Diurnal variations in cooling effects of urban parks based on ECOSTRESS data: A case study of Beijing

Urban parks create cooler microclimates, mitigating urban heat island effects, but diurnal variations in cooling remain unclear. We analyzed 97 parks within Beijing's fifth ring road using ECOSTRESS land surface temperature data to assess cooling from both maximum and cumulative perspectives. Results show that park cooling is stronger during the daytime, with the maximum median cooling area and efficiency at 51.50 ha and 3.56, respectively, compared to the nighttime minimum values of 30.21 ha and 1.97. Cumulative cooling is highest in the early afternoon (intensity 0.011, gradient 0.50 °C) and lowest at night (intensity 0.005, gradient 0.10 °C). Dominant factors influencing daytime cooling are park area, shape index, and blue-green landscapes. Specifically, park area is positively correlated with the cooling area, while water index is positively correlated with cumulative cooling indicators, and the impact of shape and vegetation indices on cooling is unstable. At night, landscape design has little effect, and poorly designed water bodies may cause warming; park area becomes the key factor, positively associated with both cooling area and cumulative cooling. The threshold for cooling efficiency in Beijing is 24 ha during the day, increasing to 29 ha at night. These findings provide valuable insights for sustainable urban park planning.