Triggering and Enhancement Mechanisms of Extreme Precipitation over the Complex Terrain in the Central Loess Plateau

Abstract

Using the WRF model, this study conducts numerical simulations to investigate the triggering and enhancement mechanisms of an extreme precipitation event over the Central Loess Plateau. By performing comparative experiments under real and smoothed terrain conditions, combined with qualitative observational validation using sparse station data and diagnostic analysis, the study reveals the physical processes responsible for the initiation of deep convection and precipitation intensification over complex terrain. The results show that the hilly and gully terrain forces the warm and moist airflow on the periphery of the subtropical high to ascend and converge, leading to a notable advancement of convective initiation by approximately two hours and a significant intensification of rainfall. Convective cells generated over multiple hills tend to converge and rapidly merge into a mesoscale convective system under the influence of the low-level wind field, resulting in a rapid expansion of precipitation intensity and coverage. The peak hourly rainfall reaches 40 - 60 mm/h under real terrain, compared with less than 20 mm/h under smoothed terrain, and the maximum accumulated rainfall increases by about 2.1 times. This study refines the understanding of the development processes of extreme precipitation under the influence of complex topography over the Loess Plateau and provides a scientific basis for improving local heavy rainfall forecasting and disaster prevention.