High Water by Month

A Century of Charleston Harbor Water Levels

I’ve been tracking tidal flooding trends in Charleston for the past decade or so. Through my work in flood resilience, including helping develop the Charleston Water Plan and my Mean High Water project, these statistics have helped tell the story of what we’re seeing and why it matters.

Anyone who’s lived in Charleston for at least a few years has noticed a change. Low-lying streets flood more often. 8-foot tides, once rare, have become more common. Hell, we even deploy electronic messaging boards to warn of flooding on sunny days.

Inspired by climate scientist Ed Hawkins’ Warming Stripes, I wanted to create a visualization that focused on water levels rather than the number of tidal floods. I developed High Water by Month.

The visualization plots the highest tide recorded during every month from 1922 through 2025 at NOAA’s Charleston Harbor tide gauge. Each bar represents a month. Bar height corresponds to the month’s highest water level, while color indicates whether that level remained below flood stage or reached minor, moderate, or major coastal flood thresholds. The ten highest water levels are labeled.

I’ve mirrored the trend below, as if reflected in water. The harbor appears to rise from the water. Hurricanes and coastal storms still stand out as spikes, but the pattern is harder to ignore. As sea levels have risen, high water levels have become more common.

Charleston has always flooded. What’s changed is the starting point. Sea level in the harbor has risen approximately 1.2 feet since the 1920s. A century ago, the highest tide in a typical month reached about 6.2 feet, well below flood stage. Today it’s about 7.4 feet, almost half a foot above flood stage.

Storms come and go. The water Charleston starts from keeps rising.