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Saturday, January 12, 2013

Mangrove forests threatened by Climate Change in the Sundarbans of Bangladesh and India

A new study has found the Sundarban coast retreating up to 200 metres in a single year due to rapidly deteriorating health of the world's largest Mangrove forest in the Sundarbans, the Ganges delta region of India and Bangladesh.

Zoological Society of London (ZSL) researcher Dr Nathalie Pettorelli, senior author of the paper says: "Our results indicate a rapidly retreating coastline that cannot be accounted for by the regular dynamics of the Sundarbans. Degradation is happening fast, weakening this natural shield for India and Bangladesh."

In the Bengali language 'Sundarban' can be literally translated as 'beautiful forest'. The area is the largest block of continuous mangrove forest in the world, being home to almost 500 species of reptile, fish, bird and mammals, including the endangered Bengal tiger.

See Also: Mangrove Alliance | Mangrove Action Project | Mangrove Watch Australia | Planners need to allow for Coastal wetlands migration due to sea level rise, climate change

The Sundarbans is the largest mangrove forest in the world. About 300 species of trees and herbs and about 425 species of wildlife including the Bengal Tiger survive in this ecosystem. The Sundarbans is also a World Heritage Site. Out of a total area of 0.6 million hectares of the Sundarbans, 0.4 million hectares are forest areas, with the remaining part comprising water bodies mostly flowing through to the sea at the south. This mangrove forest is predominantly a salt-tolerant forest ecosystem with the exception of an estimated 856.7 million Sundari (Heritiera fomes) trees which are less salt-tolerant. Sundari trees are threatened with extinction, according to Syed Azizul Haq in a 2010 conference paper, "primarily due to suffering from top-dying disease caused mainly due to increasing salinity in surrounding waters."

The mangrove forests of the Sundarbans provides an important defence in limiting climate change impacts, providing protection to coastal areas from tsunamis and cyclones. Each year about eight storms with sustained wind speeds greater than 63km/hr form in the Bay of Bengal, with an average of two becoming tropical cyclones. Tropical cyclones Sidr in 2007 and Aila in 2009 caused extensive damage. The long term trend is for cyclone frequency to reduce slightly while cyclone intensity increases. Mangroves serve each year as a biological shield protecting coastal communities from the worst effects of storm surge. Loss of mangroves escalates the disaster risk for local populations from storm surge and flooding.

They are also the most carbon rich forests in the tropics with high carbon sequestration potential, meaning their degradation and loss substantially reduce our ability to mitigate, and adapt to, predicted changes in climatic conditions. Their degradation also releases large amounts of 'blue carbon' stored in sediments to the atmosphere, a process that has been underestimated up until recently.

Agricultural land conversion destroyed 17,179 hectares of mangroves in India during 1975 to 2005. A further 7,554 hectares was lost due to Shrimp cultivation. Over the last 30 years some 7,500 hectares in Bangladesh has become submerged by rising seas.

Sarah Christie, from ZSL's tiger conservation expert said: "The Sundarbans is a critical tiger habitat; one of only a handful of remaining forests big enough to hold several hundred tigers. To lose the Sundarbans would be to move a step closer to the extinction of these majestic animals."

Mangroves comprise less than 1 per cent of all forest areas across the world. ZSL's Chief Mangrove Scientific Advisor Jurgenne Primavera says: "Mangrove protection is urgent given the continuing threats to the world's remaining 14 to 15 million hectares of mangroves from aquaculture, land development and over-exploitation. The recently established IUCN SSC Mangrove Specialist Group, hosted by ZSL, will develop a global conservation strategy for mangroves based on an assessment of research and conservation needs."

The study used satellite based using remote sensing equipment to measure changes in the Sundarbans mangrove forest environment, changes to the landscape and encroachment by the ocean. The Full paper - Advanced Land Observing Satellite Phased Array Type L-Band SAR (ALOS PALSAR) to Inform the Conservation of Mangroves: Sundarbans as a Case Study (Full paper) - is available to read online.

This excerpt from the study abstract describes the methodology used by the researchers:

"Using radar imagery, we contrast and quantify the recent impacts of cyclone Sidr and anthropogenic degradation on this ecosystem. Our results, inferred from changes in radar backscatter, confirm already reported trends in coastline retreat for this region, with areas losing as much as 200 m of coast per year. They also suggest rapid changes in mangrove dynamics for Bangladesh and India, highlighting an overall decrease in mangrove health in the east side of the Sundarbans, and an overall increase in this parameter for the west side of the Sundarbans."

"As global environmental change takes its toll in this part of the world, more detailed, regular information on mangroves' distribution and health is required: our study illustrates how different threats experienced by mangroves can be detected and mapped using radar-based information, to guide management action."

ZSL also runs a Community-based Mangrove Rehabilitation Project (CMRP) at two locations in the Philippines which started in 2008. The project aims to increase coastal protection, food resources and livelihood income of coastal communities in Panay and Guimaras (Philippines) by rehabilitating abandoned government-leased fishponds to mangroves, re-establishing legally mandated coastal greenbelts, and securing sustainable forest management agreements for local communities.

So far the project in the Philippines has planted up to 100,000 mangroves with the rehabilitation of 107.8 hectares (56.3 ha fishponds and 60.5 ha greenbelt) of mangrove forest underway. More than 4,000 people have been actively engaged in the planting, with many receiving intensive training as part of the project . Currently efforts focus on reverting abandoned fishponds to mangroves, using science-based methods implemented by communities, and integrating mangroves into marine protected areas in three provinces in the central Philippines.

Pachauri says rising sea levels a worry for Sundarbans

Degradation of the Sundarbans mangrove forests and encroachment by the ocean with rising sea level and salinity intrusion will inevitably lead to species loss in this richly biodiverse part of the world.

Dr R K Pachauri, Nobel laureate and director-general of TERI (The Energy and Resources Institute) and chairman of the IPCC, expressed strong concern over the impact of rising sea levels in the Sundarban delta while at the Indian Science Congress last weekend. It was reported by the Express News Service that "The rise in sea levels in Sundarbans is a cause of worry," he said.

He stressed the importance of strengthening mangrove plantations and defences to regulate water levels, "Dykes need to be set up at Sundarbans. It is one of the most important things to maintain biodiversity," he said.

It is estimated by researchers of the School of Oceanographic Studies, Jadavpur University, that the annual rise in sea level from 3.14 mm recorded till the year 2000 more than doubled to about 8 mm in 2010.

But it is not only seas that are rising, surface water temperatures have been rising at the rate of 0.5 degree Celsius per decade over the past three decades in the Sundarbans. A 2009 study (Mitra et al. 2009) found a change of 1.5 degrees Celsius from 1980 to 2007, a rise that will pose challenges and stresses for the survival of fauna and flora in the forest. By comparison, the IPCC documented a temperature increase rate of 0.2 degree Celsius per decade in the Indian Ocean during 1970-99. The surface water pH over the past 30 years has also reduced in the region, thus increasing acidification. The variations in salinity and increased temperature are thought to be the reasons for observed variation in pH and dissolved oxygen. The concentration of dissolved oxygen in some parts of the Sundarbans showed a decreasing trend.

Of the 102 low-lying islands in the delta about 48 are inhabited by nearly 4 million people. But Climate change is leading to increased salinity and higher tidal surges, with permanent submergence of land masses. Reports from 2006 suggest that in the past 20 years four islands (Bedford, Lohachara, Kabasgadi and Suparibhanga) were submerged and 6,000 families rendered homeless. Up to a dozen islands, home to 70,000 people, are immediately threatened by the rising seas inundating homes and livelihoods.

Scientists from University of Calcutta and Jadavpur University have predicted that one of the largest islands (Sagar island) will lose at least 15 per cent of its habitat area by 2020. A report prepared by Jadavpur University and World Wide Fund For Nature (WWF) estimates that out of five million people living in the delta, one million will become climate change refugees by 2050.

Mangrove Forests and Blue carbon storage

Coastal strips cover 6% of the earth's forests, but they make up a massive 20% of the deforestation carbon.

The mangrove forests also sequester each year a large amount of 'blue carbon'. But with habit degradation very large pools of previously-sequestered carbon residing mostly in sediments, can be released to the atmosphere. Healthy mangrove forests, as well as marshes and seagrass meadows, are important and efficient method for sequestering carbon dioxide as 'blue carbon'.

A recent study - Estimating Global "Blue Carbon" Emissions from Conversion and Degradation of Vegetated Coastal Ecosystems (Full Paper) - published in July 2012 found that the impact of release of blue carbon from degraded coastal ecosystems has been substantially underestimated. According to the conclusions of the study:

Our analysis suggests that the greenhouse consequences of conversion of these ecosystems are larger than previously appreciated, by as much as an order of magnitude. These emissions add considerably to existing estimates of land-use carbon gas emissions such as tropical deforestation. Although these ecosystems occur as relatively thin coastal fringes, the economic impacts of $US 6 to 42 billion per year are borne globally.

Mangrove losses contributed half the total blue carbon stock reduction, followed in ranking by the degradation or loss of sea grass meadows, then tidal marshes.

Reduced freshwater flow increasing salinity intrusion and forest dieback

A 2010 paper - Impact of Climate Change on "Sundarbans", the largest mangrove forest: ways forward - suggests changing salinity is the primary process of ecosystem degradation both through rising sea levels encroaching from the Bay of Bengal and reduced freshwater flow. The Sundarbans ecosystem is a balance between freshwater and salty ocean wetlands environments. It needs the flow of freshwater via the Ganges and the Gorai river, particularly during dry periods to balance the saline intrusion.

"It is feared that the anticipated sea level rise due to global warming will degrade the forest environment predominantly by increasing salinity, and hence will destroy major forest resources. Moreover, construction of Farakka Barrage on the Ganges by India has caused shrinkage of flow in the Padma River. As a result, the flow in the Gorai River, a distributary of the Ganges and a major source of fresh water flow in the Sunderbans water system, is being diminished."

There is substantial dieback of Sundari trees in the forest. "Sundari trees in the Sundarbans are being destroyed following outbreak of the top-dying disease, locally known as 'agamora'. The disease was first detected in 1930 and started
having a widespread impact from 1980. It is feared this tree species may be soon driven to extinction due to the fast spread of the disease. "The adverse effects of increased salinity on the ecosystem of the Sundarbans are manifested in the dying of tops of Sundari trees, retrogression of forest types, slow forest growth, and reduced productivity of forest sites." says the paper.

Syed Azizul Haq, the author of this study, suggests "the necessity of augmenting the Gorai River flow through construction of a barrage for raising the head of water at the Ganges-Gorai confluence, which will improve both the flow quantity and velocity." Here are his conclusions from his conference paper:

Flowing water in the rivers, canals etc through and around the Sundarbans flush out saline water intrusion from the sea. Increase in salinity intrusion due to anticipated sea level rise is one of the major threats to the Sundari trees, which are already under threat due to increased salinity levels. Majority of the negative impacts in the Sundarbans aggravate during dry periods when the flow of the Gorai River, the main feeder of thee water bodies of the Sundarbans, falls drastically. The flow characteristics of the Gorai River depend on the Ganges River from which it is originated. However, the environmental flow of the Ganges River in the Bangladesh part has shrunk to a great extent due to construction of the Farakka Barrage on the river by India. So it has become almost inevitable to construct a barrage across the Ganges River in the Bangladesh part at downstream of Ganges-Gorai junction to store water for feeding into the Gorai River. This will increase the environmental flow of the Gorai River, particularly during dry periods and minimize the anticipated negative impacts of climate change. It cannot be ignored that the proposed barrage will pose some negative impacts, which shall have to be well addressed.

Empowering Women and marginalized people with mangrove conservation

Action is being taken in combating the impacts of climate change through ecosystem based adaptation. Mangroves have the potential to adapt to sea level rise, catch runoff from soil erosion leading to accretion of coastal areas, and are of course impressive 'blue carbon' sinks.

The Indian Government recognized the need to engage local people in forestry management during the 1990s with the implementation of Joint Forest Management programs and Forest Protection Committees to manage forest resources. There are some 54 Forest Protection Committees along with 14 Eco-development Committees. One of the important attributes of the Indian program was involvement of women on these committees with equal say, and more importantly, equal income.

Forestry conservation and mangrove restoration work is particularly important income source for women and raises their social status. Alyssa L Bosold argues in a Gettysburg College paper Challenging The "Man" In Mangroves: The Missing Role Of Women In Mangrove Conservation of the importance of a gendered role analysis and a gendered approach to mangrove conservation to breakdown entrenched power in communities, access to resources and raise the status of those most marginalised, particularly women. She quotes from (Siar, 2003):

When women lose access to the intertidal zone because they are displaced by competing activities...or as a result of resource depletion, the situation is not considered as serious because women's fishing is looked upon as secondary or supplementary. Many initiatives in coastal resource management are focused on the management of coral reef fisheries (rather than intertidal mangrove areas) and reflect the importance attached to men's space vis-à-vis women's space (Siar, 2003).

The importance of giving women a central role in mangrove conservation is being recognized in the Sundarbans. There are reports that women across the region have become mangrove crusaders by guarding and planting their hamlets with mangrove belts. The mangrove saplings are gown in small village nurseries before being planted: "In a span of three-four months we prepared around 170,000 saplings which are being planted along the banks over 14 hectare land," one participant called Das said.

The project is being funded by international NGO Save the Children Fund and works employing and empowering local women.

"It is like a baby for us since we are growing and planting it with our own hands. We are telling everyone in the village including men and children to help us protect them. We will make sure that nobody cuts them for firewood when they mature," said 26-year-old Bijoli Rana.

"We have noticed that villages which are guarded by mangroves face less risk against tidal waves and floods. Even during Aila, such areas faced less damage when compared with those with only concrete embankments," said river expert Kalyan Rudra in the Zeenews report.

Bosold says we need to continue to look for innovative ways to improve mangrove conservation and provide equitable outcomes to the local people involved, particularly women who tend to be more marginalized in social and economic power in local communities:

"In order to save the world's mangroves from degradation and disappearance, we must search for new and more successful approaches to conservation and management. We must seriously consider and use a gendered approach to mangrove conservation in order to promote the type of innovative, sustainable, and equitable conservation systems vital for the success of future mangrove protection and management."


  • Eurekalert media release, 10 January 2013 - Bengali forests are fading away
  • William A. Cornforth, Temilola E. Fatoyinbo, Terri P. Freemantle and Nathalie Pettorelli, Advanced Land Observing Satellite Phased Array Type L-Band SAR (ALOS PALSAR) to Inform the Conservation of Mangroves: Sundarbans as a Case Study (Full paper), emote Sens. 2013, 5(1), 224-237; doi:10.3390/rs5010224
  • Express news service : Kolkata, Mon 7 January 2013 - Dr R K Pachauri sounds climate alert for Sundarbans
  •, 7 November 2012 - Sundarbans: Crusade launched against climate change
  • Pendleton L, Donato DC, Murray BC, Crooks S, Jenkins WA, et al. (2012), Estimating Global "Blue Carbon" Emissions from Conversion and Degradation of Vegetated Coastal Ecosystems (Full Paper) PLoS ONE 7(9): e43542. doi:10.1371/journal.pone.0043542
  • Syed Azizul Haq, 2010Impact of climate change on "Sundarbans", the largest mangrove forest: ways forward (PDF), 18th Commonwealth Forestry Conference, Edinburgh. 28 June - 2 July 2010.
  • Abhijit Mitra, Avijit Gangopadhyay, Anumeha Dube & et al, 25 November 2009, Observed changes in water mass properties in the Indian Sundarbans (northwestern Bay of Bengal) during 1980-2007 (abstract)
  • Yusuke Noguchi, Rajarshi DasGupta and Rajib Shaw, Case Study - Managing the "Man" in the Mangroves in the Indian Sundarbans Case Study as part of Chapter 4 Cooperative Management of Mangrove Ecosystems in India, in Noralene Uy and Rajib Shaw (Eds) - Ecosystem Based Adaptation (2012) ISBN 9781780526904
  • Bosold, Alyssa L., Challenging The "Man" In Mangroves: The Missing Role Of Women In Mangrove Conservation (abstract, Full paper PDF Student Publications. Paper 14.
  • Images provided courtesy Zoological Society of London, Except for satellite image: Sundarbans, Bangladesh provided by NASA Earth Observatory

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