Simulation of the Urbanization Impact on Precipitation of Landfalling Tropical Cyclone Nida(2016)

For more than half a century, changes in atmosphere induced by the land use change associated with urbanization have drawn increasing attention. However, it is still unclear how urbanization affects landfalling tropical cyclone (TC) precipitation, which may complicate precipitation processes during TC landfalls. TC precipitation is always hard to predict accurately, which still deserves further research.Several numerical experiments of tropical cyclone Nida(2016) making landfall in Guangdong Province are conducted using the Advanced Research Weather Research and Forecast system (WRF) to evaluate the urbanization effects on TC precipitation during its landfall. Specifically, WRF is coupled with the urban canopy model (UCM), and different land use data (new and old) are used for sensitive experiments. The tropical cyclone Nida(2016) landed around Shenzhen, Guangdong Province on 1 August 2016. The model performance on the track, intensity and precipitation of tropical cyclone Nida is evaluated.Both simulated spatial distribution of 6-hour (from 2200 UTC 1 Aug to 0400 UTC 2 Aug) accumulated precipitation are quite consistent with observations, indicating that the coupled UCM model simulation results are credible. Tracks and accumulated precipitation of the typhoon during landfall can be reproduced reasonably well. No significant difference of simulated TC tracks is found between experiments with and without the updated underlying surface and the coupling of the UCM, indicating that the land use change cannot strikingly affect the track. Although simulations fail to accurately capture the post landfalling intensity changes, storms simulated in experiments including the UCM and latest land use data show more rapid weakening rates after landfall, which are closer to observations. Spatial distributions of simulated 6-hour accumulated precipitation are quite consistent with observations. Furthermore, urban canopy tends to reduce TC precipitation in the urban region while the underlying surface change due to urbanization tends to increase TC precipitation. Urban canopy diminishes vapor transports and corresponding convection, resulting in a decrease in accumulated precipitation. By contrast, land use change due to urbanization decelerates the near-surface wind velocity and decreases surface latent heat fluxes, but strengthens updrafts in the urban region and increases convective available potential energy. As a result, the land use change still leads to enhancement of TC precipitation.These results show that land use change due to urbanization (use of urban canopy) tends to limit TC precipitation after landfall. The rainfall enhancement by land use change due to urbanization is partly offset by the suppression due to use of urban canopy. This will significantly affect the precipitation process of landfalling TCs, and should be taken into account in numerical simulations.