Peigean Syzygy and Storm Surge

The coastal flooding along the Northumberland Shore during the first week of January was the worst flooding ever seen in the area. Scientist have been warning us for a long time that this could happen and it has; however, I am sure that we have not seen the worst of climate change yet.

This coastal flooding was unusually severe because it coincided with an astronomical event called the perigean syzygy. A tidal effect will get stronger when syzygy and perigee occur close together. Maximal tide raising forces occur only when the Sun and Moon are in direct mutual alignment. This occurs at syzygy (either full Moon or new Moon), provided also that the Moon or Sun be in eclipse with the Earth. This usually occurs when the moon is at the closest approach to the Earth or at perigee. Remember the Saxby Gale occurred during a perigean Spring tide.

Climate change is causing the see level to rise everywhere along our coast. The sea level is rising for a combination of reasons. These include a general rise in average sea level since the last ice age, regional subsidence, or sinking of land relative to the sea, and global warming associated with climate change.

We can expect this rise in sea level to have many effects, both on the biological and physical environments, as well as an effect on the human environment. Research shows that much of Nova Scotia’s coast will feel the effects of sea level rise, with the Atlantic-facing shoreline being particularly sensitive.

The phenomenon of storm surge is particularly important, because it causes waves to pile water or in the case of last week, ice to pile onshore, creating a higher possibility of damage. Storm surges occur when seawater is driven onshore by a storm’s high winds and low pressure. The highest storm surges tend to occur along the province’s Northumberland Shore, along western Cape Breton, and at the head of the Bay of Fundy.

Projections by researchers show that because of climate change, tropical storms in the Northern Hemisphere will get more intense and track farther north than before. This result, combined with the rise in sea level, means that a storm’s consequences to the coast will be much greater than before.

The areas at greatest risk include
• areas that are low lying, such as Acadian dykelands including the Tantramar marsh
• areas with frequent storm conditions and high storm-surge potential
• areas with coastal infrastructure and property
• areas of sensitive ecology
• areas of rapid coastal erosion

To read more about the state of the province’s coast, visit the website at ww.gov.ns.ca/coast.

Lisa Emery, B.A. is currently living in Amherst. Lisa invites comments to her column. You can contact Lisa at: emeryvine@gmail.com or view her blog at http://emeryvinegrapevine.blogspot.com