Construction of a Compound Heat and Drought Damage Index and Spatiotemporal Characteristics for Tea Plants in South of the Yangtze River and South China

Based on daily maximum temperature and precipitation data of tea regions over South of the Yangtze River and South China from 494 meteorological stations from 1961 to 2022, as well as records of compound heat and drought damage of tea trees, a compound index is calculated on the basis of existing high temperature and heat damage grade index uses the number of consecutive days without rain. Considering the superimposed effect of drought and heat damage, the compound heat and drought damage grade index of tea plants is constructed based on the elliptic curve method and verified, and then spatiotemporal characteristics of compound heat and drought damage in South of the Yangtze River and South China are analyzed. Results indicate that the compound heat and drought damage grade index for tea plants is constructed using the duration of high-temperature days and the drought index as two axes of the elliptical curve. The high temperature duration days for mild to moderate and moderate to severe compound heat and drought damage are 17 d and 38 d, respectively, and the drought index for mild to moderate and moderate to severe compound heat and drought damage 15.1 d and 29.4 d, respectively. The overall accuracy and basic accuracy of the compound heat and drought damage grade index for tea plants, constructed using elliptic curves to identify validation samples, are 60% and 100%, respectively. From 1961 to 2022, the average occurrence range of moderate compound heat and drought damage in tea regions over South of the Yangtze River and South China is the largest, the average frequency of mild compound heat and drought damage is the highest, and the average range and frequency of severe compound heat and drought damage are the smallest. The range and frequency of compound heat and drought damage in tea plants over South of the Yangtze River and South China show a fluctuating upward trend from 1961 to 2022, with the lowest in the 1991-2000 period and the highest in the 2011-2022 period. The spatial distribution of compound heat and drought damage frequency is characterized by a high incidence in the central region and a low incidence in the coastal areas.