Microclimate, Thermal Stress, and Nature‑Based Solutions in Ioannina, Greece: An Integrated Field and Simulation Approach

Ioannina, a mid‑sized city in northwestern Greece, presents a highly heterogeneous urban landscape shaped by its long historical evolution, dense medieval core, and proximity to Lake Pamvotis. The combination of narrow alleys, enclosed courtyards, open plazas, and scattered green pockets creates a complex microclimatic mosaic that strongly influences human thermal perception. In recent years, rising summer temperatures and prolonged heat episodes have intensified the need to better understand how urban morphology and vegetation affect thermal comfort in Mediterranean historic cities.

This study investigates human thermal sensation in the historical center of Ioannina by integrating high‑resolution field measurements with detailed microclimate simulations. On August 8, 2025, air temperature, relative humidity, wind speed, and globe temperature were recorded along a pedestrian transect specifically designed to capture the city’s diverse urban typologies—from shaded, narrow alleys to open plazas and vegetated areas. Measurements were taken every 2 seconds at a height of 1.1 m, corresponding to the gravitational center of the human body, between 15:00 and 17:00 (UTC+3:00).

Thermal comfort was assessed using two established human‑energy‑balance indices, the Physiologically Equivalent Temperature (PET) and the Universal Thermal Climate Index (UTCI). These indicators enabled a detailed evaluation of how different urban morphologies and varying levels of shading and vegetation influence perceived heat stress. To complement the field campaign, microclimate simulations were performed using 3D modelling ENVI-met, at very high resolution (1.5m x 1.5m), providing spatially explicit estimates of PET, UTCI, and CO₂ concentrations under both existing conditions and alternative design scenarios.

The combined analysis proved spatial variability in thermal stress across the study area, driven primarily by differences in shading, surface materials, and vegetation density. Field observations and ENVI‑met outputs consistently indicated elevated PET and UTCI values in exposed plazas and narrow, sunlit streets, while vegetated pockets and shaded corridors exhibited noticeably lower thermal loads. Simulated CO₂ concentrations further emphasized the contribution of vegetation to improved air quality, with greener configurations demonstrating measurable reductions in near‑surface CO₂ levels. Building on these findings, the study evaluates targeted nature‑based mitigation strategies, including the installation of extensive green roofs and the development of a small urban woodland. Scenario simulations show that these interventions can substantially reduce radiant heat exposure, enhance evaporative cooling, and contribute to improved atmospheric conditions. Overall, the results underscore the potential of green infrastructure to enhance thermal comfort and environmental resilience within Ioannina’s historic urban core.