Mechanisms of the Extreme Wind Speed Response to Climate Change in Variable-Resolution Climate Simulations of Western, Central, and Atlantic Canada

Abstract Confidence in climate change projections of midlatitude wind extremes is limited by poor model skill at representing near-surface winds and incomplete understanding of the physical mechanisms that may cause extreme winds to respond to climate change. This study addresses these issues by analyzing climate change projections of extreme winds with regional refinement at 7 km over western, central, and Atlantic Canada, using the variable-resolution version of the National Center for Atmospheric Research’s Community Earth System Model (NCAR VR-CESM). This study extends previously reported results for Central Canada’s Southern Ontario region. VR-CESM consistently represents conditions linked with extreme winds in all regions more credibly than the global uniform (100 km) resolution version of CESM, which lends confidence to the projected climate response of the refined-resolution simulations. VR-CESM also consistently projects a strengthening of extreme wind speeds over land in all regions, albeit with mixed statistical significance, while uniform-resolution CESM projections exhibit weakening. The increased extreme wind speeds in VR-CESM are associated with downward mixing of high-momentum air in the boundary layer, which is present in all regions. This association is poorly represented with coarse resolution. However, additional factors, including increasing regional extratropical cyclone intensity, also contribute to the extreme wind response in the western and Atlantic regions. The changes to extratropical cyclone intensity exhibit resolution dependence that is harder to explain. Our results highlight the need for regionally focused dynamical downscaling of global climate projections for climate change impact assessment.