WASHINGTON D.C., DC — The remnants of Nicole brought a lot of rain to our region, and while it wasn’t too destructive this time around, the DMV is no stranger to tidal flooding.
That has some people wondering:
THE QUESTION:
Are floods happening more frequently in our area?
THE SOURCES:
William Sweet, Oceanographer from the National Oceanic and Atmospheric Administration (NOAA)
Jeremy Geiger, Meteorologist from the National Weather Service
Flood data from NOAA and the Environmental Protection Agency
THE ANSWER:
Yes, flooding is happening more frequently than in the past, and it is expected to keep getting worse.
WHAT WE FOUND:
For over 70 years, NOAA has been collecting data from gauges along the coast that measure sea levels and high tide flooding.
If you focus on our region and compare the last decade to decades before, the trend is clear.
In the two decades between 1990 and 2010, D.C. saw an average of 2.4 tidal flooding events per year. In the last decade, that increased to 7.6 per year.
That means the average number of flooding events in D.C. more than tripled (3.2x).
The jumps were even larger in some surrounding areas: 3.5-times more floods in Baltimore, and 5.5-times in Annapolis.
“That's a direct consequence due to sea level rise,” said Sweet, “the number of days of high tide flooding, often when it's sunny outside and no storm around, has doubled or upwards of tripled in frequency in the last 20 years due to about five inches or so of sea level rise.”
The geography of D.C. just feeds into the problem.
“DC is on the confluence of both the tidal Potomac and also the Potomac River coming in,” said Geiger. “So you have the tides, but you also have an influence of rain flowing down the river.”
So, floods are happening more often and D.C. is uniquely vulnerable. What about the future?
Sweet tells us that sea level rise - and the number of floods - is projected to keep going up.
“For five to 10 or so floods that we expect to occur, let's say this year or next year,” said Sweet, “that number jumps up to 55 to 85 days per year, with flooding hitting about two feet above average high tide.”