Thermal regulation potential of urban green spaces in a changing climate: Winter insights

Global warming affects both summer and winter temperatures, altering the ecological and social dynamics of urban green spaces not only during the summer months but also during the winter. Strategies to mitigate climate change impacts often emphasize increasing urban vegetation cover, but the effectiveness of these green spaces in regulating the local microclimate depends on various factors, including the vegetation structure. These effects remain largely underexplored during the winter season. To investigate the thermal regulation capacity of urban green spaces we measured air temperature and humidity in 36 parks with different sizes and vegetation structures in Munich, Germany, in their non-green surroundings, as well as in a nearby forest during the 2022-23 winter. We then analyzed the relationship between the local microclimatic differences and the vegetation structure derived from mobile laser scans. In comparison with the nearby forest, we measured a winter urban heat island effect of 1.8 degrees C in Munich. The urban microclimates in winter were mainly influenced by the urban landscape of Munich, namely the distance to the city center with increasing air temperature closer to the center. Urban green spaces in Munich provided small but consistent local cooling and humidifying effects throughout the winter. These cooling effects largely depended on the green space size but partially also on the vegetation structure. We found a significant relationship between the microclimatic difference, the vegetation density, and the vertical homogeneity of vegetation. The canopy cover, however, could not significantly predict the cooling effect in winter. We conclude that increasing the structural complexity of urban green spaces through management decisions could improve their cooling effect and ecological value, even during winter months. To maximize the ecological and climatic benefits of urban green spaces, a nuanced understanding and management of urban microclimates is needed across all seasons.