Richards equation and canopy
Combining Richards equation and the canopy module is not behaving stably under all circumstances.
The problem is that the transpiration is reducing the soil water content without taking into account the water retention curves, causing numerical problems when solving richards equation.
A solution is feasible, but requires some programmig. One solution is to apply the transpiration as a flux, with the disadvantage of loosing the different root depths from wich water is taken up by roots. But it probably is the fastest thing to program.
Another solution (and the most realistic one) is to use the source/sink term in Richards equation to deal with the transpiration.