Dimitrios Malamataris ¹ Vassilios Pisinaras ^1* Alessandro Pagano ² Valentina Baratella ³ Silvia Vanino ³ Manuel Bea ⁴ Konstantinos Babakos ¹ Anna Chatzi ¹ Stefano Fabiani ⁵ Raffaele Giordano ² Petros Kafkias ⁶ Estrella López-Moya ⁴ Christina Papadaskalopoulou ⁶ Ivan Portoghese ² Dimitris Tassopoulos ⁶ Andreas Panagopoulos ¹

• ¹ Hellenic Agricultural Organization – DIMITRA, Soil and Water Resources Institute, Thessaloniki, Greece
• ² Consiglio Nazionale delle Ricerche, Istituto di Ricerca Sulle Acque, Sede di Bari, Bari, Italy
• ³ Centro Agricoltura e Ambiente, Consiglio per la Ricerca in Agricoltura e l’Analisi dell’Economia Agraria (CREA), Rome, Italy
• ⁴ Asociación Ecoadapta, Madrid, Spain
• ⁵ Centro di Politiche e Bioeconomia, Consiglio per la Ricerca in Agricoltura e l’Analisi dell’Economia Agraria (CREA), Rome, Italy
• ⁶ DRAXIS Environmental S.A., 54-56 Themistokli Sofouli Str., Thessaloniki, Greece

Natural resources security in view of current and future use is indispensable for fostering sustainable development. The formulation of effective policies to address both the present allocation and future conservation of natural resources in an integrated way remains an essential and challenging task. In this regard, managing the Nexus is increasingly seen as a priority in resource governance. Nature-based Solutions (NbS) are gradually being advocated to enhance sustainable and resilient Nexus management efforts. Designing and planning NbS tailored to local contexts requires a thorough understanding of the specific challenges and perspectives, as well as the divergent perspectives among stakeholders. This paper presents and analyses an effective stakeholder engagement strategy, based on the Learning & Action Alliances (LAA) scheme and aimed at identifying Water-Ecosystems-Food (WEF) Nexus challenges and selecting NbS in two case studies in the Mediterranean area, namely the Agia watershed and the Pinios River Delta in Greece, and the Tarquinia plain in Italy, which are among the most resource-stressed basins in their respective countries (Greece and Italy). In total, 60 stakeholders were engaged in more than 40 events (workshops, seminars, open days, field trips etc), while 25 individual interviews were also conducted. By fostering collaboration and stakeholder ownership, the methodology provided actionable insights and promoted context-specific solutions. The stakeholders proposed 24 NbSs in the Italian case study, most of which were related to agricultural landscape management, while in the Greek case study, 2 of the 4 top-ranked measures were NbSs. The development of a Learning and Action Alliance (LAA) scheme based on active stakeholder engagement to support WEF Nexus analysis and NbS selection is detailed in this work. The participatory processes structured within the LAAs provided the basis for the identification of the main sectoral challenges and supported the elaboration and validation of Causal Loop Diagrams that helped to identify pivotal nexus challenges, as well as key measures (including NbS) to address these. The findings underline the importance of participatory approaches and transdisciplinary tools in addressing Nexus challenges, offering a replicable framework for sustainable resource management in resourcestressed regions.