Sea Level Rise Projection Map – Palembang

Palembang, the capital city of South Sumatra, is another city that experiences frequent flooding. Sea level rise projections for the end of the century will force this low-income country to make hard decisions – do they invest in adaptive measures? Weather the storm? Or give way and somehow move their capital to a better location?

Earth.Org has mapped severe flooding in Palembang by 2100 to illustrate the need for action.

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Palembang occupies a vast lowland near the Bukit Barisan Mountains, on the confluence of two major tributaries to the Musi River, the Ogan and Komering Rivers. During the rainy season, from November to April, the Musi River often overflows and drowns many areas in the city. Other factors contributing to its flood proneness are poor drainage systems, and the often-observed rapid urban expansion problems of excessive groundwater extraction coupled with natural reservoir drainage. 

The mayor, Harnojoyo, has announced a plan to make Palembang flood-free by 2022. It consists in setting up pumps for water evacuation, but the subpar drainage system will also have to be revamped if these pumps are to serve any purpose. 

A recent paper published in Nature triples the “estimates of global vulnerability to sea-level rise and coastal flooding”, predicting a 1 to 2 metre increase in sea level. This is expected to hit Indonesian cities very hard, and while floods are common and mitigation measures are being taken, these seem geared toward the current flood intensity. The government of Sumatra has a chance to show foresight and build for the uncertain, yet worrisome future. We at Earth.Org have modelled what flooding could look like by 2100 to illustrate the need for action. 

Sea level rise projections by 2100 for two scenarios with the amount of rise in meters indicated (mild = 3m; extreme = 5m).

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: is 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 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 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 to choose 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).

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.

• 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.