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## Water and Energy Conservation

When the subgrid area within a gridcell changes, the water and energy states remain unchanged on a per-area basis. This can lead to changes in the total gridcell water and energy content.

For example, if the area of a column with less water mass increases at the expense of a column with more water mass, the total gridcell water content will decrease, even though the water mass per unit area remains the same.

To conserve water and energy, the total content of each gridcell is summed before and after changes in area. Differences in liquid and ice water content are balanced by liquid and ice runoff terms, which can be positive or negative. Differences in energy content are balanced by a sensible heat flux term, which can also be positive or negative. These balancing fluxes are spread evenly throughout the following year.

There is a special case when a new crop column type comes into existence. In this case, the column's below-ground temperature and water states are copied from the natural vegetated column in its gridcell, so that these state variables begin in a close-to-spun-up state. Other state variables begin at their cold start initialization values.