Changes in grapevine budburst and harvest dates in Croatia under current and future climate conditions

The increase in temperature affected the entire plant world, including the vines. These changes are reflected in the quantity and quality of the harvest, the chemical composition, and the appearance of the phenological phases of the grapevine. The shift of budding towards the beginning of the year can be particularly worrying due to the frequent occurrence of frost in the continental area of ​​Croatia. The shift of the harvest towards the warmer part of the year brings problems when storing grapes. Due to the great importance of viticulture for agriculture and tourism in Croatia, it is necessary to examine changes in the occurrence of phenological phases in current and future climatic conditions.

Due to all of the above, statistical models were developed to describe the occurrence of phenological phases. Also, the crop model STICS was parameterized for the Croatian region and four grape varieties. Bayesian statistics were also used to get an insight into the amount of earlier and later harvests. To get a clearer picture of the changes in the future climate three CORDEX Regional Climate Models (RCMs) simulations (CLMcom-CCLM4-8-17, SMHI-RCA4, CNRM-ALADIN5.3) for the Croatian domain and varieties were used in this research. All RCMs are forced by output from Global Climate Models (GCMs) with moderate (RCP4.5) and high-end (RCP8.5) greenhouse gas (GHG) scenarios. SMHI-RCA4 is driven by five different GCMs (CNRM-CERFACS-CNRM-CM5, ICHEC-EC-EARTH, IPSL-IPSL-CM5A-MR, MOHC-HadGEM2-ES and MPI-M-MPI-ESM-LR), CLM by four (CNRM-CERFACS-CNRM-CM5, ICHEC-EC-EARTH and MOHC-HadGEM2-ES, MPI-M-MPI-ESM-LR), and CNRM-ALADIN5.3 with one (CNRM-CERFACS-CNRM-CM5). All the simulations have horizontal grid spacing of 0.11◦.

The results show clear trends in the budburst and harvest shifting in Croatia, regardless of the variety. Future climate analysis indicates a further shift in the occurrence of phenological phases towards the beginning of the year (that is, an earlier occurrence). The expected shifts in budburst in the period P2 (2041-2070) compared to the period P0 (1971-2000) are more pronounced for traditional varieties ('Graševina' and 'Plavac mali'), where median differences suggest shifts of 15 days towards the beginning of the year, regardless of the RCP scenario. The results indicate a shift in budburst to early March, which is a particular threat for white varieties that are mostly grown in continental parts of Croatia where low temperatures and frost in March can reduce most of the harvest. In addition, the results indicate a further shift in harvesting in the future climate, and an increase in the number of early harvests, and a decrease in the number of later harvests, regardless of location and variety. The reduction in later harvests is the most significant and can be expected in the range of approximately 30-75%. So, according to the results, in the 30-year period (2041-2070) 30-75% of the years will no longer have the later harvest that took place in the period 1971-2000.