A recent paper published in Nature triples the “estimates of global vulnerability to sea-level rise and coastal flooding”. The upper projection of 2 metres sea level rise would displace up to 57 million people in China, most of these in Shanghai and Guangzhou.

Earth.Org has mapped what extreme flooding could look like in Shanghai by 2100 in the absence of preventive measures.

Shanghai, the second most populous city in the world, sits on the Yangtze River estuary on low-lying, soft, sandy soil. If you’ve read any other articles from this series, you know this spells trouble. The 24 million inhabitants along with the concentration of economic and cultural activity make it a priority to implement protective measures. 

Because Shanghai isn’t particularly vulnerable to coastal flooding at the moment, there is practically no infrastructure geared toward mitigation at the moment. Coastal defences will be necessary, as will access to enough fresh water to accommodate such an agglomeration, in case the sea infiltrates groundwater reserves. 

The sheer size of metropolitan Shanghai means that a detailed, very expensive plan will have to be drafted in order to mitigate the effects of sea level rise. The city is not doomed by any means, but officials will be wise not to underestimate the challenge ahead. 

Earth.Org has modelled severe coastal flooding in Shanghai by 2100 to emphasise our call for action. 

Sea Level Rise 2100 Shanghai

Sea level rise projections by 2100 for two scenarios with the amount of rise in meters indicated (mild = 3m; extreme = 6m). 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: 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 Extreme level is based on RCP 8.5, of 4°C temperature rise.

Luck: applies to the 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).

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