Home to more than 4 million people, Chittagong is highly vulnerable to flooding from tidal surges, the North Indian Ocean tropical cyclones and monsoonal rains. Sea level rise and rapid coastal erosion are set to exacerbate these problems and possibly drive one of the first mass climate refugee migrations in the world.
Earth.Org has mapped what extreme flooding could look like in Chittagong by 2100.
Chittagong is known as the biggest port city and financial center of Bangladesh. It is built in a hilly area around the Karnaphuli River, which runs through the city center and pours into the Bay of Bengal through an estuary located 12km west of Chittagong. Its population routinely faces floods during coastal tide surges, putting entire neighborhoods into gridlock and forcing individuals to fend for themselves. But try as they may to barricade entrances and elevate their floors, the flooding always wins.
The less mundane form of this plague comes with heavy rains that cause deadly landslides and flash floods. As it is, the conditions are barely liveable, and there could be a 30cm sea level rise in as little as 20 years.
Plans for flood control have been announced, but a lack of transparency and visible action leaves citizens doubtful. If no flood control is implemented, citizens of Chittagong another 11 million people in Bangladesh will be displaced permanently by 2050. This could rise to 27 million by 2100. Left with no choice, the Bangladeshi could begin the first mass climate refugee movement on Earth, and their neighbors in India and Myanmar are unlikely to welcome them with open arms.
Earth.Org has mapped what extreme flooding could look like in Chittagong by 2100 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, 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.
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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
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.