Climate change is increasing the frequency and intensity of heatwaves and droughts, which is further amplified in cities by the urban heat island effect. Urban trees can mitigate the urban heat island and reduce heatwaves in cities. Therefore, initiatives are taken globally to increase tree cover in cities. Yet, heat and drought stress are increasingly leading to reduced growth and mortality in urban trees. To ensure sustainable green cities, we need to improve our understanding of climate change effects on urban trees. The overarching aim of this project is to better understand and predict the vulnerability of urban trees to climate change, and the relation with the local microclimate, species’ heat and drought stress and trait plasticity. I will use an extensive database of >10,000 urban trees monitored since 1999 in a large capital city, Brussels. Firstly, I will assess urban trees’ vulnerability by quantifying the overlap between current and future climatic conditions vs the trees’ climate niche. Secondly, for six widely-used urban tree species, I will assess the effect of the local microclimate on heat and drought stress. Thirdly, I will measure morphological and ecophysiological traits to gain insight in species’ drought tolerance and trait plasticity. The results of this project will provide insight in the vulnerability of urban trees to climate change and soundly inform policy and management decisions to optimise the survival of urban trees now and in the future.