Simulating the impact of climate change scenarios on phenology and crop water requirements: a case study on olive tree in Apulia region.

Assessing the potential impact of climate change on the duration of single phenological stages and whole cropping cycle is fundamental to estimate crop water requirements and optimize the allocation of limited water resources and land among different crops in Mediterranean regions. An approach based on thermal requirements (Rubino et al., 2012) was used to simulate the variation of the onset and duration of the phenological stages and the crop water requirements of olive tree under future climate change scenarios. The study was carried out in Apulia region on five locations selected within different homogeneous climatic zones delineated within the ACLA 2 project. Climate model simulations were derived from the EURO-CORDEX bias-adjusted database for each of the five locations selected. The Representative Concentration Pathway (RCP) 4.5 was considered. The database consisted of simulated bias-adjusted daily weather data for the time interval 01.01.1971-29.11.2100 of mean surface temperature, maximum surface temperature, minimum surface temperature and precipitation flux and data were obtained averaging an ensemble of 23 model members. Four time series were considered: the current period, considering the thirty-year time series 1991-2020, and three future scenarios considering the time intervals 2021-2050, 2051-2080, 2081-2100; pluriannual mean data were computed for each time interval. In each area, the reference starting dates for each phenological stage (budbreak, inflorescence emergence, flowering, pit hardening, veraison) and location were defined according to phenological observations repeated over years. With the current climatic conditions, the thermal requirements (expressed as growing degree days-GDD) to complete each phenological stage (intervals from: budbreak to inflorescence emergence; inflorescence emergence to flowering; flowering to pit hardening; pit hardening to veraison) were computed. This information was then used under future climate scenarios to assess the starting date of the stages from inflorescence emergence to veraison, whereas the date of budbreak was kept constant for each site. After defining crop cycle parameters for each climatic condition and site, daily reference evapotranspiration (ETo) was computed using Hargreaves equation and daily maximum crop evapotranspiration (ETc) was quantified.