Why do marsh plants need to adapt to drought?

There are swamps that appear only at certain times. For example in spring, after snow thaw or during rains. In hot weather, swamps can disappear completely. Then the plants need adaptation to drought. Sometimes they do not use them, if the climate in the swamp does not change and there is always moisture, but sometimes such adaptations are the only way to survive. These devices include a root that goes very deep into the ground. This is necessary to extract water from the damp earth below. And small leaves, which are needed for less water evaporation from the surface of the plant.