INTEGRATING URBAN FOREST COOLING, THERMAL MONITORING, AND ECOLOGICALDYNAMICS FOR CLIMATE-RESILIENT CITIES

Urban forests are increasingly recognized as vital assets in mitigating urban heat stress, one of the most pressing climate-related hazards across Europe. Yet important uncertainties still constrain their effective design and management. A first challenge lies in the limited knowledge of how far cooling benefits extend beyond forest edges, and how this spatial reach depends on canopy density and structural features. To address this, a network of 169 air temperature sensors was deployed across nine urban forests in the Milan Metropolitan Area. Results showed that cooling extended up to 180 meters from forest cores, with reductions of up to –3.5 °C in mean temperature and –5.5 °C in maximum temperature during the hottest months, and that higher canopy density consistently amplified both the intensity and extent of this effect. A second limitation arises from the way urban cooling is typically measured. Most studies rely on satellite-derived Land Surface Temperature (LST), despite persistent doubts about its suitability as a proxy for the air temperature actually experienced by citizens. By comparing ground-based measurements against Landsat data, systematic biases were revealed: LST underestimated air temperature under cooler conditions, but shifted to substantial overestimation during extreme heat, with the bias intensifying alongside rising LST values. These errors were strongly mediated by vegetation cover and local microstructure, underscoring the need for caution in using LST to infer human thermal exposure. A third challenge concerns the establishment of urban forests themselves, since the long-term delivery of cooling depends on planting strategies adopted in the earliest phases. By testing different planting densities in mixed-species plantations, the study found that intermediate densities (≈2000 trees per hectare) optimized root biomass while balancing competition, creating conditions for healthier, more resilient stands. 8 Together, these studies address three interlinked gaps - spatial reach, measurement accuracy, and establishment strategy - while providing concrete evidence to overcome them. They demonstrate that the heat mitigation potential of urban forests depends not only on canopy structure, but also on how their performance is measured and how plantations are initially designed. Integrating precise, ground-level monitoring with ecologically informed planting practices emerges as a necessary pathway for delivering durable and equitable cooling benefits in increasingly heat-stressed urban environments.