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Simpósio Nacional de Olivicultura, 5º, Santarém, 24-26 de Setembro, 2009 Phenological development of the olive tree is important for studying its adaptability, for management and simulation of growth and yield of olive orchards. Nevertheless, most studies that predict the date of flowering of the olive do not consider its chilling requirements, that are low, but may not be satisfied in some years, under mild climates or when global warming takes effect. In a previous study De Melo-Abreu et al. (2004) a model designed to predict the date of flowering was presented along with appropriate parameters for some cultivars. It is a two phase model. In the first phase, chilling accumulation takes place using a four parameter sub-model for determination of chilling units. In the second phase, known as the forcing phase, that starts after chilling requirements were attained and bud-break was due to occur, temperature sum above a base temperature is used to simulate development. Furthermore, it was established that all the parameters for the chilling accumulation, except the required chilling units, are conservative for all cultivars that were studied. A custom-tailored algorithm was constructed for the determination of the total sum of chilling units for bud-break and for the temperature sum necessary for the forcing phase. The resulting calibrated model is used for the prediction of the impact of global warming in the dates of flowering of the olive trees ‘Arbequina’, ‘Gordal’, ‘Hojiblanca’, ‘Manzanilla’, ‘Moraiolo’, ‘Picual’ and ‘Verdial’ for the four locations that are representative of the main olive producing regions in Portugal. The present climate is represented by a series of 19 and 30 years of maximum and minimum daily temperatures (Cen0). Three scenarios of climate change were considered. Cen1, Cen2 and Cen3 correspond, respectively, to increases of 1°C, 2°C and 3°C to both maximum and minimum temperaturesIn Vila Real, projections indicate successive advances in the date of flowering, from 11 to 12 days in Cen1 until 33 to 37 days in Cen3. In Castelo Branco, the projections indicate advances of flowering date from 11 to 13 days in Cen1 until 23 to 36 days in Cen3. In both locations, no faulty of abnormal flowering were anticipated. In Beja, the o projections indicate that advances in the date of flowering for Cen1 and Cen2 are modest, that ‘Moraiolo’ has a single event of faulty or abnormal flowering in Cen2 and that all cultivars that were studied have years with faulty or abnormal flowerings in Cen3. In Faro, important delays in the date of flowering were anticipated in all scenarios, and in many years flowering is absent or abnormal. In Cen3, the projections indicate that flowering is likely to be absent or abnormal in almost all years. The results that were obtained are an indication that may help the farmer to include or reject cultivars in future olive orchards.