Abstract: Heat damage of tea plants is the results of integrative effects of high temperature intensity and its duration during the high temperature climate. By collecting daily maximum air temperature and historical heat damage disaster records at 591 meteorological stations over tea regions in Southern Yangtze River and South China from 2011 to 2022, the critical threshold of heat damage to tea plants was determined by jointly using the methods of historical disaster inversion, receiver operating characteristic curve (ROC), and Youden index. With the sliding average of daily maximum temperature over fourteen consecutive days (T₁₄) as the indicator, we determined whether heat damage occurred in tea region of China. The value of area under ROC curve (AUC) was 0.942, corresponding to an accuracy of ‘excellent’. The Youden index was the largest when T₁₄ was 34.5 ℃. Therefore, the T₁₄≥34.5 ℃ was considered as the best critical temperature threshold for identifying the occurrence of heat damage to tea plants in tea regions of Southern Yangtze River and South China. Overall accuracy method was used to validate the critical threshold of heat damage based on random reserved validation samples, individual heat damage samples of tea plants, and typical heat damage process. It was found that the overall accuracy of critical threshold was 87.5% and 84.1% for the random reserved validation samples and the individual heat damage samples, respectively. Spatial evolution characteristics of heat damage in tea regions of Southern Yangtze River and South China in 2022 was basically consistent with heat damage records. It further confirmed that the critical threshold of heat damage found in this study can be used for dynamic monitoring and impact assessment of heat damage to tea plants.

Key words: determination of critical threshold, ROC curve, historical disaster inversion, heat damage of tea plants