Evaluating Climate Regimes and Their Temporal Evolution in ERA5-Driven EURO-CORDEX CMIP6 Simulations

Climate classifications are useful tools for assessing climate variability and change, as they aggregate multiple variables into discrete climate types representing regions with homogeneous characteristics, often corresponding to vegetation zones or eco-regions. The Köppen–Trewartha classification (KTC) defines climate regimes using temperature- and precipitation-based thresholds, synthesising conditions into discrete and comparable units for analysing their spatial distribution and temporal evolution. In this study, we assess how well the new generation of EURO-CORDEX regional climate simulations driven by ERA5 reanalysis within the CMIP6 framework reproduces the observed distribution of KTC climate types across Europe. 

As part of the coordinated EURO-CORDEX evaluation effort, individual model simulations are compared against observational reference data representing observed climate conditions and their evolution. This enables an assessment of how well each simulation reproduces the distribution of major European climate types and their boundaries. We further investigate how these patterns evolve over time, focusing on shifts in climate regimes and their spatial structure. The analysis is complemented by time series diagnostics of climate type occurrence and spatial extent. Particular attention is given to systematic biases in the extent and boundaries of selected climate types, which provide a physically meaningful indication of model performance. 

The analysis includes the full set of available ERA5-driven EURO-CORDEX CMIP6 simulations and contributes to the ongoing evaluation of the new model generation, supporting the interpretation of regional climate change signals and their emergence from natural variability. The KTC framework also enables assessment of how differences between simulations influence the representation of variability and conditions associated with climate extremes under different model configurations.