Sugar and acid accumulation dynamics in grapes Vitis vinifera L. play a key role in the production of high-quality wines, and changes in mean climate and variability, expected in the coming decades, may affect these dynamics and result in poor grape yield and quality. Simulation models may be useful tools for predicting grape quality changes under warmer conditions and thus provide fundamental information to winemakers for future vineyard management. The grape simulation model UNIFI.GrapeML was calibrated to predict the performances of the Sangiovese grape variety under different climate forcing. The model was calibrated and validated against observed data (i.e. phenology, sugar and acid content) of Sangiovese grapes at 2 Italian sites (Susegana and Montalcino), showing satisfactory performances in predicting the main phenological phases and sugar and acid contents. Future climate was simulated using the LARS-WG downscaling procedure by considering possible increases of yearly temperature (Delta T) ranging from +1 degrees C to +3 degrees C (step = 0.5 degrees C) with respect to the baseline. For each step, we considered that the temperature increase can be constant every month or can exhibit seasonality, i.e. the increase in temperature is more evident in spring-summer than autumn-winter, as projected for the Mediterranean region. The results indicate that, on average, a progressive increase of temperatures resulted in earlier phenological phases and an increasing trend of sugar content while acid content showed the opposite. This trend is more evident as seasonality in the change of temperature increases, highlighting possible distortion in the impact assessment of climate change when seasonality is not accounted for.