[From modelling to pilot site to improve the thermal comfort: the case study of Genoa (Northern Italy) within the Climactions project].

Objectives: to estimate the microclimatic improvement due to the introduction of Nature-based Solutions (NbS) in a small square (about 1,500 m²) located in a densely built area of the city of Genoa (Liguria Region, Northern Italy), and subject to the Urban Heat Island phenomenon (UHI).

Design: through the microclimatic simulation results of the current state, obtained via the ENVI-met V 4.4.5 software, different microclimatic cooling scenarios were developed and simulated, introducing different vegetation layers (herbaceous, shrubby, arboreal), in increasing quantities per scenario, and clear surfaces. One of them was then selected for the implementation of the pilot project.

Setting and participants: the study was done on Piazza Metastasio in the Cornigliano neighbourhood (VI District) in Genoa, in an area delimited by Via Cornigliano (North), Polcevera mouth (South), railway station (West), and Fiumara commercial complex (East). This area was particularly critical due to population density, absence of significant green areas, and weather and climate conditions.

Main outcome measures: Evaluating the Universal Thermal Climate Index (UTCI) allowed to estimate the users' feelings of well-being/malaise inside the examined area, and the potential improvement of these perceptions through targeted greening scenarios.

Results: the simulations of the selected scenario for the pilot project (scenario with minimum greening and with the best microclimatic performance), carried out for one of the hottest days of the last 20 years, show a decrease in the air temperature lower by around 1.8°C, compared to the current state (t current state: 34.4°C, t scenario: 32.6°C). The UTCI shows a decrease of around 4.1°C, compared to the current state, in correspondence with the trees (t current state: 42.0°C, t scenario: 37.9°C).

Conclusions: the kind and the coverage ratio of the plant layers play a fundamental role on the microclimatic parameters with thermal comfort improvement (up to -1.8°C t air, up to -5.4°C UTCI), despite a reduction in the air flow (up to -0.3 m/s).