FINAM – is not a model (v1.0): a new Python-based model coupling framework

Abstract. In this study, we present a new coupling framework named FINAM (short for "FINAM Is Not A Model"). FINAM is designed to facilitate the coupling of independently developed source codes and enable seamless model extensions by wrapping existing models into components with well-specified interfaces. Positioned between a coupling library and a full-fledged framework, FINAM allows users to couple preexisting wrapped models or to build models from scratch using its components. The primary goal of FINAM is to leverage the power of Python, facilitating rapid prototyping and ease of use for complex workflows while offloading computationally intensive parts to native models. FINAM supports bidirectional coupling of spatial models, enabling fast in-memory data exchange, and provides a consistent interface for flexible coupling. The main assumption for a successful coupling is that every model operates with a time loop at its core. This design of FINAM allows for straightforward model extensions written in Python without altering the original model source code. Python's robust interoperability features further enhance FINAM's capabilities, allowing interfaces with various programming languages including Fortran, C, C++, Rust, and others. This paper describes the main principles and modules of FINAM and presents example workflows to demonstrate its features. These examples range from simple toy models to well-established models like OpenGeoSys and Bodium covering features like bidirectional dependencies, complex model coupling, and spatio-temporal regridding.