Abstract:Constructing a quantitative index to characterize the intensity of low-temperature freezing injury of winter wheat and revealing its spatio-temporal variation characteristics is crucial for scientific prevention of low-temperature freezing injury of winter wheat. Based on the winter daily meteorological observation data in Jiangsu Province from 1972 to 2022, disaster data of freezing injury of winter wheat from 2010 to 2022, and yield data of historical extreme freezing injury years, this paper determines the impact weights of disaster-causing factors on different types of freezing injury, and establishes three main types of freezing injury indices, including low-temperature freezing injury (last November to March), freezing injury during overwintering period (late December to mid February), and freezing injury during regreening-jointing period (late February to March). Multiple mathematical statistical methods such as Mann-Kendall mutation test and k-means clustering are used to conduct spatio-temporal analysis and evaluation of low-temperature freezing injury of winter wheat. Based on the ranking of freezing injury intensity during overwintering period and regreening-jointing period, two types of freezing injuries are classified into three levels, which are mild, moderate and severe. The results show that there is a significant difference in the intensity indices of low-temperature freezing injury between the north and the south of Jiangsu Province. They can be divided into high-risk zone (Xuzhou, Lianyungang, Suqian, Huai’an and Yancheng), medium-risk zone (Nanjing, Yangzhou, Taizhou and Nantong), and low-risk zone (Zhenjiang, Changzhou, Suzhou and Wuxi). Over the past 51 years, the intensity index of low-temperature freezing injury of winter wheat experienced a sudden decline in 1989 in Jiangsu Province. The severe freezing injury during overwintering period and regreening-jointing period both jumped from a relatively more injury period to a relatively fewer injury period in the late 1980s. Although the frequency of freezing injury during the development period of winter wheat has shown a decreasing trend, the intensity of extreme freezing injury has been increasing, and even the freezing injury index in some areas exceeded the historical record of 1977 in the 21st century.