Grapevine Sugar Concentration Model (GSCM): A Decision Support Tool for the Douro Superior Winemaking Region

Climate-smart agriculture involves practices and crop modelling techniques aiming to provide practical answers to meet growers&rsquo: demands. For viticulturists, early prediction of harvest dates is critical for the success of cultural practices, which should be based on accurate planning of the annual growing cycle. We developed a modelling tool to assess the sugar concentration levels in the Douro Superior sub-region of the Douro wine region, Portugal. Two main cultivars (cv. Touriga-Nacional and Touriga-Francesa) grown in five locations across this sub-region were studied. Grape berry sugar data, with concentrations between 170 and 230 g L&minus:1, were analyzed for the growing season campaigns, from 2014&ndash:2020, as an indicator of grape ripeness conditioned by temperature factors. Field data were collected by ADVID (&ldquo:Associa&ccedil:&atilde:o Desenvolvimento Da Viticultura Duriense&rdquo:), a regional winemaker association, and by Sogrape, the leading wine company from Portugal. The &ldquo:Phenology Modeling Platform&rdquo: was used for calibrating the model with sigmoid functions. Subsequently, model optimizations were performed to achieve a harmonized model, suitable for all estates. Model performance was assessed through two metrics: root mean square error (RMSE) and the Nash&ndash:Sutcliffe coefficient of efficiency (EFF). Both a leave-one-out cross-validation and a validation with an independent dataset (for 1991&ndash:2013) were carried out. Overall, our findings demonstrate that the model calibration achieved an average EFF of 0.7 for all estates and sugar levels, with an average RMSE &lt: 6 days. Model validation, at one estate for 15 years, achieved an R2 of 0.93 and an RMSE &lt: 5. These models demonstrate that air temperature has a high predictive potential of sugar ripeness, and ultimately of the harvest dates. These models were then used to build a standalone easy-to-use computer application (GSCM&mdash:Grapevine Sugar Concentration Model), which will allow growers to better plan and manage their seasonal activities, thus being a potentially valuable decision support tool in viticulture and oenology.