Sensitivity of urban air warming to anthropogenic heat within a forcing-feedback framework
Energy consumption is increasing strikingly with population and economic development. The emitted anthropogenic heat is an important heating mechanism and influences the urban thermal environment and exacerbates the heat stress. Although numerous observational and simulation studies investigated the impacts of anthropogenic heat flux on urban climate at different spatial scales (from neighborhood-scale to global-scale), the key factors controlling the magnitude of the sensitivity of urban air temperature to anthropogenic heat flux and its spatiotemporal patterns remain elusive. Based on the urban climate model CLMU simulations, we employ a forcing-feedback framework to evaluate the sensitivity of urban air temperature to increase in anthropogenic heat (i.e., ΔTa/ΔQAH) and the associated feedback processes over the Contiguous United States (CONUS). The new framework is developed based on the energy budget of urban canopy air, which is similar to the global climate sensitivity analysis based on top-of-atmosphere energy balance. Key feedback mechanisms are identified to be associated with changes in surface temperatures (ΔTs) and aerodynamic conductance between the canopy air and the overlying atmosphere (Δca). The seasonal and diurnal cycle of ΔTa/ΔQAH and its controlling factors are further investigated. The results suggest that the framework may be broadly useful for unifying our understanding of how changes in anthropogenic heat may affect urban climate and human health.