Effects of direct heat stress on summer maize and risk assessment

The frequency and severity of extreme heat have increased in many parts of the world under global warming, seriously threatening food security and sustainable development. Disaster risk assessment provides the basis for disaster prevention and mitigation. The objective of this study was to isolate the direct impacts of extreme heat on summer maize and construct a summer maize extreme heat disaster risk assessment model by considering both extreme heat hazard and summer maize vulnerability. The results revealed that the extreme heat occurrence probability peaks at mid-June to early July in the Haihe Plain. Summer maize vegetative stage (stage I) occurs mainly in this period. This result demonstrates that extreme heat hazards are more serious in stage I than in the other two stages. Summer maize is most vulnerable to direct heat stress at the reproductive stage (stage III), but the effects are relatively limited. The final risk distribution showed that the risk value increased as the hazard level rose, especially for stage I, due primarily to the serious extreme heat hazard. The risk value for stage III is second only to stage I. Even though this stage is most vulnerable to extreme heat, the extreme heat hazard is small. The high extreme heat risk values are found in the western region and gradually decreased to the eastern coastal area. These risk assessment results provide significant guidance for mitigation strategies and reducing summer maize extreme heat disaster risk that will result from a hotter climate.