Converting NLCD data to USGS or Modis land-use data

I have found a way to convert NLCD land-use category indices to other category indices (e.g. USGS 24-category or Modis 20-category) using gdal. The data now can be processed by the geogrid.exe and everything looks good. However, the current mapping between NLCD categories and USGS categories is based on my own judgement. I have been searching for some research articles about that but couldn't find one. Does anyone have some references which can help?
Thanks.

WRF is able to take NLCD data as input. I wonder why you want to remap NLCD to MODIS or USGS ?

So do you mean the NLCD40, which merges NLCD and Modis categories?

Yes, that is the data WRF can process directly.

It works! Thanks.