This deliverable, produced within the ENVRI-Hub NEXT project, addresses the harmonisation of metadata schemas and vocabularies across European Environmental Research Infrastructures (RIs). Its primary objective is to enhance the interoperability, discoverability, and reusability of environmental data by promoting the adoption of standardised metadata practices and semantic frameworks.

The document presents a landscape analysis involving 14 RIs, revealing a moderate convergence toward widely accepted metadata standards such as ISO 19115 and DCAT-AP, and metadata services including CSW, OAI-PMH, and SPARQL. Vocabulary usage varies significantly, with some RIs employing domain-specific controlled vocabularies and others relying on free-text or partially curated lists.

The deliverable highlights the role of the ENVRI-Hub Catalogue of Services in enabling federated, standards-compliant metadata publication in DCAT metadata format. It also introduces the I-ADOPT framework as a concrete approach for achieving semantic interoperability through structured descriptions of observed variables.

Key recommendations include adopting multiple metadata schemas and services, incrementally aligning vocabularies with I-ADOPT, and ensuring metadata readiness for integration with the European Open Science Cloud (EOSC). The document concludes that while foundational steps have been taken, further harmonisation is needed to support scalable, cross-domain environmental research and data reuse.