Longer and Hotter Summers Related to Urbanization on a South China Sea Island

The cycle of seasons is an essential component of weather and climatic systems. This study utilised observational data from a meteorological station on an island in South China Sea spanning 1961 to 2020, along with ERA5 reanalysis data, to explore the variation of the season cycles and the thermal comfort characteristics on the island. The observed data revealed that the onset of summer on the island became earlier each year, whereas the onset of autumn has gradually delayed, leading to an increasing trend in the length of summer. Urbanization played an important role in elevating local temperatures and extending summer duration. The thermal comfort index exhibited a clear upward trend annually, reflecting a shift towards warmer and less comfortable conditions due to the urbanization. From 1961 to 2020, the annual average thermal comfort index indicated that 36 years (60%) were characterised by hot discomfort, whereas 24 years (40%) were within the comfortable range. The number of comfortable days per year on the island showed a declining trend. The urbanization significantly influenced thermal comfort levels on the island, contributing to an annual increase in the number of hot discomfort days. However, the reanalysis data did not reflect the actual observed changes in the comfort characteristics on the island.