The impact of climate change and aquatic salinization on mangrove species in the Bangladesh Sundarbans

Abstract

This paper investigates the possible impacts of climate change on aquatic salinity and mangrove species in the Bangladesh Sundarbans. The impact analysis combines the salinity tolerance ranges of predominant mangrove species with aquatic salinity measures in 27 scenarios of climate change by 2050. The estimates indicate significant overall losses for Heritiera fomes; substantial gains for Excoecaria agallocha; modest changes for Avicennia alba, A. marina, A. officinalis, Ceriops decandra, and Sonneratia apetala; and mixed results for species combinations. Changes in mangrove stocks are likely to change the prospects for forest-based livelihoods. The implications for neighboring communities are assessed by computing changes in high-value mangrove species for the five sub-districts in the Sundarbans. The results of the impact analysis indicate highly varied patterns of gain and loss across the five sub-districts. Overall, however, the results suggest that salinity-induced mangrove migration will have a strongly regressive impact on the value of timber stocks because of the loss of highest value timber species, Heritiera fomes. In addition, the augmented potential for honey production will likely increase conflicts between humans and wildlife in the region.

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Notes

  1. 1.

    The second largest is only about one-tenth of the Sundarbans’ size (Agarwala et al. 2003).

  2. 2.

    Approximately, 60% of the Sundarbans is in Bangladesh, covering about 6000 sq. km in certain districts of Khulna, Satkhira and Bagerhat districts.

  3. 3.

    Previous research on salinization in coastal Bangladesh has employed a variety of methods (see for example Nobi and Das Gupta 1997; Aerts et al. 2000; IWM 2003; Bhuiyan and Dutta 2011). Many of these studies have simulated salinity change in rivers and estuaries using hydraulic engineering models and have compared the results with actual measures. In the most comprehensive study to date, Dasgupta et al. (2015a) have used 27 climate change scenarios to project salinity trends in coastal rivers to 2050, with a model that links the spread and intensity of salinity to changes in the sea level, temperature, rainfall, and altered riverine flows from the Himalayas. The study provides new estimates of location-specific river salinity through 2050.

  4. 4.

    http://sdwebx.worldbank.org/climateportal/index.cfm?page=websalinity_dynamics&ThisRegion=Asia&ThisCcode=BGD Accessed April 2017.

  5. 5.

    Basic elements of the three scenarios are as follows:

    B1: rapid economic growth with convergence among regions; global population that peaks in mid-century and declines thereafter; rapid change in economic structures toward a service and information economy, with reductions in material intensity and the introduction of clean and resource-efficient technologies.

    A1B: Rapid economic growth with convergence among regions; global population that peaks in mid-century and declines thereafter; rapid introduction of new and more efficient technologies; energy from mixed fossil and renewable sources.

    A2: Non-convergent economic development; continuously increasing population; heterogeneous technologies and energy sources.

  6. 6.

    Model implementing institutions are as follows:

    IPSL-CM4: Institut Pierre Simon Laplace, France;

    MIROC3.2: Center for Climate System Research, University of Tokyo, National Institute for Environmental Studies, Japan, Frontier Research Center for Global Change, Japan;

    ECHO-G: Meteorological Institute of the University of Bonn, Germany, Model and Data Group, Max Planck Institute for Meteorology, Hamburg, Germany, Korea Meteorological Administration.

  7. 7.

    The Ganges Delta in Bangladesh is still in an active, dynamic state. Therefore, it is critical to include projections of land subsidence of the lower Bengal delta (the Ganges Delta in Bangladesh) in simulating future climate scenarios. Physical impacts of relative mean sea-level rise are caused by a combination of sea-level rise associated with global warming and vertical land movement (subsidence or accretion). At present, there is an intense controversy in Bangladesh over alternative estimates and projections of land subsidence in the coastal region (see Dasgupta et al. 2015a, b, c). In light of the widely varying estimates, the hydrological modeling for our analysis was run for three alternative scenarios of land subsidence: 2, 5, and 9 mm per year.

  8. 8.

    We use pixels for numerical convenience; pixel numbers are readily translated to areas. In our mapping system, one pixel has a side length of approximately 55 m and an area of approximately 0.3 ha.

  9. 9.

    It should be noted that there are other significant stresses on Heritiera fomes in Sundarbans unrelated to salinity. For example, since around 1970, “top-dying disease” or crown-death of millions of Heritiera fomes trees in Sundarbans has led to significant economic losses and the losses are likely to continue in the future (Rahman 1990; Rahman 1995; Iftekhar and Islam 2004; Giri et al. 2007; Awal 2014).

  10. 10.

    According to experts in Bangladesh, potential honey production is between 3000 and 5000 tons per annum if the potential is fully exploited. At present, the price is Tk. 125 to Tk. 135 per kg for honey collected from the Sundarbans with rudimentary sieving. The estimated total value of honey production from the Sundarbans is between Tk. 375 million and Tk. 675 million per annum if the full potential of honey production is exploited.

  11. 11.

    In the Sundarbans, bees display the following preference percentages for making honeycombs: Excoecaria agallocha (Gewa) (39%), Avicennia alba, A. marina, A. officinalis (Baen) (16%), Ceriops decandra (Goran) (11%), Garjan (10%), Heritiera fomes (Sundri) (9%), Sonneratia apetala (keora) (5%), and Bruguiera gymnorrhiza (Kankra) (4%). See Chakrabari (1987).

  12. 12.

    Recent research suggests that the sea level may rise by one meter or more in the twenty-first century, which would increase the vulnerable population to about one billion by 2050 (Rahmstorf 2007; Pfeffer et al. 2008; Dasgupta et al. 2009; Vermeer and Rahmstorf 2009; Hansen and Sato 2011; Brecht et al. 2012).

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Acknowledgements

The authors are grateful to Zahir Iqbal, Bangladesh Forest Department, for data on mangrove species in the Sundarbans. The authors are thankful to Yunus Ali, Chief Conservator of Forest, Bangladesh Forest Department, for his expert opinion. The authors would like to extend their special thanks to Lia Sieghart, Glenn-Marie Lange, Mainul Huq, and Michael Toman for their review comments on this paper. The authors also acknowledge help from Polly Means with the graphics.

Disclaimer

The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent.

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Dasgupta, S., Sobhan, I. & Wheeler, D. The impact of climate change and aquatic salinization on mangrove species in the Bangladesh Sundarbans. Ambio 46, 680–694 (2017). https://doi.org/10.1007/s13280-017-0911-0

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Keywords

  • Aquatic salinization
  • Bangladesh: Sundarbans
  • Climate change
  • Mangrove