HYDRA aims to advance our understanding of the climate implications of large-scale hydrogen deployment. The project began by assessing potential hydrogen leakages to the atmosphere, laying the groundwork for the development of emission scenarios and modelling their impact on atmospheric composition and climate. In parallel, HYDRA developed an innovative monitoring tool to detect H₂ leakages and enhance safety of H2 technologies. Ultimately, HYDRA aims to evaluate both the benefits and potential risks of large-scale hydrogen deployment, while identifying effective mitigation pathways to support a sustainable transition towards a hydrogen-based economy. Its findings will support evidence-based policymaking through targeted policy briefs and contribute to the update of life cycle assessment methodologies by integrating new insights on the climate and environmental impacts of hydrogen technologies.