Modeling the Impact of Global Warming on the Phenology of the Olive Tree in the Mediterranean region

Nowadays, there is observable evidence from all continents and most oceans that many natural systems have been affected by regional climate changes, particularly by the increase in temperature. This increase has also influenced the phenology of plants. As the olive tree is a plant characterizing the Mediterranean area, it is obvious that its phenology could serve as an indicator of the impact of global warming on this area. In this study, we will use the PMP model and observations of the tree phenology to predict its flowering date, which is the most remarkable and easiest to observe development phase. On the other hand, we will study by simulation the impact of climate change on the flowering of the olive tree under the conditions of Haouz of Marrakech according to three contrasting scenarios of a possible climate change. The PMP software is a tool that facilitates the development of mechanistic phenological models. It is based on thermal time calculations. In the present work, we chose to test three thermal time models: the ForcTT model, the TT model and the UniForc unified forcing model. The first two models are two versions of Growing Degree Days (GDD) which corresponds to a linear relationship of forcing rate from the initial date t₀ and a threshold temperature T_b. The third UniForc model is a sigmoidal function of temperature with the initial time t₀ as an unknown. The tests were carried out using two databases, the first recorded in the meteorological stations of the Haouz region covering the period 1985 - 2012 and the second observed on the phenology of the olive tree in the Tassaout area for the periods 1986 - 1991 and 1997 - 2012. The first result obtained shows that the UniForc is the most robust model, it is therefore retained for the study of the impact of global warming on the olive tree.In the second part of this work we have chosen three scenarios of greenhouse gas emissions, SRES (Special Report on Emissions Scenarios), which explore future development paths (demographic, economic and technological). Each of the three scenarios chosen is based on a degree of temperature increase according to the imagined development pathway: the more optimistic B1 scenario (increase of 1.1°C), the medium degree A1B scenario (increase of 2.8°C) and the more pessimistic A1F1 scenario (increase of 6.4°C). All the simulations carried out according to the chosen SRES scenarios confirm that the increase in temperature leads to the advancement (earliness) of the flowering date, this advancement varies between 0.3 and 27.3 days. The higher the temperature increase, the earlier the flowering date. Thus, the flowering date of the olive tree is univocally linked to the type of greenhouse gas emission scenario chosen. Our results therefore confirm that this agronomic variable is a good indicator of the severity of global warming that could occur in the region.