Variability of Tempranillo phenology within the toro do (Spain) and its relationship to climatic characteristics

Aims: The objective of this research was to analyse the spatial and temporal variability of vine phenology of the Tempranillo variety in the Toro Designation of Origen (DO) related to climatic conditions at present and under future climate change scenarios.

Methods and Results: Seven plots planted with Tempranillo, distributed throughout the DO, and located at elevations between 630 and 790 m a.s.l were considered in this analysis. Phenological dates referred to bud break, bloom, veraison and maturity recorded in each plot for the period 2005-2019 were analysed. The information was supplied by the Consejo Regulador of Toro Designation of Origin (Toro DO). The weather conditions recorded during the period under study were analysed using data recorded in Toro. The thermal requirements to reach each phenological stage were evaluated and expressed as the GDD accumulated from DOY=90, which were considered to predict the changes under future climatic conditions. For future climatic conditions, temperature and precipitation predicted by 2050 and 2070 under two Representative Concentration Pathway (RCP) scenarios –RCP4.5 and RCP8.5-, based on an ensemble of models, were used to predict the changes in phenology.

During the analysed period, the dates at which the different phenological stages were reached presented high variability, with bud break between April 5^th and May 7^th; bloom between May 3^rd and July 14^th, veraison between July 20^th and August 21^st and maturity between September 1^st and October 2^nd. The earliest dates were observed in the hottest year (e.g. 2017), while the latest dates were recorded in the coolest and wettest years (eg. 2008, 2013 or 2018). Water deficits also gave rise to advances in phenological timing (e.g. 2009, 2015), which affect more the later than the earlier phenological states. Water deficit in the BL-V period had a significant effect on veraison, while in general the maturity was also affected by water existing in the BB-BL period. Some spatial variability was observed in the phenological dates, although the trend was not uniform for all the stages or for all years. Taking into account the thermal requirements to reach each stage and the predictions under future climate scenarios, advances in all phenological dates were projected, higher for the later than for the earlier stages, which may be of up 6 and 8 days for bud break, 7-10 days for bloom, 8 to 11 days for veraison, and 12 to 19 days for maturity by 2050, respectively under RCP4.5 and RCP8.5 emission scenarios.

Conclusion: 

Based on the climate change projections, the Tempranillo variety cultivated in Toro DO may suffer an advance of all phenological stages, having harvest earlier and under warmer conditions, which could also affect grape composition.

Significance and Impact of the Study: Tempranillo is the third most cultivated wine variety in the world, being 88% of it cultivated in Spain, and in the Toro DO the main variety (“Tinta de Toro”) covering about 5100 ha. Thus, the knowledge of the vine response under future conditions could be a tool to adopt measurements to mitigate the effects of climate change in the area.