Quantifying the diurnal park cool island effect of Viharamahadevi Park, Colombo, Sri Lanka

Abstract

Rapid urbanisation in Colombo has exacerbated the Urban Heat Island (UHI) effect, yet localised data on mitigation strategies remains scarce. This study quantifies the diurnal Park Cool Island Intensity (PCII) of Viharamahadevi Park, critically analysing the spatial decay of cooling into the surrounding urban fabric. An intensive in-situ measurement campaign was conducted over seven clear-sky days at four synoptic intervals (06:30 AM – 07:30 AM, 12:30 PM – 01:30 PM, 03:30 PM – 04:30 PM, 06:30 PM – 07:30 PM), utilising a fixed interior station and mobile transects extending 350 meters outward. Results validate a statistically significant cooling effect (p<0.05) throughout the diurnal cycle. The PCII peaked from 12:30 PM to 1:30 PM, achieving a maximum intensity of 4.13 °C at a distance of 300 meters. Cooling remained robust in the morning (3.92 °C), but diminished significantly post-sunset (0.76 °C) as urban thermal inertia released stored heat. These findings characterise the park as a vital climate moderator rather than a simple amenity. This study provides essential empirical evidence for Landscape Architects, arguing that preserving large-scale green infrastructure is a significant and essential strategy for ensuring Colombo's thermal resilience.