Climate change projections for Southern Europe reveal warming and drying trends for the upcoming decades, bringing important challenges to Portuguese viticulture in particular. The present study analyses irrigation as an adaptation measure to ensure the future sustainability of viticultural yields in Portugal. The STICS crop model was used to simulate baseline (1981-2005) and future (2041-2070) grapevine yields in Portugal. Future yield decreases (yields are 60% with respect to baseline) over some of the innermost and most renowned winemaking regions of the country are found, following the decrease of precipitation in the growing season. As an adaptation measure, grapevine irrigation was tested for future climates. STICS irrigation replicates a highly efficient water use strategy, only applied when a certain water stress level is reached. The results indicate higher yields with this irrigation strategy, thus largely alleviating the projected yield decreases. Nonetheless, in some warmer and dryer regions, such as inner Alentejo and Douro/Porto, yield levels are still projected to decrease with irrigation (70-80% of baseline yields), though to a lesser extent when compared to non-irrigated simulations. This decrease is attributed to the synergistic effect of severe heat and water stresses in the future. Although these simulations aim at achieving the same yields and alcohol level in future scenarios as in baseline, applying irrigation may modify the wine typicity of each region and threaten the currently scarce water resources. Outlining appropriate, timely and cost-effective adaptation measures is critical for the sustainability of both the environment and the national Portuguese winemaking sector.