Impacts of orography and urbanization on extreme precipitation event in Beijing during 2023

Abstract. The effects of urbanization and topographic uplift play significant roles in extreme precipitation events, and therefore in water management. In this study, we analyzed main impact factors in an extreme precipitation event that occurred during July 2023 in Beijing, using the Weather Research and Forecasting (WRF) model. The results showed that the main cause of this precipitation event was the residual forces of Typhoon Doksuri combined with water vapor transported from the subtropical high. The orographic effect altered the spatial pattern of accumulated precipitation throughout the simulation period by changing the local circulation, as the accumulated precipitation in the southwestern mountainous regions increased by 229.42 mm (41.34 %), and the precipitation in the plain areas decreased by 83.59 mm (43.50 %). The impact of the underlying urban surface led to accumulated precipitation in the southwestern mountainous regions of Beijing decreasing by 88.07 mm (15.87 %). Further analysis showed that topographical features caused the uplift of air masses in the mountainous regions and prevented the low-pressure system propagate northward, leading to significant enhancement of the convective intensity over Beijing and precipitation for a prolonged duration. The presence of urban surfaces contributed to reductions in the latent heat flux and wind speed, resulting in decreased energy transfer to the southwestern mountainous regions via easterly winds. This reduction in energy suppressed convective activity and subsequently led to a decrease in precipitation in these regions. As extreme precipitation events become more frequent, the comprehensive research into such events may help with prevention and the response to similar events in the future.