Wang, Linying; Sun, Ting; Zhou, Wenyu; Liu, Maofeng; Li, Dan; (2023) Decipher the sensitivity of urban canopy air temperature to anthropogenic heat flux with a forcing-feedback framework. Environmental Research Letters 10.1088/1748-9326/ace7e0. (In press).

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Abstract

The sensitivity of urban canopy air temperature (Ta) to anthropogenic heat flux (QAH) is known to vary with space and time, but the key factors controlling such spatiotemporal variabilities remain elusive. To quantify the contributions of different physical processes to the magnitude and variability of ∆Ta/∆QAH (where ∆ represents a change), we develop a forcing-feedback framework based on the energy budget of air within the urban canopy layer and apply it to diagnosing ∆Ta/∆QAH simulated by the Community Land Model Urban (CLMU) over the contiguous United States (CONUS). In summer, the median ∆Ta/∆QAH is around 0.01 K (W m-2)-1over CONUS. Besides the direct effect of QAH on Ta, there are important feedbacks through changes in the surface temperature, the atmosphere-canopy air heat conductance (ca), and the surface-canopy air heat conductance. The positive and negative feedbacks nearly cancel each other and ∆Ta/∆QAH is mostly controlled by the direct effect in summer. In winter, ∆Ta/∆QAH becomes stronger, with the median value increased by about 20% due to weakened negative feedback associated with ca. The spatial and temporal (both seasonal and diurnal) of ∆Ta/∆QAH and the nonlinear response of ∆Ta to ∆QAH are strongly related to the variability of ca, highlighting the importance of correctly parameterizing convective heat transfer in urban canopy models.

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