A BIOCLIMATIC FORECASTING MODEL FOR OLIVE YIELD IN ALENTEJO (PORTUGAL)

A forecast model for estimating the annual variation in regional olive crop yield has been developed during the years 1998 to 2006 for the Alentejo region (south Portugal). This model was estimated hierarchically along three different in-season stages: i) flowering, considering only the regional airborne pollen index; ii) fruit growth with the addition of a plant water-stress index; iii) fruit maturing with the addition of a phytopathological index. Appropriated statistical tests indicated that the regional airborne pollen index accounted for 64% of the inter-annual olive yield variability with an average deviation between observed and predicted production of 16%. The addition of the variable plant water-stress index to the forecasting model allowed an increase in its accuracy of 27% while the phytopathological index allowed an increase of 6%. The final bioclimatic model, with all the three variables tested, explained 97% of the regional olive fruit yield being the average deviation between observed and predicted production of 4% for the internal validation of the model and of 9% for the external validation. The hierarchical structure of this bioclimatic model, along three different development stages, enabled an update along the growing season.