Impact of urbanization on the simulation of extreme rainfall in the city of Jeddah, Saudi Arabia

The city of Jeddah, Kingdom of Saudi Arabia is characterized by a hot and arid desert climate. Occasionally, however, extreme precipitation events have led to flooding that caused extensive damage in human life and infrastructure. This study investigates the effect of incorporating an urban canopy model and urban land cover when simulating severe weather events over Jeddah using the Weather Research and Forecasting (WRF) model at a convective-permitting scale (1.5-km resolution). Two experiments were conducted for 10 heavy rainfall events associated with the dominant large-scale patterns favoring convection over Jeddah: (i) an “urban” experiment included the urban canopy model and modern-day land cover, and (ii) a “desert” experiment replaced the city area with its pre-settlement, natural land cover. The results suggest that urbanization plays an important role in modifying rainfall around city area. The “urban” experiment enhances the amount of rainfall by 26% on average over the Jeddah city area comparing to the “desert” experiment in these extreme events. The changes in model-simulated precipitation are primarily tied to a nocturnal heat island effect that modifies the planetary boundary layer and atmospheric instability of the convective events.