Basal Temperature of Snow (BTS) measurements were used as the primary inputs to a high resolution (30 x 30 m grid cells) empirical-statistical regional permafrost probability model for the southern and central Yukon, and northernmost British Columbia (59° - 65°N). Data from seven individual study areas distributed across the region were combined using a blended distance decay technique, with an eighth area used for validation. The model predictions are reasonably consistent with previous permafrost maps for the area with some notable differences and a much higher level of detail. The modelling gives an overall permafrost probability of 52%. North of 62°N, permafrost becomes more extensive in the lowland areas whereas farther south permafrost is typically common only above treeline. Significant differences exist between the mountain environments of the Yukon and the Swiss Alps where the BTS method originated and as a result different modelling approaches had to be developed. This work therefore: (1) develops additional explanatory variables for permafrost probability modelling, the most notable of which is equivalent elevation, (2) confirms the use of ground truthing as a requirement for empirical-statistical modelling in the Yukon and (3) uses a combination of models for the region in order to spatially predict between study areas. The results of this thesis will be of use to linear infrastructure route-planning, geohazard assessment and climate change adaptation strategies. Future work employing the model will allow the effects of scenario-based climate warming to be examined.

La cryosphère désigne les milieux où l’eau est présente sous sa forme solide, comme la neige ou les glaciers. La sensibilité des composantes de la cryosphère aux fluctuations climatiques, notamment température et précipitation, permet de construire des indicateurs de première importance dans le suivi de la ressource en eau et de l’évolution du climat. Les structures sociétales sont directement impactées par les altérations de ces réservoirs naturels de montagne : irrigation, potentiel hydro-électrique, tourisme, patrimoine paysager. Dans le cadre du projet de thèse-CRYOPYR, un important travail méthodologique a été effectué pour estimer les variations de surface et de volume de neige et de glace à partir de l’imagerie optique très haute résolution. Le massif des Pyrénées (3 404 m) abrite les glaciers les plus méridionaux d’Europe, et présente un important manteau neigeux saisonnier. Nous avons pu estimer la hauteur de neige en fin de période d’accumulation dans le bassin versant de la centrale hydro-électrique de Bassiès (Ariège). Dans le cas du glacier d’Ossoue (Hautes-Pyrénées), nous avons pu cartographier les variations pluriannuelles d’altitude du glacier. Complétée par une recherche de données historiques, cette démarche a permis de reconstruire les fluctuations du glacier depuis la fin du petit âge glaciaire (1850), et de caractériser les variations du climat régional à haute altitude dans les Pyrénées. L’association de ces méthodes quantitatives et de ces sites d’études permet de fournir des éléments de réponses à la problématique hydro-climatique pyrénéenne. / The Pyrenees mountain range hosts the southernmost glaciers in Europe (south of 43 _N), and are covered by a large seasonal snowpack. Glacier and snowpack are both components of the cryosphere, the water in its frozen state, and present high sensitivity to climatic influences. In the Pyrenees, water availability from snowmelt is an important issue concerning hydropower generation, irrigation in lowlands and are potentially linked to conflict usage. Pyrenees ski resorts are highly vulnerable to a potential declining snowpack. Pyrenean glaciers are strongly out of balance with regional climate and are in jeopardy in this new century. Natural patrimony and the visual perception of the high mountain landscape could be irrevocably affected by this lost. Snow depth cartography may provide valuable information to manage human activities in link with snow presence. To date, there is no direct approach to map snow depth in mountainous areas from spaceborne sensors. Here, we examined the potential of very-high-resolution stereo satellites to map snow depth in a mountain catchment. The results showed a decimetric accuracy and precision in the Pléiades derived snow depths, and realistic snow patterns. We also validated Pléiades data to estimate the annual glacier mass balance of a Pyrenean glacier. Thanks to this new approach and a deep sounding of archives data, we reconstructed the evolution of the second largest glacier of the Pyrenees (Ossoue glacier, 42.46 _N, 0.45 km2). Ossoue glacier has retreated since the end of the little ice age (LIA) with some stable phases, and would probably disappear by the half of the 21th century. Based on a new complete inventory, we maped the outline of the Pyrenean glaciers at the end of the little ice age (1850 approximately) and in 2011. It appears clear that the Pyrenees mountain range is in its last stage of deglaciation. / El término criósfera designa al conjunto de lugares donde el agua está presente en forma sólida, como la nieve o los glaciares. La sensibilidad de los componentes de la criósfera a las fluctuaciones climáticas, en particular la temperatura y las precipitaciones, permite construir indicadores de primera magnitud en el seguimiento del recurso hídrico y de la evolución del clima. Las alteraciones de esos depósitos naturales de montaña afectan de forma directa a estructuras de tipo social, tales como la: irrigación, la energía hidroeléctrica, el turismo o el patrimonio paisajístico. En el marco del proyecto de tesis CRYOPYR, llevamos a cabo un importante trabajo metodológico a partir de imágenes ópticas por satélite de muy alta resolución con el fin de evaluar las variaciones de superficie y de volumen de las capas de nieve y de hielo. Los Pirineos (3 404 m) cobijan los glaciares más meridionales de Europa, así como un importante manto de nieve estacional. Pudimos determinar la altura de la capa de nieve al final del periodo de acumulación en la cuenca de la central hidroeléctrica de Bassiès (Ariège, Francia). En el caso del glaciar de Ossoue (Hautes-Pyrénées, Francia), cartografiamos las variaciones plurianuales de altitud del glaciar. Completamos este trabajo basado en adquisiciones de imágenes por satélite con una búsqueda de datos históricos. De este modo, reconstruimos las fluctuaciones del glaciar de Ossoue desde el final de la pequeña edad de hielo (1850), y caracterizamos las variaciones del clima regional a alta altitud en los Pirineos. La combinación de estos métodos cuantitativos con medidas en sitios representativos de los cambios en curso ofrece elementos de respuesta a la problemática hidroclimática pirenaica.

Because the earth's cryosphere influences global weather patterns and climate, the scientific community has had great interest in monitoring this important region. Microwave remote sensing has proven to be a useful tool in estimating sea and glacial ice surface characteristics with both scatterometers and radiometers exhibiting high sensitivity to important ice properties. This dissertation presents an array of studies focused on extracting key surface features from multisensor microwave data sets. First, several enhanced resolution image reconstruction issues are addressed. Among these are the optimization of the scatterometer image reconstruction (SIR) algorithm for NASA scatterometer (NSCAT) data, an analysis of Ku-band azimuthal modulation in Antarctica, and inter-sensor European Remote Sensing Satellite (ERS) calibration. Next, various methods for the removal of atmospheric distortions in image reconstruction of passive radiometer observations are considered. An automated algorithm is proposed which determines the spatial extent of sea ice in the Arctic and Antarctic regions from NSCAT data. A multisensor iterative sea ice statistical classification method which adapts to the temporally varying signatures of ice types is developed. The sea ice extent and classification algorithms are adopted for current SeaWinds scatterometer data sets. Finally, the automated inversion of large-scale forward electromagnetic scattering of models is considered and used to study the temporal evolution of the scattering properties of polar sea ice.

Radar Sounders (RSs) are active sensors that transmit in the nadir electromagnetic (EM) waves with a low frequency in the range of High-Frequency and Very-High-Frequency and relatively wide bandwidth. Such a signal penetrates the surface and propagates in the subsurface, interacting with dielectric interfaces. This interaction yields to backscattered echoes detectable by the antenna that are coherently summed and stored in radargrams. RSs are used for planetary exploration and Earth observation for their value in investigating subsurface geological structures and processes, which reveal the past geomorphological history and possible future evolution. RS instruments have several parameter configurations that have to be designed to achieve the mission science goals. On Mars, radargram visual analyses revealed the icy layered deposits and liquid water evidence in the poles. On the Earth, RSs showed relevant structures and processes in the cryosphere and the arid areas that help to monitor the subsurface geological evolution, which is critical for climate change. Despite the valuable results, visual analysis is subjective and not feasible for processing a large amount of data. Therefore, a need emerges for automatic methods extracting fast and reliable information from radargrams. The thesis addresses two main open issues of the radar-sounding literature: i) assessing target detectability in simulated orbiting radargrams to guide the design of RS instruments, and ii) designing automatic methods for information extraction from RS data. The RS design is based on assessing the performance of a given instrument parameter configuration in achieving the mission science goals and detecting critical targets. The assessment guides the parameter selection by determining the appropriate trade-off between the achievable performance and technical limitations. We propose assessing the detectability of subsurface targets (e.g., englacial layering and basal interface) from satellite radar sounders with novel performance metrics. This performance assessment strategy can be applied to guide the design of the SNR budget at the surface, which can further support the selection of the main EORS instrument parameters. The second contribution is designing automatic methods for analyzing radargrams based on fuzzy logic and deep learning. The first method aims at identifying buried cavities, such as lava tubes, exploiting their geometric and EM models. A fuzzy system is built on the model that detects candidate reflections from the surface and the lava tube boundary. The second and third proposed methods are based on deep learning, as they showed groundbreaking results in several applications. We contributed with an automatic technique for analyzing radargram acquired in icy areas to investigate the basal layer. To this end, radargrams are segmented with a deep learning network into literature classes, including englacial layers, bedrock, and echo-free zone (EFZ) and thermal noise, as well as new classes of basal ice and signal perturbation. The third method proposes an unsupervised segmentation of radargrams with deep learning for detecting subsurface features. Qualitative and quantitative experimental results obtained on planetary and terrestrial radargrams confirm the effectiveness of the proposed methods, which investigate new subsurface targets and allow an improvement in terms of accuracy when compared to other state-of-the-art methods.

This thesis examines the utility of the Rényi entropy (RE), a measure of the complexity of probability density functions, as a tool for finding physically meaningful patterns in geophysical data. Initially, the RE is applied to observational data of long-lived atmospheric tracers in order to analyse the dynamics of stratospheric transitions regions associated with barriers to horizontal mixing. Its wider applicability is investigated by testing the RE as a method for highlighting internal boundaries in snow and ice from ground penetrating radar (GPR) recordings. High-resolution 500 MHz GPR soundings of dry snow were acquired at several sites near Scott Base, Antarctica, in 2008 and 2009, with the aim of using the RE to facilitate the identification and tracking of subsurface layers to extrapolate point measurements of accumulation from snow pits and firn cores to larger areas. The atmospheric analysis focuses on applying the RE to observational tracer data from the EOS-MLS satellite instrument. Nitrous oxide (N2O) is shown to exhibit subtropical RE maxima in both hemispheres. These peaks are a measure of the tracer gradients that mark the transition between the tropics and the mid-latitudes in the stratosphere, also referred to as the edges of the tropical pipe. The RE maxima are shown to be located closer to the equator in winter than in summer. This agrees well with the expected behaviour of the tropical pipe edges and is similar to results reported by other studies. Compared to other stratospheric mixing metrics, the RE has the advantage that it is easy to calculate as it does not, for example, require conversion to equivalent latitude and does not rely on dynamical information such as wind fields. The RE analysis also reveals occasional sudden poleward shifts of the southern hemisphere tropical pipe edge during austral winter which are accompanied by increased mid-latitude N2O levels. These events are investigated in more detail by creating daily high-resolution N2O maps using a two-dimensional trajectory model and MERRA reanalysis winds to advect N2O observations forwards and backwards in time on isentropic surfaces. With the aid of this ‘domain filling’ technique it is illustrated that the increase in southern hemisphere mid-latitude N2O during austral winter is probably the result of the cumulative effect of several large-scale, episodic leaks of N2O-rich air from the tropical pipe. A comparison with the global distribution of potential vorticity strongly suggests that irreversible mixing related to planetary wave breaking is the cause of the leak events. Between 2004 and 2011 the large-scale leaks are shown to occur approximately every second year and a connection to the equatorial quasi-biennial oscillation is found to be likely, though this cannot be established conclusively due to the relatively short data set. Identification and tracking of subsurface boundaries, such as ice layers in snow or the bedrock of a glacier, is the focus of the cryospheric part of this project. The utility of the RE for detecting amplitude gradients associated with reflections in GPR recordings is initially tested on a 25 MHz sounding of an Antarctic glacier. The results show distinct regions of increased RE values that allow identification of the glacial bedrock along large parts of the profile. Due to the low computational requirements, the RE is found to be an effective pseudo gain function for initial analysis of GPR data in the field. While other gain functions often have to be tuned to give a good contrast between reflections and background noise over the whole vertical range of a profile, the RE tends to assign all detectable amplitude gradients a similar (high) value, resulting in a clear contrast between reflections and background scattering. Additionally, theoretical considerations allow the definition of a ‘standard’ data window size with which the RE can be applied to recordings made by most pulsed GPR systems and centre frequencies. This is confirmed by tests with higher frequency recordings (50 and 500 MHz) acquired on the McMurdo Ice Shelf. However, these also reveal that the RE processing is less reliable for identifying more closely spaced reflections from internal layers in dry snow. In order to complete the intended high-resolution analysis of accumulation patterns by tracking internal snow layers in the 500 MHz data from two test sites, a different processing approach is developed. Using an estimate of the emitted waveform from direct measurement, deterministic deconvolution via the Fourier domain is applied to the high-resolution GPR data. This reveals unambiguous reflection horizons which can be observed in repeat measurements made one year apart. Point measurements of average accumulation from snow pits and firn cores are extrapolated to larger areas by identifying and tracking a dateable dust layer horizon in the radargrams. Furthermore, it is shown that annual compaction rates of snow can be estimated by tracking several internal reflection horizons along the deconvolved radar profiles and calculating the average change in separation of horizon pairs from one year to the next. The technique is complementary to point measurements from other studies and the derived compaction rates agree well with published values and theoretical estimates.

Permafrost is a variable in Antarctic terrestrial ecosystems, and the role it plays in the cryosphere is not well understood. There is much still to be learnt about the thermal state, physical properties, thickness and age of permafrost in Western Dronning Maud Land (WDML). Active layer dynamics and observed change over time have the potential to improve our knowledge of climate change. Understanding the effects of a warming climate on permafrost can also be of benefit to infrastructure, especially in areas with a large amount of frozen ground such as Scandinavia, Canada and Russia. Active layer and permafrost dynamics of WDML, Antarctica, are presented and discussed using data from six study sites, namely the Robertskollen, Vesleskarvet, Flarjuven, Grunehogna, Slettjfell nunataks and the Troll research station in the Jutulsessen area. Ground and ambient air temperature, as well as ground moisture data were collected for each site. An inventory of active layer and permafrost landforms was compiled, as were the frequency of cycles over the zero-degree isotherm, and the depth of the active layer. Furthermore, 3D models, geo-referenced maps and Digital Elevation Models were created of study areas with the use of an Unmanned Aerial Vehicle (UAV). Polygonal features are the most common landscape feature and are common to most of the study sites. Robertskollen has the deepest active layer at over 66cm and Slettfjell the shallowest at 9cm. A maximum recorded air temperature of 8.76°C (10/11/2014) occurred at Troll with the second highest maximum of 6.77°C (22/12/2010) recorded at Vesleskarvet. Robertskollen has the highest observable biological growth and a maximum recorded ground temperature of 22.84°C (10/01/2014). Troll and Valterkulten, registered the second and third highest ground temperatures respectively. The high ground Temperature observed for Robertskollen may be ascribed to it being the lowest altitude site. The highest number of cycles over the zero-degree isotherm was observed at Troll (11.01%), followed by Robertskollen (10.99%). For relatively warm areas, such as Robertskollen it is recommended that two metre borehole loggers are installed in order to capture a detailed understanding of the active layer. The UAV proved to be a beneficial tool for capturing aerial photographs for post fieldwork analysis and 3D modelling.

Le nord du Chili est soumis à un contexte climatique aride à semi-aride présentant une variabilité saisonnière et inter-annuelle forte. Dans cette région les zones de haute altitude soutiennent les parties plus basses des bassins versants, mais la ressource en eau reste malgré tout limitée. Afin d'améliorer les méthodes de gestion de l'eau dans ces bassins versants, il est important de préciser le rôle des zones de haute altitude dans le soutien des parties basses, mais aussi de caractériser les modalités de transfert et d'interaction entre les compartiments constitutifs de l'hydrosystème. Ce travail porte sur la caractérisation du fonctionnement hydrologique du bassin versant de l'Elqui depuis la tête de bassin, située au cœur de la cordillère des Andes, jusqu'aux vallées de la zone inférieure situées entre 500 et 2000 mètres d'altitude. En tête de bassin, les processus d'interaction entre les compartiments cryosphériques, hydrologiques et hydrogéologiques, et leurs impacts sur le transfert des masses d'eau vers l'aval de la zone d'étude sont caractérisés. Le comportement hydrologique des sous bassins versant partiellement ou non‑englacés est également étudié. Dans la zone inférieure du bassin, l'étude porte principalement sur les processus d'interactions surface-souterrain en contexte semi‑aride et sur les impacts des forçages climatiques et anthropiques sur ces derniers. Cette étude s'appuie sur plus de 40 ans de données hydro-météorologiques disponibles sur la zone inférieure du bassin, complétés par des mesures hydrologiques sur la zone supérieure (> 2000 mètres d'altitude) et des prélèvements chimiques (majeurs et traces) et isotopiques (²D, 18O) sur la totalité de la zone d'étude, réalisés entre 2011 et 2013.Ces travaux ont montré que le modèle conceptuel de fonctionnement du bassin versant de l'Elqui généralement accepté était incomplet. Dans la zone supérieure, l'étude d'un bassin versant englacé a permis de montrer que le rôle de la cryosphère dépasse la fonction de production d'eau, avec certains compartiments stockant temporairement de l'eau en période humide et la libérant en période sèche. Ce processus permet d'amortir la variabilité temporelle des précipitations et du taux de fonte en altitude. Les analyses physico-chimiques réalisées dans le bassin versant ont également permis d'identifier des compartiments aquifères ignorés jusqu'à maintenant, comme les compartiments volcanique et plutonique. En améliorant les connaissances sur les processus d'interactions entre compartiments cryosphériques, hydrologiques et hydrogéologiques, les résultats de ce travail ont apporté des précisions sur le fonctionnement hydrologique de la zone de haute altitude. Cela a permis l'estimation des impacts potentiels de la variabilité climatique sur ces processus d'interactions et leurs conséquences sur la disponibilité et la qualité de la ressource. Dans la zone inférieure, la caractérisation des interactions surface-souterrain a montré qu'il existe un fort potentiel d'interaction entre le compartiment hydrologique et le compartiment alluvial, mais également entre le compartiment alluvial et le socle plutonique. L'étude des données hydrologiques et physico-chimiques a permis de caractériser le type d'échanges se déroulant entre les compartiments. Dans certains secteurs le processus dominant est la recharge du compartiment alluvial par le compartiment hydrologique, tandis que pour d'autres il existe une alternance entre période de drainage du compartiment alluvial par le compartiment hydrologique et période de recharge du compartiment alluvial. La réponse de ces processus face aux impacts des forçages climatiques et anthropiques contraindra la disponibilité et la qualité de la ressource dans les années à venir. Ainsi, les résultats apportés par ce travail permettront certainement de mieux anticiper les modifications futures du fonctionnement hydrologique des bassins versant montagneux en contexte semi-arides. / The north Chile is affected by an arid to semi-arid climate, associated with a strong seasonal to inter-annual variability. In this region, while mountainous areas are supporting low areas, the availability of water resources remains limited. In order to improve the water management in these basins, it is necessary to precise how the high areas support the low areas, and to characterize water transfers and interaction processes between the constitutive compartments of the hydrosystem. This work concern the characterization of the hydrodynamic behavior of the Elqui watershed from the headwaters, in the Andes, to the valleys, ranging between 500 and 2000 m.a.s.l.In the headwaters, the interactions processes between cryospheric and hydrologic compartments and their impact on water transfers to the low areas are characterized. The behavior of unglacierized or partially glacierized watershed is also studied. In the low area of the watershed, the study mainly considers groundwater-surface water interactions under semi-arid context and the impact of the climatic variability on these processes. This study is based on more than 40 years of hydro-meteorological data available in the lower zone of the basin, completed by hydrological measurements in the upper zone (> 2000 m.a.s.l.) and chemical (majors and traces elements) and isotopic samples (²D, 18O) over the whole study area realized between 2011 and 2013.This work demonstrated that the conceptual model of the Elqui basin hydrological behavior, generally accepted, was incomplete. In the high area (> 2000 m.a.s.l.), the study of a glacierized watershed show that the function of the cryosphere overpass the water production with some compartments storing water during humid periods and draining their water content during dry periods. This process buffers the temporal variability of precipitations and melting rates in the high area. Physico-chemical analysis, allows to identify some ignored aquifer compartments, as the volcanic and plutonic compartments. The results of this study improve the knowledge about interactions processes between cryospheric, hydrologic and hydrogeologic compartments, which precise the hydrological functioning of the high area. The interpretation of the hydrological behavior of the high altitude area allows to better understand the way that it support the low area, and the way that climate variability may affects it.In the low area, results show that the groundwater-surface water interaction potential is good between alluvial and hydrological compartments, but also between the plutonic and the alluvial compartments. The study of hydro-meteorological and physico-chemical data allowed to characterize the type of exchanges that take place between groundwater and surface water. In some sectors the main process is the recharge of the alluvial compartment by the hydrological compartment, while in other sectors the processes show a seasonal variability with periods of alluvial compartment recharge and periods of hydrological compartment support. The answer of these processes face to climatic and anthropic forcing will constrain the evolution of the availability and quality of the water resources in the Elqui basin. Finally, the results of this study will certainly allow to better anticipate the future modifications of the semi-arid mountainous watershed hydrological functioning.

Les plaques de glace forment de petites masses de glace et de neige permanentes qui sont considérées comme un stade intermédiaire dans le continuum neige-glacier. Elles sont omniprésentes dans les régions polaires, ce qui leur confère une fonction centrale dans l’hydrologie et la géomorphologie des versants. Pourtant, très peu d’études s’y sont intéressées jusqu’à présent. Acquérir des connaissances sur ces plaques apparait donc essentiel, non seulement pour comprendre leurs caractéristiques intrinsèques, mais aussi parce que cela ouvre des perspectives importantes pour comprendre la dynamique du géosystème polaire. Afin de répondre à ce besoin, cette thèse cherche à établir l'origine et le fonctionnement des plaques de glace à l’île Ward Hunt (Haut-Arctique canadien) et d’en comprendre les effets sur la dynamique de versant du désert polaire. Cette recherche sur les plaques de glace a été guidée par une approche multidisciplinaire, conduisant à des études glaciologiques, nivologiques, hydrologiques et biogéomorphologiques. Nos résultats ont montré que les plaques de glace se développent par l’aggradation de glace surimposée qui se forme suite au regel de l'eau de fonte à la base de l’accumulation de neige saisonnière. La texture et les propriétés physiques de cette glace varient en fonction de son âge et de l’intensité des processus de recristallisation. La variabilité spatio-temporelle des plaques de glace est principalement contrôlée par la topographie locale et les conditions micrométéorologiques. En hiver, les apports en neige dans les niches topographiques où se forment les plaques de glace sont assurés par le vent. En été, l’intensité de l’ablation est fortement influencée par le vent et le brouillard, qui modulent les échanges d’énergie à la surface des plaques. L'évolution des plaques de glace se caractérise par une stabilité à long terme due à un mécanisme d'autorégulation du bilan de masse assuré par le contexte topoclimatique. Cependant, en raison de leur petite taille, les plaques de glace peuvent disparaître rapidement lorsque l'ablation estivale dépasse un seuil à partir duquel les conditions topoclimatiques ne peuvent plus assurer leur préservation. À Ward Hunt, la présence des plaques de glace depuis au moins plusieurs siècles fait qu’elles ont fortement contribué au développement des versants. Les apports durables en eau et sédiments qui en découlent en été ont enclenché une suite de processus abiotiques et biotiques azonaux dans les marges pronivales. Il en a résulté la formation de systèmes biogéomorphologiques qui consistent en des lobes de solifluxion et des milieux humides colonisés par de la végétation et un couvert de croute biologique. Les modifications morphologiques et physiques du sol en aval des plaques de glace influencent le régime thermique de surface et les profondeurs de dégel. En outre, le développement des zones humides entraine une modification locale des propriétés physiques de la neige en exacerbant le métamorphisme cinétique qui aboutit à la croissance d’une couche de givre de profondeur à la base du manteau neigeux. En apportant une compréhension holistique des plaques de glace polaires, cette thèse permet des avancées empiriques et conceptuelles importantes qui contribuent à mieux comprendre la dynamique du géosystème de désert polaire à un moment charnière où ces environnements subissent en transition rapide en réponse au changement climatique. / Ice patches are small perennial masses of ice and snow that are considered as part of the continuum between seasonal snow and glacier. They are ubiquitous in the Polar Regions, which gives them an important function in slope hydrology and geomorphology. Ice patches have, however, received very little scientific attention so far. Gaining new knowledge on these cryospheric elements thus appears essential, not only to understand their intrinsic characteristics, but also because it holds important perspectives for understanding the dynamics of the polar geosystem. To address this need, this thesis aims to investigate the origin and functioning of the ice patches at Ward Hunt Island (Canadian High Arctic) and to understand their effects on polar desert slope dynamics. This research on ice patches was guided by a multidisciplinary approach, involving glaciological, snow, hydrological and biogeomorphological studies. Our results demonstrated that ice patches develop through the aggradation of superimposed ice that forms by the refreezing of meltwater at the base of the seasonal snowpack. The texture and physical properties of this ice vary according to its age and the intensity of recrystallization processes. The spatio-temporal variability of ice patches is mainly controlled by local topography and micrometeorological conditions. In winter, the snow supply to the topographic niches where ice patches form is provided by the wind. In summer, the intensity of ablation is strongly influenced by wind and fog, which modulate energy exchange at the surface of the patches. The evolution of ice patches is characterized by long-term stability due to a self-regulating mass balance mechanism provided by the topoclimatic context. However, because of their small size, ice patches can disappear very quickly when summer ablation exceeds a threshold at which topoclimatic conditions can no longer ensure their preservation. At Ward Hunt Island, the presence of the ice patches for at least several centuries makes them important drivers of slope development. Sustained meltwater and sediment supplies delivered by ice patches to their pronival margin have triggered a sequence of abiotic and biotic azonal processes. This led to the formation of a biogeomorphic system, consisting of solifluction lobes and humid zones colonized by vegetation and an organic crust cover. Morphological and physical changes in the soil downslope of the ice patches influenced the surface thermal regime and thaw depths. Furthermore, our results show that the humid zone development leads to a local modification of the physical properties of snow by enhancing kinetic metamorphism responsible for the growth of a depth hoar layer at the base of the snowpack. Through a comprehensive understanding of polar ice patches and their effects, this thesis provides important empirical and conceptual advances that contribute to a better understanding of polar desert geosystem dynamics at a pivotal time when these environments are undergoing a rapid transition in response to climate change.

Die Gletscher Hochasiens beeinflussen durch ihr Schmelzwasser die Wasserverfügbarkeit eines der gefährdetsten ‚globalen Wassertürme‘. Des Weiteren stellen diese Gletscher und die Gletscherseen eine Gefahr durch Überschwemmungen, Lawinen und Erdrutsche dar. Die Sensitivität und Variabilität von Gletschermassenbilanzen in Hochasien werden in dieser Dissertation untersucht. Das Energie- und Massenbilanzmodell „COupled Snowpack and Ice surface energy and mass balance model in PYthon (COSIPY)“ ist dabei das Hauptwerkzeug. Neun verschiedene gegitterte Niederschlagsdatensätze wurden verglichen, um Aussagen über deren Anwendungsmöglichkeiten zu treffen. Es wurden Verfahren für die Vorverarbeitung von Reanalyse-Datensätzen entwickelt, um diese als klimatische Antriebsdaten für COSIPY zu verwenden. Dazu standen Daten von drei automatischen Wetterstationen an verschiedenen Gletschern zur Verfügung. Die Modellevaluation auf der Basis von Beobachtungsdaten bildete den Ausgangspunkt, um die klimatische Massenbilanz von 14 Gletschern in allen großen Gebirgszügen Hochasiens mit einem konsistenten Ansatz zu modellieren. Die räumlich aufgelösten klimatischen Massenbilanzen von 2000 bis 2018 wurden mithilfe geodätischer Massenbilanzen aus Fernerkundungsdaten kalibriert. Generell haben mehr südöstlich gelegene Gletscher höhere Massenumsätze und diese sind sensitiver gegenüber Schwankungen von Temperatur und Niederschlag. Alle Gletschermassenbilanzen sind am sensitivsten gegenüber Temperaturänderungen im Sommer und gegenüber Niederschlagsänderungen im Sommer oder Frühling. Die Resultate unterstreichen die Notwendigkeit zukünftiger Forschung zu räumlich aufgelösten Reaktionen von Gletschern auf Klimaantrieb und daraus resultierender Variabilität von Schmelzwasser unter Verwendung interdisziplinärer Methoden in Hochasien. Aufgrund der Heterogenität der Gletscher in Hochasien ist diese Forschung essentiell für die künftige Anpassung an Klimavariabilität und Klimawandel in der Region. / The meltwater from the glaciers of High Mountain Asia (HMA) impacts water availability of one of the most vulnerable ‘water towers’ of the globe. Furthermore, glaciers and glacial lakes represent a danger through floods, avalanches and landslides. The climatic sensitivity and variability of the glacier mass balances are investigated within this thesis. The COupled Snowpack and Ice surface energy and mass balance model in PYthon (COSIPY) is thereby the main tool. Nine gridded precipitation datasets have been compared to evaluate possible applications in HMA. The variability and timing of precipitation between May and September 2017 are consistent between the datasets, whereas great differences in precipitation amount were found. A preprocessing toolbox has been developed to use reanalysis datasets as climate forcing for COSIPY within the thesis. Measurements of three automatic weather stations at different glaciers were available for bias correction. Based on these model validations with observed data, climatic mass balances of 14 glaciers in all major mountain ranges in HMA were simulated using a consistent approach. The distributed climatic mass balances for the period from October 2000 to September 2018 were calibrated with remote-sensing-based geodetic mass balances. In general, glaciers with higher mass turnover are located in the southeast of HMA. They are more sensitive to perturbations of temperature and precipitation. All glaciers are most sensitive to monthly temperature perturbations in summer and to precipitation perturbations in summer, spring or spring and summer. The results emphasise the need for future research on spatially resolved responses of glaciers to climate forcing and resulting variability of meltwater using coherent interdisciplinary methods in HMA. Due to the heterogeneity of glaciers in HMA, such research is essential for adaptation to future climate variability and climate change in the region.