High-Resolution Modelling of Urban Extreme Rainfall in Singapore

Singapore, a tropical island city-state located near the equator, experiences a year-round warm and humid climate. Its specific location and rapid urbanization make it particularly susceptible to extreme weather events, which have the potential to adversely impact large populations. Intense rainfall, accompanied by subsequent flash floods, ranks among the most severe local natural hazards experienced. Weather phenomena contributing to heavy rainfall in Singapore include localized thunderstorms, Sumatra squalls, and monsoon surges. Modelling studies suggest that urbanization significantly influences the weather in coastal cities like Singapore by altering land-atmosphere dynamics. For example, urban environments promote localized wind convergence zones that, together with differential surface heating across disparate land types, can enhance convection and increase the likelihood of heavy rainfall. This study explores a few case studies of heavy rainfall over Singapore, triggered mainly by afternoon localized wind convergence. The analysis is conducted using the uSINGV model, a customized urban version of the operational Numerical Weather Prediction system SINGV for Singapore and the region developed at CCRS/MSS based on the UK Met Office Unified Model (UM) Regional Atmosphere and Land configuration. The results will demonstrate the performance of 100-meter high-resolution model simulations compared to larger resolutions traditionally used (300 m and 1.5 km). The primary aim is to evaluate the model’s capability at different resolutions to simulate the processes driving the initiation, organization, and intensification of deep convection over urbanized regions linked to extreme rainfall events. Findings from this study will inform the advancement of urban-scale numerical modelling, enabling the provision of more detailed weather and climate insights to benefit society.

Key words: Urban weather and climate, urban modelling, extreme rainfall, uSINGV model