Malin Ahlbäck

• Ahlbäck, Malin; Pirk, Norbert; Tallaksen, Lena M. & Silantyeva, Olga (2025). Temporal Dynamics and Hydrological Impacts of Snow-Atmosphere Vapor Exchanges in a High-Altitude Catchment. doi: https:/www.hydrologiraadet.no/wp-content/uploads/2025/08/AbstractsLillehammer2025_210825.pdf. Full text in Research Archive Show summary

  The evolution of the snowpack is strongly influenced by turbulent fluxes, where latent heat transfer alters the snowpack water equivalent through processes such as snow sublimation and deposition, in addition to changing the cold content and structure of the snow. In alpine regions, the contribution of sublimation to the water balance varies widely, with results indicating only a negligible part of snowfall is sublimated, to up to 90% locally at wind-exposed ridges and crests. To improve our understanding of these dynamics, this study integrates small-scale micrometeorological observations with catchment-scale modelling, enabling a multi-scale analysis of snow-atmosphere water vapour exchanges and their impacts on the snowpack water balance in a high-altitude catchment in southern Norway. We will outline preliminary insights into the temporal scales governing water vapour fluxes and its linkage to environmental drivers, using micrometeorological site data and wavelet analysis. Compared to the commonly used eddy covariance method, processing the high-frequency site data using wavelet analysis allowed for resolving fluxes over small (<1 min) time scales, and offer a detailed analysis of the eddy distribution over time, and as such, new insights into the dynamics governing sublimation. In addition, the wavelet analysis method handled non-stationary time periods where the eddy covariance method fails, indicating the potential for using wavelet analysis over eddy covariance for processing complex micrometeorological data where traditional methods are not possible. To evaluate the broader hydrological impacts of sublimation and deposition fluxes, we also plan to present results from a snow model framework over the whole catchment and contrast the annual variability between dry and wet winters. Our findings are expected to contribute to a deeper understanding of sublimation and deposition processes in Nordic regions, and how they may change in a future climate. By combining field measurements and modelling approaches, these insights can be used for advancing the parametrisation of winter vapour fluxes for applications in snow hydrology.

• Silantyeva, Olga; Ahlbäck, Malin & Dar, Shaakir (2025). Assessing snow sublimation in Norway: insights from field and laboratory work of SnowSub project. doi: https:/www.hydrologiraadet.no/wp-content/uploads/2025/08/AbstractsLillehammer2025_210825.pdf. Full text in Research Archive Show summary

  Hydrologic modelling is an important part of decision making within hydropower companies in Norway, as the country produces most of its electricity from hydropower. In the SnowSub project we work towards improving hydrologic modelling within Shyft software, used by companies such as Statkraft AS and Skagerak AS in their operations. A major aspect of hydrology in Norwegian catchments is snow, which acts as a storage for streamflow. However, this storage can lose its reserves due to sublimation. Dry air, strong wind and solar radiation favor sublimation in certain areas of Norway. Sublimation flux can be measured in the field using eddy covariance flux station. However, filed observations can not be controlled, making it difficult to systematically test different hypotheses. Given this, our project combines field measurements in the Tuddal site with experimental studies of sublimation under the controlled conditions of the Cold Climate Container facility at the University of Oslo. These studies provide insights into sublimation and snow processes in Norway, which can further inform hydrological modeling within Shyft. In this talk, we present results from the two field seasons at Tuddal. Fluxes were analyzed using eddy covariance method and wavelet analysis, with the two methods showing good agreement. The analysis revealed the importance of smaller timescales for distinguishing sublimation fluxes. Laboratory studies were conducted during two periods, in November 2024 and February 2025. The wind tunnel in the laboratory showed good stability of temperatures and relative humidity, allowing us to investigate effects of wind and humidity across temperature ranges from -20 to 0 degrees Celsius and time scales from 3 to 24 hours. Experiments were performed in two setups – one with continuous isotopic content measurement in the air and snowpack, and another measuring mass changes using Petri dishes setup. The results showed that even air speeds below 3.2 m/s can cause noticeable snow mass loss, with relative humidity maintained between 58% to 80%, matching the lower humidity values observed at the Tuddal site. As a part of the project, we also investigate potential of FSM2 snow model in its ability to capture sublimation effects at our study site. The flexible hydrological modelling framework Shyft can incorporate the FSM2 approach into its architecture, providing a physics-based snow model as part of the operational components. We benchmarked hydrologic models within Shyft across a large sample of catchments in Norway. The results suggest that, although the model performs well in discharge simulations over historical periods, the snow modelling capabilities of the toolbox – despite offering a variety of model choices - still remain limited and could be substantially improved. This project is supported by Norwegian Research Council NFR 336621.

• Ahlbäck, Malin & Huang, Shaochun (2025). Assessing snow sublimation in Norway: Lessons learned from field and laboratory work of SnowSub project. doi: https:/www.hydrologiraadet.no/wp-content/uploads/2025/08/AbstractsLillehammer2025_210825.pdf. Full text in Research Archive Show summary

  Hydrologic modelling is an important part of decision making within hydropower companies in Norway, as the country produces most of its electricity from hydropower. In the SnowSub project we work towards improving hydrologic modelling within Shyft software, used by companies such as Statkraft AS and Skagerak AS in their operations. A major aspect of hydrology in Norwegian catchments is snow, which acts as a storage for streamflow. However, this storage can lose its reserves due to sublimation. Dry air, strong wind and solar radiation favor sublimation in certain areas of Norway. Sublimation flux can be measured in the field using eddy covariance flux station. However, filed observations can not be controlled, making it difficult to systematically test different hypotheses. Given this, our project combines field measurements in the Tuddal site with experimental studies of sublimation under the controlled conditions of the Cold Climate Container facility at the University of Oslo. These studies provide insights into sublimation and snow processes in Norway, which can further inform hydrological modeling within Shyft. In this talk, we present results from the two field seasons at Tuddal. Fluxes were analyzed using eddy covariance method and wavelet analysis, with the two methods showing good agreement. The analysis revealed the importance of smaller timescales for distinguishing sublimation fluxes. Laboratory studies were conducted during two periods, in November 2024 and February 2025. The wind tunnel in the laboratory showed good stability of temperatures and relative humidity, allowing us to investigate effects of wind and humidity across temperature ranges from -20 to 0 degrees Celsius and time scales from 3 to 24 hours. Experiments were performed in two setups – one with continuous isotopic content measurement in the air and snowpack, and another measuring mass changes using Petri dishes setup. The results showed that even air speeds below 3.2 m/s can cause noticeable snow mass loss, with relative humidity maintained between 58% to 80%, matching the lower humidity values observed at the Tuddal site. As a part of the project, we also investigate potential of FSM2 snow model in its ability to capture sublimation effects at our study site. The flexible hydrological modelling framework Shyft can incorporate the FSM2 approach into its architecture, providing a physics-based snow model as part of the operational components. We benchmarked hydrologic models within Shyft across a large sample of catchments in Norway. The results suggest that, although the model performs well in discharge simulations over historical periods, the snow modelling capabilities of the toolbox – despite offering a variety of model choices - still remain limited and could be substantially improved. This project is supported by Norwegian Research Council NFR 336621. Keywords: snow; sublimation; Norway; Tuddal; catchment hydrology; Cold Climate Container; laboratory experiments;

• Silantyeva, Olga; Ahlbäck, Malin; Yilmaz, Yeliz A.; Tallaksen, Lena M.; Lappegard, Gaute & Erlandsen, Helene B. [Show all 11 contributors for this article] (2024). SnowSub: Assessing snow sublimation for hydropower production in Norway. Project results at Snow Bridges workshop. Full text in Research Archive
• Ahlbäck, Malin (2024). Assessing the impact of sublimation for hydrologic modelling. Full text in Research Archive
• Ahlbäck, Malin; Pirk, Norbert; Tallaksen, Lena M. & Silantyeva, Olga (2024). Assessing the impact of sublimation for hydrological forecasting. Full text in Research Archive
• Ahlbäck, Malin (2024). Assessing the impact of sublimation for hydrological modelling. Full text in Research Archive

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