Addressing complex social-hydrogeological challenges through inter- and transdisciplinary knowledge co-production, Bewältigung komplexer sozial-hydrogeologischer Herausforderungen durch inter- und transdisziplinäre Wissens-Ko-Produktion, Relever des défis sociaux et hydrogéologiques complexes grâce à la coproduction de connaissances inter- et transdisciplinaires, Respuesta a desafíos socio-hidrogeológicos complejos mediante la coproducción de conocimientos interdisciplinarios y transdisciplinarios, 通过跨学科与跨界的知识共创应对复杂社会-水文地质挑战, Enfrentando desafios socio-hidrogeológicos complexos por meio da coprodução de conhecimento inter- e transdisciplinar, Rješavanje složenih društveno-hidrogeoloških izazova kroz interdisciplinarnu i transdisciplinarnu koprodukciju znanja, Решавање сложених друштвено-хидрогеолошких изазова кроз интердисциплинарну и трансдисциплинарну копродукцију знања

<jats:title>Abstract</jats:title> <jats:p>Knowledge co-production (KCP) between science and practice is essential to address complex social-hydrogeological challenges. However, there is a need to clarify and operationalize KCP within collaborative research. This study characterizes KCP and evaluates its impact on developing sustainable groundwater management strategies based on two case studies in Europe, where transdisciplinary research enabled scientists and stakeholders to collaboratively develop sustainable groundwater management strategies. Utilizing workshop evaluations, ethnographic field notes, an interdisciplinary interview, and reflection meetings, the study identifies when, where, and how KCP occured within the transdisciplinary processes. Moreover, the study evaluates the value of interdisciplinary collaboration between natural and reflexive sciences to enhance groundwater management. The results reveal that KCP can be characterized by specific instances where diverse knowledge converged, occurring at interdisciplinary (within science), intersectoral (among stakeholders), and transdisciplinary (between science and stakeholders) levels. The study found that interdisciplinary KCP enhanced comprehensive system knowledge among scientists, while transdisciplinary KCP established a normative foundation for sustainable groundwater management. Intersectoral KCP improved collaboration efficiency among stakeholders. The collaboration between natural and reflexive science supported a critical examination of methods, objectives, and approaches employed, fostering a deeper understanding of site-specific groundwater-related challenges and enabling the development of tailored management actions. Evaluation of the collaborative research processes deepened the understanding and impacts of KCP, informing future research design for sustainability problem-solving. However, facilitating and evaluating KCP requires sufficient resources. The presented design of a transdisciplinary process, including KCP instances and evaluation principles, can guide other case studies to enable, evaluate, and sustain KCP.</jats:p>