Framtidens översvämningsrisker.

Type: Report
Series: RH 19
Author: Bengt Carlsson, Sten Bergström, Johan Andréasson, Sara-Sofia Hellström


A study of the impacts of global warming on future risks for floods and inundations in Sweden has been carried out on contract from Länsförsäkringsbolagens Forskningsfond. The work focussed on River Dalälven and the big lakes Vänern, Mälaren and Hjälmaren but some nationwide analyses were carried out as well. The methodology was based on two global climate models, two assumptions about the future emissions of greenhouse gases and a regional climate model for dynamical downscaling to Swedish conditions. The regional climate scenarios are further processed by the HBV hydrological model and the resulting river runoff or water levels are treated statistically by frequency analysis. The results show that future risk exposure is changing in a different way depending on location in the country. The situation seems to be aggravated in particular in the Vänern area in southwest Sweden and along its outlet, River Göta älv. There will also be increased risks in the western parts of the Scandinavian mountains. The risks for heavy rainfalls, which may cause severe local flooding are likely to increase even though it is difficult to discern a consistent regional pattern between the models, in this respect. The study has also addressed the uncertainty in the assessments of flood risks. It is obvious that uncertainties in the global climate scenarios are responsible for a lot of the uncertainty in the end results, but there are also uncertainties inflicted by the strategy used when transferring the climate change signal from climate models to the hydrological model.