The Community Land Model (CLM4.5 in CESM1.2.0) is the latest in a series of global land models developed by the CESM Land Model Working Group (LMWG) and maintained at the National Center for Atmospheric Research (NCAR). This guide is intended to instruct both the novice and experienced user on running CLM. This guide pertains to the latest version CLM4.5 in CESM1.2.0 available for download from the public release subversion repository as a part of CESM1.2.0. Documentation may be different if you are using an older version, you should either use the documentation for that release version, update to the latest version, or use the documentation inside your own source tree. There is information in the ChangeLog file and in the What is new with CLM4.5 in CESM1.2.0 since previous public releases? regarding the changes from previous versions of CESM.

Note: This release of CLM4.5 in CESM1.2.0 includes BOTH CLM4.0 physics used in previous releases as well as the updated CLM4.5 physics. Both CLM as well as CLM support tools allow you to trigger between the two physics modes. Most often when we refer to CLM4.0 we are referring to the CLM4.0 physics in CLM4.5 in CESM1.2.0 rather than to a specific version of CLM4.0 (where we would give the exact version). Likewise, when referring to CLM4.5 we are referring to the CLM4.5 physics in CLM4.5 in CESM1.2.0.

The novice user should read Chapter 1 in detail before beginning work, while the expert user should read What is new with CLM4.5 in CESM1.2.0 since previous public releases? and Quickstart to using CLM4.5 chapters, and then use the more detailed chapters as reference. Before novice users go onto more technical problems covered in Chapter 2, Chapter 3, Chapter 4, or Chapter 5 they should know the material covered in Chapter 1 and be able to replicate some of the examples given there.

All users should read the How to Use This Document and Other resources to get help from sections to understand the document conventions and the various ways of getting help on using CLM4.5. Users should also read the What is scientifically validated and functional in CLM4.5 in CESM1.2.0? section to see if their planned use of the model is something that has been scientifically validated and well tested. Users that are NOT using NCAR machines or our list of well tested machines should also read the What are the UNIX utilities required to use CLM4.5? section to make sure they have all the required UNIX utilities on the system they want to do their work.

Developers that are making changes to CLM either for their own development or for development that they hope will eventually become a part of the main CLM should read the Chapter 8 chapter. We have a suite of test scripts that automatically test many different model configurations and namelist options, as well as ensuring things like restarts are bit-for-bit and the like. It's helpful to use these scripts to ensure your changes are working correctly. As well as being a required part of the process to bring in new code developments. And it's far easier to use the automated scripts rather than having to figure out, what to test, how to do it, and then finally do it by hand. If you are using non supported machines you may also want to use the test scripts to make sure your machine is working correctly.