Dec 212014

U.S. Cities Already Flooding

We already posted an article about U.S. cities that are predicted to go underwater because of climate change but not about cities that are already at the tipping point of experiencing at least nuisance-level flooding at an accelerated rate. Accelerated flooding is already mostly noted along the Gulf Coast and East Cost of the United States. These means that the rate of flooding is not just increasing but that it is also accelerating. Particularly noteworthy is what is known as sunny day flooding, times when streets flood and there is no big storm to account for it, just high tide.

The tipping point has been described as nuisance flooding at least 30 days out of the year. The main point from the chart displayed below is that Wilmington, NC, Washington, DC, and Annapolis, MD. are already past the tipping point. At least a half dozen more major cities are expected to reach it by 2020 and dozens more in the next few decades after that.

Defining Nuisance Flooding and Tipping Points

Cities already at the tipping point:  Image: Earth's Future/Sweet and Park 2014

Cities already at the tipping point:
Image: Earth’s Future/Sweet and Park 2014

Nuisance flooding is defined as sea levels of about one to two feet over typical high tides, and these floods tend to impact city streets of areas that are no more than a couple of feet over sea level. The problem is that this used to be rare or caused by large weather events, and it is not becoming common. In other words, the ecology of coastal areas in the United States and all around the globe has already reached a tipping point or a new equilibrium, but there is no way to provide assurance that the situation won’t get worse. Because of accelerated rates of minor flooding, it would probably be prudent to expect that it will get worse.

Major U.S. Cities Studied for Nuisance Flooding

These conclusions were drawn from measurements taken over 100 years. The reason that Miami, currently experiencing plenty of sunny day flooding, was not included is because the measurement point was moved after Hurricane Andrew, so 100 years of consistent data is not available.

These are the major cities highlighted in the study:

  • Boston, MA
  • Providence, RI
  • New London, CT
  • New York City, NY
  • Atlantic City, NJ
  • Washington, DC
  • Philadelphia, PA
  • Baltimore, MA
  • Charleston, SC
  • Key West, FL
  • Galveston, TX
  • Port Isabel, TX
  • La Jolla, CA
  • San Francisco, CA
  • Seattle, WA

Rates are different at different spots along U.S. coastlines. The scientists remind us that the ocean is not flat and level like a bathtub. Currently, in the U.S., The Gulf of Mexico and the Atlantic cities are experiencing worse rates of accelerated flooding than is getting experienced along the Pacific.

Conclusions About Accelerated Flooding in U.S. Coastal Cities

This is the conclusion of the study cited in the first source:

Impacts from recurrent coastal flooding include overwhelmed storm water drainage capacity at high tide, frequent road closures, and general deterioration and corrosion of infrastructure not designed to withstand frequent inundation or saltwater exposure. As sea levels continue to rise and with an anticipated acceleration in the rate of rise from ocean warming and land ice melt, concern exists as to when more substantive impacts from tidal flooding of greater frequency and duration will regularly occur. Information quantifying these occurrences and the associated frequency-based tipping points is critical for assisting decision makers who are responsible for the necessary mitigation and adaptation efforts in response to sea level rise.


From the extreme to the mean: Acceleration and tipping points of coastal inundation from sea level rise :

Dec 102014
U.S. cities under water

According to a PBS article, Will Your City be Under Water, previous estimates of just how many U.S. cities would flood were too conservative because scientists only considered the relation of the land to sea level but not to high tide. For example, about 5 million people live in about a quarter of a million residences that are less than four feet over high tide. That’s within a century, but sea levels could rise by 19 inches by 2050, and that’s well within many of our reader’s lifetime.

The Surging Seas Interactive Map

This widget comes from, and it allows you to adjust for different predicted levels of rising waters and high tides to see current predictions. You can choose to view maps, see quick summaries, and spend time viewing a very detailed analysis. In some cases, this drills down to the neighborhood level or threatened cities.

If you’re interested in seeing if your own city is threatened by rising tides, you can also visit for an interactive map and much more detailed analysis. The estimates of rising sea levels and tides in the next century is from two to seven feet. The map allows you to adjust for different increases to see how it impacts different cities and regions under a variety of sea level and high tide rise scenarios .

Note: The map does not account for future preventative members like the erection of sea walls.

States with the greatest populations in harm’s way of a sea level rise:

  • Florida
  • Louisiana
  • California
  • New York
  • New Jersey

Florida is the state with the greatest population at risk of losing their homes.There have already been many dire predictions that large parts of the Miami Metro area are doomed. So far, attempts to build sea walls and increase the elevation of buildings have not worked. The problem is that the water is beginning to saturate the limestone that provides the land for the tip of Florida, and the city is actually sinking as the sea rises.

All of  these states also have very dense populations near the sea, so it does not mean they are the only states with a lot of land area to lose. Any state with a coastline by the Atlantic, Pacific, or Gulf of Mexico faces the same threats. Of course this includes Texas and other Gulf Coast state, the Pacific coast, and the Atlantic coast.

Most of these percentages are calculated by the number of residents, and they are not calculated by the square miles of land lost. Of course, the loss of many square miles of land could mean the loss of agriculture, ports, industry, and much more.

Will Sea Level Rise Predictions Come True?

Even the folks at Climate Central caution against taking predictions for any one area as something engraved in stone. However, they do say that when spread over all areas, these predictions are likely to average out as close to correct. For example, they may have overestimated the threat to one city, or not accounted for future preventative measures, but it is likely they were too conservative in other areas. For comparison, this is similar to estimating an athlete’s performance over all games and not just one.

Past Sea Level Increases

According to the Climate Change organization, global temperature changes have increased average sea levels by about 8 inches since the 1880’s, but the rise is now accelerating. Of course, various weather patterns means that the rise is slow some years and catastrophic in others. In other words, the loss of dry land doesn’t just come in a steady line on a graph but in a more jagged one.