Prediction of Wind Speeds based on Digital Elevation Models using Boosted Regression Trees

In this paper a new approach is presented to predict maximum wind speeds using Gradient Boosted Regression Trees (GBRT). GBRT are a non-parametric regression technique used in various applications, suitable to make predictions without having an in-depth a-priori knowledge about the functional dependancies between the predictors and the response variables. Our aim is to predict maximum wind speeds based on predictors, which are derived from a digital elevation model (DEM). The predictors describe the orography of the Area-of-Interest (AoI) by various means like first and second order derivatives of the DEM, but also higher sophisticated classifications describing exposure and shelterness of the terrain to wind flux. In order to take the different scales into account which probably influence the streams and turbulences of wind flow over complex terrain, the predictors are computed on different spatial resolutions ranging from 30 m up to 2000 m. The geographic area used for examination of the approach is Switzerland, a mountainious region in the heart of europe, dominated by the alps, but also covering large valleys. The full workflow is described in this paper, which consists of data preparation using image processing techniques, model training using a state-of-the-art machine learning algorithm, in-depth analysis of the trained model, validation of the model and application of the model to generate a wind speed map

Comparison of OpenFOAM turbulence models for numerical simulation of thermally-driven winds

Commercial computational fluid dynamics (CFD) codes have often been used for simulation of atmospheric boundary layer (ABL) flows. The present work explores the potential of the open-source CFD software OpenFOAM for simulating thermally-driven winds, by comparing several turbulence models. Indeed, in ABL and other large-scale flows, turbulence is critical to the mixing process of momentum and buoyancy, and simulations with commercial CFD codes have usually been done with Reynolds-Averaged Navier-Stokes (RANS) turbulence modelling. In this work, the formation of thermally-driven winds is studied in an idealised mountain-valley system, with realistic values of parameters such as the slope angle, the diurnal temperature cycle, etc. Performances of various OpenFOAM RANS turbulence models (k–e, re-normalisation group (RNG) k–e, k–¿ shear stress transport (SST)) are compared. A preliminary study of LES using Smagorinsky closure is also contemplated. Velocity contours, velocity and temperature profiles, the shapes of vortexes/convective cells, and the computational times are presented for all the studied turbulence models, to help identify the most suitable one for simulation of thermally-driven winds.This work is supported by the project PID2019-105162RB-I00 funded by MCIN/AEI/10.13039/501100011033 and by the project 2017 SGR 1278 from the AGAUR Generalitat de Catalunya.Peer ReviewedObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.1 - Per a 2030, garantir l’accés universal a serveis d’energia assequibles, confiables i modernsObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No ContaminantObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.2 - Per a 2030, augmentar substancialment el percentatge d’energia renovable en el con­junt de fonts d’energiaPostprint (published version

Contrôle géodynamique des transferts de masses entre une chaîne et son piémont : exemples du mégacône du Napo-Pastaza (Equateur-Pérou)

Les relations entre un bassin versant et son piedmont sont complexes. Elles mettent notamment en œuvre ont appel à des phénomènes physiques incluant l'érosion, le transport et la répartition 3D des zones d'accumulations de sédiments. L'étude du méga-cône de piedmont du Napo-Pastaza sur le piedmont des Andes d'Equateur et du Pérou et de ses relations avec son bassin d'alimentation permet de mettre en évidence divers types de contrôles, liés à la géodynamique, influant sur la morphologie fluviale, la structure du réseau hydrographique et les transferts de masse entre la chaine des Andes et son piedmont amazonien. A partir de données hydro-pluviométriques et hydro-sédimentologiques recueillies sur une période de 5 ans sur le Rio Napo et contenant un épisode éruptif d'un volcan se situant dans le bassin versant, nous pouvons mettre en évidence le rôle de l'érosion et du transport des produits de l'éruption (cendres) sur le transport de matières en suspension et l'évolution de la morphologie du cours d'eau. L'exploitation de données cartographiques, photogrammétriques et d'imagerie satellitaire couvrant le dernier siècle (de 1906 à 2008) concernant un tronçon du Rio Pastaza, localisé dans une zone sismiquement active de la zone subandine permet de mettre en évidence un changement de morphologie associé une série d'avulsions partielle directement liées à la déformation de surface. L'étude sur les derniers 20 000ans de l'évolution du drainage distributif du cône du Rio Pastaza montre un grand nombre de traces d'avulsions successives. Ces avulsions peuvent être reliées, suivant leur localisation et leur enchainement, soit à un contrôle tectonique direct quand ces avulsions sont situées aux voisinages du front actif de la chaîne, soit à un contrôle indirect, lié a des phénomènes d'augmentation brusque de la charge sédimentaire lorsque ces avulsions ce sont produites dans le partie distale du cône de piedmont. Dans ce cas ces surcroît de sédiments peuvent-être, entre autres, lié aux éruptions volcaniques dans le bassin versant.The relationships between a catchment and sedimentation on its foothill are complex. They involve physical phenomena such as erosion, particles transport and location of sedimentation area. The study of the Napo-Pastaza megafan, on the Amazonian foothills of Ecuador end Northern Peru and in relation with its catchment led us to evidence different kind of controlling factors related to the local geodynamic context. These factors control fluvial morphology, drainage network structure as well as suspended load transport from the Andes to the amazonian foothill. A study led on Hydropluviometric and hydrosedimentologic data concerning the Rio Napo, covering 5 years and a volcanc eruption of the Reventador volcano, located in the Rio Napo catchment, we can evidence the role of the erosion and the transport of the products of eruption such as cinders on the transport of the suspended load and the morphology of the river. The compilation of historic topographic data, aerial photography and satelite images over the last century (from 1906 to 2008) of a reach of the Rio Pastaza located in a sismically active area of the andean foothill show a progressive change of the morphology of the Rio Pastaza associated with several partial avulsions. These avulsions are directly controlled by local superficial deformation. The mapping of the successive reaches of the Rio Pastaza since the Last Glacial Maximum revealed a great amount of avulsions traces. Depending on the location of the avulsions nodes, these avulsions can be related to several controlling factors. The nodes located close to the active tectonic front of the Andes can be the result of local tectonics. The nodes located in the distal part of the megafan results from sharp increase of the sedimentary load in the channel and its sedimentation in the lower reach of the river. Such an increase of the sedimentary can result, among others, from volcanic eruptions in the catchment

Low altitude wind simulation over Mount Saint Helens using NASA SRTM digital terrain model

On February 11, 2000, the Shuttle Radar Topography Mission (SRTM) was launched into space as part of one of the payload of the Shuttle Endeavor Using a new radar sweeping technique most of the Earth's surfaces was digitized in 3D in approximately 10 days. SRTM acquired enough data during its mission to obtain a near-global high-resolution database of the Earth's topography. This paper describe how this revolutionary data set can be used to simulate anywhere around the Earth low altitude wind conditions for various atmospheric conditions. More specifically, we will describe the various processing steps necessary to convert this high-resolution terrain model provided by the SRTM database into a Computational Fluid Dynamic (CFD) volumetric mesh that is compatible with an open source CFD solver called OpenFOAM running in parallel on large West-Grid supercomputers. This work is the result of a new virtual wind-tunnel under development at the University of Alberta. In the paper, we present wind flow over the Mount-Saint Helens in the United States for a simple wind flow boundary condition

Etude d'une résurgence active dans la caldera de Siwi (Tanna, Vanuatu) : le système Yenkahe-Yasur

Resurgence, defined as the post-collapse uplift of the caldera floor, is widespread phenomenon worldwide but it is still poorly understood. This work is a multidisciplinary study of a resurgent dome: the Yenkahe dome, located inside the Siwi caldera, in Vanuatu. The relevance of this dome is multiple: firstly, resurgence is currently active, secondly it is fast, so the associated structures are well-preserved, and lastly, the Yenkahe dome presents the originality to be associated with a volcanic cone which has been permanently active for at least several hundred years: the Yasur volcano. A primary tectonic study based on field observations, satellite images and available low-resolution digital elevation models brought the evidence of a two-stage (at least) dome growth history. The first stage is a vertical growth that produced the longitudinal graben on top of the dome. It was followed, in the second stage, by an eastward displacement of the deformation source, generating an uplift of the eastern dome relative to the western dome. The Yenkahe structural map was then refined through the computation of a high-resolution photogrammetric digital surface model (DSM). Besides the great number of details allowing precise fault mapping, this DSM highlights the presence of numerous destabilization scars associated with the evolution of the dome. In the future, similar destabilization events may produce tsunamis reaching inhabited areas in a couple of minutes. The characteristics of the long-term deformation source of the Yenkahe dome, and of other resurgent domes with a similar morphology, were investigated by analogue modeling (intrusion of silicone putty in a sand-plaster mixture). The results of the study show the width of the graben created by an elongated intrusion source mostly depends on the depth of this source. The source of the Yenkahe dome, presumably a magmatic intrusion, would be approximately one-kilometer deep. A second study, based on a punching process in a numerically modeled elastoplastic medium, shows a different internal structure for the dome. However, it confirms the order of magnitude obtained for the source depth (1-2 km), making this result more robust. The presumed magmatic source may be connected to the Yasurvolcano, exhibiting an open conduit activity for several hundred years, which would imply an incremental growth governed by transient over-pressurizing events at depth (such as magma injections). Lastly, a panel of geophysical methods were carried out within the caldera (magnetics, gravimetry, electrical methods, etc.). They revealed that the post-collapse history of Siwi involved, not only resurgence tectonics, but also the emplacement of lava fields and of several volcanic edifices. They also demonstrate the presence of an extended hydrothermal system, particularly deep (more than 300 m) and active on the eastern side of the dome. The associated extended alteration may favor the destabilization of the resurgent edifice.La résurgence, définie comme le soulèvement du plancher des calderas postérieurement à leur effondrement, est largement répandue mais encore très mal comprise. L'objectif de cette thèse est l'étude pluridisciplinaire d'un dôme résurgent: le Yenkahe, au sein de la caldera de Siwi au Vanuatu. L'intérêt de ce dôme est multiple. D'une part, la résurgence est active, d'autre part, elle est très rapide donc elle est associée à des structures relativement préservées. Enfin le Yenkahe présente l'originalité d'être associé à un cône volcanique en éruption permanente depuis au moins plusieurs centaines d'années: le Yasur. Une première étude tectonique basée sur des observations de terrain, complétées par l'exploitation d'images satellites et de modèles numériques de terrain à basse résolution existants, a permis de mettre en évidence une histoire en deux temps (au moins) de la croissance du dôme résurgent. Une première phase de croissance verticale engendrant un graben longitudinal aurait été suivie par une seconde phase de déplacement vers l'est de la source de la déformation, occasionnant un soulèvement de la partie est du dôme par rapport à la partie ouest. Ces grands traits structuraux ont pu être raffinés, par la suite, par le calcul d'un modèle numérique de surface à haute résolution issu de la photogrammétrie. Outre le haut niveau de détails permettant une cartographie plus fine des failles, ce modèle a apporté la mise en évidence de nombreuses traces de déstabilisations sur les flancs du Yenkahe. Dans l'avenir, de telles déstabilisations pourraient engendrer des tsunamis atteignant des zones habitées en quelques minutes. Les caractéristiques de la source de déformation à long terme du Yenkahe, et d'autres dômes résurgents présentant une morphologie similaire, ont fait l'objet d'une étude en modélisation analogique (intrusion de silicone dans un mélange de sable-plâtre). Les résultats de cette étude montrent que la taille du graben engendré en surface par l'intrusion d'une source allongée dépend surtout de la profondeur de cette source. On tire de cette étude que l'intrusion associée au Yenkahe, supposée magmatique, serait située aux alentours d'un kilomètre sous la surface.Une seconde étude en modélisation numérique, basée sur un processus de poinçonnement dans un milieu élastoplastique, met en avant une géométrie interne de dôme différente mais confirme l'ordre de grandeur obtenu pour la profondeur de source (1-2 km), rendant le résultat plus robuste. Cette source magmatique est peut-être connectée au Yasur, qui montre une activité de dégazage en conduit ouvert depuis plusieurs centaines d'années. Ceci qui impliquerait un mode de croissance incrémental gouverné par des événements de surpression transitoires (tels que des injections magmatiques). Enfin, un ensemble de méthodes géophysiques appliquées à l'étude de la caldera de Siwi (gravimétrie, mesures magnétiques et électriques, etc.) révèle que l'histoire post-effondrement de cette caldera comporte, outre la résurgence tectonique, des événements effusifs et la construction de plusieurs édifices volcaniques successifs. Ces méthodes mettent également en évidence la présence d'un système hydrothermal très étendu, particulièrement profond (plus de 300 m) et actif à l'est du dôme. L'altération hydrothermale associée pourrait favoriser des déstabilisations de l'édifice résurgent

Lahars and Lyrics: Learning from Adjustments in Landscape and Culture Following prolonged Volcanic Disturbance on the Island of Montserrat

Explosive volcanic eruptions can profoundly disturb surrounding landscapes. Volcanic phenomena (e.g., pyroclastic density currents, tephra fallout) inundate the headwaters of proximal river systems with vast quantities of sediment. This perturbs the hydrology of these systems which then respond by increasing sediment and water flux to downstream reaches via lahars. These hazardous sediment-laden flows can induce dramatic, potentially destructive, and long-lived geomorphic changes within affected drainages. Most understanding of the readjustment of rivers following volcanic disturbances comes from studies following short-lived, transient eruptions. By contrast, limited research has considered responses to prolonged episodic eruptions, characterised by repeat phases of eruption and quiescence. This thesis addresses this research gap by exploring how the morphodynamics and lahar activity within the Belham Valley, Montserrat, have evolved in response to episodic disturbance by the eruption of Soufriere Hills Volcano, 1995 - present. Methods involved include novel longitudinal synthesis of a range of observational data, from ground-based photographic surveys to satellite-derived Digital Surface Models, as well as statistical analysis, and numerical modelling. I show: 1) episodic eruptions induce distinct fluvial responses, manifesting in aggradation-degradation cycles driven by evolving sediment availability, water supply, and vegetation cover; 2) lahar hazard is mediated by evolving catchment-scale conditions; 3) modelling the temporal evolution of lahar activity in such systems shows promise but remains a challenge. During a research assistantship alongside my PhD, I was heavily involved in the development of a co-created public engagement project on Montserrat, Mountain Aglow. This project sought to incorporate the lived experience of eruption in the form of arts – i.e., lyrics – into Disaster Risk Management (DRM) strategies. The final chapter of this thesis presents an evaluative study of this project. I demonstrate that incorporation of lived experience and co-creation of DRM practices is an effective and recommendable means of improving engagement with at-risk populations

Progress in Landslide Research and Technology, Volume 1 Issue 1, 2022

This open access book provides an overview of the progress in landslide research and technology and is part of a book series of the International Consortium on Landslides (ICL). The book provides a common platform for the publication of recent progress in landslide research and technology for practical applications and the benefit for the society contributing to the Kyoto Landslide Commitment 2020, which is expected to continue up to 2030 and even beyond to globally promote the understanding and reduction of landslide disaster risk, as well as to address the 2030 Agenda Sustainable Development Goals

Spacelab Science Results Study

Beginning with OSTA-1 in November 1981 and ending with Neurolab in March 1998, a total of 36 Shuttle missions carried various Spacelab components such as the Spacelab module, pallet, instrument pointing system, or mission peculiar experiment support structure. The experiments carried out during these flights included astrophysics, solar physics, plasma physics, atmospheric science, Earth observations, and a wide range of microgravity experiments in life sciences, biotechnology, materials science, and fluid physics which includes combustion and critical point phenomena. In all, some 764 experiments were conducted by investigators from the U.S., Europe, and Japan. The purpose of this Spacelab Science Results Study is to document the contributions made in each of the major research areas by giving a brief synopsis of the more significant experiments and an extensive list of the publications that were produced. We have also endeavored to show how these results impacted the existing body of knowledge, where they have spawned new fields, and if appropriate, where the knowledge they produced has been applied