Designing Climate-Resilient School playgrounds: A Microclimatic Assessment of Outdoor Thermal Stress in a Mediterranean City (Coimbra, Portugal)

Abstract

Outdoor thermal comfort in Mediterranean school playgrounds is increasingly compromised by climate change, 20th-century morphological legacies, and inadequate vegetation planning. This study quantifies outdoor thermal conditions at José Falcão High School (Coimbra, Portugal) using the SOLWEIG microclimatic model within the UMEP framework. High-resolution LiDAR-derived morphology (0.3 m) and in-situ meteorological forcing for 9 May 2024 supported hourly simulations of mean radiant temperature (Tmrt), Universal Thermal Climate Index (UTCI), and ground surface temperature (Ts) across nine Points of Interest. Results reveal a daily-averaged Tmrt gradient of nearly 25 °C between dense canopies (≈31 °C beneath Eriobotrya japonica and Tilia spp.) and the asphalt sports field (≈51 °C). The pooled regression UTCI = 15.43 + 0.349 · Tmrt (R² = 0.94) demonstrates that, under clear-sky conditions, Tmrt alone explains 94% of intra-site UTCI variability. Asphalt sports areas exceed the 55 °C ASTM C1055-20 cutaneous burn-risk threshold for three consecutive hours and accumulate up to 11 hours of strong-to-very-strong heat stress. Hence, a clear accessibility paradox emerges: the most thermally favourable spaces are institutionally restricted. Findings support a hybrid green–grey adaptation strategy combining the opening of existing thermal refugia, asphalt-to-canopy conversion with broadleaved deciduous species, cool-pavement coatings, and vegetated shade structures.