Irregular anisotropy in surface urban heat island footprint

• Identifies the irregular anisotropy of the surface urban heat footprint • Proposes an AIA model to reduce the bias in footprint estimation • Reveals unequal proportional differences between footprint directions • Improves spatial heterogeneity assessment of the footprint by 1.1%–44.1% Footprint and intensity are key indicators for quantitatively analyzing the characteristics of the SUHI effect. Currently, methods based on angle-segmentation and anisotropy have been developed to estimate footprints, but are still greatly challenged by spatial heterogeneity, especially for directional difference. Therefore, this study develops an adaptive irregular anisotropy (AIA) model to explore the irregular anisotropy in the SUHI effect. The developed AIA model is used to assess the SUHI effect in Sydney, Melbourne, Brisbane, Perth, and Adelaide, Australia. The model dynamically adjusts sector divisions based on the q value to maximize temperature differences between sectors. The results show that the AIA model displays reliable directional adaptability. The SUHI footprint ratio extracted by the AIA model generally ranges from 0 to 8 times the urban area. It is more concentrated in areas with a high proportion of artificial surfaces or natural bare land. The AIA model also reduces the mean bias in SUHI intensity estimates. Furthermore, compared with other anisotropy-based extraction methods, the AIA model improves the q value by 1.1% to 44.1%. In summary, this study provides an adaptive SUHI effect estimation method, which facilitates the development of SUHI mitigation strategies.