Urban green infrastructures offer thermal regulation to mitigate urban heat island effects. To gain a better understanding of the cooling ability of transpiring plants at the leaf level, we developed a method to measure the time series of thermal data with a miniaturized, uncalibrated thermal infrared camera. We examined the canopy temperature of four characteristic living wall plants (Heuchera x cultorum, Bergenia cordifolia, Geranium sanguineum, and Brunnera macrophylla) under increasing drought stress and compared them with a well-watered control group. The method proved suitable to evaluate differences in canopy temperature between the different treatments. Leaf temperatures of water-stressed plants were 6 to 8 °C higher than those well-watered, with differences among species. In order to cool through transpiration, vegetation in green infrastructures must be sufficiently supplied with water. Thermal cameras were found to be useful to monitor vertical greening because leaf surface temperature is closely related to drought stress. The usage of thermal cameras mounted on unmanned aerial vehicles could be a rapid and easy monitoring system to cover large façades.

At the time of the restrictions and lockdown during the COVID-19 pandemic, it became apparent how difficult it is for city dwellers to adhere to the prescribed behavioural measures and the protective distance in densely built urban areas. Inner-city parks and green spaces were heavily used for recreational purposes and were thus periodically overcrowded. These observations highlight the need for green open spaces in urban areas, especially in exceptional situations regarding pandemics and climate-related heat periods. Green open spaces and greened buildings help cities and the population cope with the consequences of climate change and have a decisive positive effect on human health and well-being. This paper aims to outline which social issues are related to the availability of green infrastructure close to home and which health consequences need to be considered. The COVID-19 challenges could offer a chance and an opportunity to increase the resilience of cities and their inhabitants in various terms. A cross-disciplinary team of authors (public health, urban and landscape planning, landscaping and vegetation technologies science) describes and discusses challenges and opportunities that arise from this crisis for cities from an inter-disciplinary perspective, concluding that urban green infrastructure helps in two ways: to adapt to climate change and the challenges posed by COVID-19.