Thermal comfort on hot days in Munich, Germany: How does vegetation structure in small urban green spaces matter?

Public green spaces play an increasingly important role in urban planning and public health, particularly for providing thermal comfort during hot days. Small green spaces enhance social equity by being more accessible and easier to integrate into existing urban structures across neighborhoods. The thermal regulation potential of green spaces generally increases with size but also largely depends on vegetation structure. To optimize the potential of small green spaces, it is essential to understand how their structural design and spatial configuration are linked to their local cooling effects. Based on field measurements on hot days in 2024, we modeled the modified physical equivalent temperature (mPET) across 12 small parks (0.25 - 2 ha) in the inner city of Munich, Germany, and in their urban surroundings. The structural composition of the park vegetation covered a gradient, ranging from sparse to forest-like. We recorded the vegetation structure using mobile laser scanning and derived the sky view factor from hemispherical photographs. Our results show that parks with high structural complexity reduced the mPET by up to 14 °C, whereas parks with low structural complexity provided only minimal cooling. According to a mixed-model analysis, the cooling effects of small green spaces were primarily influenced by the sky view factor and the tree canopy. Increased tree coverage and reduced visible sky correlated with greater cooling. However, high vegetation density negatively impacted cooling, likely due to restricted airflow, while subcanopy vegetation had little effect. We conclude that small green spaces with high canopy cover and large trees can mitigate extreme heat in cities. To increase the thermal regulation potential of parks during the hottest times of the day, particularly in summer months, it is critical to maintain and systematically increase high tree canopy coverage.