Future projections of atmospheric icing in Norway

Atmospheric icing is a major weather hazard, known to cause problems for many sectors of society, in particular for power transmission lines. Considering that such structures are designed with a typical expected lifetime of 70 years, climate change impacts on extreme ice loads should be considered. Atmospheric ice accumulation can be modelled with meteorological input from numerical weather prediction models and extreme loads can thereby be estimated. Here we apply dynamical downscaling of the two global climate models, CESM2 and MPI-ESM1-2-HR, and three future scenarios, using a regional model, WRF, to obtain high resolution data for future atmospheric ice load projections. Results based on both climate models indicate that future 10-year return values of wet snow loads are generally decreasing in the lowlands and increasing at higher elevation for all three scenarios, linked to a general increase in temperature and extreme precipitation. Results for future 10-year rime ice loads differ between the two downscaled models due to differences in regional warming levels and model biases. More research, involving downscaling of more climate models or the use of other methodologies, is needed to obtain more robust projections and uncertainty estimates before design engineers can make any considerations about future ice loads. However, large uncertainties in climate model projections of regional climate challenge the constraint.