Process-based dynamic identification indicators of soybean chilling damage and analysis of the corresponding spatiotemporal characteristics in Northeast China

Northeast China (NEC) is one of the main soybean-producing areas among the northern-latitude regions. Climate warming leads to frequent extreme disasters, and the threat of chilling damage to soybean production in NEC cannot be ignored. The study aimed to construct a dynamic disaster identification index based on the static evaluation of soybean after the disaster, taking into account the process of soybean chilling damage and using the historical disaster records to realize the dynamic prediction and analysis before the disaster. Taking soybean in NEC as the research object, chilling damage indicators of soybeans in NEC were constructed by dividing the mature regions, using daily temperature anomaly and negative temperature anomaly day data with the comprehensive consideration of the chilling damage intensity, duration, and temperature recovery. The results showed that the comprehensive indicators determined by the cumulative value of temperature anomaly-the cumulative days of negative temperature anomaly had better applicability in NEC than the single factor indicator. The indicator results were basically consistent with the historical disaster records, and the accuracy rate of the indicator verification reached 90.9%. Based on the analysis of the constructed indicators, the frequency of delayed chilling damage in NEC showed a fluctuating downward trend from 1961 to 2020. The station ratio of delayed chilling damage in NEC showed a fluctuating downward trend, with the most obvious downward trend occurring for severe damage, followed by moderate damage, and the least obvious trend observed for light damage. The scope of chilling damage gradually narrowed, with the frequency increasing from southeast to northwest. The high-risk areas of chilling damage were concentrated mainly in the northern part of Heilongjiang Province and the East Four Leagues. The risk of chilling damage in most areas of Jilin Province and Liaoning Province was relatively low. The study results provide basic support for the risk research of soybean chilling damage and for ensuring disaster monitoring and early warnings, and the risk assessment based on the chilling damage process has positive significance for adjusting agricultural structure and improving the distribution of soybean varieties.