High-spatial-resolution mapping of annual anthropogenic heat flux in the Beijing-Tianjin-Hebei urban agglomeration using the CUNTLI-based inventory method

Multisource anthropogenic heat flux (AHF) data provide valuable insights into urban climate, air quality, and human health. However, most AHF products at regional or global scales suffer from coarse spatial resolution. Meanwhile, the lack of high-spatial-resolution blue-band nighttime light (NTL) observations limits the updating of AHF maps derived from NTL-based inventory methods in increasingly light-emitting diode (LED)-dominated urban environments. Conventional NTL datasets containing mainly green-red-near-infrared spectral information may lead to biased AHF estimates because of their limited sensitivity to blue light in LED-dominated urban areas. The newly available 40 m SDGSAT-1 multispectral NTL data, with blue, green, red and near-infrared bands, provide opportunity to address these limitations. Here, we propose a generalizable approach: a Comprehensive Urban NTL Index (CUNTLI)-based inventory method, which primarily integrates SDGSAT-1 multispectral NTL imagery, urban form, and urban function data to generate the annual AHF at 40 m spatial resolution. Applying our method to the Beijing-Tianjin-Hebei region of China, we characterized the spatial distribution of AHF in 2021 therein and quantified the contribution of blue-band information to AHF estimation. Our findings show that (1) NTL feature, incorporating the blue band with other spectral bands, exhibited strong correlations with most heat components at the county level (R 2 > 0.5); (2) the final gridded AHF product showed good agreement with inventory-derived anthropogenic heat estimates (Pearson's r = 0.84; MAE = 1.58 W/m 2 ), with stronger associations with nighttime land surface temperature at both pixel and land-use scales, and improved discrimination of built-type local climate zones compared to conventional NTL-based products; and (3) our gridded AHF maps could reveal spatial heterogeneity in inter-urban and intra-urban scales and their characteristics from various heat sectors were distinct. These findings underscore the significance of the blue lighting information in AHF estimation and highlight the potential applications of our AHF products for fine-scale urban studies.