Present and future downslope windstorms in the Scandinavian Mountains from a kilometre‐scale climate model

Abstract Climatological studies of downslope windstorms (DWs) in the Scandinavian mountains (Scandes) are rare. Here we use 20‐year long simulations with the kilometre‐scale regional climate model HCLIM38‐AROME to study DWs in the Scandes in present and future climate, their connection to large‐scale atmospheric circulation, and their cooling and warming effect. A DW is identified in a model grid point using a two‐step conceptual model based on terrain features, and dynamic and thermodynamic variables. We find that DWs occur most frequently in winter, which is therefore the focal season for the analyses. Normally, DWs are predominantly either warming (foehn type) or cooling (bora type), but our results indicate that this distinction does not hold for the DWs in the Scandes. Even though there is a slight overall tendency towards warming, almost all locations with DWs can experience both cooling and warming. The future simulations using two parent global climate models (GCMs) show an overall decrease in the total number of DW occurrences between 7% and 17% toward the end of the century, with a decrease in the northern and central parts of the Scandes and an increase in the southeastern part. These changes can be attributed to two factors: the frequency change of certain circulation types and internal changes within the circulation types. Despite the agreement in the sign of future changes for both GCM forcings, the difference in the contribution of the two factors indicates that different mechanisms are responsible for the total future change in the DW occurrence. The complexity of DWs in the Scandes and their future change indicates that kilometre‐scale or finer climate models are required for a proper depiction of DWs and that a larger ensemble of simulations with different GCM forcing is required for evaluation of different mechanisms of the future change.