Olive tree irrigation as a climate change adaptation measure in Alentejo, Portugal

Climate change projections for Southern Europe reveal warming and drying trends for the upcoming decades, bringing important challenges to Portuguese olive orchards in particular. We analyzed irrigation as an adaptation measure to ensure the future sustainability of olive tree yields in Alentejo, the main olive producing area in Portugal. A dynamic crop model was used to simulate olive tree yields over the baseline (1981-2005) and two future scenarios (RCP4.5 and RCP8.5, 2021-2080), using a 4 member-ensemble of state-of-the-art climate model chains. Climate change projections point to an increase in mean temperature (of up to 2 degrees C by 2080) and potential evapotranspiration (40 - 50 mm), while a decrease in precipitation (-80 to -90 mm) and actual evapotranspiration (-50 to - 70 mm), under both future scenarios. Future yield decreases 15-20% (for RCP4.5 and RCP8.5) and accumulated losses can reach -8 t/ha to -10 t/ha by 2080. This decrease is due to enhanced heat and water stress under future climate conditions. As an adaptation measure, irrigation was simulated, but only applied at a certain water stress level. The results indicate higher yields due to this adaptation strategy, in range with the present values (+/- 1%), thus alleviating the projected yield decreases in the future. The amount of water required for irrigation ranges from 60 to 85 mm, depending on the RCP, which corresponds to 0.6-1 times the projected decrease in precipitation. However, this value can reach up to 2 times for one climate model chain. We conclude that while irrigation is a feasible adaptation measure against the threats of climate change in Alentejo olive orchards, this strategy may be threatened by the scarcity of water resources. Outlining appropriate, timely and cost-effective adaptation measures is critical for the sustainability of both the environment and the Alentejo olive sector.