Coping with Difficult Weather and Snow Conditions : Reindeer herders’ views on climate change impacts and coping strategies

Peer reviewe

SNOWPACK: where do we stand today?

The Swiss snow-cover model SNOWPACK is presently used in many applications from snow sports and engineering to climate change assessment but also for avalanche warning. The core routines are packed in a library that also serves as the basic module for the land surface scheme Alpine3D. The separate application MeteoIO handles all input data in both applications. These components, including a visualization tool, are available as open source packages (models.slf.ch). Since 2002, the year three papers describing the model in detail appeared (for example, see Lehning et al., 2002), SNOWPACK evolved in many respects. Based on newly acquired data sets, we updated the parameterizations of the density of new snow (see Schmucki et al., submitted) or of the albedo. We also revisited some concepts of the model such as snow settlement: we now divide the stress applied to the snow into a purely static overburden and a stress rate dependent term that allows mimicking the relaxation behavior of new and older snow. In addition, we adapted the temperature dependence of viscosity to cover a large temperature range from about -70 °C up to the melting point (Groot et al., 2013). Finally, we maximized the accuracy of both mass and energy balance. This is necessary for implementing advanced water transport equations such as the recent solver for the Richards equation (Wever et al., 2013)

Distributed snow and rock temperature modelling in steep rock walls using Alpine3D

In this study we modelled the influence of the spatially and temporally heterogeneous snow cover on the surface energy balance and thus on rock temperatures in two rugged, steep rock walls on the Gemsstock ridge in the central Swiss Alps. The heterogeneous snow depth distribution in the rock walls was introduced to the distributed, process-based energy balance model Alpine3D with a precipitation scaling method based on snow depth data measured by terrestrial laser scanning. The influence of the snow cover on rock temperatures was investigated by comparing a snow-covered model scenario (precipitation input provided by precipitation scaling) with a snow-free (zero precipitation input) one. Model uncertainties are discussed and evaluated at both the point and spatial scales against 22 near-surface rock temperature measurements and high-resolution snow depth data from winter terrestrial laser scans.In the rough rock walls, the heterogeneously distributed snow cover was moderately well reproduced by Alpine3D with mean absolute errors ranging between 0.31 and 0.81 m. However, snow cover duration was reproduced well and, consequently, near-surface rock temperatures were modelled convincingly. Uncertainties in rock temperature modelling were found to be around 1.6 °C. Errors in snow cover modelling and hence in rock temperature simulations are explained by inadequate snow settlement due to linear precipitation scaling, missing lateral heat fluxes in the rock, and by errors caused by interpolation of shortwave radiation, wind and air temperature into the rock walls.Mean annual near-surface rock temperature increases were both measured and modelled in the steep rock walls as a consequence of a thick, long-lasting snow cover. Rock temperatures were 1.3–2.5 °C higher in the shaded and sunny rock walls, while comparing snow-covered to snow- free simulations. This helps to assess the potential error made in ground temperature modelling when neglecting snow in steep bedrock

Climate scenarios for Switzerland CH2018 - approach and implications

To make sound decisions in the face of climate change, government agencies, policymakers and private stakeholders require suitable climate information on local to regional scales. In Switzerland, the development of climate change scenarios is strongly linked to the climate adaptation strategy of the Confederation. The current climate scenarios for Switzerland CH2018 - released in form of six user-oriented products - were the result of an intensive collaboration between academia and administration under the umbrella of the National Centre for Climate Services (NCCS), accounting for user needs and stakeholder dialogues from the beginning. A rigorous scientific concept ensured consistency throughout the various analysis steps of the EURO-CORDEX projections and a common procedure on how to extract robust results and deal with associated uncertainties. The main results show that Switzerland?s climate will face dry summers, heavy precipitation, more hot days and snow-scarce winters. Approximately half of these changes could be alleviated by mid-century through strong global mitigation efforts. A comprehensive communication concept ensured that the results were rolled out and distilled in specific user-oriented communication measures to increase their uptake and to make them actionable. A narrative approach with four fictitious persons was used to communicate the key messages to the general public. Three years after the release, the climate scenarios have proven to be an indispensable information basis for users in climate adaptation and for downstream applications. Potential for extensions and updates has been identified since then and will shape the concept and planning of the next scenario generation in Switzerland

Compression de flux magnétique dans le régime sub-microseconde pour l'obtention de hautes pressions et de rayonnement X intense

Afin de démontrer la faisabilité d'une source de rayonnement X intense pour la France, le Centre d'Études de Gramat (CEG) explore un certain nombre de voies technologiques. Le projet SYRINX étudie les possibilités offertes par les hautes puissances pulsées (HPP) pour des applications de compression isentropique, de cavités à hautes températures (hohlraum) et de durcissement (rayonnement X entre 1 et 10 keV produit par un Z-pinch). Il est alors nécessaire de disposer d'un étage d'amplification de la puissance électrique permettant d'atteindre des courants de l'ordre de 10 MA en une centaine de nano secondes. Les générateurs habituels utilisent des lignes de compression d'impulsion ou bien des commutateurs à plasma. Une autre possibilité, appelée compression de flux magnétique, est l'objet de ce travail. Elle a permis de comprimer l'impulsion de 100 ns du générateur Z des Sandia National Laboratories en une impulsion de 40 ns et l'impulsion de 1 ms du générateur ECF du CEG en une impulsion de 100 ns. Cette voie offre l'avantage d'un temps caractéristique d'implosion inférieur à la micro seconde et évite alors un grand nombre de problèmes posés par les compresseurs de flux à explosifs. Ce travail a consisté tout d'abord à paramétrer des codes numériques divers (codes circuit, codes plasma, ...) afin de les adapter à la problématique de la compression de flux. Les outils numériques ainsi mis au point ont ensuite servis aux dimensionnements d'expériences, réalisées sur les générateurs Z et ECF, qui ont permis d'atteindre 5 Mbar sous choc et plus de 2 Mbar en compression isentropique ainsi qu'une température de cavité voisine de 110 eV. Les enseignements issus de l'interprétation des tirs ont été confrontés à notre compréhension du système et des charges employées. Enfin, ceci a permis d'améliorer les outils numériques et d'optimiser le concept. Le travail réalisé doit permettre d'extrapoler le concept à un générateur de rayons X intenses de la classe 60 MA.In order to study the feasibility of creating an intense X ray source for France, the Centre d'Études de Gramat (CEG) is investigating several technologies. The Syrinx project is looking at the potential of High Pulse Power technologies for Isentropic Compression Experiments, High Temperatures Hohlraums and Radiation Hardening (X rays between 1 eV and 10 eV radiated by a Z-pinch). Then it is necessary to provide a power amplification stage allowing electrical currents of the order of 10 MA with a hundred nanoseconds rise rime to be delivered to the load. Usually, generators use pulse forming lines or plasma opening switches. Magnetic Flux Compression, another power amplification possibility, is studied in this dissertation. It has enabled the compression of the 100 ns pulse of the Z machine (Sandia National Laboratories) into a 40 ns pulse and the compression of the 1 ms pulse of the ECF generator (CEG) into a 100 ns pulse. This technology bas the advantage of a characteristic implosion time less than a micro second avoiding many of the problems the explosive driven flux compression ran into. This research work consisted initially in finding the right parameters for several codes (circuits codes, plasma codes... ) in order to adapt them to the Flux Compression. These numerical tools have then been used to design experiments on Z and ECF. These experiments have reached 5 Mbar with shock and more than 2 Mbar in isentropic compression as well as 110 eV in a hohlraum. Insights gleaned from the interpretation of the shots have been compared to our understanding of the power amplification system and of the loads. Finally, this allows us to improve our numerical tools and to optimize the Flux Compression concept. The work which has been done should lead to the extrapolation of the concept to an X ray generator of the 60 MA class.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Snow cover runoff and stream discharge modelling during snow melt in Alpine terrain

The understanding of the role of snow cover runoff in complex terrain for the hydrological cycle is still limited. Water flow in snow is a complex process, because the strong layering of the snow cover causes strong vertical variation in hydraulic properties. It has already been shown that describing melt water flow through a snow cover using Richards equation for 1D unsaturated flow and taking into account the snow stratigraphy, improves snow cover runoff estimations locally. However, the small-scale spatial variability in snow cover height, snow stratigraphy and external influences such as incoming solar radiation and wind speed, is causing a complex relation between local snow melt and overall streamflow discharge. In this study, an advanced physically based snow cover model (SNOWPACK) is used in a spatially explicit mode for alpine terrain. The aim is to investigate whether the use of Richards equation in a distributed snowpack model (Alpine3D) can improve spatially explicit snow cover runoff estimations. The model setup simulates the snow cover development and runoff over a snow season for the Dischma catchment in Switzerland. The snow cover runoff is used as input for a stream discharge model and the modelled discharge is then compared to measured discharge at the catchment outlet. Solving Richards equation for snow yields better agreement than simpler (bucket) methods for liquid water flow in snow. It is also shown that the simulated snow cover runoff exhibits a strong spatial variability, which is a function of slope exposition and angle. This can be associated with different shortwave radiation input for snow melt. The results show that solving Richards equation for snow improves the estimation of the contribution of snow cover runoff to the hydrological cycle

How much can we save? Impact of different emission scenarios on future snow cover in the Alps

This study focuses on an assessment of the future snow depth for two larger Alpine catchments. Automatic weather station data from two diverse regions in the Swiss Alps have been used as input for the Alpine3D surface process model to compute the snow cover at a 200m horizontal resolution for the reference period (1999-2012). Future temperature and precipitation changes have been computed from 20 downscaled GCM-RCM chains for three different emission scenarios, including one intervention scenario (2 degrees C target) and for three future time periods (2020-2049, 20452074, 2070-2099). By applying simple daily change values to measured time series of temperature and precipitation, small-scale climate scenarios have been calculated for the median estimate and extreme changes. The projections reveal a decrease in snow depth for all elevations, time periods and emission scenarios. The non-intervention scenarios demonstrate a decrease of about 50% even for elevations above 3000 m. The most affected elevation zone for climate change is located below 1200 m, where the simulations show almost no snow towards the end of the century. Depending on the emission scenario and elevation zone the winter season starts half a month to 1 month later and ends 1 to 3 months earlier in this last scenario period. The resulting snow cover changes may be roughly equivalent to an elevation shift of 500-800 or 700-1000m for the two non-intervention emission scenarios. At the end of the century the number of snow days may be more than halved at an elevation of around 1500m and only 0-2 snow days are predicted in the lowlands. The results for the intervention scenario reveal no differences for the first scenario period but clearly demonstrate a stabilization there-after, comprising much lower snow cover reductions towards the end of the century (ca. 30% instead of 70 %)

Snow: Hydro-CH2018 synthesis report chapters: “future changes in hydrology“

This report was prepared as one of the synthesis report chapters of the Hydro-CH2018 project of the Federal Office for the Environment (FOEN). An important feature of snow cover is the fact that its volume and duration is subject to large year-to-year fluctuations. As frozen precipitation, snow cover is nothing other than a natural water reservoir that delays precipitation to runoff and is thus of outstanding importance for the seasonal water balance in Switzerland. Over a whole year, approximately 40% (22 km3) of the annual runoff currently comes from snow melting and only 1% from glacier melting. Typically, the snow cover in the Alpine region builds up over the autumn and winter months, reaches its maximum between February and May, depending on the altitude, and dominates the runoff processes during melting in the following spring and summer months.Due to the great dependence on minus temperatures and precipitation, the snow cover reacts sensitively to temperatures above 0° Celsius and more or less precipitation. Due to climate change and the associated warming, the proportion of precipitation that falls as snow decreases measurably. In addition to this reduction in snowfall, the warmer temperatures also cause the snow cover to melt more quickly. The decline in snowfall has so far mainly affected lower altitudes, where winter temperatures often reach positive levels. As climate change progresses, this trend is likely to continue and above all affect higher zones. Even at higher altitudes, the snow cover will then start later, melt away earlier and is increasingly no longer permanently present. This development will also have an effect on the water bodies. Today nival regimes, i.e. regimes shaped by snow, are shifting towards pluvial regimes, i.e. regimes dominated by rain. Overall, winter runoff increases, summer runoff decreases. By the end of the century, the proportion of runoff from snowmelt will decrease throughout Switzerland, albeit to a lesser extent than the proportion from glacier melt