Relationship between urban spatial form and extreme heat events of major prefecture-level and above cities in China.

Global climate change has increased the frequency, intensity, and scope of extreme heat events, while urbanization has intensified the urban heat island effect. To alleviate the negative effects of extreme heat events, the demand for urban form optimization increases. Treating 326 major prefecture-level and above cities in China as the study objects, and applying the 85th percentile threshold to daily temperature time series spanning the past 30 years, we obtained the number of extreme heat days in each city in 2020, and identified the distribution characte-ristics of extreme heat events. We further explored the relationship between the spatial form of different cities and extreme heat events by using the negative binomial regression model. The spatial distribution of urban form and extreme heat events in 2020 exhibited pronounced regional differences. Cities exhibiting high aggregation index were mainly located in the coastal areas, the Beijing-Tianjin-Hebei region, Chengdu, Chongqing, and Kunming. Cities with higher mean shape index and mean patch fractal index were mainly concentrated in the Central China and Southwest China. Cities with higher largest patch index were mainly concentrated in provincial capitals or cities with high levels of economic development. In addition, extreme heat events occurred predominantly in the cities of South China, Central China, and Southwest China. The urban spatial forms were significantly associated with extreme heat events. Among them, the aggregation index was significantly positively associated with extreme heat events, while the mean shape index and largest patch index were significantly negatively associated with extreme heat events. Urban extreme heat events could be mitigated by increasing the compactness of urban center development, promoting boundary control of urban development, and controlling the size of individual construction land patches.