En zone de montagne, et particulièrement dans les Alpes du Nord, l'amélioration des modèles de prévision de crues est un enjeu scientifique et opérationnel important, du fait notamment des changements climatiques et environnementaux qui modifient le fonctionnement des systèmes hydrologiques. Les apports liés à la fonte nivale constituent une difficulté spécifique à la modélisation hydrologique dans les Alpes. Cette thèse entend contribuer à améliorer les modèles dans ce domaine, à deux niveaux. Dans un premier temps un modèle de fonte de neige performant à l'échelle ponctuelle a été explicité, utilisant un minimum de variables météorologiques. Pour cela l'approche dite « degré jour », qui permet d'estimer en fonction de la température de l'air la lame d'eau déstockée par le manteau neigeux, a été reprise. Grâce aux données acquises par le Centre d'Etude de la Neige sur le site expérimental du Col de Porte (Chartreuse), plusieurs formulations ont été testées prenant notamment en compte le stock de froid du manteau neigeux et les effets liés au cycle saisonnier, à travers un coefficient de fonte explicité à l'aide d'une sinusoïde. Dans un deuxième temps, l'accent est mis sur la régionalisation de la donnée d'entrée fondamentale pour ce modèle degré jour : la température de l'air. La spatialisation des champs de température a été étudiée à l'aide d'outils géostatistiques, en se focalisant sur une meilleure compréhension des gradients altimétriques de température. L'objectif est de mieux cartographier les températures au pas de temps infra journalier et de déterminer un modèle d'interpolation pertinent et simple. Les perspectives sur l'utilisation des résultats obtenus dans ces deux phases de modélisation sont abordées en vue d'une utilisation future des modèles degré jour sur des bassins versants de montagne. / In mountain areas, and especially in the northern Alps, the improving of flood forecasting models is an important scientific and operational issue, due to environmental and climatic changes which modify hydrological system. Snow melt contributions are a specific difficulty in the hydrological modelling in the Alps. This thesis is concerning in improving snow melt modelling for hydrological forecasting. In a first step a snow melt model at a local scale is formulated, using a minimum of meteorological variables. For this the “degree day” model, which allows predicting the water release by snow function of air temperature, is used. Thanks to data of the Centre d'Etude de la Neige on the experimental site of Col de Porte (Chartreuse), several formulations have been tested with some interesting concepts, like the cold content of snow and the effect of seasons with a melt factor given with a sinusoidal expression. In a second step, we are interested in the regionalization of the most important parameter for the snow melt model: air temperature. The spatial interpolation of temperature in mountainous areas is done with geostatistical tools, focusing on a better understanding of the elevation lapse rate of temperature. The goal is mapping air temperatures at a sub daily time step and to propose a simple and relevant model. Prospects about these results of snowmelt modelling and temperatures interpolation are given for using them in mountainous catchments.

Dollar spot, caused by the pathogen S. homoeocarpa (F.T. Bennett), is a common disease that infects a wide variety of turfgrasses all over the world. Yet it is significant problem on golf course putting greens and fairways consisting of creeping bentgrass (Agrostis stolonifera L.) and annual bluegrass (Poa annua L.). It is active in a wide variety of environmental conditions ranging from 16-30˚C but favors warm, humid days, followed by cool nights. Sclerotinia homoeocarpa overwinters as dormant mycelium in dead plant tissue. In the spring, germinating mycelia begin to infect leaf blades causing foliar lesions, which then spread via mycelium by means of wind, rain, animals and equipment. While there are a number of cultural practices that can reduce disease severity, frequent fungicide applications are required to maintain acceptable playing conditions on a golf course. The repeated use of fungicides with the same mode of action has led to the development of fungicide resistance of S. homoeocarpa to certain fungicide classes. Most notably, demethylase inhibitor (DMI) fungicides have been found to have varying levels of inefficacy against S. homoeocarpa across North America. The cause for reduced efficacy is suspected to the shifted sensitivity levels of many S. homoeocarpa populations, which are resulted from repeated use of the DMI fungicide. Recently, “early-spring fungicide applications” targeting to reduce initial inoculum density of dollar spot have gained popularity in an attempt to reduce dollar spot severity. In addition, preventative fungicide applications (from late October through mid-November) containing DMI fungicides have been traditionally practiced to target snow molds (caused by Microdochium nivale, Typhula spp.) in the northeastern United States. To date, there is not a clear understanding as to what effect, if any, these applications have on S. homoeocarpa DMI sensitivity or residual dollar spot control the following year. Traditional preventative snow mold applications were also investigated on the effect of S. homoeocarpa DMI sensitivity and early-season dollar spot control. The objective of this study was to investigate the effect of early-spring dollar spot application and late-fall snow mold application on S. homoeocarpa population with a bimodal distribution of DMI sensitive and insensitive isolates.

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Mild traumatic brain injury in snowsports is a prevalent concern. With as many as 130,000 hospitalized injuries in the U.S. associated with snowsports in 2017, head injury constitutes about 28% and is the main cause of fatality. Studies have found that a combination of rotational and linear velocities is the most mechanistic way to model brain injury, but despite decades of research, the biomechanical mechanisms remain largely unknown. However, evidence suggests a difference in concussion tolerance may exist between athlete populations. To improve the ability to predict and therefore reduce concussions, we need to understand the impact conditions associated with head impacts across various sports. There is limited research on the conditions associated with head impacts in snowsports. These head impacts often occur on an angled slope, creating a normal and tangential linear velocity component. Additionally, the impact surface friction in a snowsport environment is highly variable, but could greatly influence the rotational kinematics of head impact. Currently helmet testing standards don't consider these rotational kinematics, or varying friction conditions that potentially occur in real-world scenarios. The purpose of this study is to investigate the head impact conditions in a snowsport environment to inform laboratory testing and evaluate snow helmet design. We determined head impact conditions through video analysis to determine the impact locations, mechanism of fall, and the kinematics pre-impact. We used these data to develop a test protocol that evaluates snowsport helmets in a realistic manner. Ultimately, the results from this research will provide snowsport participants unbiased impact data to make informed helmet purchases, while concurrently providing a realistic test protocol that allows for design interventions to reduce the risk of injury. / Master of Science / Mild traumatic brain injury in snowsports is a prevalent concern. With as many as 130,000 hospitalized injuries in the U.S. associated with snowsports in 2017, head injury constitutes about 28% and is the main cause of fatality. Studies have found that a combination of rotational and linear velocities is the most mechanistic way to model brain injury, but despite decades of research, the biomechanical mechanisms remain largely unknown. However, evidence suggests a difference in concussion tolerance may exist between athlete populations. To improve the ability to predict and therefore reduce concussions, we need to understand the impact conditions associated with head impacts across various sports. There is limited research on the conditions associated with head impacts in snowsports. These head impacts often occur on an angled slope, creating a normal and tangential linear velocity component. Additionally, the impact surface friction in a snowsport environment is highly variable, but could greatly influence the rotational kinematics of head impact. Currently helmet testing standards don't consider these rotational kinematics, or varying friction conditions that potentially occur in real-world scenarios. The purpose of this study is to investigate the head impact conditions in a snowsport environment to inform laboratory testing and evaluate snow helmet design. We determined head impact conditions through video analysis to determine the impact locations, mechanism of fall, and the kinematics pre-impact. We used these data to develop a test protocol that evaluates snowsport helmets in a realistic manner. Ultimately, the results from this research will provide snowsport participants unbiased impact data to make informed helmet purchases, while concurrently providing a realistic test protocol that allows for design interventions to reduce the risk of injury.

The rapid development of ski resorts has added to environmental problems. In these environments, snow deposition and its accompanying problems are a major element in architectural design and planning. The objectives of this research were to investigate the background of ski resort development and the problems encountered in their design, construction, and operation. The research undertaken found specific areas of systematic problem solution to be necessary, including the use of historical and indigenous building techniques, related modern technology, detailed site analysis, field testing, and wind tunnel testing. Observation of ski resorts in New England revealed that ice and snow accumulation are major problems and present hazards to pedestrians, vehicles, and structures. Field tests of flat, restricted area roofs were conducted at Snowshoe, West Virginia to discover the possible applications of ice expansion problems in test models. It was observed that expansion and contraction of ice on the roof resulted in structural damage. Wind tunnel testing was used to determine applications of drifting and migration patterns of snow. Buildings with larger surface areas exposed to the wind create more diffuse wind eddy patterns at ground level and less movement of simulated snow. Increased building size in the downwind direction created less movement. Vegetation was found to provide shelter for and inhibit snow drifting around models placed near it. / M. Arch.

Résumé: La mesure de l’équivalent en eau de la neige (EEN) sur le terrain permet de prédire la quantité d’eau libérée par la fonte de la neige. La télédétection dans les micro-ondes passives offre le potentiel d’estimer I’EEN et peut complémenter ces observations de façon synoptique pour l’ensemble du territoire. Un produit de cartographie de I’EEN couvrant l’ensemble du globe a été élaboré par le NSIDC basé sur le capteur AMSR-E. Cet instrument, lancé en 2002, a une résolution améliorée par rapport aux capteurs antérieurs. L’estimation de I’EEN se base sur la différence entre un canal peu affecté (19 GHz) et un canal affecté (37 GHz) par la diffusion de volume de la neige. La précision de ce produit a été évaluée pour la province de Québec à l’hiver 2003 et à l’hiver 2004 qui ont un EEN moyen de 170 mm. Des sous-estimations importantes ont été révélées et une certaine difficulté à détecter la présence de neige. Des modèles régionaux de régressions linéaires ont été développés pour le Québec. Des corrections pour la fraction d’eau et de forêt ont été appliquées à la combinaison T19v.37v et ont permis d’améliorer les résultats. Ces corrections sont basées sur la température de l’air du modèle GEM. Les meilleurs résultats sont pour la classe de neige taïga à l’hiver 2003 avec une erreur relative de 24 % tandis que l’erreur relative est d’environ 40 % pour la région maritime. Les erreurs élevées dans la classe taïga ont été attribuées à des couverts de neige plus épais que la capacité de pénétration des micro-ondes tandis que les erreurs de la classe maritime a des fractions forêt élevées et à la neige mouillée. La présence d’importante quantité de neige et la forêt dense de la province de Québec compliquent l’estimation de I’EEN au Québec avec un modèle de régression. || Abstract: Snow water equivalent (SWE) measurements in the field allow estimation of the quantity of released water from the melting of snow. This is useful to predict the water reserve available for production of hydro-electricity. Remote sensing with microwave can estimate SWE and complement those observations synoptically for whole territories. A SWE mapping products was developed by NSIDC based on the AMSR-E sensor launched in 2002 with an improved resolution compared to previous sensors. SWE estimation is based on difference between a channel weakly affected (19 GHz) and a channel strongly affected by volume scattering. The precision of this product was evaluated for the province of Quebec in winter 2003 and winter 2004 with a mean SWE of 170 mm. Important underestimation and some difficulty of detecting the snow was revealed. Regional linear regression models were developed for the province of Quebec. Corrections for forest and water fraction were applied on T19V-37V combination and permit to improve the results. Those corrections were based on air temperature from the GEM model. Best results were found for taiga snow class in winter 2003 with a relative error of 28% and approximately 40% for maritime snow class. High errors in the taiga region were attributed to snow depth higher than the penetration depth of the microwave and errors in the maritime region to high forest density and wet snow. The important snow amount and high density forest of the province of Quebec hampers the estimation of SWE with a regression model.

Les travaux présentés portent sur les étapes successives qui ont conduit au développement dans les années 1980 d'un modèle numérique qui simule l'évolution temporelle d'un manteau neigeux saisonnier en fonction des conditions météorologiques. Une première partie décrit le développement d'un modèle de neige multi-couches qui calcule les échanges d'énergie entre la neige et l'atmosphère et simule les principaux processus physiques qui contrôlent les échanges au sein du manteau neigeux.Une deuxième partie décrit comment ont été quantifiées les lois de métamorphose de la neige humide et de la neige sèche soumise à un faible gradient de température, de façon à compléter les connaissances existantes et proposer un jeu relativement complet de lois de métamorphoses de la neige saisonnière. Une troisième partie décrit l'implémentation de ces lois dans le modèle numérique, permettant ainsi de simuler la stratification du manteau neigeux, fonctionnalité qui n'existait dans aucun autre modèle à cette époque. Une évaluation détaillée de ce modèle sur le site du Col de Porte est présentée. La dernière partie introduit trois applications originales qui ont ensuite exploité les fonctionnalités de ce modèle : la simulation en temps réel de l'état caractéristique du manteau neigeux dans les Alpes françaises, l'étude de l'impact du changement climatique sur l'enneigement et la simulation de l'état du manteau neigeux dans un modèle hydrologique distribué / The thesis describes the different steps which lead during the 1980's to the development of an original numerical snow model. This model aimed at simulating the evolution of a seasonal snow cover as a function of the prevailing meteorological conditions. A first part describes the methods and algorithms used to compute the energy and mass exchange at the snow/atmosphere interface and inside the snowpack. The second part describes the experimental study which made possible the quantification of the metamorphism rate of snow samples submitted to weak temperature gradient and to liquid water content, in order to complete pre-existing knowledge on metamorphism. A third part describes the implementation of a set of metamorphism laws into the preliminary version of the snow model, which lead to the availability of the first numerical model able to simulate seasonal snowpack layering. The evaluation of the model at Col de Porte is presented. The last part introduces three applications of this model: real time monitoring of snowpack characteristics in the French Alps, assessment of the impact of climate change on snow climatology and simulation of the snowpack in a distributed hydrological model

This study is a result from a major investigation about the snow conditions in Sweden since the beginning of the twentieth century. For this purpose, data were analysed with respect to the maximum snow depth and the number of days with snow cover every year from some more than forty selected stations. These stations were then divided into different regions and means were calculated for each series. The data are presented in the shape of different histograms in the four following categories; the whole period in request (1900-2003), the latest 43 years (1961-2003), consecutive mean values for every decade and time series with the highest frequented fluctuations equalized. To be able to detect any trends in the plotted time series two statistical methods, simple linear regression and Mann-Kendall’s test, were applied. The calculations belonging to these tests are showed in tables. To be able to answer the question if the global warming can be related to the latest 3-4 decades predominantly warm winters in the southern part of Sweden I have been studying correlations in snow data with respect to the northern hemispheres mean temperature for the winter season. Corresponding estimates of the correlation coefficients have also been made with respect to the Swedish winter mean temperature. The response of the tests shows that it has not been such dramatic change in the snow conditions in the long run. The magnitude of the slope for the adjusted regression lines implies that the maximum snow depth and the number of days with snow cover in average have been on a fairly constant level during the latest hundred years. When it comes to the maximum snow depth one can distinguish a tendency for a small rise in Götaland and northern Norrland. This is also the only cases which are statistical significant for the period in request (1905-2003). For the shorter period 1961-2003 however, the number of days with snow cover has decreased quite substantially in the southern part of Sweden corresponding to a decrease about 40% in Götaland and 20% in Svealand. The test based on simple linear regression gives significant results in both cases while Mann-Kendall only establishes the trend for Götaland. A closer view of the maximum snow depth for the shorter period (1961-2003) does not give the same response but there is at least evidence for a significant decrease in Svealand in the test with simple linear regression. It corresponds to a decrease of about 30% since 1960. One cannot immediately relate the changes in the Swedish snow climate to the global warming. Estimated values of the correlation coefficient do not even give significant results for the period 1961-2003 despite of the fact that the global mean temperature has raised quite considerably since 1970. The corresponding calculations for the Swedish winter mean temperature show that it plays a very important roll if the precipitation in Götaland and Svealand is coming as rain or snow while it does not matter at all in northern Norrland. / Denna studie är ett resultat av en omfattande undersökning av snöförhållandena i Sverige sedan början av 1900-talet. Jag har för detta ändamål analyserat data av maximala snödjup och antalet dagar med snötäcke per kalenderår från ett 40-tal utvalda stationer. Dessa stationer har sedan delats upp på olika regioner varefter medelvärden har räknats fram i resp. fall. Datamaterialet illustreras här i form av olika stapeldiagram uppdelat på fyra följande kategorier; hela tidsserien, perioden 1961-2003, konsekutiva 10-årsmedelvärden samt en tidsserie med de mest högfrekventa svängningarna bortdämpade. För att kunna bedöma eventuella trender i de uppritade tidsserierna så har jag använt mig av de båda statistiska metoderna enkel linjär regression resp. Mann-Kendall's test. Tillhörande beräkningar redovisas på tabellform. För att svara på frågan om den globala uppvärmningen kan sättas i samband med de senaste 30-40 årens övervägande snöfattiga vintrar i södra Sverige så har jag studerat korrelationen av snödata gentemot det norra halvklotets vintermedeltemperatur. Motsvarande beräkningar av korrelationskoefficienter har också genomförts för den svenska vintermedeltemperaturen Utslaget på testerna visar att det inte har skett så dramatiska förändringar i snöförhållandena på lång sikt. Magnituden på lutningskoefficienten för de anpassade regressionslinjerna tyder på att det maximala snödjupet och antalet dagar med snötäcke i medeltal har legat på en ganska konstant nivå under de senaste hundra åren. När det gäller maximala snödjup så kan man paradoxalt nog se en tendens till en svag uppgång för Götaland och norra Norrland. Det är också de enda fallen som är statistiskt säkerställda för tidsserien som helhet. För den kortare perioden 1961-2003 så kan man däremot se att antalet dagar med snötäcke har minskat relativt kraftigt i södra Sverige motsvarande en nedgång på cirka 40% i Götaland och 20% i Svealand. Test med enkel linjär regression ger signifikanta resultat i båda fallen medan Mann-Kendall endast fastställer trenden för Götaland. En närmare undersökning av det maximala snödjupet för den kortare tidsserien ger dock inte lika tydligt utslag i statistiken men man kan trots allt urskilja en signifikant minskning för Svealand i testet med enkel linjär regression. Det rör sig här om en nedgång på cirka 30% efter 1960. Det går inte att omedelbart relatera förändringarna i det svenska snöklimatet till den globala uppvärmningen. Beräknade värden på korrelationskoefficienten ger inte ens signifikant utslag för perioden 1961-2003 trots att den globala medeltemperaturen har ökat ganska markant sedan 1970. Motsvarande beräkningar för den svenska vintermedeltemperaturen visar att den har väldigt stor betydelse för om nederbörden i Götaland och Svealand faller som regn eller snö medan det för norra Norrland inte har någon nämnvärd påverkan.