Climate change impact on Nor'easters: An increased storm surge threat

The historic Nor'easter that buried New England under up to 40" of snow Friday and Saturday was the most intense winter storm event on record for southeastern Maine, and second most for Long Island, Connecticut, eastern Massachusetts, and perhaps Rhode Island, writes wunderground's weather historian Christopher C. Burt. His rating was based upon both snowfall amounts and winds. For Long Island and Connecticut, the Blizzard of 1888 remains unparalleled, whereas for Rhode Island and eastern Massachusetts, the Blizzard of 1978 remains the top event. His rating took into account snowfall and winds, and took into account historical storms going back over 300 years. So, what impact is climate change having upon these great storms?


Figure 1. Is it a hurricane or an extratropical storm? Satellite image of Winter Storm Nemo taken at 3 pm EST Saturday, February 9, 2013 shows a very hurricane-like storm. The storm had undergone a process known as "occlusion", which trapped a shallow area of warm air near the center. These "warm air seclusions" are not uncommon in intense wintertime extratropical storms, and Nemo was not very hurricane-like in structure, despite the appearance of this satellite image. Image credit: NASA/GSFC.

Climate change impact on Nor'easters: an increased storm surge threat
We should not be surprised to see climate change causing significant changes in the frequency and intensity of Nor'easters, since the atmosphere is undergoing great changes in its circulation patterns and moisture content that will affect all storms. As I wrote in my post, The future of intense winter storms, climate models predict that intense winter storms will become more common globally, and will shift closer to the poles. However, in the Atlantic, intense Nor'easters affecting the U.S. are not predicted to increase in number (but several studies predict an increase in intense winter storms for Northwest Europe.) The number of intense Nor'easters affecting the Northeast U.S. has not increased in recent decades, according to several studies. This analysis is supported by the fact that wintertime wave heights recorded during the period 1975 - 2005 by the three buoys along the central U.S. Atlantic coast showed little change (Komar and Allan, 2008). The damage potential from the storm surges associated with Nor'easters and hurricanes in New England is steadily increasing, though, due to global warming.


Figure 2. Surf from the infamous blizzard of 1978 pounds the coast of Scituate, Massachusetts on February 9, 1978. The storm brought Boston's highest water level on record. Hurricane Sandy brought a higher storm surge to Boston, but the storm hit when the tide was going out, and thus did not set a record high water mark. Image credit: NOAA Photo Library.

An increased storm surge threat for Boston
Of the top ten water levels measured in Boston Harbor since 1921 (all due to Nor'easters), all but one of these events occurred during the the second half of that 92-year period. That's due to rising sea levels. The official top ten storm tides since 1921 at the Boston tide gauge, relative to high tide (Mean Higher High Water, MHHW):

1. 4.82' - February 7, 1978 (Blizzard of 1978)
2. 3.92' - January 2, 1987
3. 3.86' - October 30, 1991 (Perfect Storm)
4. 3.76' - January 28, 1979
5. 3.75' - December 12, 1992
6. 3.70' - December 12, 1959
7. 3.62' - February 2, 1972
8. 3.52' - April 4, 2007
9. 3.51' - May 5, 2005
10. 3.43' - December 12, 2010

Sea level at the Boston tide gauge has risen about a foot (.25 meters) since records began in 1921. Most of that rise is due to the expansion of ocean waters due to global warming, plus increased melting from glaciers and icecaps. According to an excellent analysis by Andrew Freedman of Climate Central, continued sea level rise in Boston will increase the odds of a 1-in-100 year coastal storm surge flood by a factor of 2.5 by the year 2030. Even given the low end of sea level rise scenarios, and without assuming any changes in storms, 1-in-10-year coastal flooding events in the Northeast could triple by 2100, occurring roughly once every 3 years, simply in response to higher sea levels (Tebaldi et al. 2012). Nemo arrives just days after a report the nonprofit Boston Harbor Alliance warned of the region’s growing vulnerability to such storm surge events. The report found that coastal flooding of 5 feet above the current average high tide--a 1-in-100 year flood--would inundate 6.6 percent of the city of Boston. At 7.5 feet above the current average high tide, more than 30 percent of Boston could be flooded, the study found. Boston has gotten lucky two storms in row now--both Hurricane Sandy (storm surge of 4.57') and Winter Storm Nemo (storm surge of 4.21') brought their peak surge near low tide, so the water level during these storms did not make the top-ten list, even though these were two of the four highest storm surges ever measured in Boston. Mr. Burt comments, "it is a bit unsettling that two of the most significant storms in the past 300 years to strike the northeastern quadrant of the U.S. have occurred within just four months from one another." Rising sea levels are already making coastal living at low elevations an increasingly precarious proposition in the Northeast. If Sandy and Nemo are harbingers of a new era of stronger storms for the Northeast U.S., the double-whammy combination of bigger storm surges riding in on higher sea levels will make abandoning higher-risk portions of the coast a necessity.


Figure 3. Severe beach erosion on Plum Island, MA, observed on February 10, 2013, in the wake of Winter Storm Nemo. It was lucky the peak storm surge hit near low tide, or else the coastal damage would have been far more severe. Image credit: Mike Seidel.


Figure 4. Sea level at the Boston tide gauge from 1921 - 2011 shows 2.77 mm/year of rise, or .98 feet (.25 meters) in 91 years. Image credit: NOAA Tides and Currents.

Links and references
My blog post, The future of intense winter storms

My blog post, Heavy snowfall in a warming world

Andrew Freedman of Climate Central's post, Blizzard of 2013 Brings Another Threat: Coastal Flooding

Joe Romm of climateprogress.org has a post, Climate Change and Winter Storm Nemo that has an excellent discussion of how climate change has modified the environment within which storms form, increasing their potential to cause heavy precipitation events.

Komar, P.D. and J.C. Allan, 2008: Increasing hurricane-generated wave heights along the U.S. East coast and their climate controls. Journal of Coastal Research, 24(2), 479-488.

Tebaldi, C., B.H. Strauss, and C.E. Zervas, 2012: Modelling sea level rise impacts on storm surges along US coasts. Environmental Research Letters, 7, 014032

Tom Niziol has an interesting post showing why Connecticut got so much snow from the storm: Northeast snow storm--the pivot point

Lee Grenci discusses how the two winter systems that combined to create the mighty snowstorm didn't really merge, but instead rotated around each other: Looming Snowstorm and the Fujiwhara.

Jeff Masters