At the global scale, sea level is rising. Measured at tide gauges on every continent and by satellites on orbit, global average sea level has risen about 10-12 inches over the last 100 years (1920-2020)

During extremely high tides, the sea literally spills onto land in some locations, inundating low-lying areas with seawater until high tide has passed. Because this flooding causes public inconveniences such as road closures and overwhelmed storm drains, the events were initially called nuisance flooding. To help people understand the cause of these events, they are now referred to as high-tide floods.

By definition, inland flooding doesn't occur on the coast, yet hazard specialists consider it with other coastal issues because it is often the result of landfalling coastal storms.

Inland floods can also occur after rain falls for many days in a row, as a result of brief periods of intense precipitation, when snowpack melts quickly, or when dams or levees fail. Whenever the volume of water on land overcomes the capacity of natural and built drainage systems to carry it away, inland flooding can result.

When severe storms such as hurricanes, cyclones, and nor'easters move toward land from the ocean, low pressure and strong winds can push abnormally high water levels onto the coast. Storms moving across the Great Lakes can also produce flood-causing surges.