Impact of urbanization patterns on the local climate of a tropical city, Singapore: An ensemble study

The effect of urbanization and urbanization pattern on the thermal environment and local rainfall is investigated in the tropical coastal city, Singapore. The Weather Research and Forecasting (WRF) model is employed with 5 one-way nested domains and the highest horizontal resolution is 300 m. The urban effect is taken into account by a single-layer urban canopy model. Several scenarios with idealized urbanization patterns are designed and simulated for an ensemble of 28 members. In the asymmetric urbanization scenarios, in which either the southern or northern part of Singapore is urbanized while the other part is forest, the magnitude of urban heat island (UHI) intensity is higher than that in the symmetric urbanization scenario, in which the urban and forest land use is homogeneously distributed in Singapore. The anthropogenic heat (AH) associated with the urban areas will exacerbate the UHI intensity. Most of the rainfall in the examined cases occurs from late morning to afternoon when the sea breeze blows northeastward. The results suggest that sea breezes have stronger influence on the rainfall than the urbanization pattern since the downwind part always gets more rainfall than the upwind part. The urbanization and associated AH can have two opposite effects on the rainfall amount: increasing rainfall through increasing buoyancy by AH and decreasing rainfall through reducing evaporation by converting greenery to impervious surfaces. The ultimate effect is dependent on the relative strength of these two influences