https://www.mentalfloss.com/article/66523/how-do-anthills-survive-rain

"The ant fortresses you find on your lawn have a number of defenses. The first is the anthill that sits right on top of the nest. The mounds are usually made with special kinds of dirt or sand that absorbs water and dries quickly. Water hitting the convex dirt tends to bead and run off the side.
Some colonies, like mangrove ants, will send a soldier ant to plug up the entrance hole with its head. This living stopper prevents rain from entering but is only a temporary fix, as it blocks gas exchange with the surrounding area outside the anthill.
When heavy rain leads to water entering the tunnel, it usually doesn’t go far. Ants tend to burrow at least a foot underground and have an intricate system of tunnels that work like storm drains. As long as the rainfall isn’t too heavy, the water will pass through the nest without pooling.
With some clever tunneling, ants can trap air in various chambers throughout the nest, and entrances to chambers come from below, preventing water from coming in. "