The goal of UrbanAIR is to develop a new digital twin that supports decision-makers in urban areas to deal with urban design dilemmas in atmospheric heat and air quality to maximise the health and socio-economic well-being of its citizens affected by climate change. It will provide critical tools for climate adaptation and hazard control through urban design and planning, including very high-resolution model components of the urban atmosphere. UrbanAIR is designed by a consortium that covers the full value chain to revolutionize digital twin platforms by starting from the perspective of the end user. Through co-creation with the end users and a balanced evaluation of the decision criteria, the overall objective of UrbanAIR is to yield a dynamic, user-friendly infrastructure integrated into the Destination Earth infrastructure that empowers municipalities and industries to face urgent urban climate risks. The scales in the atmospheric models in UrbanAIR cover the full range from the regional to the neighbourhood level. This innovative multiscale approach is achieved through the development of software interfaces for the modular coupling of atmospheric models. AI-based emulators allow for the acceleration of these computationally expensive models, which, together with the application of advanced data assimilation techniques, allows the quantification of risks and uncertainties for the UrbanAIR scenarios. Corresponding behavioural models simulate the human response to changes in climate and associated hazards. The resulting scenarios form the input to the objective evaluation of the criteria for decision-making. With these science-based tools for scenario simulation of natural and human behaviour, reliable risk assessment, and balanced decision analysis, UrbanAIR will develop tools and the infrastructure to support decision-makers in cities. This will pave the way for effective climate adaptation by developing tools for a safer, healthier, and more resilient future.