Desiccation is the process of becoming completely dry — not a little dry, but dried out. Scientists use it for soil and wetlands that lose their water, for food dried so it will keep, and for living things or samples dried until almost no moisture is left. In geography it can name what happens when a lake or marsh slowly dies. It is a formal, textbook word. In everyday talk people just say drying out. Though actually, it is the process, the becoming-dry, not merely the dry state at the end; once the thing is already dry, you are looking at the result of desiccation.