Decadal predictions outperform climate projections in forecasting Mediterranean wintertime precipitation

Abstract The Mediterranean region is highly sensitive to climate change, having experienced an intense warming and drying trend in recent decades. In the context of decision-making processes, there is growing interest in understanding the near-term climate evolution of this region. Climate change projections consistently indicate that Southern Europe and the Mediterranean region will undergo significantly drier conditions in the latter half of the 21st century. However, in considering the upcoming decade, a critical question arises: Are climate change projections the best product for understanding climate evolution in the near future? This is a matter of great importance for numerous stakeholders and decision-makers. In this study, using retrospective forecasts from eight decadal prediction systems contributing to the CMIP6 Decadal Climate Prediction Project and the corresponding ensemble of non-initialized simulations (historical and projections), we compare the capabilities of the state-of-the-art climate models in predicting the near-term climate anomalies of the wintertime Mediterranean region for some key quantities, also assessing the added value of initialization. Our findings indicate the superior performance of the decadal predictions, exhibiting higher skill than uninitialized historical simulations and projections, particularly over the North Atlantic subpolar gyre for surface temperature and over Southern Europe for precipitation. We also develop a hybrid (dynamical-statistical) model to explore the role of the North Atlantic Oscillation and subpolar sea surface temperatures on Mediterranean precipitation predictability. It is shown that the developed hybrid model further enhances predictive skill, underscoring the importance of using initialized decadal predictions for precipitation across Europe and the Mediterranean region.