The analysis of climatic indicators using different growing season calculation methods – an application to grapevine grown in Hungary

The precise knowledge of the beginning and the end of the growing season is necessary for the calculation of climatic indicators with evident effect on grapevine production. The aim of this study is to develop suitable methods on the basis of thermal conditions that can be used for calculation of the beginning, the end, and the length of the growing season for every single year. The two most accurate methods (5mid' and 'int') are selected using the root-mean-square error compared to the reference growing season values based on averaging the daily mean temperature for several decades. In case of the `5mid' method, the beginning (or the end) is the middle day of the first (or last) 5-day period with temperature not less than 10 degrees C. In case of the 'int' method, the beginning (or the end) of the growing season is the day after March 15 (or September 15), when the smoothed series of daily temperature using the monthly average temperatures of March and April (or September and October) exceeds 10 degrees C (or falls below 10 degrees C). As a next step, several climatic indicators (e.g., Huglin index and hydrothermal coefficient) are calculated for Hungary for three time periods (1961-1990, 2021-2050, and 2071-2100*) using the '5mid' and 'int' methods. For this purpose, the bias-corrected daily mean, minimum, and maximum temperature and daily precipitation outputs of three different regional climate models (RegCM, ALADIN, and PRECIS) are used. Extreme temperature and precipitation indices are also evaluated as they determine the risk of grapevine production. The spatial distributions of the indicators are presented on maps. We compare the indicators for the past and for the future using one-way completely randomized robust ANOVA (analysis of variance). Results suggest that changes of temperature conditions in the 21st century will favor the production of red grapevine and late-ripening cultivars. Furthermore, drought seasons will be longer and extreme high summer temperatures will become more frequent, which are clearly considered as high risk factors in grapevine production. Besides the negative effects, the risk of winter frost damage is expected to decrease, which is evidently a favorable change in terms of grapevine production