Climate-Focus-Paper "Regional Sea Level Rise - South Asia"

Changes in mean sea level are the result of the complex interplay of a number of climatic and non-climatic factors. Regional and local mean sea level may differ significantly from global mean sea level because of variation in the relative importance of the different factors across the world. A Focus Paper on Global Sea Level Rise is also available which discusses these issues. Particularly at the regional and local level, the importance of non-climatic factors, e.g. subsidence or uplift, may be more important drivers of sea level change than climatic ones.

As such, when developing projects and considering investment decisions that may be sensitive to changes in sea level, it is important that adequate consideration of all relevant factors has been taken, and the implications this may have for projects are well understood. This Focus Paper highlights the challenge of understanding changes in sea level, and the associated impacts for the Bay of Bengal, a region in south Asia.

The key messages

  • South Asian countries bordering the Bay of Bengal are subject to a number of climate related hazards, high among which is rising sea levels. Rising sea levels lead to impacts in many different economic sectors, including agriculture, water resources, and human health. As such, many economic sectors will need to adapt to the threat posed by rising sea levels.
  • Successful adaptation to rising sea levels requires an understanding of the various drivers of change, whether these be climatic, or non-climatic factors. Understanding changes in sea level in the highly populated and low-lying south Asian region is of major importance, but is challenging because of inadequate tide-gauge, and subsidence time-series data.
  • Tide gauge observations of changes in sea level in the region show a large variation in linear rates of relative sea level rise (RSLR), ranging from 0.7 mm yr-1 at Chennai, to 8.2 mm yr-1 at Charchanga, in the Ganges delta.
  • Projections of future changes in RSLR across the region, in 2080-2099, are fairly similar, with mean increases in the range of 0.32 m to 0.38 m under a stringent mitigation scenario (RCP2.6), and 0.53 m to 0.58 m under a business-as-usual scenario (RCP8.5). These projections do not take account of local subsidence, however, which in some areas is a more important driver of changes in RSLR than climatic factors.
  • Coastal flooding is one of the most important impacts associated with rising sea levels, and a major study shows the avoided damage costs by investing in infrastructure adaptation, i.e. dikes and sea walls, to maintain present day standards, may be as high as 1800%.

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Dr. Paul Bowyer
Dr. Paul Bowyer

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