Trends and future projections of Olea flowering in the western Mediterranean: The example of the Alentejo region (Portugal)

Abstract

Olives are one of the most economically relevant crops in the Mediterranean area but this region is experiencing a strong warming due to climate change. Therefore, it would be of great interest to estimate the possible implications of climate change on olive flowering timing by modelling its thermal requirements, and aerobiological records have proved to be a useful tool for monitoring regional olive phenology. Recently, a new phenological modelling framework has been developed called PhenoFlex. It has shown excellent results in estimating the thermal requirements of fruit trees. However, this framework has not previously been applied to olive trees or tested using aerobiological data, which could present greater spatial distribution than in situ phenological observations. This study has a threefold aim: i) to detect the trends in the main pollen season start date of Olea during the past 25 years in a western Mediterranean region (Alentejo, Portugal); ii) to evaluate the applicability of the PhenoFlex modelling framework to olive aerobiological data, and iii) to use the modelled parameter estimates to evaluate the influence of projected future climate change scenarios on Olea flowering regional onset dates. Our results showed that global warming had not produced any significant trend in the olive flowering onset dates until the present time, and they are not expected to do so in the near future, either. A temperature increase during winter was observed that is delaying the fulfilment of the Olea chilling requirements, but this is compensated for by a reduction in the forcing period due to higher temperatures observed during spring. However, our study points out a significant increase in the interannual variability of flowering onset dates, which could compromise fruit development and adversely affect the yield, raising uncertainty in olive fruit production in the near future.