Multi-city local climate zone mapping and its quantitative applications on measuring surface urban heat Island in China

Local climate zone (LCZ) provides a detailed classification system for building types in urban areas and offers a unified standard for block-scale surface urban heat island (SUHI) studies. However, LCZ mapping methods with high classification accuracy for global applicability, and multi-city comparison of SUHI based on LCZ are still needed. In this study, we developed a transferable LCZ mapping framework for 30 China cities at 120 m by using multi-source remote sensing and GIS data, and random forest model. The gap-filled LST for 21 cities among 30 cities with diverse urbanized levels and climate conditions were generated, utilizing Landsat 8 data, LST retrieval algorithm and gap-filling method. Spatial patterns of SUHI intensity across climate zones and cities of different sizes were explored, and the impacts of urban morphology on SUHI in built-up LCZs were analyzed using the boosted regression trees model. Results showed that the proposed LCZ mapping framework achieved high accuracy in China cities, with overall accuracy from 0.86 to 0.93. Its robustness and transferability were further demonstrated in three cities in the United States with overall accuracy of 0.91 to 0.93. LST gap-filling method also performed well, with R from 0.71 to 0.91 and RMSE from 1.86 °C to 3.59 °C, respectively. Our multi-city assessment revealed consistent patterns of SUHI in LCZs across climate zones: compact mid-rise (LCZ 2) and large low-rise (LCZ 8) had the highest SUHI intensity, while sparsely built (LCZ 9) and open low-rise (LCZ 6) had the lowest values. Moreover, LCZ 2 tended to have higher SUHI intensity in colder climate regions, while LCZ 8 exhibited higher values in warmer climate regions. City size also influenced SUHI effect in built-up LCZs, with large cities exhibiting SUHI intensity up to 1 °C higher than small cities. Additionally, vegetation exhibited the largest of relative importance (20 % to 68 %) which impacted SUHI intensity in built-up LCZs, with a higher value in cold cities compared to warm cities. Impervious or building surface fraction also accounted for 13 % to 45 % of the SUHI contribution across LCZs, with relative importance about 3 % to 10 % greater in warmer and larger cities. The findings of this study can be useful in developing urban planning policies for intra-city SUHI mitigation, and our transferable LCZ mapping framework can be applied to other global cities for SUHI studies.