Asymmetric influence of urban morphology changes on land surface temperature between daytime and nighttime

Urban development is not solely about the outward expansion of city boundaries but also involves internal renewal within urban areas. While the warming effect of urban expansion is well-documented, the thermal impact of various urban morphology changes remains less clear. Our study investigates the changes in land surface temperature (LST) associated with urbanization, utilizing Local Climate Zone (LCZ) time-series data and satellite-derived LST measurements from three major Chinese urban agglomerations. Time series analysis was applied to examine LST variations over the period from 2003 to 2020. Our research indicates that urban renewal, predominantly characterized by vertical development, exerts an asymmetric effect on urban temperatures: it mitigates urban warming during daytime (-0.13±0.067 °C(mean ± se)) but intensifies it at night (0.20±0.02 °C (mean ± se)). The effect of urban expansion on urban warming is markedly more pronounced during the day (0.55±0.041 °C (mean ± se)) than at night (0.20±0.015 °C (mean ± se)). At the city scale, changes in urban morphology generally contribute to a warming effect, both diurnally and nocturnally. Urban expansion is identified as the primary urban morphology change contributing to the rise in LST. However, the divergent impacts of vertical development, which is likely to account for a larger share of future urbanization, must not be underestimated.