When potatoes are in the ground, do they swell when it rains?

Potatoes do not swell when it rains. When it rains the potatoes absorbs water mostly through its roots. 

Potatoes are considered as a starchy, tuberous root crop. Since it is a root crop, therefore, it is part of the root of the plant and is grown underground. The answer would be NO. Potatoes that are in the ground do not swell when it rains. Instead, these potatoes also absorb the rain water just like any other roots of plants do.