January 29, 2010

Climate change and Sunrderban

Due to increased rate of emissions of greenhouse gases (carbon  dioxide, methane, nitrous oxide, ozone and chlorofluorocarbons) from  different sources such as burning of fossil fuels, deforestation and  other human activities, the rate of global temperature increase  accelerated from +0.6°C over the past century to an equivalent rate of  +1.0°C per century in the past two decades (Natural Resource Defence  Council, USA 2006). Sea-level rise as a consequence of global warming  is caused by increase in seawater temperatures resulting in thermal  expansion of water and melting of glacier and polar iceberg (Kennedy  et. al. 2002). The climate change has already affected the ecosystems  of northern hemisphere including the coastal forests.

The out  flow of water from Bangladesh is the third highest in the world, next  to the Amazonia and Congo basin. Major rivers of Bangladesh flow from  north to south, silting up the mangroves delta and draining into the  Bay of Bengal. The mangroves delta is also a region of transition  between the freshwater of the rivers originating from the Ganges and  the saline water of the Bay of Bengal.

The ecosystems as well as the  luxuriant biodiversity of Sunderbans have strong interactions with  marine environments. The Sunderbans is considered as the largest single  halophytic mangroves unit in the world. It has been declared as a  UNESCO World Heritage Site and Ramsar Site. The environmental  parameters with the direct influences on Sunderbans in terms of global  climate change are sea-level rise, natural calamities like cyclones,  temperature rising, salinity and drought. The structure and composition  of Sunderbans may undergo major change, depending on the severity of  human disturbances and predicted climate change.

The vegetation  of the Sundarbans differs greatly from other non-deltaic mangroves and  upland forests. It is a tropical moist forest having a mosaic pattern  of old growth and successional vegetations. A total of 334 plant  species were recorded in 1903 (Prain 1903). Sundari and Gewa are the  dominant species throughout the old growth forests with uneven  distributions of Dhundul and Kankara. Sometimes successional forests  are dominated by Keora, aquatic plants and dune vegetation. There are  strong correlations among vegetations, salinity, freshwater flushing,  silting, inundation and mudflat accretion. Golpata, Hantol and Goran  are also indicator plant species of these ecosystems.

A total  number of 375 species of birds, 55 species of mammals, 83 species of  reptiles and amphibians, 150 species of fish, 50 species of shrimp and  other invertebrates were recorded in the Sundarbans (The Daily Star  2009). Hog deer, water buffalo, swamp deer, Javan rhinoceros, single  horned rhinoceros and the mugger crocodile became extinct at the  beginning of the last century. It is the paradise of eponymous Royal  Bengal tiger, salt water crocodile and spotted deer. Besides, dolphins,  rhesus monkey, snakes, river terrapin, forest owl, sea eagle, Indian  flap-shelled turtle, peacock soft-shelled turtle, swamp partridge,  trogon, ground thrush, yellow monitor, water monitor, Indian python,  fishing cats, macaques, forest wagtail, wild boar, green frog, grey  mongoose, scarlet minivet, fox, ring lizard, jungle cat, flying fox,  pangolin, pigmy woodpecker, brown wing kingfisher, racket tailed  drongo, chital and other threatened species live in the Sundarbans.

Sea level rise

  One-metre  rise of sea level will destroy the whole ecosystem of Sunderbans. Dune  vegetation will be submerged under water. The pioneer or indicator  species Sundari will be replaced by Goran and Gewa species, which are  less valuable than Sundari. All ground animals will lose their  habitats. Herbivorous animals like deer, monkey and wild boar will face  shortage of food. Carnivorous animals like tigers and fishing cats will  face the same problem due to lack of herbivorous animals in the forest.  Marine turtles, crabs, shrimps, crocodiles, frogs, snakes, fresh water  fishes and dolphins will lose their breeding grounds and habitat as  well. The impacts of different rate of sea level rise on Sunderbans can  be projected by the study of Clough (1994).

(a) Low level rise: The old growth and successional forests will be able to keep pace with  a sea level rise of 8-9cm/100 years. Few species will be highly  vulnerable and many species will be threatened on islands.

(b) Medium level rise: Sunderbans will be under stress, especially islands with a sea level  rise of 9-12cm/100 years. A good number of species will be vulnerable  and maximum species on islands will face high risk of extinction.

(c) High level rise: Sunderbans will be squeezed with a sea level rise of above 12cm/100  years. Loss of species will occur in short period of time on islands.


  There  has been a noticeable change, almost 26 percent over past 120 years, in  the frequency of cyclones in the Bay of Bengal, which may be increased  further with the intensifying of El Nino in the upcoming days. Four  disastrous cyclones originated in the Bay of Bengal since 2006 -- Sidr,  Nargis, Bijli and Aila. Cyclones impact Sunderbans through three  primary mechanisms: wind damage, storm surge, and sedimentation. The  highly affected areas will become unsuitable for habitation till 2020.  Most of the inhabitants will be climate refugees with the repetition of  such cyclones. Strong winds uproot, topple stems, break off trunks and  defoliate the canopy. Taller stems are uprooted and knocked over when a  storm ashore comes. Sediments carried by storm surges are deposited on  the forest floor as the surge recedes, cause plants mortality by  interfering with root and soil gas exchange, leading to eventual death  of the plants. Storm surges reduce the viability of seeds, seedling  germination and seedling recruitment. The recovery of forest dynamics  from cyclone damage can be altered by other kinds of changes to the  landscape. Many exotic plant species have the ability to rapidly  colonize disturbed areas, and out-compete slower-growing native trees  and plant.

These cyclones do not affect the Royal Bengal tigers  too much as they can swim a long distance. But the problem is that they  may lose bearing. When they do not know in which direction they have to  move, they may die due to exhaustion. Strong wind destroys honey bee  colonies causing high mortality. Coral reefs, woodpecker, sea turtles  and parrots are vulnerable to cyclones. The arboreal monkey and lizards  face shortage of foods.

Coral reefs are hit hard, fractured, and  sponges and sea fans are ripped from their bases. Branching corals are  broken and transported over the reef top. Dunes and beaches are washed  away, and large areas completely submerged. Fish dies when the decay of  foliage stripped from trees lower oxygen levels in the water. Cyclones  have heavier impact on wetlands and the organisms that depend on them.  Ground birds are severely affected by losing their habitats, nesting  and breeding sites.


  Sunderbans is the  transitional zone between freshwater supplied by rivers and saline  water pushed by the Bay of Bengal. Sundari, the pioneer tree species  will suffer from "Top dyeing" disease with the increase of salinity.  Salinity increases the tree mortality rate by reducing the production  of new leaves, leaf longevity and the leaf area (Su├írez and Medina,  2005). Net photosynthesis rate, stomata conductance and transpiration  rate of leaves decrease with the increase of salt concentration (Yan  and Guizhu, 2007). It is believed that Royal Bengal Tigers are  suffering from various diseases by drinking saline water and their  normal behaviour is also being changed. Aquatic organisms will migrate  inward. Many fish species and other crustaceans utilize fresh water for  spawning and juvenile feeding. The Hilsa needs less salinity to lay  their eggs and enter various creeks in search of sweet water. The  hatchlings move towards the sea where they attain adulthood, before  returning to the rivers. Migration of fish species will have an adverse  effect on the economy of the country.

How to combat: Some suggestions

  * Designing and establishing sea-level / climate modelling network

* Establishing databases and information systems

* Data collection of Sundarbans" resources and their uses

* Integrated coastal and marine management

* Monitoring the impact of climate change on coral reef, Royal Bengal Tiger, crocodiles and Sundari tree

* Coastal vulnerability and risk assessment

* Economic valuation of Sundarbans" resources

* Improving catchment  management

* Facilitating natural regeneration and natural succession of native tree species

* Increasing waterfront setbacks in beach front areas

*  Education on climate change and emergency preparedness needs to take  place at all levels by incorporating it into education curricula

* Creating public awareness through mass media

* Developing coastal infrastructure

* Initiating community based coastal forestation

* Protecting existing mangroves against encroachment and cutting

* Afforestation and reforestation by salt tolerant species

* Initiating ex-situ conservation of rare species

* Establishing mechanisms to promote carbon uptake

* Raising funds for conservation programme

* Strict control of Tigers" poaching


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