Urban areas are currently facing significant new and/or aggravated existing challenges due to the impacts of climate change, including increased frequency and intensity of extreme weather events, urban greenness loss, urban flash floods, air quality degradation and increased greenhouse gas emissions, geo-hazards, and urban heat fluxes among others. To enhance urban resilience and efficiently mitigate those impacts, sophisticated digital tools and Decision Support Systems (DSS) could play a determinant role in assisting decision-makers by means of providing access to pertinent data, analytical models as well as thorough insights for prioritizing the most effective mitigation strategies. The Horizon 2020 research and innovation project entitled "Development of a Support System for Improved Resilience and Sustainable Urban areas to cope with Climate Change and Extreme Events based on GEOSS and Advanced Modelling Tools - HARMONIA GA 101003517"introduces a series of innovative digital tools along with novel data services and products. This paper outlines the functioning of an urban-planning DSS that exploits the Harmonia multiparametric risk assessment methodology for a spectrum of different urban perils to eventually offer comprehensive and tangible urban recommendations for mitigating future hazard-driven adverse impacts. The proposed solution will be offered as a webbased application with a user-friendly interface, able to efficiently handle and visualize multidimensional (4D) geospatial information. The overall methodology and the capabilities of the DSS will be demonstrated in four different and diverse European urban environments, i.e., the cities of Milan, Piraeus, Sofia, and Ixelles.