Η πιθανή επίδραση της μεταβλητότητας της ροής της κοσμικής ακτινοβολίας στη νέφωση, στην ατμοσφαιρική κατακρήμνιση και συνεπώς στο πλανητικό ισοζύγιο ακτινοβολίας έχει εγείρει μια έντονη έρευνα τα τελευταία χρόνια. Επιχειρείται μια κριτική ανασκόπηση των εργασιών στις οποίες έχει μελετηθεί η σχέση μεταξύ γαλαξιακών κοσμικών ακτίνων και ατμοσφαιρικών διεργασιών και το ενδιαφέρον επικεντρώνεται σε αυτές που αφορούν στην επίδραση των βραχυχρόνιων μεταβολών της γαλαξιακής κοσμικής ροής στα νέφη και την ατμοσφαιρική κατακρήμνιση. Η συσχέτιση μεταξύ των επεισοδίων βροχόπτωσης και της κοσμικής ακτινοβολίας είναι πολύ μικρή για να αποδείξει άμεση επίδραση των κοσμικών ακτίνων στην ατμόσφαιρα. Συνεπώς, σκοπός αυτής της μελέτης είναι να ερευνήσει τη συσχέτιση μεταξύ των επεισοδίων βροχόπτωσης και των μειώσεων της γαλαξιακής κοσμικής ακτινοβολίας σε ημερήσια βάση. Η μεθοδολογία που υιοθετείται παρέχει έναν χρήσιμο τρόπο διαχωρισμού του σήματος της γαλαξιακής κοσμικής ακτινοβολίας από άλλες πιθανές εξωτερικές και εσωτερικές επιδράσεις στην ατμοσφαιρική κατακρήμνιση. Η βασικότερη μέριμνα αυτής της μελέτης είναι ο προσδιορισμός ενός προτύπου επιβεβαίωσης του ορίου μείωσης και της χρονικής περιόδου της κοσμικής ακτινοβολίας που θεωρείται ως μείωση Forbush, αφού και στη βιβλιογραφία η μείωση Forbush ορίζεται μάλλον αυθαίρετα. Η μείωση του ρυθμού ατμοσφαιρικής κατακρήμνισης κατά τη διάρκεια των μειώσεων Forbush είναι σύμφωνη με τα αποτελέσματα της ερευνητικής εργασίας και άλλων επιστημόνων. Τέλος, εκτιμάται ένας πιθανός μηχανισμός μικροφυσικής των νεφών που ερμηνεύει τη συμπεριφορά των μειώσεων Forbush για τα πολύ έντονα επεισόδια βροχόπτωσης. Η πειραματική μελέτη των θεμελιωδών μικροφυσικών αλληλεπιδράσεων μεταξύ της κοσμικής ακτινοβολίας και των νεφών και η ανάπτυξη νέας τεχνολογίας οργάνων θα βοηθήσει στην κατανόηση του φυσικού μηχανισμού κοσμικές ακτίνες - νέφη - κλίμα. / The possible influence of variability of the cosmic ray flux on cloud cover, on precipitation and thus on the radiation budget of the planet, has stimulated a lively investigation during the recent years. We attempt a critical review cites of those papers studying the relation between galactic cosmic rays and atmospheric processes and we focus on those which pertain the influence of short - term changes of galactic cosmic flux on clouds and precipitation. The correlation between precipitation events and cosmic rays is very low to prove the direct influence of cosmic rays in the atmosphere. Consequently, the scope of this study is to investigate the correlation between precipitation events and galactic cosmic ray decreases on a diurnal basis. The methodology adopted provides a useful way to dissociate the signal of galactic cosmic rays from other possible external and internal influences on precipitation. The basic concern of this study is the determination of a model to confirm the limit of cosmic ray decrease and the corresponding time of occurrence assumed as a Forbush decrease, since this decrease is arbitrarily defined in literature. The determined decrease of precipitation rate during the Forbush decreases is in accordance to the results of other scientists. Finally, we estimate a possible cloud microphysical mechanism which may interpret the impact of Forbush decreases for the heavy precipitation events. The experimental study of the fundamental microphysical interactions between cosmic rays and clouds and the development of new instrumentation will help to understand the physical mechanism cosmic rays – clouds – climate.

It is proven that the ongoing refinement of the quality of rainfall data hand in hand with time and space variability of the rainfall has immense effect on the management of watercourses, flood control and hydrologic modelling. The aim of this thesis is to do an analysis of selected precipitation events in the Kopaninský stream research basin for more accurate information on rainfall-runoff processes. The aim of the analysis of individual precipitation events is to evaluate differences in total precipitation and volume measurements recorded in the basin and radar estimated precipitation. The output is detailed data series of spatial and temporal distribution of major precipitation events in the GIS used as input to hydrologic models. The issues of atmospheric precipitatio and meteorological radars are discussed in the literature review, which explains selected basic concepts and principles of these topics.

<p dir="ltr">The escalating threat of flooding due to climate change, urbanization, and population growth calls for accurate flood estimation, especially as annual flood losses are projected to reach up to $52 billion by 2050. However, factors like changing precipitation patterns, watershed changes, and model uncertainties complicate future flood estimation. Rising global temperatures not only intensify extreme storms but also alter their spatial and temporal characteristics, yet these changes remain poorly understood across different climate regions, hindering effective hydrological response planning. This study investigates how climate change affects storm spatio-temporal patterns and probable maximum precipitation (PMP) estimates, pinpointing regions most vulnerable to these shifts. The specific three objectives of this study are 1) to understand how the spatial extent of short duration precipitation extreme changes across the globe particularly in response to climate variables like temperature 2) to understand and quantify the changes in combined spatio-temporal characteristics of extreme storms in response to rising temperatures; and 3) to evaluate changes in probable maximum precipitation (PMP) estimates in response to climate change, specifically identifying critical infrastructure—such as dams and nuclear facilities—that may be at increased risk.</p><p dir="ltr">In the first objective, a novel grid-based metric called the Spatial Homogeneity (SH) metric is developed to assess the changes in spatial extent of extreme storms of different intensity and across different regions. The study finds that rising temperature results in smaller size extreme storms in the tropics, but larger size storms in the arid regions. It is also found that more intense precipitation events have a smaller spatial extent. Furthermore, larger spatial extent storms were found to be associated with higher total precipitable water, while overall cold vs warm year or overall year around wetness vs dryness of a region had limited impact on the spatial extent of these extreme storms. The results of this study imply that rising temperatures will result in spatially smaller and more intense extreme precipitation storms in the tropics.</p><p dir="ltr">Adding a temporal dimension to the Spatial Homogeneity metric, the second objective introduces the Spatio-Temporal Homogeneity (STH) metric to analyze global patterns in the combined spatio-temporal characteristics of short-duration extreme storms. Findings reveal that extreme storms contract in both space and time in the tropics, while expanding in temperate zones as temperatures rise. Additionally, storms in the tropics and southern temperate regions exhibit increased front-loading, whereas northern temperate storms become slightly more rear-loaded. Short-duration (6–12 hours) storms show heightened sensitivity to temperature increases, underscoring the need for region-specific flood management and adaptation strategies.</p><p dir="ltr">Finally, the third objective assesses how climate change impacts global PMP estimates, focusing on changes in precipitation efficiency and maximum precipitable water<i> </i>𝑃𝑊_𝑚𝑎𝑥. While precipitation efficiency remains relatively unchanged, 𝑃𝑊_𝑚𝑎𝑥 has increased up to 40% in certain regions since the 1960s, establishing a conservative baseline for PMP rises. Future climate projections highlight that PMP estimates are expected to continue increasing even further. Furthermore, longer-duration PMPs show the most significant increases, stressing the need to reassess safety standards for large dams in high-risk areas. The study identifies the regions most at risk and highlights the necessity for updated PMP standards and targeted infrastructure adaptation in vulnerable regions.</p><p dir="ltr">This dissertation advances our understanding of how climate change is reshaping extreme precipitation characteristics, particularly from a hydrologic flood-generation perspective. By providing refined, climate-adjusted representations of future precipitation patterns, it marks a step toward improved accuracy in future flood and hydrologic response estimation. These insights lay a foundation for more informed flood risk assessments and support the development of targeted, resilient water management strategies essential for adapting to a changing climate.</p>

Chaque automne, des événements de précipitations intenses (HPEs) ont lieu en Méditerranée nord-occidentale. Cette thèse adopte une approche par la modélisation climatique régionale couplée atmosphère-océan pour traiter de la sensibilité de ces événements à des changements de température de surface de la mer (SST) résultant soit de biais dans le modèle couplé, soit de la réponse de la couche de mélange océanique à des forçages atmosphériques. Deux cas d’études mettent en évidence la sensibilité particulière des zones de convergence d’humidité aux changements de SST. L’élaboration d’indices synthétiques de changements dans les précipitations et de changements de SST en amont des zones précipitantes met en lumière dans plusieurs régions (Cévennes, région de Valence, Calabre) une relation linéaire entre ces deux quantités dans deux plateformes de modélisation différentes : MORCE et CNRM-RCSM4. Dans la région de Valence, en Espagne, nous montrons en outre que les événements de précipitations intenses sont souvent précédés d’un épisode de Mistral qui refroidit la zone amont des précipitations dans les jours précédant celles-ci, refroidissement qui tend ensuite à réduire l’intensité de l’événement précipitant. / Every year in autumn, heavy precipitation events (HPEs) occur in the northwestern Mediterrranean. This thesis uses coupled atmosphere-ocean regional climate modeling to tackle the sensitivity of these events to sea surface temperature (SST) changes coming either from model biases or from the oceanic mixed layer response to atmospheric forcing. Two case studies show the particular sensitivity of moisture convergence zones to SST changes. The use of synthetic indexes of precipitation changes and SST changes in the upstream zones shows a linear relationship between the two indexes in several regions (Cévennes, the region of Valencia, Calabria) in the modeling platforms MORCE and CNRM-RCSM4. Furthermore, we show that the HPEs in the region of Valencia are often preceded by a Mistral event which cools the upstream zone whithin 5 days before the HPEs. In turn, this cooling tends to reduce the intensity of the HPE.