Abstract:Establishing climatic index and its garding standard to determine high temperature damage to summer maize at florescence is critical for disaster monitoring and early warning. It is also a critical element for field survey and assessment. Four key meteorological factors were selected using the principal component analysis method to build integrated climatic index for this purpose. The indexes included extreme maximum temperature, number of days with maximum temperature higher than 35 ℃, average minimum relative humidity of days with daily maximum temperature higher than 35 ℃ and accumulative temperature of days with daily maximum temperature higher than 35 ℃. An integrated climatic index for high temperature damage was established to determine the extent of high temperature damage to of summer maize at florescence in the Huaibei Plain by using principal component analysis. Cluster correction analysis combined with yield reduction rate in typical years of high temperature damage was used to amend gratification of the integrated climatic index for high temperature damage to summer maize at florescence. The integrated climatic index was further validated with field investigation results of bald tip rate, yield reduction rate and plant symptoms of summer maize in 2013. And the grades and their thresholds were obtained finally. Based on the results, high temperature damage to summer maize at florescence was divided into four grades of slight, moderate, severe, extreme severe, with respectively integrated climatic indexes ( D) of 0.11 < D≤ 0.21, 0.21 < D≤ 0.45, 0.45 < D≤ 0.72 and D> 0.72. A significant positive correlation was noted between integrated climatic index ( D) and yield reduction rate in typically high temperature years, with a correlation coefficient of 0.967 1. High temperature damage at florescence of summer maize caused significant damage to ears and tassel. The extent of damage was closely related to the bald tip rate and ratio of grain to stem, with respective correlation coefficients of 0.819 8 and 0.872 7. The frequency of high temperature damage to summer maize at florescence was once every 1.7 years in the Huaibei Plain. The frequencies of moderate and severe grades of high temperature damage were higher than those of the other two grades, accounting respectively for over 15% and 20% of high temperature damage frequency. Under global warming, it was beneficial to use high temperature-resistant varieties for breeding, cultivation and over arrangement, and use supplementary artificial pollination, pesticides or other measures to mitigate the effect and damage of high temperature to summer maize.