Sunny Day Flooding: When High Tides Become a Crisis

Sunny day flooding, also called nuisance flooding or blue-sky flooding, occurs when high tides push seawater into streets and neighborhoods without any storm or rainfall. It has increased by 300% since 2000 in many US coastal cities. Miami now experiences over 20 days of sunny day flooding per year, up from just 2 days in 2000. Charleston, Norfolk, and Savannah face similar trends.

The root cause is simple: higher baseline sea levels mean that normal high tides now reach levels that once only occurred during storms. King tides, the highest astronomical tides that occur during new and full moons, provide a preview of permanent future conditions. A king tide today shows what average high tide will look like in 30 years. Cities are spending billions on responses: Miami has invested $500 million in storm water pumps, Norfolk is elevating roads, and Charleston is building a $2 billion seawall.

These are temporary measures against a rising baseline. By 2050, NOAA projects that moderate flooding will occur 10 times more frequently than today in most coastal locations..