Sea Level Rise in Saint JOhn
Two studies have looked at regional projections for the 21st century for Saint John, New Brunswick. They account for regional factors that affect local sea level rise. Both studies are based on the most recent global projections published in the 5th Assessment Report released by the Intergovernmental Panel on Climate Change (IPCC) in 2013. These studies can be found using the links at the bottom of this page.
Current understanding of sea level rise for Saint John based on the two regional studies looks like this:
- Within the blue line scenario (significant and immediate mitigation), a sea level rise of 48cm ±29cm is projected by 2100 in Saint John relative to the levels recorded from 1986 to 2005 (James et al.).
- Within the red line scenario (“business as usual”), a sea level rise of 81cm ± 38cm is projected by 2100 in Saint John relative to the levels recorded from 1986 to 2005 (Daigle).
- Within the red line scenario (“business as usual”), a sea level rise of 81cm ± 38cm is projected by 2100 in Saint John relative to the levels recorded from 1986 to 2005 (James et al.).
In the Bay of Fundy region, the majority of the coastal changes are primarily caused by tidal driven forces of erosion, and the changing of the sea level throughout geologic time (Shaw et al., 1994; Stea et al., 1998). The last glaciation in the region occurred 18 000 years ago and was known as the Wisconsin Glaciation and since its disappearance, certain regions along the Bay of Fundy have been submerging. It has been estimated that since people first arrived in this region, the sea level has risen approximately 40 m, and around 1.2 m since Pere Pierre Baird described the Saint John Harbour. Therefore, it can be assumed that certain areas that used to be be too high to be subjected to wave action, now are (Desplanque and Mossman, 2004). The latest IPCC report concluded that it was an extremely likely event, with more than 95% confidence, that the observed warming since the mid-20th century has been dominantly caused as the result of human activity (Daigle, 2014).
The impacts embarked upon marine and terrestrial ecosystems in regards to sea level rise and accelerated coastal erosion remains to be poorly quantified. However, in cases where there continues to be primarily historical sea level rise occurring, ecosystems naturally reestablish an equilibrium. As an example, within salt marshes if the rate of accretion is able to keep up with sea level rise, there would be a limited impact acted upon it. Consequently, if the sea level rise exceeds to ability of such marsh area to accrete, or where the shore is blocked by natural or artificial barriers, the loss of habitat and of valuable ecosystem services will be lost (Atkinson et al., 2016). Moreover, this is an important consideration in the response to the East Coast’s coastal systems in regards to sea level rise as it holds the potential loss of important habitat through a process known as coastal squeeze. This process is not limited solely to tidal marshes but also estuaries, eel grasses, beaches, and mudflats which also provide valuable ecosystem services along our coastlines.
In order for coastal squeeze to not occur, the extent of the new marsh system is largely dependent on the extent of its backwards migration on the landward slope which can provide room for its movement. However, though a high backshore relief can limit the backwards migration of the new marsh system, it is the artificial barriers of roads, causeways, sea walls, dikes, and foundation fill that are all dominant causes in coastal squeeze.
These particular ecosystems provide a diverse array of services both for native wildlife and anthropogenic needs. These ecosystems provide: the provision of spawning and nursery habitats for the Atlantic’s aquatic species including commerce fish, crucial nesting habitats for multiple types of bird species, nutrient and absorption, and sediment retention for the area (Atkinson et al., 2016). In particular, the tidal flats in the Bay of Fundy provide a critical feeding habitat for migratory birds (Hicklin, 1987; Hill et al., 2013) and as such there is a global concern about the protected losses of intertidal habitats available for these birds (Galbraith et al., 2002). Without regards to accelerating sea level rise, it is predicted that two thirds of the coastal salt marshes within Atlantic Canada have been either drained and converted to agricultural land or diminished by industrial or urban development (Austen and Hanson, 2007).
In the recent decades, coastal areas have become more industrial and urbanized due to their associated aesthetic and demand for waterfront living. As such, there has been considerable alterations occurring along our coastlines due to present and historical settlement patterns. Many of the coastal communities, in any area around Canada, are now characterized by significant residential and commercial waterfront developments whereas they have previously been warehouses, wharves, and traditional docks (Mercer Clarke et al., 2016). Most of the modern infrastructure in place as of right now has been designed to a standard that is based on historical climate conditions. However, no that there is evidence of increased storm frequencies, increased precipitation, as well as an increased sea level rise coupled with accelerated erosion rates, it is likely that these designs will be overtopped in the future. As such, any changes to the land cover in the coastal zone can destroy or impair any native species in those locations (Ban and Alder, 2008; Halpern et al., 2008; Burkett and Davidson, 2012) and any hard engineering technique emplaced to protect societal assets can also lead to the loss of intertidal habitats. Additionally, any increased amount of development within coastal zones can increase coastal squeeze and lead to a loss of valuable marshes, dunes, and beaches in the forthcoming decades (Jolicoeur and O’Carroll, 2007; Craft et al., 2009; Bernatchez et al., 2010; Feagin et al., 2010; Doody, 2013; Torio and Chmura, 2013; Cooper and Pile, 2014).
The extreme total sea level values, or flooding scenarios, have been calculated in the Saint John region to represent the worst possible scenario in regards to flooding. This scenario would occur where a storm surge event occurs near the high portion of the tidal cycle (the spring tide). Each of the return period statistics have been calculated and in turn provide a relative probability that a given storm surge would coincide with the spring tide. A return period represents the average time between two similar occurrences of an event that exceeded a given level (Daigle, 2014).
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