UniPhen – a unified high resolution model approach to simulate the phenological development of a broad range of grape cultivars as well as a potential new bioclimatic indicator

Abstract

Present investigations aimed at developing a unified cumulative degree day based model approach allowing for (i) a precise simulation of grapevine phenological development of a broad range of cultivars and (ii) a classification of the cultivar specific relative precocity of different cultivars at different stages of grape development. Based on a long-term (7-year) data set of high-resolution phenological observations for 11 cool climate cultivars originating from Remich/Luxembourg, the unified phenological model (UniPhen) was developed using a cumulative degree day approach with three temperature thresholds (lower threshold: 10 °C; upper threshold: 20 °C; heat threshold: 30 °C). The average normalized standard deviation of UniPhen over all stages and cultivars was 5.26 corresponding to 5.26 days at 15 °C. In the cross-validated model, on average 53% of the observations were located in a range of ± 3 days and 82% in a range of ±7 days (assuming daily mean temperatures of 15 °C) around the predicted date. The sequence of the cultivar-specific relative precocity was not stable over the different stages of phenological development. The model approach (i) enables a precise simulation of all 31 BBCH stages between beginning of the bud swell (01) and berries being ripe for harvest (89) for 11 cultivars grown in the climatic conditions of the Luxembourgish grapegrowing region and (ii) is open to being extended to other grape cultivars and re-calibrated under deviant climatic conditions. Due to their instability, a classification of the cultivars’ relative precocity is only reasonable if it relates to a specific phenological stage. UniPhen represents a precise high-resolution phenological model approach and might be applied as a bioclimatic indicator describing the suitability of a location/region for the cultivation of specific cultivars.