Impact of Quasi‐Idealized Future Land Cover Scenarios at High Latitudes in Complex Terrain.

Afforestation is gaining popularity as a climate mitigation policy in many countries, including high latitude regions such as Norway. However, the impacts of afforestation on local‐to‐regional climate is poorly understood. This study uses the Weather Research and Forecasting model to investigate the biogeophysical impacts of different forestry scenarios on the local‐to‐regional climate of Norway. The forestry scenarios considered are the conversion of open spaces to either evergreen forest by active afforestation or to mixed forest by natural succession. Results show both forestry scenarios lead to additional warming of surface temperatures in winter and spring (between 1.0°C and 1.5°C) and cooling in summer (between −1.6°C and −1.3°C). A temperature decomposition analysis shows that the warming in winter and spring is driven by surface albedo changes while summer cooling is driven by changes in sensible heat fluxes for afforestation and surface albedo for natural succession. Maximum 2 m air temperature increases considerably in spring in both forestry scenarios (∼0.8°C to 1.0°C). Analysis of precipitation, multiple climate indices and extremes, reveal little or no response to the different forestry scenarios. The largest societally relevant response to the forestry scenarios is the partial mitigation of the reduction in snow days expected from global warming by 10–20 days. This suggests that implementing current afforestation policies for climate mitigation in Norway may adversely exacerbate some effects of global warming locally while mitigating others. As such, the impacts of afforestation on the local‐to‐regional climate at high latitudes are complex and cannot support or dismiss afforestation as a climate mitigation policy. Plain Language Summary: The conversion of existing open spaces such as grasslands and shrublands to forests is gaining popularity as a climate mitigation policy in many countries, including high latitude regions such as Norway. However, the impacts of such afforestation policies on the local‐to‐regional climate is poorly understood, particularly at high latitudes. This study uses a state‐of‐the‐art regional climate model to show that at high latitudes afforestation warms surface (or skin) temperature in winter and spring (between 1.0°C and 1.5°C) and cooling in summer (between −1.6°C and −1.3°C). This study also shows that afforestation considerably increases the maximum 2 m air temperature in spring (∼0.8°C to 1.0°C) but has no impact on precipitation, multiple climate indices, and extremes. The largest societally relevant response to the forestry scenarios is the partial mitigation of the reduction in snow days expected from global warming by 10–20 days. This suggests that implementing current afforestation policies for climate mitigation in Norway may adversely exacerbate some effects of global warming locally while mitigating others. As such, the impacts of afforestation on the local‐to‐regional climate at high latitudes are complex and cannot support or dismiss afforestation as a climate mitigation policy. Key Points: Impacts of land use and land cover changes on temperature and snow are localized and most pronounced in springTemperature response to land use and land cover changes is largely independent of forestry scenario in these experimentsAfforestation enhances surface warming under RCP8.5 but mitigates other impacts [ABSTRACT FROM AUTHOR]