Assessing the influence of aerosols on urban precipitation: A sensitivity study of Dallas–Fort Worth

Urbanization influences tropospheric circulation, particularly around large cities. While the Urban Heat Island (UHI) effect on regional rainfall is well-documented, larger uncertainties still remain for urban aerosol’s effect on precipitation. This study employs the Weather Research and Forecasting model with Chemistry (WRF-Chem) to examine aerosol-driven modifications to urban precipitation in Dallas–Fort Worth, TX, during both a deep convective and a stratiform event. We generate a WRF-Chem ensemble that explores multiple scenarios, including simulations with and without atmospheric chemistry, aerosols, land use perturbations, and altered background emissions, enabling the isolation of key physical and chemical drivers of rainfall variability. From this analysis it emerges that urban and background aerosols exert a significant influence on precipitation affecting cloud life-cycle and storm dynamics through changes in cloud condensation nuclei concentrations, cloud water paths, latent heat fluxes, and vertical velocities. During the analyzed deep convective event, numerous ultrafine anthropogenic aerosols activated in the lower atmosphere, forming a transient neutral layer beneath an intrusion of dry air. This process initially suppressed convection; however, as the system evolved, convection progressively intensified through enhanced mixed-phase processes, resulting in a significant increase in urban precipitation. The absence of this aerosol-driven mechanism in the simulation without chemistry led to an underestimation of urban rainfall intensity. In contrast, no significant changes are found for the stratiform event due to land-use perturbation and aerosols. These findings highlight the importance of aerosol-cloud interactions in urban meteorology and provide insights for potentially improving weather forecasting in densely populated regions.