Summary:

## Reconciling Changes in Area

This section discusses how the Community Land Model (CLM) handles changes in the area of different land units, such as crop land and glacier, over time.

Key Points:
1. Changes in crop land area come from the landuse.timeseries dataset, while changes in glacier area come from the ice sheet model.
2. If the total area of crops and glaciers decreases, the natural vegetation land unit is increased to fill the abandoned land. If the total area increases, other land unit areas are decreased in a specified order (natural vegetation, crop, urban, wetland, lake).
3. The model always matches the glacier areas from the ice sheet model exactly, even if that means disagreeing with prescribed crop areas.
4. For land units other than crops, glaciers, and natural vegetation, their areas can decrease but never increase.
5. The model only tracks net changes in area, not gross transitions between land units. This can lead to less accurate adjustments of carbon and nitrogen states compared to tracking gross transitions.

Overall, the article describes the rules and implications of how CLM reconciles changes in the area of different land units over time to maintain a total land area of 100%.