NOAA Report – El Niño May Increase Tidal Flooding in USA


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According to a NOAA report released earlier this month, many coastal communities in the USA could experience a higher number a floods between now and April next year. In some cases there could be between 33 to 125 percent increase in “nuisance flooding days”.

The report says that higher sea levels and frequent storm surge, compounded by the strengthening El Niño, will result in the highest number of nuisance flooding days on record in some communities along the Mid-Atlantic and West Coast.

Norfolk, Virginia, for example, saw 8 days of nuisance flooding during the 2014 meteorological year. Thanks to El Niño, Norfolk may experience 18 days of nuisance flooding during the 2015 meteorological year, an increase of 125 percent, according to the report. Atlantic City, New Jersey, may see 36 days (33% increase), and San Francisco, California, 21 days (75% increase) of nuisance flooding.

el nino and flooding
This table shows communities in the US that may see an increase in predicted nuisance flooding due to El Nino. Credit: NOAA

Tidal Flooding – A Growing Trend in the USA

The recent findings build upon two nuisance flooding reports issued last year led by NOAA scientists William Sweet and John Marra. The previously published reports show coastal communities in the United States have experienced a rapid growth in the frequency of nuisance tidal flooding, a 300 to 925 percent increase since the 1960s, and will likely cross inundation tipping points in the coming decades as tides become higher with sea level rise.

“We know that nuisance flooding is happening more often because of rising sea levels, but it is important to recognize that weather and ocean patterns brought on by El Niño can compound this trend,” said Sweet. “By using the historic data that NOAA has collected from tide gauges for more than 50 years, we can better understand and anticipate how the weather patterns may affect nuisance flooding in these communities.”

The Risks of Nuisance Flooding

Nuisance flooding causes public inconveniences such as frequent road closures, overwhelmed storm water systems, and compromised infrastructure. The extent of nuisance flooding depends on multiple factors, including topography and land cover.

NOAA’s study defines nuisance flooding as a daily rise in water level above minor flooding thresholds set locally by NOAA weather forecasters and emergency managers for coastal areas prone to flooding.

“Improving the resilience of coastal communities means helping them to understand their risks,” said Holly Bamford, Ph.D., assistant NOAA administrator for the National Ocean Service, performing duties of the assistant secretary of commerce for conservation and management.

“NOAA monitors sea level trends and interprets how those trends project into the future. This is especially important for coastal community and regional planners in preparing to protect their communities from both nuisance flooding and the increased risk of storm surge which can come from it.”

nuisance flooding due to El Nino. Credit: NOAA
A car splashes through a flooded Charleston neighborhood. Nuisance flooding causes public inconveniences such as frequent road closures, overwhelmed storm water systems, and compromised infrastructure.
Credit: NOAA

Find the full NOAA report here.