Meteorology and air quality are key aspects for city life and urban metabolism. Both aspects build upon urban and natural processes, involve stocks and flows of heat and pollution, with in the end consequences for stocks and flows concerning other urban entities and processes such as human outdoor activities, leisure, transport modes, as well as for urban design and planning. During hot summer days cities experience an urban heat island effect mainly at the start of the evening and at night. As a result inhabitants might be subject to a reduced human thermal comfort. Hot summer days often also coincide with relatively poor air quality conditions. Both short-term effects are known to increase the mortality rates, and it is challenging to distinguish their impacts on health effects. Moreover, climate change scenarios indicate an enhancement of future heat wave frequency and intensity and a further deterioration of human thermal comfort. These issues raise the need and the urgency for city adaptation, but an integrated method for the assessment is still missing. Effective city adaptation is hampered by the complexity of the urban climate (induced by both meteorology and urban morphological characteristics) and its potential health risks, combined with the complex spatial interaction of stakeholders and economical functions. To warn the general public, and to effectively perform urban planning interventions, straightforward environmental indicators are required. Indicators have been developed for the individual aspects before, but indices that combine both air quality and urban heat are rather scarce (Rainham and Smoyer-Tomic, 2003). This study develops a novel metric that combines the impact of thermal comfort and air quality by accounting for the relative health risk for both aspects. A straightforward quantification method for this metric has been developed to provide an objective, rational assessment. The application of this new Urban Climate assessment tool is then applied to a case study for a heat wave in the Northwestern Europe, and applied for a sample intervention in the city center of Ghent (Belgium).