Best- and Worst-Case Scenarios for the Douro Winemaking Region: Dynamic Crop Modelling and Ensemble Projections for Yield, Alcohol Content, and Phenology.

Climate change is expected to significantly reshape viticulture across traditional wine regions, including the Douro winemaking region (DWR) in northern Portugal. This study evaluates projected impacts of climate change on key viticultural parameters, such as grapevine yield, phenology, and potential alcohol content, using an ensemble of high-resolution downscaled climate simulations for the recent-past (1986 to 2015) and for two emission scenarios: SSP1-2.6 (low-emissions pathway) and SSP5-8.5 (high-emissions pathway), for mid-century (2041-2070). Spatial and temporal analyses reveal a consistent and robust signal of change across all indicators, with magnitude and variability increasing under SSP5-8.5. Yield projections indicate a widespread decline across the region (-1 to -3 t/ha), especially under SSP5-8.5, with particularly strong reductions in currently high-yielding areas, such as Douro-Superior. This spatial heterogeneity suggests heightened vulnerability throughout the DWR, underscoring the importance of targeted adaptation strategies. Phenological analysis shows a marked advancement in flowering dates, shifting by up to 30 days earlier in the season, amplified under SSP5-8.5. These changes could impact grape development, increase exposure to early-season frost events, and disrupt traditional vineyard management schedules. Furthermore, potential alcohol content is projected to rise substantially across the region, with increases exceeding 2% vol in some areas under the more severe scenario. This trend may challenge wine typicity, regulatory classifications and geographical boundaries of the denominations of origin, and quality control, requiring both vineyard and oenological adaptations to manage elevated sugar levels. These findings point to significant, spatially variable climate-driven transformations in Douro viticulture. While some impacts may be partially mitigated under SSP1-2.6, SSP5-8.5 may require urgent adaptation to preserve wine quality, socioeconomic sustainability, and regional identity.