Quantifying seasonal and diurnal contributions of urban landscapes to heat energy dynamics

Cooling energy consumption in urban areas is affected significantly by the dynamics of urban heat flux. However, we still lack a clear understanding of the quantitative contribution rate and underlying mechanism of typical urban landscapes to urban heat dynamics, especially in seasonal and diurnal patterns. Here we used a thermal infrared camera and portable meteorological instruments to examine the sensible heat flux (SHF) changes of five typical urban landscapes in Beijing based on surface temperature and concurrent microclimate conditions. Diurnal and seasonal variations of SHF were quantified by comparing changes in forenoon and afternoon in different seasons. Results showed that (1) walls and roads act as heat-source, while forests and water act as heat-sink in all seasons; however, grassland served as heat-sink in summer and spring-autumn, but it becomes a heat-source in winter. (2) The seasonal variation of sensible heat flux of the wall is the greatest, followed by water, while that of trees is the smallest. Besides, the highest sensible heat flux and the maximum variation among typical urban landscapes occur between noon and 2:00 pm. (3) The numerical contribution rate of typical landscapes to sensible heat flux varies with daytime (forenoon and afternoon) and seasonal changes, and these ratios can be used as parameters to adjust the numerical models to obtain more reliable results in surface-energy-flux-related studies. The results of this study can provide a reference for explaining controversial findings based on remote-sensing data, and provide insights into revealing the sensible heat flux mechanism of typical urban landscapes and cooling energy conservation in cities.