Threshold study on the impact of compound drought and heat events on maize yield in the Three Provinces of Northeast China

Global warming has increased the frequency of compound drought and heat events (CDHEs), posing a serious threat to maize production and food security in the Three Provinces of Northeast China. Nevertheless, quantitative damage thresholds that account for regional climatic adaptation and phenological growth-stage differences are still lacking. Based on meteorological, phenological, and yield datasets from 1982 to 2022, this study established maize drought damage thresholds using the Standardized Precipitation Evapotranspiration Index (SPEI) and heat damage thresholds using the Standardized Temperature Index (STI), via a three-step framework of boxplot filtering, kernel density estimation, and ROC–Youden Index optimization. The synergistic yield damage induced by CDHEs was further quantified, and the reliability of the obtained thresholds was comprehensively verified. The results indicated that drought thresholds followed the spatial gradient of Liaoning < Jilin < Heilongjiang, while heat thresholds exhibited the opposite pattern. CDHEs exhibited a significant "1 + 1 > 2" synergistic amplification effect. High CDHEs risk was mainly concentrated in western Liaoning and western Jilin. This study provides a reliable scientific reference for disaster early warning, differentiated agricultural water management, and targeted risk mitigation for maize under ongoing climate change in the Three Provinces of Northeast China.