Scenarios of Köppen-Trewartha climate types in Europe based on GCM-RCM combined projections

Abstract Climate classifications represent a convenient tool for an integrated analysis of possible future climate changes. We employ the Köppen-Trewartha classification (KTC). While global climate models (GCMs) are the principal means of climate research on a planetary scale, regional climate models (RCMs) can provide information on finer scales. The hybrid method enables combining the advantages of both kinds of models while incorporating the whole ensemble of available GCMs, unlike RCM ensembles with limited number of driving GCMs. We assess projected changes in the distribution of KTC types over Europe based on three sets of projections: results of the hybrid method combining two sets of GCMs (CMIP6 and CMIP5) with the EURO-CORDEX RCMs, and the original EURO-CORDEX simulations driven by CMIP5. We look into changes in geographical distribution of KTC types throughout the 21st century under two socio-economic scenarios. We also investigate the boundary shifts between Europe’s most common types, D (temperate climate) and E (boreal climate). The continental Ec type and tundra type Ft are projected to shrink radically by the end of the 21st century. Oceanic Eo and continental Dc are also projected to decline, but not so dramatically. Oceanic temperate type Do, humid subtropical type Cf, and steppe climate BS are projected to expand. One of the most striking outcomes is the expansion of dry climate types BS and Cs in parts of southern and south-eastern Europe. The boundary between subtypes of D and E is expected to shift northward and eastward. The hybrid method provides an easy-to-apply approach to investigate uncertainties connected with the limited number of driving GCMs within the RCM ensembles. We provide an updated CMIP6-based projections of KTC climate types over Europe as the first assessment before the new EURO-CORDEX simulations dynamically downscaling CMIP6 will be available. The results can serve as a basis for adaptation strategies and planning.