Source code repositories

The GEOS-Chem Classic source code is distributed into 3 Github repositories, as described below. This setup allows the GEOS-Chem core science routines to be easily integrated into several modeling contexts, such as:

  • GEOS-Chem Classic

  • GCHP

  • GEOS-Chem within the NASA/GEOS ESM

  • GEOS-Chem within CESM

  • GEOS-Chem withn WRF (aka WRF-GC)

This repository setup also aligns with our GEOS-Chem Vision and Mission statements.

GEOS-Chem Science Codebase

The GEOS-Chem “Science” Codebase repository ( contains the GEOS-Chem science routines, plus:

  • Scripts to create GEOS-Chem run directories, plus template configuration files for all simulations;

  • Scripts to create GEOS-Chem integration tests;

  • Interfaces (i.e. the driver programs) for GEOS-Chem Classic, GCHP, etc.


The HEMCO repository ( contains the source code for the Harmonized Emissions Component, which is used to read and regrid emissions, met fields, and other inputs to GEOS-Chem.


The GCClassic repository ( is a lightweight wrapper that encompasses GEOS-Chem and HEMCO. We say that GCClassic is the superproject (i.e. top-level source code folder), and that GEOS-Chem (science codebase) and HEMCO are submodules.