Quantifying the Impacts of High-Resolution Urban Information on the Urban Thermal Environment

Detailed urban information, including land use/land cover (LULC), anthropogenic heat (AH) release, and urban canopy parameters (UCP), play critical roles in meteorological field simulations. It is particularly relevant for the Weather Research and Forecasting (WRF) model coupled with the single-layer urban canopy model (SLUCM). Thus, we develop high-resolution LULC, AH, and UCP data sets for Nanjing, a megacity in China, and conduct a series of numerical experiments with WRF/SLUCM to evaluate the impacts of urban parameters on the urban thermal environment. Model simulations with LULC scenarios have good agreement with the observed 2-m temperature (T-2) with a correlation coefficient of around 0.85, and present strong spatial homogeneity due to the more realistic representation of urban categories. The LULC change directly decreases the surface wind speed and increases (decreases) the sensible (latent) heat flux (Q(sH) (Q(LH))) in urban areas during the daytime; meanwhile increases Q(sH) and releases ground heat storage (Q(GH)) during the nighttime, resulting in urban warming by 0.91 degrees C in urban areas, compared with the control simulation (CTL) that does not take into account urban surfaces. In the LULC experiments combined with the UCP or AH, the UCP change enhances Q(sH) and releases more Q(GH) during nighttime, which increases T-2 by 0.13 degrees C relative to LULC simulation. Also, the UCP effect reduces surface roughness and increases the width of the urban canopy, resulting in slightly enhanced wind speed, which is favorable for a warming environment in the urban area; the AH change contributes to increasing T-2 by 0.19 degrees C through directly enhancing Q(sH) relative to LULC simulation. AH combined with the UCP further strengthens the UCP effect in the urban area. Overall, the influence of urban parameters on the T-2 is more pronounced during nighttime than daytime, which presents a decreasing trend with an increase in wind speed and spatial humidity in the urban area.