Spatial and temporal characteristics of near-surface air temperature across local climate zones in a tropical city

The present study examines the temporal and spatial variability of near-surface air temperature and the canopy layer urban heat island (UHI) in Singapore. Observations collected at 20 locations across the island city-state and during 6 years make this one of the most extensive studies carried out in a tropical city. Local climate zones (LCZs), defined as urban built and rural land cover types which produce a unique air temperature response, are used to standardize intersite comparison. The results show that the choice of the rural reference can affect the night-time UHI magnitude by up to 2 degrees C under "ideal" (dry, clear, calm) conditions. The most frequently observed median UHI magnitude increases from 2.8 during all-weather to 3.7 degrees C during "ideal" conditions, respectively. A seasonality is present with lowest (highest) mean all-weather values of similar to 2.0 degrees C (similar to 3.3 degrees C), observed during the wet (dry) December-January (April-October) period. Mean night-time UHI intensity across seven built-type LCZs ranges between 1.8 and 3.5 degrees C (2.5 and 4.3 degrees C) for all-weather ("ideal") conditions. Corresponding daily values are 1.1-2.3 degrees C (1.5-2.7 degrees C). The lowest (highest) night-time magnitudes are associated with open low-rise LCZ 6 (compact high-rise LCZ 1) built type. In the middle of the day LCZ 1 can experience a cool island effect. The average UHI values presented here give an indication of the extra warmth experienced in the built-up spaces of Singapore relative to one possible rural reference land cover type (scattered trees LCZ B). Highest daytime heat exposure is observed in LCZs 3 and 8 which are characterized by low building heights, high impervious surface fraction and lack of vegetation. The present results can be used to support the development and evaluation of urban climate models, develop urban planning policies and improve local weather forecasts and the delivery of integrated urban services.