Tianjin, located along the Hai River, a tributary of the oft-overflowing Yangtze, is highly vulnerable to sea level rise. It already suffers from flooding during heavy downpours, and rising water levels will hamper its struggling drainage systems. Officials will have to invest heavily in mitigation measures over the next two decades to protect this economic hub.
Earth.Org has mapped what extreme flooding could look like by 2100 to illustrate the need for action.
Climate Change is making extreme weather events more likely, as demonstrated by the exceptional downpours affecting over 24 million people in China this year. Sea level rise is set to exacerbate this problem, as it increases tidal surges in rivers and hampers drainage in coastal areas.
Located in the low-lying, flat Hai River basin, Tianjin is a vibrant economic hub housing 285 Fortune 500 companies, and 15 million inhabitants. While it has a coastal wall, part of it cannot withstand a 1-in-100 year storm surge (whose intensity has a 1% chance of occurring in any given year). A recent study has shown that by 2030, 1-in-100 year floods could submerge over 3000 km2 of the 11 000 km2 area.
No public cost analysis has been released, but it is evidently worth investing in coastal defenses. These will have to take land subsidence, sea level rise, and extreme storm surge events into consideration. Earth.Org has modelled what a mild and extreme flooding event could look like in Tianjin by 2100 under a high emissions scenario to illustrate the need for action.
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
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.
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.
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.
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).
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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
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