Study on the Impact and Mechanism of underlying surface morphology on a local heavy rainfall event in Beijing urban area

The rapid development of urbanization has led to a rapid succession of underlying surfaces, which affects surface energy balance and local meteorological environment by altering properties such as dynamic conduction and hydraulic infiltration, and may significantly alter local precipitation distribution. To investigate the potential impact of urban three-dimensional morphological characteristics on precipitation process in Beijing area, this study first analyzed the composition of Beijing’s underlying surface categories by local climate zone (LCZ) method and the applicability of LCZ grid resolution. After that, the LCZ classification data is diverted into the mesoscale numerical weather prediction model WRF, in order to conduct simulation experiments on a heavy rainfall event occurred in Beijing area on August 20, 2023. The results show that: (1) The underlying surface of buildings in the urban area of Beijing accounts for 52.0% of the total area, mainly consisting of open mid-rise buildings (LCZ5), open high-rise buildings (LCZ4), and dense low rise buildings (LCZ3). Using a grid resolution of 500 m or higher for the semivariogram model can more accurately characterize the distribution characteristics of building morphology; (2) The impact of Beijing's urban building morphology on the maximum precipitation amount and hourly rainfall intensity during this precipitation process can reach -16.1% to 21.1% and -22.9% to 15.0%, respectively. Overall, urban morphologies characterized by high building density and vertical scale are conducive to precipitation enhancement (3) Altering the underlying surface morphology has multifaceted effects on local precipitation process. Increasing urban building density or vertical height can enhance low-level thermal convergence, accumulate convective instability energy, and strengthen local vertical upward movement, which are beneficial for precipitation development and intensification. At the same time, it may also weaken the local water vapor supply due to the increase in surface roughness and the proportion of impermeable underlying surfaces, which is detrimental to precipitation development. These complex mechanisms may lead to uncertainty in the comprehensive impact of urban three-dimensional morphological characteristics on precipitation process. The findings of this study can provide reference for refined meteorological services and urban planning.