Key Facts

The Ganges-Brahmaputra Delta in Bangladesh and India is home to more than 100 million people.⁵ Accelerated sea-level rise caused by global warming⁶ is putting added stress on land, water, and food in this already at-risk region.^3,4,5

• Bangladesh, the world's seventh-most-populous country¹⁰, is highly vulnerable to the effects of sea-level rise—including increased salinity of ground and surface waters.^3,4,11
• Local sea-level rise of as much as 1 inch (25 millimeters) per year has been recorded in parts of the delta.^5,2
• By 2050, scientists estimate that sea-level rise in the delta could directly affect more than 3 million people.⁵ Bangladesh could lose nearly one-quarter of the land area it had in 1989 by the end of this century, in a worst-case scenario.⁵

Details

The Ganges-Brahmaputra Delta—which encompasses nearly 33,707 square miles (87,300 square kilometers) in Bangladesh and West Bengal, India—is Asia's largest delta.^3,5 It is also the world's most populated delta,⁴ home to some 111 million people.⁵ The residents of this region are particularly at risk from accelerated global sea-level rise linked to climate change.^5,6 Sea-level rise is projected to increase the salinity of the water and soil of this now-fertile region, endangering crops and food security.^3,4

During the twentieth century, global mean sea level rose at an average of 0.07 inches (1.8 millimeters) per year.⁷ But from 1993 to 2003, that rate increased to 0.12 inches (3.1 millimeters) per year.⁸ Scientists attribute rising sea levels to expansion of the oceans as they warm, as well as to the melting of mountain glaciers and the Greenland and Antarctic ice sheets.^7,9

Bangladesh, one of the world's most populous countries,¹⁰ is highly vulnerable to the effects of sea-level rise—including more salinization of both ground and surface waters.^3,4,11 The deltaic plains of the Ganges, Brahmaputra, and Meghna rivers compose most of the country's land area,⁴ and the vast majority of the coastal zone is at an elevation of less than 16 feet (5 meters).¹²

Local sea-level rise of as much as 1 inch (25 millimeters) per year has been recorded in sections of the Ganges-Brahmaputra Delta.^5,2 Most deltas experience natural sinking and settling of land (subsidence), which can increase relative, or local, sea-level rise.⁴ Human interventions such as extraction of groundwater can speed up subsidence, as has been the case in the Ganges-Brahmaputra basin.^4,5

Local sinking and groundwater extraction can allow seawater to creep inland, displacing coastal plant and animal communities that depend on brackish or freshwater.⁴ Encroaching seawater and salty groundwater may also increase soil salinity, which can hinder growth of crops.¹³ For example, increased salinity inhibits rice growth and can lower rice yield.¹⁴

What the Future Holds

By mid-century, more than 3 million people stand to be directly affected by sea-level rise in the Ganges-Brahmaputra Delta.⁵ In a worst-case scenario, Bangladesh could lose nearly 25 percent of its 1989 land area by around 2100.⁵

Climate change is projected to cause further sea-level rise during this century and beyond.^15,16 If we do nothing to reduce our heat-trapping emissions,¹⁷ global sea level is projected to increase some 23 inches (59 centimeters) over recent average levels by the end of this century.¹⁸

However, if we make significant efforts to reduce emissions,¹⁷ sea-level rise could be limited to about 15 inches (38 centimeters) by the end of this century.¹⁸ Recent evidence of higher rates of global sea-level rise suggests that these projections may be low.^6,7,9 And regional variations in sea-level rise are expected to continue.⁹

In Bangladesh, the impact of sea-level rise may be worsened by other effects of global warming, such as variable precipitation, more frequent droughts and floods, and shrinking of the glaciers that supply water to the rivers of the delta.¹⁹ Reduced rainfall during the dry season, for example, can increase the salinity of rivers through encroaching seawater that moves upstream during periods of low flow.¹²

Human activities such as shrimp farming and damming of rivers are also expected to intensify the effects of sea-level rise. Dams can retain sediment that would otherwise replenish eroded or subsided land in the river delta.⁴ More dams are planned in Asia, which are likely to increase erosion as well as relative sea-level rise, and might worsen water shortages and extend the area affected by salinity during the dry months.^3,4,5

With the added pressure of rising air temperatures, rice production in Bangladesh could drop by 8 percent, and wheat production by 32 percent, by the middle of this century.^3,20 Unless we act now to cut our heat-trapping emissions, and take steps to prepare for the warming already projected to occur in the coming decades, the food and freshwater supply of millions of people in the Ganges-Brahmaputra Delta is likely to be in danger.

Credits

Endnotes

1. Photograph used by permission. Jenneke Arens. ↑
2. Alam, M. 1996. Subsidence of the Ganges-Brahamaputra Delta of Bangladesh and associated drainage, sedimentation and salinity problems. In: Sea-level rise and coastal subsidence. Edited by J.D. Milliman and B.U. Haq. Kluwer Academic Publishers, pp. 169-187. ↑
3. Cruz, R.V., H. Harasawa, M. Lal, S. Wu, Y. Anokhin, B. Punsalmaa, Y. Honda, M. Jafari, C. Li, and N. Huu Ninh, 2007: Asia. In: Climate change 2007: Impacts, adaptation and vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden, and C.E. Hanson. Cambridge University Press, pp. 469-506. ↑
4. Nicholls, R.J., P.P. Wong, V.R. Burkett, J.O. Codignotto, J.E. Hay, R.F. McLean, S. Ragoonaden, and C.D. Woodroffe. 2007. Coastal systems and low-lying areas. In: Climate change 2007: Impacts, adaptation and vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden, and C.E. Hanson. Cambridge University Press, pp. 315-356. ↑
5. Ericson, J.P., C.J. Vorosmarty, S.L. Dingman, L.G. Ward, and M. Meybeck. 2005. Effective sea-level rise and deltas: Causes of change and human dimension implications. Global Planetary Change 50:63-82. ↑
6. Rahmstorf, S., A. Cazenave, J.A. Church, J.E. Hansen, R.F. Keeling, D.E. Parker, and R.C.J. Somerville. 2007: Recent climate observations compared to projections. Science 316 (5825):709. ↑
7. Bindoff, N.L., J. Willebrand, V. Artale, A. Cazenave, J. Gregory, S. Gulev, K. Hanawa, C. Le Qu&eacué, S. Levitus, Y. Nojiri, C.K. Shum, L.D. Talley, and A. Unnikrishnan. 2007. Observations: Oceanic climate change and sea level. In: Climate change 2007: The physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H.L. Miller. Cambridge University Press. ↑
8. Douglas, B.C. 1997. Global sea rise: A redetermination. Surveys in Geophysics 18:279-292. doi:10.1023/A:1006544227856. ↑
9. Karl, T.R., J.M. Melillo, and T.C. Peterson, eds. 2009. Global climate change impacts in the United States. U.S. Global Change Research Program. Cambridge University Press. ↑
10. Central Intelligence Agency. 2010. The world factbook. Washington, DC. Online at https://www.cia.gov/ library/ publications/ the-world-factbook/ geos/ bg.html. Accessed May 17, 2010. ↑
11. Han, M., M.H. Zhao, D.G. Li, and X.Y. Cao. 1999. Relationship between ancient channel and seawater intrusion in the south coastal plain of the Laizhou Bay. Journal of Natural Disasters 8:73-80. ↑
12. Mohal, N., Z.H. Khan, and N. Rahman. 2006. Impact of sea level rise on coastal rivers of Bangladesh. Bangladesh: Coast, Port and Estuary Division, Institute of Water Modelling. Online at www.riversymposium.com/ 2006/ index.php? element=06MOHALNasreen. Accessed May 17, 2010. ↑
13. Brouwer, C., A. Goffeau, and M. Heibloem. 1985. Salty soils. In: Irrigation water management, training manual no.1: Introduction to irrigation. Rome: United Nations Food and Agriculture Organization. Online at www.fao.org/ docrep/ R4082E/ R4082E00.htm#Contents. Accessed May 17, 2010. ↑
14. Castillo, E., T.P. Tuong, H.T.T. Trang, T.N.Q. Thu, and T.T.K. Phuong. 2003. Phenological and physiological responses of a rice cultivar to level and timing of salinity stress. In: Rice-shrimp farming in the Mekong Delta: Biophysical and socioeconomic issues. Edited by N. Preston and H. Clayton. Technical report no. 52e. Canberra: Australian Centre for International Agricultural Research. ↑
15. Meehl, G.A., T.F. Stocker, W.D. Collins, P. Friedlingstein, A.T. Gaye, J.M. Gregory, A. Kitoh, R. Knutti, J.M. Murphy, A. Noda, S.C.B. Raper, I.G. Watterson, A.J. Weaver, and Z.-C. Zhao. 2007. Global climate projections. In: Climate change 2007: The physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H. L. Miller. Cambridge University Press, pp. 747-845. ↑
16. Clark, P.U., A.J. Weaver, E. Brook, E.R. Cook, T.L. Delworth, and K. Steffen. 2008. Introduction: Abrupt changes in the Earth's climate system. In: Abrupt climate change. Synthesis and assessment product 3.4. Reston, VA: U.S. Geological Survey, pp. 19-59. ↑
17. The emissions scenarios referred to here are the high-emissions path known as A1FI and the low-emissions path known as B1 from the Intergovernmental Panel on Climate Change. ↑
18. Solomon, S., D. Qin, M. Manning, R.B. Alley, T. Berntsen, N.L. Bindoff, Z. Chen, A. Chidthaisong, J.M. Gregory, G.C. Hegerl, M. Heimann, B. Hewitson, B.J. Hoskins, F. Joos, J. Jouzel, V. Kattsov, U. Lohmann, T. Matsuno, M. Molina, N. Nicholls, J. Overpeck, G. Raga, V. Ramaswamy, J. Ren, M. Rusticucci, R. Somerville, T.F. Stocker, P. Whetton, R.A. Wood, and D. Wratt. 2007. Technical summary. In: Climate change 2007: The physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H. L. Miller. Cambridge University Press, pp. 20-91. ↑
19. Nishat, A. 2008. Climate change and water management in Bangladesh. Conference on Global Climate Change and Its Effects, International Union for Conservation of Nature, Dhaka. Online at http://www.wamis.org/ agm/ meetings/ rsama08/ S308-Nishat_Climate-Change-Water-Mgmt-Bangladesh.pdf. Accessed May 17, 2010. ↑
20. Faisal, I.M., and S. Parveen. 2004. Food security in the face of climate change, population growth and resource constraints: implications for Bangladesh. Environmental Management 34:487-498. ↑