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Flood risk of natural and embanked landscapes on the Ganges–Brahmaputra tidal delta plain

Nature Climate Change volume 5, pages 153–157 (2015)Cite this article

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Abstract

The Ganges–Brahmaputra river delta, with 170 million people and a vast, low-lying coastal plain, is perceived to be at great risk of increased flooding and submergence from sea-level rise1,2,3,4,5. However, human alteration of the landscape can create similar risks to sea-level rise. Here, we report that islands in southwest Bangladesh, enclosed by embankments in the 1960s, have lost 1.0–1.5 m of elevation, whereas the neighbouring Sundarban mangrove forest has remained comparatively stable6,7,8. We attribute this elevation loss to interruption of sedimentation inside the embankments, combined with accelerated compaction, removal of forest biomass, and a regionally increased tidal range. One major consequence of this elevation loss occurred in 2009 when the embankments of several large islands failed during Cyclone Aila, leaving large areas of land tidally inundated for up to two years until embankments were repaired. Despite sustained human suffering during this time9,10, the newly reconnected landscape received tens of centimetres of tidally deposited sediment, equivalent to decades’ worth of normal sedimentation. Although many areas still lie well below mean high water and remain at risk of severe flooding, we conclude that elevation recovery may be possible through controlled embankment breaches.

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Figure 1: DigitalGlobe image of Polder 32 located on the tidal delta plain of southwest Bangladesh, collected in May 2012, three years after Cyclone Aila.
Figure 2: Surface elevations and landscape model for Polder 32 and adjacent Sundarbans.
Figure 3: Landsat and DigitalGlobe images of Polder 32 before and after embankment breaches and post-breach tidal-splay deposits.

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Acknowledgements

We thank D. Datta, B. Kumar, S. Hossain, Md R. Karim and F. Akter for their assistance with field data collection. As noted Figs 1, 3c, and Supplementary Fig. 8 include copyrighted material of DigitalGlobe, Inc., All Rights Reserved. Figure 3a, b includes Landsat imagery distributed by the Land Processes Distributed Active Archive Center (LP DAAC), located at USGS/EROS, Sioux Falls, South Dakota (http://lpdaac.usgs.gov). This research was financially supported by grants from the Office of Naval Research (N00014-11-1-0683) and National Science Foundation–Belmont Forum (No. 1342946). This paper is a contribution to the ICSU 2015 Sustainable Deltas Initiative.

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Authors and Affiliations

  1. Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, Tennessee 37240, USA

    L. W. Auerbach, S. L. Goodbred Jr, C. A. Wilson & J. M. Gilligan

  2. School of Earth and Environmental Sciences, Queens College—City University of New York, Queens, New York 11367, USA

    D. R. Mondal

  3. Environmental Science Discipline, Khulna University, Khulna 9208 Bangladesh,

    K. R. Ahmed & K. Roy

  4. Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA

    M. S. Steckler & C. Small

  5. Department of Political Science, Vanderbilt University, Nashville, Tennessee 37203, USA

    B. A. Ackerly

Authors
  1. L. W. Auerbach
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Contributions

All authors contributed extensively to the work presented in this paper. L.W.A., S.L.G.Jr, M.S.S. and D.R.M. designed the field project. L.W.A., S.L.G.Jr, D.R.M., C.A.W., K.R.A. and K.R. collected data. L.W.A., S.L.G.Jr, D.R.M., C.A.W., M.S.S. and C.S. processed and analysed data. L.W.A., S.L.G.Jr, C.A.W. and J.M.G. wrote the manuscript. L.W.A., S.L.G.Jr, D.R.M., M.S.S. and C.A.W. wrote the Supplementary Information. All authors discussed the results and implications and commented on the manuscript at all stages.

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Correspondence to S. L. Goodbred Jr.

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Auerbach, L., Goodbred Jr, S., Mondal, D. et al. Flood risk of natural and embanked landscapes on the Ganges–Brahmaputra tidal delta plain. Nature Clim Change 5, 153–157 (2015). https://doi.org/10.1038/nclimate2472

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