Spatiotemporal patterns and influencing factors of remotely sensed regional heat islands from 2001 to 2020 in Zhengzhou Metropolitan area

Developing urban agglomerations and establishing metropolitan areas have led to urban heat islands breaking through the original single urban scale to form regional heat islands (RHIs) with a large influencing range in recent decades. However, the spatial and temporal patterns of regional heat islands and their evolution are still poorly understood, which limit the decisionmakers to make more informed decisions to improve the regional environment. We selected Zhengzhou Metropolitan Area as the case study with MOD11A2 surface temperature products from 2001 to 2020 to describe the intensity and range of RHIs by calculating the relative surface temperature. Then multi-scale spatiotemporal patterns and characteristics of RHI were identified with the help of Sen + MK trend analysis, contribution index analysis and standard deviation ellipse analysis, and the main driving factors of RHI and their internal relations were discussed by correlation analysis and Random Forest (RF) regression analysis. We found that (1) RHIs in the Zhengzhou Metropolitan Area increased from 2970 km2 in 2001 to 5776 km2 in 2020, a growth rate of about 0.46% per year. The contributions of each county-level region to the RHI differ significantly. The positive contribution areas include Zhengzhou City, Kaifeng City, Zhongmu County, and Xinzheng City, while the negative areas include Lankao County, Fengqiu County, and Huixian City. (2) There are two aggregated RHIs within the metropolitan area. Xinxiang City and Jiaozuo City formed a complete, cross-city, large-area RHI from 2001 to 2005, accounting for 63% of the total area. The RHI in Zhengzhou, Kaifeng, and Xuchang Cities developed in an all-round, cross-regional, and rapid manner from 2010 to 2020, accounting for 78% of the total area. (3) Different land cover types have varying effects on RHIs. The cooling effect of forests and water is better than that of grasslands. Human and social factors positively affect the RHI, vegetation cover strongly inhibits the RHI, and meteorological factors have less influence. The methods and results of this study play a significant role in analyzing urban construction status, optimizing urban spatial layouts, and improving urban thermal environments of the Zhengzhou Metropolitan Area. Insights into thermal environment research and practice are also provided for other urban agglomerations.