Mountains are playing a major role in shaping the weather and climate of the world. They are among the most sensitive ecosystems to climate change and are experiencing more rapid changes in temperature than environments at lower elevations. The complex topography is a major limiting factor in gaining a deeper understanding of processes and extreme events often associated with mountainous regions. Recent advances in measurement techniques and modelling over the European Alps are, however, enabling progress in our understanding. The proposed session focuses on Alpine weather and climate from past, present, and future, with an emphasis on atmospheric processes and climate change.
The session invites studies using high-resolution observations, reanalyses, numerical weather prediction, climate modelling, and regional downscaling to assess present-day Alpine weather and climate and its future changes. Contributions focusing on process understanding of mountain meteorology, land-atmosphere interactions, and the influence of complex topography on regional climate are particularly encouraged. The session also invites studies of trends in temperature, precipitation, circulation patterns, and extreme weather in the Alpine region.
By linking past, present, and future perspectives, this session aims to advance understanding of the mechanisms governing Alpine weather and climate and to support robust projections of climate change in complex terrain. The session provides a place to discuss recent methodological advances and emerging challenges in mountain climate research.
Registered Abstracts
ID: 3.210
The Role of Horizontal Shear Production in Hectometre-Scale WRF Simulations over Alpine Terrain
Traditional planetary boundary layer (PBL) parametrisations in numerical weather prediction (NWP) models assume horizontally homogeneous conditions. Under this assumption, one-dimensional (1D) PBL parametrisations are used, which only consider vertical mixing and neglect horizontal shear production in the prognostic turbulent kinetic energy (TKE) equation used by 1.5-order parametrisations. However, as high-performance computing capabilities continue to improve, NWP model resolutions are reaching the hectometre scale, resolving more surface features and smaller atmospheric processes, thus increasingly violating the 1D PBL assumption. This is especially true in complex terrain, where, for example, thermally driven circulations create persistent slope and valley winds characterised by intense shear in both horizontal speed and direction.
We set up nested simulations with the Weather Research and Forecasting (WRF) model for the Inn Valley, Austria, down to a hectometre-scale resolution using a modified PBL parametrisation that introduces an additional tendency for horizontal shear production into the TKE equation.
This helps to account for horizontal heterogeneity in the atmosphere induced by local flow processes and acts as an intermediate step towards a complete representation of horizontal wind shear.
During the TEAMx 2025 summer Extended Observation Period (sEOP), uncrewed aircraft systems (UAS) measured vertical profiles — including TKE and turbulent fluxes — at multiple locations along a transect across the Inn Valley. Complementary radiosoundings and remote-sensing measurements captured mean wind and temperature profiles at various locations along the valley. These observations allow us to evaluate modelled vertical and horizontal wind shear, as well as turbulent properties. Results using the modified PBL parametrisation are compared with those using the traditional PBL parametrisation, which does not take into account horizontal wind shear.
ID: 3.218
Warming on the edge: topographic controls on temperature trends in the Alps
Simon Zitzmann Fersch, Benjamin; Kunstmann, Harald
Abstract/Description
Elevation-dependent warming (EDW) is a prominent feature of climate change in mountain regions, often leading to enhanced warming at higher altitudes. Understanding the mechanisms behind this pattern is essential for assessing climate impacts in the Alps. While processes such as snow-albedo feedbacks and the high climate sensitivity of cold environments are discussed in literature, the contribution of topographic controls beyond elevation has received less attention.
This study explores spatial variations in warming across the Alps with a particular focus on how terrain characteristics influence local warming trends. Long-term temperature observations from the HISTALP dataset are used to analyze relationships between temperature trends and topographic factors throughout the Greater Alpine Region.
For the period 1951–2010, warming trends range from 0.4 to 2.9 K per century across elevations. Higher-altitude locations generally experience stronger warming, yielding an EDW signal of 0.25 K km-1 century-1 for annual mean temperatures. Seasonal differences are evident: the strongest elevation dependence occurs in summer (0.34 K km-1 century-1), whereas winter warming peaks at mid-elevations between 250 and 1000 m. Slope orientation further modulates warming, with northeastern-orientated slopes showing more pronounced trends.
Ongoing work extends the analysis by incorporating additional terrain variables, such as topographic incision, and by applying the approach to the extensive high-density observational dataset EEAR-Clim.
ID: 3.217
Reconstructing long-term temperature trends in the Alps: Assessing the performance of RASCAL along elevation gradients
Globally, mountain regions remain sparsely covered by long-term meteorological observations, and the number of monitoring stations has been declining. Coarse-resolution global climate models (GCMs) and gridded observational datasets fail to adequately represent small-scale orographic and local climatic drivers and characteristics, which hampers reliable assessments of climate change impacts in high-altitude environments. This study assesses the empirical downscaling tool RASCAL (Reconstruction by AnalogS of ClimatologicAL time series), which reconstructs local temperature variability by linking station observations to large-scale predictors. Seventeen long-term stations along the Alpine ridge in Switzerland, Austria, Germany, Italy and Slovenia were selected for reconstruction. They span elevations from valleys to more than 3000 m a.s.l. and represent a broad topographic gradient.
The evaluation, based on reconstructions using geopotential height at 925 hPa as predictor, indicates that reconstruction skill varies substantially across sites. While RASCAL generally reproduces the mean temperature series and, in most cases, the trend, its ability to capture long-term climatic trend differences along the elevation gradient is inconsistent. Some reconstructions reproduce elevation-dependent warming rates (EDW), but their magnitude is highly variable and strongly dependent on local topography, elevation, and site-specific climatic factors. Further analyses will incorporate multiple predictor variables, including geopotential height at different pressure levels and radiation, to reconstruct minimum, maximum and mean temperature series, to assess whether this improves reconstruction accuracy.
ID: 3.1
User-tailored climate scenarios in the Alpine space: The new Swiss CH2025 scenarios
Sven Kotlarski Mülchi, Regula; Gubler, Stefanie; Genné, Nina; Herrmann, Michael; Rajczak, Jan; Scherrer, Simon C.; Senoner, Anna; Girlanda, Omar; Team, The Climate CH2025
Abstract/Description
Climate change scenarios are a cornerstone for understanding future weather and climate conditions and for climate adaptation, yet their development remains particularly challenging in complex mountain environments. The European Alps are warming faster than the global average, and recent updates such as the Swiss Climate CH2025 scenarios (www.climate-scenarios.ch) project substantial further changes in temperature, precipitation patterns, snow cover, and climate extremes over the coming decades. Translating climate model-based projections into both reliable and actionable information for the Alps requires addressing strong spatial heterogeneity driven by elevation, topography, and land-surface processes.
A key challenge lies in the downscaling of climate model outputs to the fine spatial and temporal scales needed to capture Alpine weather dynamics. Orographic effects, local circulation patterns, and elevation-dependent warming are often insufficiently resolved, leading to uncertainties that are especially relevant for extremes such as heavy precipitation, heatwaves, droughts, and snow-related processes. These uncertainties are compounded by limited long-term observations at high elevations and by non-linear feedbacks linked to snow, glaciers, and permafrost.
Using the Climate CH2025 framework, we discuss methodological aspects of scenario construction for the Alpine space and present a dedicated analysis for the Swiss National Park. This case study illustrates how regional climate signals manifest in a protected high-mountain environment and highlights sensitivities in seasonal temperature evolution, precipitation regimes, and snow conditions. The results underscore both the value and the limitations of current climate scenarios for Alpine applications, and their implications for interpreting future weather and climate in mountain regions.
ID: 3.59
Seasonal and elevation-dependent differences in temperature trends in the Tyrolean Alps (Austria): An assessment based on station observations
In this study, we aim to quantify the magnitude and significance of temperature trends on the sub-seasonal scale across elevations by collecting, processing and analyzing daily as well as hourly observational data from a dense network of climate stations located in the Tyrolean Alps (Austria). Our analysis reveals a 2.46°C rise in temperature for the 60-year period 1964–2023 and an increasing sub-seasonal variability of trends when shortening the investigated period from 60 to 30 years. We also find indications for a stronger warming at lower elevations, whereby this elevation-dependent signal can be traced back to strong differences in temperature trends in January with warming at low-elevation stations and a slight cooling at high elevations. The analysis of observation data to derive a picture of past climatic changes in mountain regions is of great importance to support our general process understanding and to complement the use of modeled data.
ID: 3.70
Large-scale weather and climate, local-scale impacts – bridging the gap with statistics
Michael Matiu Crespi, Alice; Toldo, Francesco; Bozzoli, Michele; Bertoldi, Giacomo; Strasser, Ulrich; Majone, Bruno
Abstract/Description
Quantitative climate information is paramount for good decision-making. However, its usage in complex mountain terrain is often challenging because of the scale mismatch between provided meteorological variables and needs of input models. Sometimes, this scale gap is overcome using statistical methods. Here we explore different topics related to mostly statistical downscaling and bias adjustment, for example why we could, why we should, or maybe should not do it.
1) Using in-situ observations of snow depth and snowfall, we examine spatial and temporal variability. We show that even variables with high spatial and interannual variability like snow can share similar characteristics under long-term climate forcing.
2) We assess the role of multivariate bias adjustment and downscaling techniques with an ensemble of climate models to drive hydrological models that simulate snow water equivalent and runoff. This highlights the benefits and pitfalls of statistical post-processing of climate model output.
3) We present a novel downscaling technique based on principal components analysis that is able to merge information from different sources that are not in temporal synchrony. The contrasting results for temperature and precipitation should make us cautious when applying statistical methods that do not align with the processes resolved in climate models.
Consequently, we present conclusions from statistical analyses of climate variables and some statistical tools applied in post-processing of climate projections or (seasonal) weather forecasts, which are helpful to derive more meaningful and accurate climate and weather information for society. One such example of how these approaches can be used to create useful information is the Frame3S project that aims to provide seasonal forecasts of snow cover for the Tyrol-SouthTyrol-Trentino region.
ID: 3.100
Regional Climate Analysis of the Tyrolean Inn Valley as a Basis for Climate-Adapted Spatial Development in the Alpine Region
Gloria Faltl Ortner, Birgit; Karl, Schönhuber
Abstract/Description
The Tyrolean Inn Valley is a climatically sensitive area due to its function as an alpine trough valley with a high settlement density. Approximately half of Tyrol’s population lives along this central valley axis between the Northern Limestone Alps and the Central Alps. Over recent decades, a clear warming trend has been observed, expressed by an increasing number of hot days and heat waves. In general, the Alpine region is particularly affected by climate change. Against this background, climatic stress conditions and compensatory processes in the Inn Valley between Landeck and Kufstein were analysed.
The analysis is based on high-resolution simulations using the numerical, physically based climate model FITNAH-3D, a mesoscale wind field model specifically designed for simulations in complex terrain. Simulated parameters include air temperature, Physiologically Equivalent Temperature (PET), as well as indicators of cold air production and cold air dynamics. For the first time in Austria, spatially continuous results for a region of this extent are available at a spatial resolution of 5 × 5 m, allowing the representation of small-scale climatic differences and processes.
The results indicate pronounced thermal stress in densely built-up and highly sealed areas of the valley floor. High heat loads during the day combined with limited cooling at night indicate a pronounced urban heat island effect. At night, cold air processes can contribute substantially to thermal relief in settlement areas, particularly during radiation nights with low atmospheric exchange.
Based on defined limit and threshold values, climatic hotspots within settlement areas were identified, allowing the prioritisation of adaptation measures. The analysis of cold air drainage pathways enabled the identification of climatically effective open spaces and slope areas as well as settlement edges sensitive to cold air processes. The preservation and consideration of these areas is essential for maintaining the functionality of cold air formation and drainage. The results therefore provide a technical basis for future land-use and development decisions in the Inn Valley.
Based on the analysis, measures for heat mitigation and for safeguarding climatic compensation processes were derived. Further integration with spatial planning and sociodemographic data will allow a more detailed assessment in the future. In view of increasing land-use conflicts, the analysis highlights the need to integrate climatic aspects early and systematically into planning and development processes in the Alpine region.
ID: 3.111
Long-term Development of Avalanche Hazard Levels in the Austrian Alps
Philipp Maier Jutz, Mira; Formayer, Herbert
Abstract/Description
Anthropogenic climate change strongly affects the Alpine water cycle. Shifts in the timing, intensity and spatial distribution of precipitation and increasing winter temperatures alter the frequency and timing of snowfall and snowmelt, as well as the structure of the snowpack. As a result, avalanche risk and the regionally assessed avalanche hazard levels are expected to change under ongoing climate change.
In this study, we present novel climatologies for avalanche hazard levels in the Austrian Alps covering the period of 1950 – 2025. These climatologies are based on the back-extension of a consistent multi-year observational dataset of avalanche hazard levels aggregated from regional avalanche hazard assessments. Individual mountain ranges are clustered into units that exhibit similar avalanche hazard responses to different types of weather patterns. These response units are then used to train a machine-learning algorithm to predict avalanche hazard levels based on pattern recognition and circulation analogues from meteorological ERA5 reanalysis data. Applying the algorithm to the full ERA5 dataset yields a reconstruction of past avalanche hazard levels, which are validated against long-term observations from Tyrol. The resulting climatologies reveal interannual and decadal variability as well as the possible influence of anthropogenic climate change on avalanche hazard over the past 75 years.
When applied to the latest generation of regional climate projections, the trained algorithm will provide new insights into how future climate change may further affect avalanche hazard in the Austrian Alps.
ID: 3.126
Structure of the convective mountain boundary layer over the European Alps from large-eddy simulations
Juerg Schmidli
Abstract/Description
The atmospheric boundary layer (ABL) over mountainous regions, such as the European Alps, plays a key role in controlling surface–atmosphere exchange processes, with direct implications for mountain weather, air quality, and climate. Owing to strong topographic heterogeneity, the Alpine boundary layer exhibits a wide range of interacting motions, spanning small-scale turbulence and coherent thermals, as well as thermally driven slope and valley circulations. Despite recent advances in high-resolution modelling, the three-dimensional structure of these flows, their evolution and role in vertical exchange processes remain insufficiently understood.
In this study, we investigate the structure of the convective Alpine boundary layer using the ICON model in large-eddy simulation (LES) mode. Real-case simulations are performed at horizontal grid spacings down to 65 m using a nested-domain configuration over highly complex Alpine terrain. A brief evaluation against observations from the TEAMx field campaign is presented to demonstrate the realism of the simulated boundary-layer structure. The main focus of the analysis is on the spatial organization, persistence, and diurnal evolution of the resulting coherent structures. The simulations reveal that thermals preferentially form at distinct locations tied to topography and surface forcing, exhibiting a robust diurnal cycle. These coherent structures play a central role in mediating vertical exchange of heat and momentum between the surface and the free atmosphere, while their interaction with slope and valley flows modulates boundary-layer depth and ventilation efficiency.
By providing a detailed three-dimensional view of boundary-layer processes over the Alps, this work advances process understanding of Alpine meteorology and demonstrates the value of LES for studying surface–atmosphere exchange and transport in complex terrain. The insights gained may provide guidance for constraining the representation of exchange processes in weather and climate models applied to mountainous regions.
ID: 3.123
Temperature Biases in convection-permitting models in complex terrain: ongoing challenges
Isabella Kohlhauser Medvedova, Alzbeta; Ban, Nikolina; Maraun, Douglas
Abstract/Description
In recent years, convection-permitting models have become a frequently used tool to study climate and climate change in regions with complex terrain. While convection-permitting models have been shown to add value for variables like wind and precipitation, temperature is rarely in the focus, despite being a key climate variable. In our research we evaluate the representation of minimum and maximum daily temperatures in the convection-permitting CORDEX-FPS Convection ensemble. Additionally, we compare the kilometer-scale, convection-permitting ensemble to its corresponding driving coarse-scale ensemble with grid spacings of 2.2-4 km and 12-15 km, respectively. We identify severe negative elevation-dependent biases ensemble at both resolutions, which become progressively worse at higher elevations. Further, both ensembles overestimate extremes like hot days and frost days, which is more pronounced in the convection-permitting ensemble. In our analysis, we found little to no added value of convection-permitting models in comparison to the convection-parameterizing regional climate models. This is underlined by the high spread across ensemble members which is present in both ensembles. Our results highlight that even at the convection-permitting scale, model tuning and adapting parameterizations remains crucial.
ID: 3.165
Troposphere to stratosphere transport over the Alps
Petr Šácha
Abstract/Description
The stratosphere-troposphere exchange couples the troposphere and the stratosphere and affects the chemical composition in the upper-troposphere/lower stratosphere region, which is important for the global radiative budget. This study combines high-resolution Weather Research and Forecasting model simulations of the Alpine region validated by observations during selected intensive observational periods of TEAMx and the Lagrangian particle dispersion model FLEXPART-WRF to investigate the transport of boundary layer emissions during the events of pronounced dynamical interaction between the orography and the flow. The Alpine orography was found to enhance transport and modify pathways through which emissions can penetrate the tropopause and the stratosphere region. This results from a non-trivial combination of convective updrafts, orographic lifting and mixing due to breaking orographic gravity waves near the surface and in the vicinity of the tropopause. Our study has important implications for climate model development in terms of parameterizing subgrid-scale orography effects and for our understanding of the transport of pollution in mountain regions and globally.
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