Analyzing the water-energy-food-ecosystem nexus by integrating hydrological modeling and system dynamics tools

Effective and integrated management of natural resources is crucial for achieving sustainability, particularly in the context of interrelated challenges posed by using these resources. This study addresses four complementary as-pects of resource management using a ‘Nexus’ approach within the Tarquinia/ Marta River, highlighting how this region serves as a model that could be ap-plied to other areas of the Mediterranean. The study proposes an innovative approach based on System Dynamics Modeling techniques and hydrological modeling, which is summarized below. The first chapter emphasizes the Nexus concept, which has gained inter-est as a theoretical framework for understanding the complex interconnections among natural resources. It highlights the need for tools and methods to effec-tively map and analyze these interdependencies, facilitating stakeholder en-gagement in sustainability transitions. In this context, the study employs a Par-ticipatory System Dynamics Modeling (PSDM) approach to enhance the under-standing and management of the Water-Energy-Food-Ecosystem Nexus (WEFE Nexus). This approach is tested concerning the Tarquinia plain in Italy, where a strong interdependency and conflict exists between agriculture and environ-mental conditions. The approach aims to achieve stakeholder consensus on challenges arising from conflicts between different sectors and subsectors in areas under intensive agricultural activity, while also considering future chang-es due to climate change. The analysis of the Causal Loop Diagram (CLD) helps identify the main challenges for the area and highlights the need for a better understanding and modeling of key phenomena. The centrality of agricultural activities, in terms of productivity, relevance for farmers, and impacts on water quality and natural areas, underscores the necessity of investigating these im-pacts and potential mitigation measures using specific agro-hydrological mod-els. The second chapter builds on the main challenges identified using PSDM and proposes well-established hydrological modeling (SWAT) to further en-hance the understanding and management of the WEFE Nexus. In line with the research objectives, the SWAT model has been utilized with the available da-tasets to first establish the current conditions in the watershed and, secondly, to develop specific scenarios representing the effects of climate change. The Sequential Uncertainty Fitting algorithm version 2 (SUFI-2), a part of the SWAT-CUP tool package, has been employed for calibration, validation, and sensitivity analysis. Data from the EURO-CORDEX initiative includes various climate models involving regional climate models (RCMs) nested in different global circulation models (GCMs) used in this study. Historical experiments and future projections (based on the RCP 8.5 worst-case greenhouse gas emission scenario) have been selected. The most reliable EURO-CORDEX climate projec-tions have been selected following a rigorous performance evaluation of sever-al high-resolution combinations (GCMs-RCMs) over the area. This section of the study has investigated the hydrological balance, soil erosion and nutrient yield in the study watershed, focusing particularly on agricultural practices and cli-mate change impacts. The study findings have revealed significant soil loss and changes in total nitrogen (TN) and total phosphorus (TP) yield under both cur-rent and future scenarios, with agricultural practices exacerbating these issues. Conclusively, this chapter highlights the need for the implementation of effec-tive management strategies and mitigation measures to address these chal-lenges. The third chapter explores the implementation of Best Management Practices (BMPs) to address on- and off-site impacts resulting from soil erosion and nutrient pollution in the study area, a region susceptible to these environ-mental challenges due to its Mediterranean climate and intensive agricultural practices. Utilizing the Soil and Water Assessment Tool (SWAT), the study as-sesses different individual BMPs, such as terracing, contour farming, no-tillage, and residue management as well as their combination. The results underscore the effectiveness of combined BMPs in reducing erosion and nutrient pollution, with terracing being particularly impactful in minimizing soil loss in hotspot ar-eas within the watershed and reducing sediment and nutrient loading into the river. The analysis emphasizes the importance of integrated BMP approaches for sustainable soil and water management in agricultural areas as well as highlighting the need for targeted management strategies to mitigate envi-ronmental impacts and enhance water quality. The last chapter focuses on the application of PSDM, describing how a transition from Causal Loop Diagrams to quantitative models (stock and flow) can help explore potential future trajectories of the system under various condi-tions, particularly aiming to enhance its resilience. Stakeholders, including poli-cy and decision-makers, were actively involved in co-designing, analyzing, and discussing relevant scenarios. The study emphasizes the integration of stake-holder knowledge with technical modeling efforts to identify sustainable man-agement strategies for water resources, ecosystems, and agricultural practices in the region. At the core of the chapter is the development of a comprehensive stock and flow model, coupled with the SWAT hydrological model, to investi-gate the long-term impacts of agricultural practices on water resources and ecosystem sustainability. This integrated modeling approach enables a detailed analysis of how management strategies, particularly those involving Nature-Based Solutions (NBS) affect water quantity, quality, and agricultural productiv-ity under varying climate change scenarios. Besides supporting system under-standing, the proposed approach showed the potential to foster stakeholder di-alogue, which is crucial for building consensus on sustainable development pathways for the area. Key methodological challenges and potential needs for further innovation are also included.