Evolution of microclimate following small patch de-sealing and revegetation in urban context

Abstract

This research explores the impact of de-sealing a 64 m² patch (Oasis) after introducing indigenous vegetation, four trees and herbaceous species, on local microclimate conditions in an urban context. Over two years, microclimate variables were monitored and thermal comfort was evaluated with the Universal Thermal Climate Index (UTCI). The Oasis experienced a noticeable reduction in Ts compared to surrounding asphalted areas, with a daily mean difference in maximum surface temperatures of 18.4 °C the first summer and 23.0 °C the second, attributed to the development of the herbaceous layer, which covered 60 % of the Oasis three months after sowing and above 90 % from the second year. This Ts is partly responsible for improving thermal comfort during the day. Tree shading induced further local cooling, with a decrease of up to 8 °C of UTCI in shaded areas. No evidence of lower nocturnal Ta compared to sealed reference was shown, possibly due to the small size of the patch and air mixing with the surroundings. However, as the low vegetation grew, the nocturnal de-sealed patch Ta got closer to mature meadow values. Modeling using UMEP and SOLWEIG projected further improvements in thermal comfort in the coming years during the daytime considering future tree dimensions. During nighttime, the trees would induce a significant radiative trapping. This study demonstrates that small-scale de-sealing and revegetation projects can provide meaningful microclimate improvements in urban environment as early as the first year. In the following years, the development of vegetation further helps cities to adapt to climate change.