Sea Level Rise Projection Map – Boston

Staring Boston right in the eye, sea level rise taunts the city to devise countermeasures against the continuously lapping water that have increased almost a foot since 1921 and will continue to rise to 1.5 feet by 2050. Considering many factors, cost-efficient but effective measures are taken as Boston braced themselves for more war against the sea.

Earth.Org has mapped the potential look of the floods Boston might have to fend off more often by 2100 with current sea level rise projections. 

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Situated right by the shore, Boston is ranked as the 8th most vulnerable coastal city to flooding according to the Organization for Economic Cooperation and Development (OECD). Even without the occurrence of a storm, high tide on a usual day is enough to drench parts of the city. Thermal expansion of seawater and ice sheet melt are the driving factors behind sea level rise.  It has increased tidal flood frequency by nine events per year (compared to the 1970s), and could go up to 70 more per year by 2045. Aware of the danger this represents, the city has declared a city-wide redesigning of its shorefronts to minimize flood impact on day to day life. 

Large areas of the city will still be flood-prone, especially when considering the possibility of a 1-in-100 year storm surge (whose intensity has a 1% chance of occurring in any given year) on top of sea level rise. The question is then whether it is worth investing in costly adaptation or simply relocating communities. “You either protect people or you get them out of the way,” Michael Oppenheimer from Princeton University’s geosciences and international affairs said. “There just isn’t a choice”. The socio-economic disparity between some of the vulnerable areas will have to be carefully considered by officials when making this decision.

Adaptation is already underway: the main street in Charleston is raised by about two feet, watertight steel doors were erected at the rail tunnel entrance near Fenway Park and a 10 feet high flood protection berm is installed to serve as a reservoir beneath Joe Moakley Park, also boasting its height.

The cumulative damage and adaptation cost between the period of 2000 to 2100 for coastal flooding range from approximately US$6 billion to US$94 billion. Countries still hesitant to invest in mitigation measures would do well to follow Boston’s example. 

As a call for awareness, Earth.Org has mapped what extreme flooding would look like in Boston by 2100 if no action were taken.

Sea level rise projections by 2100 for two scenarios with the amount of rise in meters indicated (mild = 2m; extreme = 4m). Percentage and total population displacement indicated bottom right.

Methodology

Global mean sea level is projected to rise by 2m at the end of this century. However, in order to determine local sea level rise (SLR), one has to take into account local coastal flood levels which could be 2.8m above Mean Higher-High Water (MHHW) at extreme forecasts. These local levels bring variability to the projected SLR from 1m to 6.5m (eg. Rio vs Kolkata).

The SLR scenarios used in this study are based on the forecasts from Climate Central – Coastal Risk Screening Tool  with the following parameters:

• Sea level Projection Source
• Coastal Flood Level
• Pollution Scenario
• Luck

Sea level Projection Source:

From two highly cited journals by Kopp et al., estimating SLR mainly due to ocean thermal expansion and ice melt. The mid-range scenario projected 0.5-1.2m of SLR based on different representative concentration pathways (RCP) defined by the IPCC. While the pessimistic scenario added more mechanisms of ice-sheet melting, estimating SLR at 1m-2.5m in 2100, with a projection of 10m SLR at 2300.

Coastal Flooding

More frequent coastal flooding is a direct impact of sea-level rise. Based on the Global tides and surge reanalysis by Muis et al., (2016), it is estimated that the extreme coastal water level could be from 0.2 – 2.8m over the mean level. While in extreme cases like China and the Netherlands it could experience 5-10m of extreme sea levels. Here, the coastal local flood level is added on top of the projected SLR.

Pollution Scenario:

Allows choosing the RCP, the greenhouse gas concentration trajectory defined by the IPCC.  The mild level is based on RCP4.5, of 2°C temperature rise; while the Extreme level is based on RCP 8.5, of 4°C temperature rise.

Luck:

Applies to the baseline SLR, defined in the “Sea level projection” section, upon which we add flooding. “Mild” refers to the mid-range scenario of 0.5-1.2m, and “extreme” to the pessimistic scenario of 1-2.5m. We used the high-end value of each scenario (mild = 1m; extreme = 2.5m).

Mapping by Braundt Lau. Article written by Eva Angela Seputra and Owen Mulhern. 

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References:

• Kulp, Scott A., and Benjamin H. Strauss. “New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding.” Nature communications 10.1 (2019): 1-12.

• Florczyk, A. J., Corbane, C., Ehrlich, D., Freire, S., Kemper, T., Maffenini, L., Melchiorri, M., Politis, P., Schiavina, M., Sabo, F. & Zanchetta, L. (2019). GHSL Data Package 2019 Public Release.

• Kopp, R. E., DeConto, R. M., Bader, D. A., Hay, C. C., Horton, R. M., Kulp, S., Oppenheimer, M., Pollard, D. & Strauss, B. H. (2017). Evolving Understanding of Antarctic Ice-Sheet Physics and Ambiguity in Probabilistic Sea-Level Projections. Earth’s Future, 5(12), 1217–1233.

• Kopp, R. E., Horton, R. M., Little, C. M., Mitrovica, J. X., Oppenheimer, M., Rasmussen, D. J., Strauss, B. H. & Tebaldi, C. (2014). Probabilistic 21st and 22nd Century Sea-Level Projections at a Global Network of Tide-Gauge Sites. Earth’s Future, 2(8), 383–406.

• Kulp, S. A. & Strauss, B. H. (2019). New Elevation Data Triple Estimates of Global Vulnerability to Sea-Level Rise and Coastal Flooding. Nature Communications, 10(1), 4844. Retrieved June 21, 2020, from http://www.nature.com/articles/s41467-019-12808-z

• Muis, S., Verlaan, M., Winsemius, H. C., Aerts, J. C. J. H. & Ward, P. J. (2016). A Global Reanalysis of Storm Surges and Extreme Sea Levels. Nature Communications, 7.