Urbanisation as an amplifier of an extreme rainfall event over Jakarta, Indonesia

Abstract Jakarta experienced an extreme rainfall event on 31 December 2019, which led to widespread flooding and important socioeconomic impacts. We examine whether urbanisation amplified this extreme rainfall event using the convection-permitting Weather Research and Forecasting (WRF) model and simulations with both urban and natural land cover. To robustly assess model sensitivity, we conducted simulations spanning multiple combinations of physical parameterisations in the WRF model. The large-scale mechanisms which led to the extreme rainfall, including the cross-equatorial northerly surge and mesoscale convective systems, were not impacted by the existence of Jakarta. However, the presence of the city did affect the surface energy fluxes, moisture transport, and low-level moisture convergence, and these led to a substantial increase in the rainfall intensity, a result largely independent of how WRF was configured. Our findings suggest that there may be value in exploring whether urban planning, particularly in rapidly growing cities like Jakarta and Nusantara (Borneo), might ameliorate some meteorological hazards.