Warming temperature reduces the risk of pre-harvest freezing injury and modifies variety suitability in the main winegrape-growing regions of China

Abstract

Rising temperatures cause advanced phenology of grapevines and increased sugar concentration in berries, which ultimately modify variety suitability in a given region. Here, four bioclimatic indices and a refined Grapevine Sugar Ripeness (GSR) model were employed to assess the suitability of six winegrape varieties across six winegrape-growing regions of China under historical climate conditions (1961-2020). First, four indices were compared between two periods, one before (P1) and one after (P2) an abrupt climate change events identified during 1988-2002 in these regions. Results showed three temperature related indices increased in six regions while the first fall frost day (FFD) was delayed by 0-16 days in five out of the six regions during P2 compared with P1. Second, GSR model was applied to simulate target sugar concentrations as a proxy for grape harvest dates (GHDs). Direct utilization of original GSR model yielded unsatisfactory predictions with clear bias. Consequently, GSR model was recalibrated with local data to obtain an acceptable performance with R2 and NRMSE values of 0.83 and 2.8% as well as 0.83 and 3.1% for the calibration and validation datasets, respectively and further simulated GHDs of six varieties with advanced values of 6-30 days in six regions for P2 in comparison with P1. To provide a holistic view of freezing injury risk before harvest, comprehensive freezing injury index (CFI) was developed by integrating the frequency, duration, and severity of the freezing risk. CFI decreased (2%-60%) during P2 in all regions and the magnitudes of decrease was elevation dependent. These findings provide valuable insights for the selection of varieties that can more reliably achieve fully mature fruit, producing more balanced wines with greater typicity under warming climate.