Holistic approaches are required to protect urban populations from the impact of heat and air pollution. Focusing on heat- and air-pollution-related early warning systems and action plans and their implementation at the urban scale, this session welcomes contributions related, but not limited, to: integrated methodological frameworks to (i) quantify the heat and air pollution health effects, and (ii) define city-specific warning thresholds accounting for intra-urban variations; (iii) fine-scale vulnerability assessments considering socio-economic effect modifiers; (iv) the implementation and validation of warning systems and associated action plans; (v) communication and dissemination practices. Contributions taking into account the complex interactions between heat and air pollution and their synergistic impact on human health are particularly encouraged, as well as those adopting a broader perspective in early warning and action planning within the frameworks of "One Health" and "Planetary Health".