Summer drought predictability in the Euro-Mediterranean region in seasonal forecasts

Abstract Seasonal drought forecasts are essential for risk management in climate-sensitive sectors, yet their performance across Europe remains uncertain. This study evaluates the ability of state-of-the-art seasonal forecast systems from the Copernicus Climate Change Service (C3S) to predict summer drought conditions in Europe using the June-July-August Standardized Precipitation Evapotranspiration Index (SPEI-3), which shows more spatially coherent and higher forecast skill across the region than the Standardized Precipitation Index (SPI). Leveraging this superior performance, we adopt SPEI-3 as the reference drought indicator. We then implement a systematic multi-metric evaluation framework to benchmark individual systems, their multi-model ensemble (MME) and to identify patterns of predictive skill across regions and lead times. Our findings reveal that when SPEI forecasts are initialized at the onset of the summer season, all models exhibit on average good quality in terms of correlation, accuracy, reliability, and discrimination skills, though with local variability. The performance is better for all models in Southern Europe, indicating higher predictability of SPEI in that region compared to Northern Europe, where summer drought variability is mainly driven by precipitation, which is inherently less predictable than temperature. Results show that, when a general analysis at regional scale is needed, the MME offers the most robust solution, demonstrating more widespread significant skill compared to single models, up to a 1-month lead time. These findings highlight the value of SPEI-based ensemble forecasts for early summer drought detection and provide actionable insights into where and when seasonal predictions offer the greatest utility across Europe.