Urban anthropogenic heat index derived from satellite data

Abstract

The increasing anthropogenic heat, which is emitted from human activities and energy consumption in urban areas and migrates to the atmosphere, significantly alters surface energy balances and the local climate and in turn generates urban heat islands (UHIs). Anthropogenic heat flux (AHF) has been estimated with energy balance residual and inventory methods. However, these methods have large uncertainty and fail to further explore the spatial distribution of anthropogenic heat at large scales due to limited data availability and the complexities of human activities, urban geometry, landscapes and building thermal properties. From the heat sources of the UHIs and based on thermodynamics, this study deduces that the AHE difference between urban and surrounding rural areas can be quantified as the residual of the heat for increasing UHIs and the heat difference from natural radiation between urban and rural areas. Thus, an urban anthropogenic heat index (UAHI) is proposed to quantify the contribution of AHF to UHIs, as a proxy of AHF. The UAHI is generated using the normalized differences in urban–rural land surface temperature (LST) and albedo derived from both Landsat and MODIS data. We investigate the spatial and temporal association between the UAHI and AHF in Beijing. The results demonstrated that the average annual UAHIs in Beijing ranged from 0.168 to 0.208 and steadily improved in the last decade. The UAHI can represent detailed spatial heterogeneity and temporal variations in AHF with correlation coefficients in the range from 35% to 50%. UAHI can also identify the dynamics of AHF hotspots and the heating and cooling sources in Beijing. Overall, the UAHI is a convincing indicator of the contribution of urban anthropogenic heat to UHIs, providing a new option for quantifying AHF dynamics and improving the knowledge of urban thermal environments.