Key takeaways
- Even small increases in sea level make high tide and storm flooding much more frequent.
- Erosion, wetland loss and saltwater intrusion threaten coasts before they are permanently flooded.
- Communities can protect, accommodate or retreat, and most will use a mix.
Rising seas reach inland
A few centimeters of rise may seem small, but it changes how often the sea reaches places it used to touch only rarely. Higher baseline sea level means that ordinary high tides, storm surges and big waves all reach farther and last longer.
High tide flooding
Often called nuisance or sunny day flooding, high tide flooding happens when tides alone push water onto streets and into storm drains. In many U.S. coastal cities, these floods now happen several times more often than in 2000, and they are projected to occur dozens of days per year by 2050 in many places.
Storm surge
Sea level rise adds directly to the height of every storm surge. A storm today pushes water higher and farther inland than an identical storm a century ago, and floods that were once expected every hundred years are becoming far more frequent.
Erosion and wetland loss
Higher water erodes beaches and bluffs and drowns marshes and mangroves that cannot build up or move inland fast enough. These ecosystems protect coasts from waves and are home to fisheries and wildlife.
Saltwater intrusion
Salt water pushes into rivers, wells and the groundwater below farms and cities. In low lying islands and deltas, this can make land unusable well before it is permanently flooded.
Compound flooding and adaptation
Compound events
The most damaging floods often happen when several drivers line up: a high tide, a storm surge, heavy rain and swollen rivers, sometimes on top of an El Niño or a warm ocean that has raised regional sea level. Rising seas make each combination more likely to cross a damaging threshold.
Thresholds matter more than averages
Impacts grow sharply once water crosses a threshold such as the top of a seawall or the elevation of a road. Because the distribution of high water levels is narrow at many sites, a modest rise in the average can multiply the number of days above that threshold. This is why flood frequency is growing much faster than sea level itself.
Adapting to rising seas
Communities have several options, usually used together:
- Protect with seawalls, levees, surge barriers and natural defenses such as restored marshes, reefs and dunes.
- Accommodate by raising buildings and roads, improving drainage and updating building codes.
- Retreat from the most exposed places over time, through planned relocation and buyouts.
Good decisions depend on good information: local projections, flood forecasts and continued measurements that show whether the sea is following the expected path. Supplying that information is the purpose of this site and of the tools built by Blue Earth Systems.