Complex crack patterns are ubiquitous, covering surfaces from films in
technology to old paintings, from areas on geological scales to
biological systems. They are often induced by material change of
volume, caused either by thermal or desiccation shrinkage. We
investigate emergent morphologies of cracking patterns in
directionally drying systems. In our simulations, rectangular slabs
attached to a substrate are exposed to a moving desiccation front.
This induces stress in the samples, which is released by cracks that
follow the front. Depending on the adhesion to the substrate,
thickness of the sample and imposed desiccation gradient we observe
two topologically distinct cracking patterns: purly branching, and
interconnected networks of cracks. We discuss the two sources of
stress in the system: (i) adhesion to the bottom and (ii) desiccation
gradient. We show how the scalings and topology of the
patterns change, depending on which of them dominates.