Enhanced short-duration precipitation and divergent rainfall spatial patterns of Typhoon Nida (2016) under the impact of urbanization

Abstract

Tropical cyclones (TCs), when approaching coasts and after landfalling, may exhibit significant interactions with heavily urbanized surfaces. Despite numerous studies, the effects of urbanization on TCs and their landfalling processes remain insufficiently explored. Typhoon Nida, landfalling in the Pearl River Delta region on August 1, 2016, provides an interesting case for us to revisit the issue. We use the Weather Research and Forecasting model in paired numerical experiments to isolate the urban effects. Urban land cover has a small impact on the track and the intensity of the typhoon. Urban effect on landfalling precipitation in this event is mainly profound in changing rainfall spatial patterns rather than the average rain rate. The accumulated precipitation and the rain rate of the major urban area are reduced. During different stages of the TC rapid movement, enhanced precipitation is observed at the downwind and upwind regions within a short duration. The increase in surface temperature and sensible heat flux enhances thermal circulation; however, this effect is weakened under the strong synoptic background during landfall. Increasing urban surface roughness decelerates airflows and enhances updrafts along the urban boundaries, producing enhanced water vapor convergence and bifurcated winds, increasing downwind precipitation with a maximum value of 46.17 mm in 6 h. Throughout the TC rapid movement, urban modification on precipitation patterns displays high spatial variability over short periods. The study raises concern about more extreme hazards occurring in multiple locations over urban areas caused by urban-induced TC rainfall redistribution.