Modeling Study of the Effects of Urbanization on Deep Convection, Precipitation, and Lightning Around the Houston Metropolitan Area

Urban development is one of the most significant anthropogenic modifications of land surface characteristics that can have serious impacts on weather and climate. In particular, the effects on clouds and precipitation through deep convection are complex because increased air pollution from social and industrial activities can affect clouds and precipitation through modification of radiative and microphysical processes, in addition to direct effects from modification of land surface properties. In this study, sensitivity experiments are conducted to estimate the first-order effects of urban land use and anthropogenic gas/aerosol emissions on regional meteorological phenomena using the NASA Unified Weather Research and Forecasting (NU-WRF) model, a fully coupled regional chemical transport model. Previous modeling and observational studies have extensively investigated these effects on precipitation. However, this study broadens the focus to include effects on lightning. This is made possible by a new implementation of the Goddard Chemistry Aerosols Radiation Transport model (GOCART) and the National Severe Storms Laboratory (NSSL) 2-moment microphysics scheme for cloud charging and discharging process parameterization in NU-WRF. To elucidate the complicated effects of urbanization, we set up four simulations, i.e., a control hindcast simulation, a simulation without anthropogenic gas/aerosol emissions, a simulation in which the urban land use is replaced by a natural mosaic, and a simulation that includes both. We use the Land Information System (LIS) model to adequately prepare initial conditions for the NU-WRF simulations that modify the land use mosaics. The hindcast and sensitivity simulations target the Houston metropolitan area in August 2022, which was in the Intensive Operational Period (IOP) of the Tracking Aerosol Convection interactions ExpeRiment (TRACER) field campaign. The Houston Lightning Mapping Array data are used to validate the flash extent density simulated in the control simulation.