 This prevents use of the method in general applications where the risk of non-convergence is high.The method has also been criticized for over-emphasizing the role of capillarity, and for being in some ways 'overly simplistic'  In one dimensional simulations of rainfall infiltration into dry soils, fine spatial discretization less than one cm is required near the land surface., which is due to the small size of the representative elementary volume for multiphase flow in porous media.In three-dimensional applications the numerical solution of Richards' equation is subject to aspect ratio constraints where the ratio of horizontal to vertical resolution in the solution domain should be less than about 7.