Title: Snow water content modelling in small catchments This work deals with modeling of amount of snow cover, snow water equivalent, respectively, on an experimental catchment in the Jizerské hory Mts. Measuring and modelling of the snow cover is an important part of water management practice from the perspective of reservoir operation and flood management. The first part of this thesis describes physical-geographical characteristics of the Jizerské hory Mts.especially from the climatological and hydrological point of view but also other charakteristics and conditions that may affect the dynamic of snow accumulation and melting are described with detailed focus on the experimental catchment of Černá Desná river - Jezdecká. Two modelling approaches were applied to simulate snow water equivalent (SWE) based on observed precipitation and temperature. Beside the well knowen SNOW17 model a simple method based on heat index was developed in this work and its parameters were calibrated based on measured timeseries of daily average air temperature, daily precipitation and observed SWE for winter periods 2001 to 2009. Both methods provided reasonably accurate estimates of SWE over the tested period, however it was found that the results for winters with extreme conditions (very warm or very cold) are less...

La neige est une composante essentielle du système climatique arctique. Au nord de l'Eurasie et de l'Amérique du Nord, la couverture neigeuse est présente de 7 à 10 mois par an et son extension saisonnière maximale représente plus de 40% de la surface terrestre de l'hémisphère nord. La neige affecte une variété de processus climatiques et de rétroactions aux hautes latitudes. Sa forte réflectivité et sa faible conductivité thermique ont un effet de refroidissement et modulent la rétroaction neige-albédo. Sa contribution au bilan radiatif de la Terre est comparable à celle de la banquise. De plus, en empêchant d'importantes pertes d'énergie du sol sous-jacent, la neige limite la progression de la glace et le développement du pergélisol saisonnier. Réserve d'eau naturelle, la neige joue un rôle essentiel dans le cycle hydrologique aux hautes latitudes, notamment en ce qui concerne l'évaporation et le ruissellement. La neige est l'une des composantes du système climatique présentant la plus forte variabilité. Le réchauffement de l'Arctique étant deux fois plus rapide que celui du reste du globe, la variabilité présente et future des caractéristiques de la neige est cruciale pour une meilleure compréhension des processus et des changements climatiques.Cependant, notre capacité à observer l'Arctique terrestre étant limitée, les modèles climatiques jouent un rôle clé dans notre aptitude à comprendre les processus liés à la neige. À cet égard, la représentation des rétroactions associées à la neige dans les modèles climatiques, en particulier pendant les saisons intermédiaires (lorsque la couverture neigeuse de l'Arctique présente la plus forte variabilité), est primordiale.Notre étude porte principalement sur la représentation de la neige terrestre arctique dans les modèles de circulation générale issus du projet CMIP5 (Coupled Model Intercomparison Project) au cours du printemps (mars-avril) et de l’automne (octobre-novembre) de 1979 à 2005. Les caractéristiques de la neige des modèles de circulation générale ont été validées par rapport aux mesures de neige in situ, ainsi qu’à des produits satellitaires et à des réanalyses.Nous avons constaté que les caractéristiques de la neige dans les modèles ont un biais plus marqué au printemps qu'en automne. Le cycle annuel de la couverture neigeuse est bien reproduit par les modèles. Cependant, les cycles annuels d'équivalent en eau de la neige et de sa profondeur sont largement surestimés par les modèles, notamment en Amérique du Nord. Il y a un meilleur accord entre les modèles et les observations dans la position de la marge de neige au printemps plutôt qu'en automne. Les amplitudes de variabilité interannuelle pour toutes les variables de la neige sont nettement sous-estimées par la plupart des modèles CMIP5. Pour les deux saisons, les tendances des variables de la neige dans les modèles sont principalement négatives, mais plus faibles et moins significatives que celles observées. Les distributions spatiales des tendances de la couverture neigeuse sont relativement bien reproduites par les modèles, toutefois, la distribution spatiale des tendances en équivalent-eau et en profondeur de la neige présente de fortes hétérogénéités régionales.Enfin, nous concluons que les modèles CMIP5 fournissent des informations précieuses sur les caractéristiques de la neige en Arctique terrestre, mais qu’ils présentent encore des limites. Il y a un manque d’accord entre l’ensemble des modèles sur la distribution spatiale de la neige par rapport aux observations et aux réanalyses. Ces écarts sont particulièrement marqués dans les régions où la variabilité de la neige est la plus forte. Notre objectif dans cette étude était d'identifier les circonstances dans lesquelles ces modèles reproduisent ou non les caractéristiques observées de la neige en Arctique. Nous attirons l’attention de la communauté scientifique sur la nécessité de prendre compte nos résultats pour les futures études climatiques. / Snow is a critical component of the Arctic climate system. Over Northern Eurasia and North America the duration of snow cover is 7 to 10 months per year and a maximum snow extension is over 40% of the Northern Hemisphere land each year. Snow affects a variety of high latitude climate processes and feedbacks. High reflectivity of snow and low thermal conductivity have a cooling effect and modulates the snow-albedo feedback. A contribution from terrestrial snow to the Earth’s radiation budget at the top of the atmosphere is close to that from the sea ice. Snow also prevents large energy losses from the underlying soil and notably the ice growth and the development of seasonal permafrost. Being a natural water storage, snow plays a critical role in high latitude hydrological cycle, including evaporation and run-off. Snow is also one of the most variable components of climate system. With the Arctic warming twice as fast as the globe, the present and future variability of snow characteristics are crucially important for better understanding of the processes and changes undergoing with climate. However, our capacity to observe the terrestrial Arctic is limited compared to the mid-latitudes and climate models play very important role in our ability to understand the snow-related processes especially in the context of a warming cryosphere. In this respect representation of snow-associated feedbacks in climate models, especially during the shoulder seasons (when Arctic snow cover exhibits the strongest variability) is of a special interest.The focus of this study is on the representation of the Arctic terrestrial snow in global circulation models from Coupled Model Intercomparison Project (CMIP5) ensemble during the melting (March-April) and the onset (October-November) season for the period from 1979 to 2005. Snow characteristics from the general circulation models have been validated against in situ snow measurements, different satellite-based products and reanalyses.We found that snow characteristics in models have stronger bias in spring than in autumn. The annual cycle of snow cover is well captured by models in comparison with observations, however, the annual cycles of snow water equivalent and snow depth are largely overestimated by models, especially in North America. There is better agreement between models and observations in the snow margin position in spring rather than in autumn. Magnitudes of interannual variability for all snow characteristics are significantly underestimated in most CMIP5 models compared to observations. For both seasons, trends of snow characteristics in models are primarily negative but weaker and less significant than those from observations. The patterns of snow cover trends are relatively well reproduced in models, however, the spatial distribution of trends for snow water equivalent and snow depth display strong regional heterogeneities.Finally, we have concluded CMIP5 general circulation models provides valuable information about the snow characteristics in the terrestrial Arctic, however, they have still limitations. There is a lack of agreement among the ensemble of models in the spatial distribution of snow compared to the observations and reanalysis. And these discrepancies are accentuated in regions where variability of snow is higher in areas with complex terrain such as Canada and Alaska and during the melting and the onset season. Our goal in this study was to identify where and when these models are or are not reproducing the real snow characteristics in the Arctic, thus we hope that our results should be considered when using these snow-related variables from CMIP5 historical output in future climate studies.

No description available.

From the Proceedings of the 1974 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 19-20, 1974, Flagstaff, Arizona / Profiles of snowpack build-up in openings in forest overstories have been widely observed; however, a quantitative characterization of such a snowpack profile would aid in developing empirical guidelines for improving water yields from snowpacks. A technique is outlined that illustrates (a) evaluating snowpack profiles in and adjacent to individual forest openings in terms of increase or decrease in water equivalent, and (b) defining trade-offs between the estimated increase or decrease in snowpack water equivalent and the forest resource removed. Snowpack water equivalent during peak seasonal accumulation was measured in and adjacent to a clearcut strip in a ponderosa pine stand in north-central Arizona. A 4-degree polynomial, which defines the snowpack profile in terms of deposition, redistribution, and ablation characteristics, was empirically selected to describe snowpack water equivalent data points. An increase of 60 percent in snowpack water equivalent was realized by removing 46 percent of the ponderosa pine in the zone of influence, using a strip equal to one and one-half the height of the adjacent overstory.

From the Proceedings of the 1975 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 11-12, 1975, Tempe, Arizona / The quantification of snowpacks in relation to inventory-prediction may be useful in the development of water yield improvement practices involving vegetation management in the mixed conifer forests in Arizona. While mixed conifer forests are relatively limited in extent in Arizona, the potential for water yield improvement by manipulation of snow storage through vegetation management may be high. Sample points on the north fork of Thomas Creek showed high initial snow storage followed by slow melt in association with low forest densities, low potential insolation values, and high elevation. Sample points exhibiting these conditions also possessed maximum storage-duration index values. Low initial snow storage followed by rapid melt was associated with high forest densities, high potential insolation values, and low elevations

From the Proceedings of the 1975 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 11-12, 1975, Tempe, Arizona / The possibility of using imagery from the earth resources technology satellites (ERTS) to monitor changes in areal snow cover in east-central Arizona is examined. Four methods were used in the interpretation of areal snow cover from the ERTS imagery, the densitometer, dot grid, squares grid and projection-planimeter methods providing results of 69, 71, 72 and 74 percent of areal cover respectively. No one method for interpretation of ERTS imagery should be ruled unusable, but any use made of ERTS imagery is dependent upon turn-around time for obtaining the imagery, as snow cover information which cannot be obtained within 24 hours is limited in practical application.

Bakgrund: Visuell snö är ett perceptionsstörande neurooftalmologiskt tillstånd karakteriserat av bestående mikroskopiska flimrande prickar som täcker hela det bilaterala synfältet. Det kan liknas vid att titta genom en flimrande tv-skärm, eller Gaussiskt brus. Några etablerade riktlinjer för behandling finns inte för närvarande. Syfte: Denna litteraturstudie syftar till att undersöka tillgänglig litteratur rörande effekten av olika behandlingsalternativ för tillståndet visuell snö.  Metod: En sökning utfördes i sökmotorn PubMed den 20 mars 2023. Söksträngen som användes var “visual snow” OR “visual snow syndrome” AND “treatment”. Fler studier tillkom genom granskning av referenser. Begränsningar i urvalet baserades på relevans rörande behandling, samt en litteraturstudie utförd av Eren & Schankin publicerad 2020. Den här studien tar upp arbeten tillkomna därefter, totalt 8 artiklar utgivna mellan 2020-2022.  Resultat: Vår studie har lyckats identifiera behandlingsalternativ för visuell snö i form av neuro-optometrisk synträning, farmaceutika, kosttillskott, kiropraktik, filterglasögon, antikroppar, mydriatika, synstimuli, samt repetitiv transkraniell magnetstimulering. Samtliga studier utfördes på deltagare med bekräftad och diagnostiserad visuell snö, antingen som isolerat symptom, som del av Visual Snow Syndrome, eller som sekundärt tillstånd. Positiva behandlingssvar med partiell remission förekommer, samt enstaka fall av total remission. Samtliga inkluderade studier har sina begränsningar, en gemensam sådan är svårigheten att kvantifiera symptomen. Med hjälp av enkäter och symptomdagböcker har 7 av 8 studier visat på viss subjektiv effekt av behandling, av okänd magnitud.  Slutsats: Patofysiologin bakom visuell snö är ännu inte klarlagd. I dagsläget finns ingen generellt applicerbar behandling för visuell snö, men enstaka fall av total remission samt ett antal fall av partiell remission förekommer i litteraturen. Vid behandling av patienter med visuell snö bör hänsyn tas till individuella patienters förutsättningar, komorbiditet och tidigare prövad behandling. / Background: Visual snow is a neuro-ophthalmological perception disorder characterized by persistent microscopic flickering dots covering the bilateral field of vision. It can be described as looking through TV static, or Gaussian noise. There are currently no established guidelines regarding treatment. Purpose: This literature survey aimed to investigate available literature regarding the efficacy of different therapeutic approaches for the condition of visual snow.   Method: A search was performed in the PubMed search engine on March 20, 2023. The search string used was “visual snow” OR “visual snow syndrome” AND “treatment”. Further studies were added through references. Restrictions in article selection were based on relevance regarding treatment, as well as a review by Eren & Schankin published in 2020. This study covers subsequent articles, a total of 8 articles published between 2020-2022. Results: Our study has identified therapeutic approaches to visual snow in the form of neuro-optometric rehabilitation therapy, pharmaceuticals, nutraceuticals, chiropractic treatment, filter glasses, antibodies, mydriatics, visual stimuli, and repetitive transcranial magnetic stimulation. All participants had confirmed and diagnosed visual snow either as an isolated symptom, as part of Visual Snow Syndrome, or as a secondary condition. Positive responses with partial remission occur, as well as occasional total remissions. All included studies have some limitations, a common one being the difficulty in quantifying the symptoms. Using questionnaires and symptom diaries, 7 out of 8 studies have shown some subjective effect of treatment of unknown magnitude.  Conclusion: The pathophysiology behind visual snow is not yet fully understood. Currently, there is no generally applicable treatment for visual snow, but occasional cases of total remission and a number of cases of partial remission appear in the literature. When treating patients with visual snow, the individual patient’s conditions, comorbidity and previously tried treatment should be taken into account.

Markmonterade solcellsanläggningar i norra Sverige behöver ta hänsyn till förekomsten av snö och risken för markinterferens, vilket innebär att snömängden i framkant av panelerna gör att den snö som ackumuleras ovanpå inte kan glida av. Följden blir skuggning av panelerna som därmed får nedsatt eller helt utebliven elproduktion. Syftet med arbetet var att besvara frågeställningar kring vilken montagehöjd som krävs för att undvika problemet samt om den ökade engångskostnaden kompenseras av potentialen till ökad produktion under vintermånaderna. Metoden bestod främst av att jämföra produktionsdata från en solpark i Östersund med värden för solinstrålning och snödjup från SMHI för att avgöra vilken effekt snöskuggning haft på produktionen och hur utfallet skulle ha sett ut vid olika monteringshöjder av anläggningen. Resultaten visar att det finns stor potential till goda produktionsvärden under vårvintern, förutsatt att markinterferens inte finns närvarande. Anledningen beror troligtvis på högt albedo från snötäckt mark och lägre lufttemperaturer vilket har en positiv inverkan på modulernas verkningsgrad. En beräkningsmodell utvecklades för att uppskatta en lämplig monteringshöjd för en solpark utifrån dess tänkta utformning och det förväntade snödjupet på platsen. Förhoppningen är att modellen kan bidra till ökad kunskap för att främja utbyggnad av markmonterade solcellsanläggningar även på nordliga breddgrader. Lönsamheten för ett högre montage undersöktes genom en jämförelse mellan ett prisexempel från en uppförd solpark och ett uppskattat produktionsbortfall från solparken i Östersund vid en teoretiskt lägre monteringshöjd. Det visade att en höjning av Östersundsparken från 50 till 90 centimeter skulle betala av sig enbart genom tillskottet i produktion under perioden februari till april de tre första vintrarna. / Ground-mounted PV installations in northern Sweden need to consider the presence of snow and the risk of ground interference, meaning that the buildup of snow in front of the panels prevents the snow accumulated on top from sliding off. The result is shading of the panels, which in turn reduces or eliminates the electricity production. The purpose of this work was to answer questions regarding the mounting height required to avoid this problem and whether the increased one-time cost for higher mounting is compensated for by the enhanced production during winter months. The method consisted mainly of comparing production data from a solar park in Östersund to solar radiation values and snow depth from SMHI to determine the effect of snow shading on production and the outcome at different installation heights of the plant. The results showed that there is great potential for valuable energy production during the late winter season, provided that ground interference is not present. This is probably due to high albedo from snow-covered ground and lower air temperatures resulting in a positive impact on the efficiency of the modules. A computational model was developed to estimate a suitable mounting height for a solar park based on the intended design and expected snow depth at the site. The intention is that the model can contribute to increased knowledge to promote the deployment of ground-mounted PV systems in northern latitudes. The profitability of higher mounting was investigated by comparing a price example from an existing solar facility and an estimated production loss from the solar park in Östersund at a theoretical lower mounting height. It showed that  increasing the height of the Östersund site from 50 to 90 centimeters in front would pay off solely on the enhanced production during the period February to April of the first three winters.

Investigating flow and turbulence structure around a barrier mounted on the ground or placed in its vicinity is a fundamental problem in wind engineering because of many practical applications related to protection against adverse effects induced by major wind storms (e.g., hurricanes) and snow events (e.g., snow fences used to reduce adverse effects of snow drifting on the roads). In this work the focus is on the case when the obstacle/barrier is porous and the shape of the obstacle is close to a high-aspect-ratio rectangular cylinder situated in the vicinity of the ground. The study employs a range of numerical and experimental techniques to achieve this goal that include 3D LES and 2D RANS numerical simulations, and RTK survey and 3D photogrammetry techniques to measure ground elevations and snow deposits in the field. In the first part of the study, high-resolution large eddy simulations are used to understand the fundamental flow physics of flow past 2D solid and porous vertical plates with a special focus on describing the unsteady wind loads on the obstacle, vortical structure of the turbulent wake, spectral content of the wake, the separated shear layers and of the characteristics of the large-scale vortex shedding behind the plate, if present. Results show that LES can accurately predict mean flow and turbulence statistics around solid/porous cylinders. Then, a detailed parametric study of flow past vertical solid and porous plates situated in the vicinity of a horizontal bed is performed for the purpose of understanding changes in the mean flow structure, turbulence statistics and dynamics of large scale coherent structures as a function of the main nondimensional geometrical parameters (bottom gap for solid and porous plates, and porosity and average hole size of porous plates) and flow variables (e.g., bed roughness) that affect the wake flow. In particular, the LES flow fields allowed clarifying how the interactions between the bottom and the top separated shear layers change with increasing bottom gap and what is the effect of the bleeding flow on the interactions between the separated shear layers that determine the coherence of the large-scale eddies at large distances from the wake. In the second part of the thesis, a novel methodology based on field monitoring of the snow deposits and RANS numerical simulations is proposed to improve the design of snow fences and in particular the design of lightweight plastic snow fences that are commonly used to protect roads in the US Midwest against the snow drifting. The goal of the design optimization procedure is to propose a snow fence design that can retain a considerable amount of snow within a shorter downwind distance compared to fences of standard design. A major contribution of the present thesis was the development of a novel non-intrusive image-based technique that can be used to quantitatively estimate the temporal evolution of the volume of snow trapped by a fence over long periods of time. This technique is based on 3-D close range photogrammetry. Results showed that this technique can produce estimations of the snow deposits of comparable accuracy to that given by commonly used methods. This is the first application of this type of techniques to measurements of the snow deposits.

Rates of snowmelt distributed across Emerald Lake watershed, an alpine basin located in the Sierra Nevada, California, were estimated for water year 1987 using a point snowmelt model applied to regions that were classified based on distributed snow water equivalence and net solar radiation (NSR). A 5-m resolution digital elevation model (DEM) and a 5-m classified digital terrain model of snow water equivalence (SWE) were resampled to coarser resolutions (25-m, 30-m, 50-m, and 100-m) using the nearest neighbor approach. These images were used to define other snowmelt physical parameters and the initial state of the snowpack before melting. Topographic parameters calculated at 50-m and 100-m resolution exhibited significant differences in their histogram distribution as compared to the 5-m DEM. The most important were variations in slope, aspect, sky view factor, and terrain configuration factor, which influenced radiation calculations and the definition of distributed parameters for snowmelt calculations. Elevations, however, did not change significantly from one resolution to the other. The distribution of topographic parameters modeled at 25-m and 30-m, remained almost unchanged. Four, seven and ten classes of snow water equivalence and net solar radiation were combined using a band interleave process to determine the maximum number of combined classes. The point snowmelt model was then applied to these areas, which shared similar SWE and NSR characteristics, to obtain hourly melt rates. Modeled snowmelt rates were compared to the total daily discharge observed at the outlet of Emerald Lake watershed. There was good agreement for resolutions S-, 25-, 30-, and 50-m but not for the 100-m OEM, as modeled net solar radiation was too high and water was released from the basin too early. Model performance using three tests (Nash-Sutcliffe criteria, sum of squares of the deviations and the sum of the absolute differences between observed discharge and computed melting) showed that the 30-m resolution OEM with combined classes of 7 SWE and 7 NSR provided the best snowmelt performance for this distributed approach. Finally, fractional snow cover area at one month intervals were estimated, showing that this approach offers the potential to model spatially distributed snow covered area in alpine regions.