Sea Level Rise Projection Map – Wallis and Futuna

Wallis and Futuna is a French overseas territory located midway between New Caledonia and Tahiti. A study has shown that several hundred seaside homes in Uvea, central island of the Wallis archipelago, would have to be evacuated with as little as 50 cm of sea level rise. 

Earth.Org has mapped what extreme flooding could look like by 2100 to illustrate the need for preparation.

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Wallis and Futuna does not face an immediate threat of submersion, but it still faces serious challenges due to climate change. Composed of two distinct archipelagos, the Wallis and the Horn archipelagos, the French overseas collectivity is home to around 14,000 residents. Most of whom reside in and near the islands’ low-lying coastal zones. 

A study led by the Secretariat of the Pacific Regional Environmental Programme (Sprep) used a model to illustrate the potential submersion of Uvea, central island of the Wallis archipelago; it used a range from 0.5 to 3 metres sea level rise. The result was alarming, with only 0.5 metres of sea level rise, several hundreds of seaside homes in the area would be under threat. Coastal erosion can already be observed, chipping away at beaches and uprooting coastal vegetation. Other impacts include aquifer contamination and crop failure, along with damage to critical infrastructure like ports, roads and hospitals. 

To combat erosion, several measures have been implemented at a local level, for example, shoring up the seafront, installation for sea walls and planting erosion-resistant vegetation. However, these initiatives are just local and temporary solutions, a long-term protection against the significant sea level rise is still not found.

Earth.Org has mapped the worst case scenario floods the islands could experience as a call to action. 

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

Sea level rise mapping 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 Wing Ki Leung 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.