Spatiotemporal scale-dependent effects of urban morphology on meteorology: A case study in Beijing using observations and simulations

Abstract

Urban morphology has a great impact on urban meteorology, but the scaling effects in the underlying relationships have seen little research. In this work, the controls of building and vegetation morphology on urban meteorology at different spatial (30 m, 90 m, 300 m, 500 m, 1 km) and temporal (diurnal, seasonal) scales are explored, using in-situ observations and WRF (Weather Research and Forecast) modeling. The random forest method is employed to derive the importance of morphological indicators for meteorology, based on in-situ observations from weather stations. This work reaches the following conclusions. (1) Morphological factors have the largest impacts at 30-m scale, and are the strongest influences on air temperature (Ta), wind speed (WS) and relative humidity (RH). The sky view factor (SVF) is the most important of these factors at the 30-m scale. Vegetation strongly affects Ta and RH in summer at scales of >90 m. (2) The main indicators during daytime and night-time are different: vegetation has a more impact on Ta during the night than during the day in summer, while SVF is the main factor controlling Ta at night during winter. Morphology has greater influence on diurnal variations in Ta at scales of <100 m. (3) The WRF simulation is consistent with observations and reveals that building height is the most important indicator for WS. This is because building height affects the roughness length for momentum (Z0m), which is the main factor influencing WS. This work can help in urban planning, to improve the urban thermal and wind environment.