This paper presents the Scenario Application Domain Extension (Scenario ADE) for CityGML 2.0 and the rationale behind its development. CityGML 2.0 and its ADEs are primarily designed to represent one coherent state of an urban environment. No concurrent hypothetical alternatives are supported, nor are simulation results connected to the precise city-model state, engine, settings and boundary conditions that produced them. In this work, scenario information is decomposed into three pillars: Context, Strategy and Configuration. These pillars are translated into design principles and used to evaluate the proposed data model for the Scenario ADE. The Scenario ADE is available in two encodings: XML and SQL, the latter for the 3DCityDB relational database. Results show that the current version can represent parallel scenario branches in a unified approach, avoid unnecessary duplication of data, preserve object and attribute lineage, and bind simulation outputs to their originating features and configurations. Our findings, based on energy simulations carried out in Rotterdam, show confirm that the Scenario ADE can act as a domain-agnostic scenario-management and lightweight provenance layer for CityGML 2.0, although its treatment of context, attribute semantics and non-simulation provenance requires further refinement.