Climate change impacts on phenology and ripening of cv. Touriga Nacional in the Dao wine region, Portugal

The present study is devoted to climate change impact assessment on the phenological development and ripening of cv. Touriga Nacional in the Dao Wine Region, Portugal. For this purpose, the dates of the three main phenological stages (budbreak, flowering and veraison) and two maturity stages are projected for two future periods (2041-2070 and 2071-2100), under two anthropogenic radiative forcing scenarios (RCP4.5 and RCP8.5), and compared against a baseline period (1991-2020). The phenological and maturity stages are simulated using phenological development models (PDMs) and a temperature-based ripeness model (TRM), respectively. An overall advancement in both phenology and ripening stages are identified under future warmer climates, though site-dependent. Furthermore, the advancements in phenology are more pronounced (a) for stages between the beginning of veraison and end of ripening than for the earlier stages, (b) for the long-term future period (2071-2100) under RCP8.5 and (c) for the vineyard site "Viseu." These changes are due to the combination of budbreak advancement with a shortening of some phenophases. The strongest shortening is found in the ripening period, while no significant changes in flowering timings and duration of the berry development period are projected. The advancement and the shortening of the grapevine growing season will shift ripening to the warmest part of the year. This twofold climate change impact of the air temperature on ripening may affect the sugar and organic acid balance, as well as the colour of the must. The current findings can be used by the regional winemaking sector in planning and implementing suitable climate change adaptation to enhance its climate resiliency and sustainability. Subsequent studies for this wine region should be carried out to assess the climate change impacts on late frost risk, on climatic viticultural zoning, on yield and berry quality at harvest.