Maria Vrachioli

The Upper Main River Basin in Germany is projected to experience increasing water scarcity by 2050, driven by rising agricultural water demand and climate-induced precipitation variability. Excessive fertilizer application leads to nitrate runoff, reducing water quality and compounding pressures on agricultural production. These dynamics pose a threat to agricultural production in the area, which is predominantly cereal-based. Given the multidimensional nature of water security, we adopt the Water-Energy-Food-Ecosystem (WEFE) Nexus framework to quantify cross-sectoral feedback mechanisms and inform efficient resource allocation. We integrate System Dynamics modelling with Stochastic Frontier Analysis to quantify hydroeconomic trade-offs, project cereal production under water constraints, and derive shadow prices for water use. The integrated framework simulates interactions between water availability, agricultural demand, and water quality under multiple climate and input-use scenarios over the period 2000–2050. Under a worst-case scenario, groundwater resources are projected to decline by 29.4% by 2050, primarily due to increasing agricultural water demand. Declining water availability further concentrates nitrate pollution when fertilizer application remains unchanged. Results from the Stochastic Frontier Analysis indicate that water has the highest marginal product among agricultural inputs, while System Dynamics projections show declining cereal production under increasing water scarcity. The derived shadow price for water, ranging from €0.20 to €0.57 per m3, provides a policy-relevant economic signal for incentive-based measures aimed at improving the efficient, cross-sectoral allocation of water resources. Integrating economic valuation within the WEFE nexus framework strengthens water governance by enabling a more explicit assessment of trade-offs under growing resource constraints.

Europe’s water resources face growing pressures from climate change and competing demands. Addressing these pressures requires integrated approaches that capture interdependencies among sectors. This paper develops a unified hydro-economic modeling framework that embeds Water–Energy–Food–Ecosystem (WEFE) linkages directly into water policy analysis. Unlike existing approaches, the framework systematically combines hydrological processes, economic behavior, and policy instrument design, enabling analysis of cross-sectoral trade-offs and welfare outcomes. Its modular structure makes it suitable for both detailed numerical models and stylized applications. We illustrate its use with two European river basins, the Júcar in Spain and the Upper Main in Germany, showing how water trading and pricing policies can be evaluated within a nexus perspective. These cases demonstrate how the framework operationalizes nexus thinking and provides a transparent, policy-relevant basis for more coherent and resilient water governance.

The Policy Brief: • Proposes a new definition of the Nexus • Identifies steps for the operationalisation and certification of the Resource Nexus • Demonstrates how a Resource Nexus Framework can improve policy coherence, manage trade-offs, and unlock synergies across sectors and scales

Coffee producers deal with uncertainty due to high volatility in coffee prices. To navigate these challenges, producers must balance the tradeoff between higher yield and better quality utilising heterogeneous technologies, such as intensive production methods and environmental management practices. The aim of this study is to identify the extent to which heterogeneous technologies, particularly those focused on sustainable management, can influence the technical efficiency of Colombian coffee farms. Using the Latent Class Stochastic Frontier Model (LCSFM), we studied the unobserved differences in technologies among 387 Colombian coffee farms in the Andes. Our findings show that farms adhering to sustainable standards achieved an efficiency rate of 95.68%, compared to 74.93% for farms heavily reliant on chemical pesticides. These results underscore the efficiency benefits of sustainable practices and provide targeted recommendations to improve productivity among different groups of coffee growers. This research contributes to the broader understanding of how adopting sustainable technologies can enhance efficiency in coffee production, offering key insights for policymakers and practitioners aiming to stabilise and develop the sector.

China's diversified agricultural policies have effectively improved both the yield and environmental performance of the crop sector. Quantifying productivity trends and their drivers is key to formulating strategies for high‐quality and low‐carbon crop development. This study uses input–output panel data of crop products to examine changes in the environmental total factor productivity (ETFP) of the crop sector and its major sub‐sectors across 30 Chinese provinces from 2001 to 2020. The results show that the ETFP of the crop sector exhibited a wavelike growth pattern, mainly driven by technological progress. In addition, reducing greenhouse gas (GHG) emissions can significantly improve the ETFP and shows considerable potential. Over the entire study period, the crop sector could mitigate up to 35.5% of GHG emissions to reach the frontier target value. The average marginal abatement cost is 4106 yuan/tonne CO ₂ e. Spatially, the GHG emission mitigation potential and cost‐effectiveness in the western and central regions are higher than those in the eastern region. Therefore, inter‐regional cooperation can leverage regional differences to optimise total reduction costs and establish a carbon market, which would positively impact both the crop economy and the environment.

Sustainable resource management in the face of climate change is a pressing challenge for our society. This paper delves into the water-energy-food-ecosystems (WEFE) nexus, a scientific framework that supports the integrated assessment and management of the interconnected resources. Shifting from sectoral to cross-sectoral and transdisciplinary perspectives, the WEFE nexus addresses interdependencies and interactions among water, energy, food, ecosystems, and climate. This paper focuses on the extended nexus, incorporating ecosystems as a fourth pillar, underscoring the importance of considering ecosystems on an equal footing with water, energy, and food sectors. In addition, the paper emphasizes the significance of monitoring and modelling techniques, laying the foundations for understanding the nexus complexities and assessing uncertainty. The paper offers an overview of integrated nexus modelling, system analysis and socio-economic modelling, bridging the gap between nexus science and practice. It highlights the role of multifaceted stakeholder engagement methods, policy assessment, and institutional analysis in nexus models. Quantifying the nexus through indicators, and its alignment with the Sustainable Development Goals, EU Green Deal, and EU Blue Deal are also key focal points. Finally, the last part of the paper addresses challenges in existing nexus modelling attempts, advocates for the integration of transdisciplinary information, and presents lessons learned. The paper concludes with recommendations for the future of the WEFE nexus, emphasizing its potential in fostering transformative change toward sustainable resource management and inclusive policymaking.

Modelling is an important tool to support policy-making. A review of the existing bioeconomy modelling capacity indicates that most models focus on agriculture, forestry, and connected sectors of food, energy, and wood and paper products. Future development of bioeconomy modelling capacities should focus on including bio-based products such as textiles and plastics, and especially chemicals and pharmaceuticals. To address such gaps in existing capacities, the BioMonitor Model Toolbox has been developed; it is composed of five improved bioeconomy models to support policy-makers in executing consistent, coherent, and longer-term strategies with desirable consequences for multiple objectives. Further model development needs to consider key processes such as technological change (or innovation), circularity, consumer behaviour, climate change, and biodiversity. Whereas concepts like circularity could be included in existing models with reasonable effort, other important concepts require the development of new models that build on emerging modelling techniques.