over France. Finally, regional modeling experiments of severe heatwaves in the climate of the end of the 21st century in Europe are performed. These severe heatwaves are selected cases from a global climate model trajectory. The experiments results show the role of the soil-atmosphere interactions in the amplification of the extreme temperatures during such future severe warm events. The occurrence of the heatwave is first caused by the atmospheric circulation, but the temperature anomaly can then be amplified according to the soil moisture content before the event, and thus the climatic conditions of the preceding weeks and months.

Cette thèse s’attache à développer des outils et modèles adaptés a l’étude de certains risques spatiaux et en réseaux. Elle est divisée en cinq chapitres. Le premier consiste en une introduction générale, contenant l’état de l’art au sein duquel s’inscrivent les différents travaux, ainsi que les principaux résultats obtenus. Le Chapitre 2 propose un nouveau générateur de précipitations multi-site. Il est important de disposer de modèles capables de produire des séries de précipitations statistiquement réalistes. Alors que les modèles précédemment introduits dans la littérature concernent essentiellement les précipitations journalières, nous développons un modèle horaire. Il n’implique qu’une seule équation et introduit ainsi une dépendance entre occurrence et intensité, processus souvent considérés comme indépendants dans la littérature. Il comporte un facteur commun prenant en compte les conditions atmosphériques grande échelle et un terme de contagion auto-regressif multivarié, représentant la propagation locale des pluies. Malgré sa relative simplicité, ce modèle reproduit très bien les intensités, les durées de sècheresse ainsi que la dépendance spatiale dans le cas de la Bretagne Nord. Dans le Chapitre 3, nous proposons une méthode d’estimation des processus maxstables, basée sur des techniques de vraisemblance simulée. Les processus max-stables sont très adaptés à la modélisation statistique des extrêmes spatiaux mais leur estimation s’avère délicate. En effet, la densité multivariée n’a pas de forme explicite et les méthodes d’estimation standards liées à la vraisemblance ne peuvent donc pas être appliquées. Sous des hypothèses adéquates, notre estimateur est efficace quand le nombre d’observations temporelles et le nombre de simulations tendent vers l’infini. Cette approche par simulation peut être utilisée pour de nombreuses classes de processus max-stables et peut fournir de meilleurs résultats que les méthodes actuelles utilisant la vraisemblance composite, notamment dans le cas où seules quelques observations temporelles sont disponibles et où la dépendance spatiale est importante / This thesis aims at developing tools and models that are relevant for the study of some spatial risks and risks in networks. The thesis is divided into five chapters. The first one is a general introduction containing the state of the art related to each study as well as the main results. Chapter 2 develops a new multi-site precipitation generator. It is crucial to dispose of models able to produce statistically realistic precipitation series. Whereas previously introduced models in the literature deal with daily precipitation, we develop a hourly model. The latter involves only one equation and thus introduces dependence between occurrence and intensity; the aforementioned literature assumes that these processes are independent. Our model contains a common factor taking large scale atmospheric conditions into account and a multivariate autoregressive contagion term accounting for local propagation of rainfall. Despite its relative simplicity, this model shows an impressive ability to reproduce real intensities, lengths of dry periods as well as the spatial dependence structure. In Chapter 3, we propose an estimation method for max-stable processes, based on simulated likelihood techniques. Max-stable processes are ideally suited for the statistical modeling of spatial extremes but their inference is difficult. Indeed the multivariate density function is not available and thus standard likelihood-based estimation methods cannot be applied. Under appropriate assumptions, our estimator is efficient as both the temporal dimension and the number of simulation draws tend towards infinity. This approach by simulation can be used for many classes of max-stable processes and can provide better results than composite-based methods, especially in the case where only a few temporal observations are available and the spatial dependence is high

Les technologies du sommeil connaissent une révolution numérique à laquelle nous avons apporté une validation avec pour objectif une meilleure analyse des troubles du sommeil en Unité de Soins Intensifs, dans la maladie d’Alzheimer et dans l’évaluation de l’hypovigilance en vol de longue durée en milieu militaire. Ainsi, nous avons évalué le temps de sommeil sur 24 heures en relation avec les nuisances sonores en soins intensifs. Cette évaluation a été réalisée à l’aide d’un nouveau polysomnographe l’Actiwave couplé à un polygraphe Nox T3 qui ont permis d’enregistrer les cycles du sommeil et les niveaux sonores sur les 24 heures dans une Unité de Soins Intensif. Nous avons montré que l’Actiwave est un outil performant pour enregistrer le sommeil dans de telles conditions. Combiné au Nox T3, il permet d’explorer l’impact des niveaux sonores sur la qualité et quantité du sommeil. Nous avons retrouvé un Temps Total de Sommeil médian de 6 heures par nuit et de 2,5 heures pendant la journée, la qualité de sommeil étant plus perturbée que sa quantité. Nous avons démontré que 60% des éveils intra-sommeil étaient associés à un bruit supérieur à 77 dB et identifié les sources sonores principales qui agissent sur la pathogénèse des troubles du sommeil en Unité de Soins Intensif, à savoir les alarmes des respirateurs mécaniques avec un risque relatif de 10.9 (9.8-11.9) et les alarmes des constantes vitales avec un risque relatif de 9.8 (8.6-11.3). Une deuxième étude, l’évaluation de l’hypovigilance en vol de longue durée, a été réalisée à l’aide de l’ActiWave. Pour cela, nos équipes ont conçu un algorithme d’analyse automatique de détection du sommeil. Nous avons montré que l’ActiWave est un polysomnographe fiable en conditions extrêmes, l’analyse automatique montrant une bonne concordance avec l’analyse manuelle de deux experts du sommeil (Kappa>80%). Nous démontrons donc qu’il est possible de coder automatiquement les stades de sommeil à l’aide du ratio (+)/ sur la région occipitale O1-M2 vs C3-M2 (p<0.05). Nous avons validé un nouvel actimètre le MotionWatch 8 pour l’évaluation du temps de sommeil chez 208 patients présentant la maladie d’Alzheimer. Ce travail a permis de montrer que le MotionWatch 8 est un outil fiable avec de bonnes sensibilité et spécificité dans l’évaluation des troubles du sommeil chez ces patients. Le Temps Total de Sommeil est dans la norme (TTS moyen 7h35 minutes) et est significativement associé au score d’apathie (7h46 minutes vs 7h26 minutes ; p=0.04). Le marqueur chrono-biologique SIJ est également associé à l’apathie (p=0.04) ainsi qu’aux troubles cognitifs (p=0.02). Finalement, la fragmentation de rythmes veille/sommeil (VIJ) est associée au score du handicap de la maladie d’Alzheimer (p=0.02). Dans une quatrième étude, nous nous sommes intéressés à la nouvelle technologie de télé-observance dans le traitement du syndrome d’apnées du sommeil par pression positive continue, qui permet d’alerter le médecin de la compliance du patient. Nous avons validé un nouveau dispositif médical de télé-observance du traitement du syndrome d’apnées du sommeil, le NOWAPI. Nous montrons que le NOWAPI mesure avec précision et de manière fiable les niveaux de pressions et de débits des PPC disponibles sur le marché et qu’il permet de calculer les indicateurs d'observance des patients souffrants du syndrome d’apnées du sommeil (IAH Nowapi de 2,5 (-1.4 ; 3.6)/h vs IAH Polygraphie respiratoire de 2,3 (1.2 ;3.4)/h). En conclusion, les études présentées ici mettent en exergue l’importance de l’innovation technologique dans le domaine du sommeil pour une meilleure prise en charge des patients. A l’ère du 21ème siècle, une nouvelle médecine commence à émerger, la médecine 2.0, avec pour corollaire l’eSanté. (...) / Scientific research into sleep over the past thirty years has progressed so speedily that it is now possible to speak of “Sleep Medicine”. This specialty is placed incontestably at the frontier of Science and Medicine. The issues have been recently driven by the advances in the technology of recording biological parameter and analysis of the data, in parallel with a deeper understanding of the physiopathology and therapeutic advances in sleep disorders. The subject of this thesis lies at the crossover of two areas of professional expertise; sleep technology and bio-engineering, with notably the aim of validating new tools in research as well as in the diagnosis and treatment of sleep disorders. We have tested a miniaturized polysomnographic new technology, the Actiwave, capable of detecting sleep and alert states in extreme conditions, notably in patients hospitalized in Intensive Care Units and in aircraft pilots in long duration military flights. In intensive care units, we have explored the relation between sleep and noise in the immediate environment of the patients. In brief, Total Sleep Time was not disturbed whereas the sleep quality was altered. Wake episodes after sleep onset were mostly associated with noise over 77 dB, and the main disturbances were triggered by the alarms of breathing machines and those from vital parameters. In military flights of long duration, we have explored the presence of hypovigilance episodes. This allowed us to validate the Actiwave for polysomnography in extreme conditions. In a third study, we have analyzed the sleep patterns in a total of 202 patients with Alzheimer’s disease by using a new actimeter, the MotionWatch8. We have shown that the latter device has a good sensitivity and specificity or evaluating sleep-wake parameters in these patients. In particular, we find that the TST is in the normal range and is associated with the aptathy score. The SIJ score is associated with the apathy score and also with the cognitive impairments. Finally, the sleep fragmentation is associated with the disability status. In a last study, we explored the parameter of sleep apneas in patients with SAS using the NOWAPI. We validated this new device by demonstrating that it provides on-line reliable data about pressure and flow levels of various CPAP. In conclusion, this thesis considers possible future avenues of research into sleep technology and discusses the crucial importance of a scientific approach capable of leading the development of appropriate and lasting diagnostic and therapeutic tools. The next step will be the era of the 2.0 medicine for which I am developing the iSommeil application that will allow patients to be the actual actors of their disease and also to facilitate the diagnostic and the prevention of sleep disorders.

L’objectif des travaux de la thèse est d’étudier les propriétés statistiques de correction des prévisionsde température et de les appliquer au système des prévisions d’ensemble (SPE) de MétéoFrance. Ce SPE est utilisé dans la gestion du système électrique, à EDF R&D, il contient 51membres (prévisions par pas de temps) et fournit des prévisions à 14 jours. La thèse comportetrois parties. Dans la première partie on présente les SPE, dont le principe est de faire tournerplusieurs scénarios du même modèle avec des données d’entrée légèrement différentes pour simulerl’incertitude. On propose après des méthodes statistiques (la méthode du meilleur membre etla méthode bayésienne) que l’on implémente pour améliorer la précision ou la fiabilité du SPEdont nous disposons et nous mettons en place des critères de comparaison des résultats. Dansla deuxième partie nous présentons la théorie des valeurs extrêmes et les modèles de mélange etnous proposons des modèles de mélange contenant le modèle présenté dans la première partieet des fonctions de distributions des extrêmes. Dans la troisième partie nous introduisons larégression quantile pour mieux estimer les queues de distribution. / The thesis has for objective to study new statistical methods to correct temperature predictionsthat may be implemented on the ensemble prediction system (EPS) of Meteo France so toimprove its use for the electric system management, at EDF France. The EPS of Meteo Francewe are working on contains 51 members (forecasts by time-step) and gives the temperaturepredictions for 14 days. The thesis contains three parts: in the first one we present the EPSand we implement two statistical methods improving the accuracy or the spread of the EPS andwe introduce criteria for comparing results. In the second part we introduce the extreme valuetheory and the mixture models we use to combine the model we build in the first part withmodels for fitting the distributions tails. In the third part we introduce the quantile regressionas another way of studying the tails of the distribution.

The rising temperature of the earth due to climate change has shown to alter the variations of hydro-climate variables, including their intensities, frequencies and durations. Extreme events such as floods are, in particular, susceptible to any disturbances in climate cycles. As such it is important to provide policymakers with sufficient knowledge about the probable impacts of climate change on hydrologic extremes and most importantly on floods, which have the highest impacts on the societies. For this reason analysis of hydro-climate extremes is commonly performed using data at each site (or grid cell), however due to the limited number of extreme events, these analyses are not robust. Current methods, such as the regional frequency analysis, which combine data from different locations are incapable of incorporating the spatial structure of the data as well as other explanatory variables, and do not explicitly, assess the uncertainties. In this thesis the spatial hierarchical Bayesian model is proposed for hydro-climate extreme analyses using data recorded at each site or grid. This method combines limited number of data from different locations, estimates the uncertainties in different stages of the hierarchy, incorporates additional explanatory variables (covariates), and can be used to estimate extreme events at un-gaged sites. The first project develops a spatial hierarchical Bayesian method to model the extreme runoffs over two spatial domains in the Columbia River Basin, U.S. The model is also employed to estimate floods with different return levels within time slices of fifteen years in order to detect possible trends in runoff extremes. Continuing on the extreme analysis, the impact of climate change on runoff extremes is investigated over the whole Pacific Northwest (PNW). This study aims to address the question of how the runoff extremes will change in the future compared to the historical time period, investigate the different behaviors of the regional climate models (RCMs) regarding the runoff extremes, and assess the seasonal variations of runoff extremes. Given the increasing number of climate model simulations the goal of the third project is to provide a multi-model ensemble average of hydro-climate extremes and characterize the inherent uncertainties. Outputs from several regional climate models provided by NARCCAP are considered for the analysis in all seasons. Three combination scenarios are defined and compared for multi-modeling of extreme runoffs. The biases of each scenario are calculated and the scenario with the least bias is selected for projecting seasonal runoff extremes. The aim of the fourth project is to quantify and compare the uncertainties regarding global climate models to the ones from the hydrologic model structures in climate change impact studies. Various methods have been proposed to downscale the coarse resolution General Circulation Model (GCM) climatological variables to the fine scale regional variables; however fewer studies have been focused on the selection of GCM predictors. Additionally, the results obtained from one downscaling technique may not be robust and the uncertainties related to the downscaling scheme are not realized. To address these issues, in the fifth study we employed Independent Component Analysis (ICA) for predictor selection which determines spatially independent GCM variables (as discussed in Appendix A). Cross validation of the independent components is employed to find the predictor combination that describes the regional precipitation over the upper Willamette basin with minimum error. These climate variables along with the observed precipitation are used to calibrate three downscaling models: Multi Linear Regression (MLR), Support Vector Machine (SVM) and Adaptive-Network-Based Fuzzy Inference System (ANFIS).

In this project, we identified and examined the 50 coldest extreme temperature eventsin North America (CENA) and the 50 warmest extreme temperature events insouthwestern Europe (WEEU) during the winter seasons from 1948 to 2023. For theanalysis, we utilized daily NCEP-NCAR reanalysis data for temperature, sea levelpressure (SLP), and 500hPa geopotential height (Z500). Our main objective was toinvestigate the co-occurrence of CENA-WEEU events. To deepen our understandingof the recurrence of these events and their relationship with large-scale atmosphericpatterns and drivers, we examined the SLP and Z500 for the selected extreme events.The results revealed clear indications of an interconnection between CENA andWEEU. During the CENA, above-normal temperatures were observed over Europe,while negative temperature anomalies affected the eastern USA during the WEEU.This co-occurrence was further supported by the identification of seven CENA-WEEUextremes that occurred almost simultaneously. The findings regarding the large-scaleatmospheric drivers of these extremes align with previous studies. The CENAappears to be driven by an anomalous high ridge over the Gulf of Alaska and anortherly flow over North America, while the WEEU seems to be influenced by astrong, zonal and southerly shifted flow across the North Atlantic, associated with adeep trough over the British Isles and a ridge over the Mediterranean basin. Acommon feature of CENA-WEEU events is the presence of a negative North AtlanticOscillation (NAO)-like atmospheric pattern over the Atlantic Ocean prior to theiroccurrence.Despite the significant similarities between these events, some disparities relatedto the atmospheric flow and the magnitude of temperature anomalies in the twocontinents suggest the need for further investigation to enhance our understanding ofthe co-occurrence of CENA-WEEU events. / I detta projekt identifierades och studerades de 50 kallaste extrematemperaturhändelserna i Nordamerika (CENA) och de 50 varmaste extrematemperaturhändelserna i sydvästra Europa (WEEU) under vintersäsongerna från1948 till 2023. För analysen, användes dagliga NCEP-NCAR återanalys för demeteorologiska variablerna temperatur, tryck (SLP) och 500hPa geopotentialhöjd(Z500). Huvudsyftet med denna studie är att undersöka samförekomsten avCENA-WEEU-händelserna. För att fördjupa vår förståelse för återkommandehändelser och deras förhållande till storskaliga atmosfäriska mönster och drivkrafter,användes SLP och Z500 variablar för de utvalda extrema händelserna.Resultaten visade tydliga tecken på sammankoppling mellan CENA och WEEU.Temperaturer över det normala observerades över Europa under CENA, medannegativa temperaturanomalier påverkade östra USA under WEEU. Samförekomstenstöds ytterligare av identifieringen av sju CENA-WEEU-extremer som inträffadenästan samtidigt. När det gäller de storskaliga atmosfäriska drivfaktorer förextremerna, stämmer resultaten överens med tidigare studier. En starkhögtrycskrygg över Alaskagolfen och ett nordligt flöde över Nordamerika verkar drivaCENA, medan ett ett starkt, zon- och sydligt förskjutet flöde över Nordatlanten,associerat med intensiv cyklonaktivitet över de brittiska öarna och en högtrycksryggöver Medelhavsområdet, verkar vara källan till WEEU. Ett gemensamt drag förCENA-WEEU är förekomsten av ett negativt NAO-liknande atmosfäriskt mönster överAtlanten innan de inträffade.Trots de starka och många likheterna mellan händelserna, tyder vissa skillnaderrelaterade till atmosfärsflödet och extrema temperaturavvikelser på de bådakontinenterna, på behovet av ytterligare undersökningar för att fördjupa vår förståelseav samförekomsten mellan CENA och WEEU.

A consequence of climate change may be higher frequencies and higher intensities of extreme climate events all over the world. This paper takes a closer look at the Northern Vietnam climate conditions. The area of interest are the geographical regions North East, North West, Red River Delta and North Central Coast. For research of extreme climate, the data from 72 meteorological stations for the time period from 1975 to 2006 were used and tested for the rainy season with the method of indices for climate change research created by Expert Team on Climate Change Detection (ETCCDI). Apparently, there is a linkage between the indices and topics of social and economic impacts, but this is not a clear fact. The climate change and extreme precipitation indices of the annual total precipitation above the 95th percentile (R95p), the annual total precipitation above the 99th percentile (R99p), the simple precipitation intensity amount (SDII), the annual total precipitation on wet days (PRCPTOT) and a modified annual total precipitation above 50 mm (R50mm) are used in this study. The question, whether there are statistically significant trends is answered using the Mann-Kendall Trend test. The results show that the indices are strongly influenced by the variations of the Vietnamese climate. Hence many stations have no significant trends. For the investigated time period, most of significance trends were decreasing. But there is a positive correlation between the total precipitation in the rainy season (PRCPTOT) and the frequencies of extreme climate events above the indices thresholds from R95p and R99p. Concluding, climate models show that higher total precipitations are likely for the area of interest. Therefore, it can be expected that, in a changing climate, more extreme climate events with higher intensities will occur. / Biến đổi khí hậu có thể dẫn đến sự gia tăng về tần số và cường độ của các hiện tượng thời tiết cực đoan trên toàn thế giới. Nghiên cứu này sẽ xem xét kỹ hơn về các điều kiện khí hậu ở miền Bắc Việt Nam. Địa điểm nghiên cứu bao gồm các khu vực địa lý Đông Bắc, Tây Bắc, Đồng bằng sông Hồng và Bắc Trung Bộ. Để nghiên cứu về khí hậu cực đoan, các dữ liệu trong khoảng thời gian từ 1975 đến 2006 đã được thu thập từ 72 trạm khí tượng. Những dữ liệu này được dùng để kiểm chứng đối với mùa mưa theo phương pháp chỉ số nghiên cứu biến đổi khí hậu của Nhóm chuyên gia về phát hiện biến đổi khí hậu (ETCCCDI). Hiển nhiên có một mối liên hệ giữa các chỉ số với các chủ đề về tác động kinh tế và xã hội, tuy nhiên thực tế này vẫn chưa rõ ràng. Các chỉ số biến đổi khí hậu và mưa cực đoan của tổng mưa hằng năm trên 95 phần trăm (R95p), tổng mưa hằng năm trên 99 phần trăm (R99p), chỉ số cường độ mưa trên ngày (SDII), tổng mưa hằng năm vào những ngày ẩm ướt – mùa mưa (PRCPTOT) và tổng mưa hằng năm biến đổi trên 50mm (R50mm) được sử dụng trong nghiên cứu này. Câu hỏi về sự tồn tại của các xu hướng quan trọng về mặt thống kê được trả lời bằng phương pháp Mann-Kendall Trend. Các kết quả chỉ ra rằng các chỉ số chịu ảnh hưởng lớn từ sự biến đổi của khí hậu Việt Nam. Do vậy, ở một số trạm khí tượng không có các xu hướng có ý nghĩa. Trong khoảng thời gian nghiên cứu, các xu hướng quan trọng đều giảm. Tuy nhiên, có một mối tương quan thuận giữa tổng lượng mưa trong mùa mưa (PRCPTOT) và cường độ của các hiện tượng thời tiết cực đoan trên các cực của chỉ số từ R95P và R99p. Kết luận, các mô hình thời tiết cho thấy tổng lượng mưa lớn hơn có khả năng sẽ xảy ra trên địa bàn nghiên cứu. Vì vậy, có thể phỏng đoán rằng khi thay đổi khí hậu, sẽ diễn ra nhiều hiện tượng thời tiết cực đoan với cường độ cao.

In context of catastrophic floods and extreme droughts in recent years there is an urgent need of solving of issues dealing with protection against hydrological extremes, not using just classical engineering methods but also untraditional practices. There is a new protection strategy focusing on gradual increase of river catchment retention capacity including its headwater regions. All of the issues related to various possibilities and measures leading to river headstream areas retention capacity increase should be discussed by experts in various fields taking into account objectives and priorities of a supra-regional, regional and local significance. Natural runoff process is affected by man already by its birth, thus in headwaters where numerous procedures related to runoff retardation and water retention increase in headstream areas could be realized. Suitable conditions for the research realization at present is related to the Otava River headwaters (sw. Czechia) representing the core zone of a number of extreme runoff events and with high heterogeneity in the terms of physical-geographic and socio-economic aspects. To understand and clarify the runoff generation process and the effect of various physical-geographic factors on its dynamics, the detailed analyses of runoff regime in chosen...