Designing for mild winters: evidence-based thermal comfort benchmarks from urban parks in a sub-tropical city

Outdoor thermal comfort in the cool season remains under-specified for humid subtropical cities. We conducted a winter field study across four urban parks in Hong Kong, collecting 611 paired questionnaire-microclimate records (December-March). On-site measurements (air temperature, globe temperature, humidity, wind) were linked at 60-s resolution to Cantonese surveys of thermal sensation. Neutral temperature was estimated with ordinary least squares and confirmed with proportional-odds models; 2,000-fold bootstrap confidence intervals and 0.5 °C binned regressions quantified uncertainty and sensitivity. Whole-sample neutral points were Air Temperature (Ta) 20.6 °C (95% CI 19.7–21.6 °C), Physiological Equivalent Temperature (PET) 23.7 °C (22.2–25.8 °C), and Universal Thermal Climate Index (UTCI) 20.7 °C (19.3–22.5 °C). Ta was the strongest single predictor of mean thermal sensation in binned fits (R² = 0.62), followed by UTCI (R² = 0.54) and PET (R²= 0.22). Females showed slightly steeper vote-temperature slopes but similar neutralities to males. Age had a clear effect: neutral UTCI rose from 18.6 °C (< 60 years) to 23.1 °C (> 75 years), with flatter slopes in older cohorts. Park type also mattered. Neutral PET and UTCI were about 2 °C warmer in larger, greener district parks than in compact street parks, consistent with higher sky-view and lower turbulence. Robustness checks (ordinal-logit, trimmed bins, meteorological filtering) shifted whole-sample neutralities by ≤ 0.4 °C. We propose UTCI 20–22 °C as a practical winter design target for subtropical parks, complemented by 2–3 °C warmer micro-niches for older users through solar access and wind shelter. These calibrated benchmarks support climate-responsive park design that sustains outdoor use through mild winters in ageing, high-density cities.