1 Synopsis

This document describes software requirements for the Community Land Model (CLM) which serves as the land component of the Community Climate System Model (CCSM). CLM2 is the latest in a series of global land surface models. Derived initially from the Common Land Model (CLM), it simulates biogeophysical and biogeochemical land-atmosphere interactions, especially the effects of land surfaces on climate and atmospheric chemistry. The model grid may range from a single point to the entire globe, and it may be run stand-alone, coupled to an atmospheric model, or fully coupled with CCSM. Additional processes have been added to CLM to handle dynamic global vegetation, biogenic volatile organic compounds, and river transport. It is expected that these and other model features will be further developed as the model is improved.

The software requirements for CLM are derived from the needs of a diverse group of scientists and users most of whom participate in the Land Model Working Group (LMWG). The overall requirements can be categorized as follows:

• Scientific - specifications of biogeophysical and biogeochemical processes which the model must effectively simulate.

• Software - specifications of code performance, functionality, configurability, extensibility, usability, reliability, and style with an emphasis on performance targeting particular computer platforms including the IBM SP, the SGI Origin, and networked clusters while maintaining performance portability.