Hardwood is standard in wood floor planking because it's attractive and can withstand a lot of wear and tear. When installed correctly and protected with a quality wood finish, a hardwood floor can last for decades. Unfortunately, errors in construction and some living environments are not beneficial for hardwood flooring. If your floor is bulging, you could have a major problem.
Flooring contractors bring hardwood into the room where it will be installed a couple of weeks before they install it. Because wood is a natural material that moves, the planks need this time to acclimate to the interior living environment. Planks that come from an air-conditioned warehouse and are installed without the benefit of having adjusted to the humidity level in the room can swell and bulge.
During installation, a small space remains between the hardwood flooring planks and the wall. This gap, which is about 1/4-inch wide, allows the wood to expand without bulging. The gap isn't noticeable after the floor is finished and covered with decorative baseboard.
When wood absorbs water, it swells. Repairing a hardwood floor that experiences a flood or standing water for any length of time can be difficult if not impossible. Mop up liquid spills immediately. Even if you're vigilant, some liquid can seep between the hardwood planks and result in swelling and warping.
If the bulging is minimal -- just barely visible to the eye -- you can screw the raised section(s) down and fill the holes with matching wood filler to level the floor. Before attempting to screw down the raised areas, cover the bulging board with a damp towel, rewetting it as it dries, for at least two days. If only a few boards are warping, you can take them off, install new boards and stain and finish them to match the existing flooring. If the majority of the boards have large bulges, you can screw them down as instructed above; but if the boards split, you may have to remove them and install a new floor.