In this study a method for propagating the hydrological model uncertainty in discharge predictions of ungauged Mediterranean catchments using a model parameter regionalization approach is presented. The method is developed and tested for the Thau catchment located in Southern France using the SWAT hydrological model. Regionalization of model parameters, based on physical similarity measured between gauged and ungauged catchment attributes, is a popular methodology for discharge prediction in ungauged basins, but it is often confronted with an arbitrary criterion for selecting the "behavioral" model parameter sets (Mps) at the gauged catchment. A more objective method is provided in this paper where the transferrable Mps are selected based on the similarity between the donor and the receptor catchments. In addition, the method allows propagating the modeling uncertainty while transferring the Mps to the ungauged catchments. Results indicate that physically similar catchments located within the same geographic and climatic region may exhibit similar hydrological behavior and can also be affected by similar model prediction uncertainty. Furthermore, the results suggest that model prediction uncertainty at the ungauged catchment increases as the dissimilarity between the donor and the receptor catchments increases. The methodology presented in this paper can be replicated and used in regionalization of any hydrological model parameters for estimating streamflow at ungauged catchment.

The food, energy, and water domains are strongly interrelated. The body of literature investigating these interlinkages developed into water–energy–food and, more recently, ecosystem (WEFE) nexus thinking. The WEFE nexus is concerned with cross-sectoral resource management requiring dedicated WEFE governance approaches. Among the existing WEFE nexus conceptualizations, the one that places the ecosystem at the center emphasizes the importance of ecosystem services for human well-being and as the basis for the functioning of the water, energy, and food domains. Such conceptualization, however, lacks clear definition and explanation of implications for WEFE nexus governance as well as practical tools for implementation. Accordingly, based on an in-depth analysis of WEFE nexus interlinkages, associated governance challenges, and practical experience, we propose the WEFE Nexus Governance Approach as an operationalization of the ecosystem-centric WEFE nexus conceptual framework. This approach takes policy coherence and stakeholder co-creation at its core, integrated with quantitative modeling of WEFE nexus interlinkages, and is organized in four steps: problem identification; formulation of substantive ambitions through stakeholder dialogue; embedding of ambitions and action into a stakeholder agreement; and implementation of actions. The approach is oriented to practical application and can be implemented by any actor (e.g., research institutes, governments, non-governmental organizations) having the ambition to initiate a stakeholders co-creation process toward nexus governance in a specific context. Furthermore, it can be applied to different scales and nexus domains depending on the identified nexus problems, while accounting for the vital role of ecosystem services. The approach’s applicability and needs for future research are discussed. Graphical abstract