The Community Terrestrial System Model: Facilitating the Transition of Land Model Research to Operations for Applications Spanning Weather to Climate

Land surface models exist within a wide spectrum of complexity and have diverse user and developer communities. Historically, land model research at the National Center for Atmospheric Research (NCAR) has occurred in two separate and mostly-independent groups that focus respectively on climate and weather applications. Recently, an initiative commenced to unify NCAR’s land modeling efforts toward the development of a general terrestrial systems model (the Community Terrestrial System Model, or CTSM). CTSM integrates modeling approaches across multiple labs at NCAR and is suitable for use as the land modeling component in climate models, numerical weather prediction models, ecological models, hydrologic prediction frameworks, as well as turbulence-resolving large-eddy simulation models and simple 1D atmospheric boundary layer models for process-level land-atmosphere coupling investigations. One significant CTSM goal is to facilitate the transition of community land surface model research to operations.

The CTSM computational infrastructure enables scientists throughout the land/hydrology/ecology community to work with the same code base. CTSM implementation entails restructuring the NCAR Community Land Model (the climate-application CLM) code in state-space form in conjunction with incorporating unique weather-application Noah-MP land model parameterizations. These changes both improve model robustness, and through modularization, make it easier to add new science capabilities. CTSM also leverages multiple sources of validation and benchmarking from the climate and weather communities. This CTSM unification effort will expedite community involvement in land model development, contribute to looking beyond the land surface model as a boundary condition by providing land surface process-level information to expanding user communities, and increase both atmospheric and land surface data assimilation.

CTSM introduces a modeling agility that allows the user community to choose an application-specific complexity from a single land model while promoting community advances in specific model processes through a more focused development environment. Recent advances have also included the coupling of CTSM to a generic atmospheric model through the Lightweight Infrastructure for Land-Atmosphere Coupling (LILAC). The specific case of coupling CTSM with the Weather Research and Forecasting (WRF) model will be shown and contrasted with existing WRF land surface models.