100 m resolution projection of future urban heat Island of a tropical Coastal City

Cities face rising heat exposure due to climate change, yet the extent to which urban heat islands (UHI) intensify relative to overall warming remains unclear. This study examines Singapore, a highly urbanised tropical coastal city, focusing on near-surface air temperature (Tas) and UHI intensity patterns under future climate and land-use scenarios using a 100 m urban modelling system (uSINGV). We analyse diurnal cycles and spatial distributions to understand the influence of sea breezes and assess cooling effects from one million additional trees. Key findings include: (1) although Tas increases significantly in future climate, island-wide UHI intensity remains comparable to historical periods during the day and decreases slightly at night; (2) island-wide UHI intensity exhibits a distinct diurnal pattern, positive at night driven by heat storage and reduced ventilation but negative during the day due to cooler marine air advected to urban areas by sea breezes; (3) one million additional trees provides modest spatial cooling without substantially altering island-wide Tas or UHI compared to the dominant influences of sea breezes and background warming. These results suggest that in coastal cities, mesoscale ventilation primarily controls daytime urban heat patterns and can locally suppress or reverse UHI despite rising temperatures.