Hydrological modeling to support co-designed NEXUS management strategies

The introduction of participatory processes directly and actively involving stakeholders has been steadily gaining importance also in the definition of water management policies. Moreover, for policies to be sustainable, the decision-making process has to keep a multisectorial vision of water management, for instance taking into account the mutual interactions between water, agriculture and energy production, while being careful to move within the limits of the ecosystem. This inclusive approach to the water-energy-food-ecosystem nexus (WEFE Nexus) is the way in which a community of practice made by both technicians and stakeholders can make conscious and sustainable decisions. In this context, the use of hydrological models takes on a key role, not only to describe the current state of resources use, but also to evaluate the impact on resources of different management strategies. However, it is fundamental to properly structure the information pathway from the stakeholders to the model, as well as the return pathway of model results to the stakeholders. On this depends the successful creation of a fruitful and transparent interaction between technicians and stakeholders. An instance of how models can be applied to this context is the use, within the PRIMA NEXUS-NESS project, of the spatially distributed hydrological model WATNEEDS, developed at Politecnico di Milano,. The project aims at co-creating WEFE Nexus management strategies in 4 different case studies, defined as Nexus Ecosystem Labs (NELs) in 4 different countries of the Mediterranean area: Spain, Italy, Tunisia, and Egypt. The 4 NELs are very different from each other in terms of characterizations and problématiques, but they all present major sustainability challenges that can be conceptualized in terms of WEFE Nexus. In the context of NEXUS NESS, WATNEEDS has been enhanced in terms of spatial ductility and range of possible model scenarios, with the aim to describe the current status of water resources in each NEL and to evaluate the management alternatives proposed by the different stakeholders. Among the alternatives the model can analyse, we report changing the crop calendar, implementing new crops or redistributing the existing crops in the territory, changing or modernizing the irrigation systems, and moving towards indoor cultivation techniques. As an example, we report the results relative to some of the interventions proposed by the stakeholders during the first set of project Workshops, held between May and June 2022. The final results will be provided to the stakeholders in November, to illustrate the different impacts that each choice can lead to, not only in terms of water use, but also of WEFE Nexus in general. In this way, using hydrological models in the evaluation of co-created and participatory policy decisions demonstrates its crucial role in the definition of shared and sustainable management strategies.