Climate change impacts on irrigated agriculture in the Guadiana river basin (Portugal)

This study evaluates climate change potential impacts on irrigated agriculture in the Guadiana river basin,in the south of Portugal, by running long-term soil water balance simulations using the ISAREG modeland taking into consideration the maximum potential yield. The ISAREG simulations were focused in aset of the most locally representative crops to assess the evolution of net and total water requirements,considering a monthly time step for two 30-year future periods,(20112040) and (20412070). Referenceevapotranspiration was estimated using the temperature-based HargreavesSamani equation, and thesimulations were performed using, as inputs, a combination of five climate change scenarios built usingthe Ensemble-Delta technique fromCMIP3 climateprojectionsdatasets to setdifferent alternative climatechange bracketing conditions for rainfall and air temperature.Water balance outputs for different climatescenarios were combined with four agricultural scenarios allowing for the estimation of total irrigationrequirements.A general increase in crop irrigation requirements was estimated, mainly for those crops as maize, pasture,and orchards that are already big irrigation water consumers. Crops as olive groves and vineyards,well adapted to the Mediterranean conditions, show less sensitivity to climate change. The combinedresults of crop irrigation requirements for climate change and agricultural scenarios allow for the expectationof sustainability for the agricultural scenarios A and C, essentially defined by the complete use ofthe irrigation network and systems currently being