Sunderbans – Vulnerable to Climate Change

Gautam Kumar Das

Sunderbans is not adequately protected to avert its floral assemblages as well as human settlements in the island habitation from the effect of inundation for sea-level rise due to climate change. Climate change and its effect upon the Sunderbans region followed by rapid coastal subsidence and sinking of landmass, last for many years. The rapid subsidence of coastal areas of the Sunderbans is the result of combined effects of long-term tectonic subsidence as the outer delta is slowly sinking over geological time due to its position at the eastern edge of the northeastward drifting Indian plate. Again, sediment compaction in the lower deltaic plain of the Bengal Basin covering entire Sunderbans and wasting away of peat accelerate the subsidence. Last in order, but not on this account the least in importance, the eustatic sea-level rise leads to the subsidence of the Sunderbans region, though global sea-level is assumed to have been stable during the 18th century, while eustatic sea-level rise of 60 mm in the 19th century and 190 mm in the 20th century is supposed to be taken for consideration. Inundation of relatively huge quantity of waters upon the river flood plain as a result of eustatic sea-level rise is restricted by the man-made embankment and causes adverse effects on the surrounding environment. Eustatic sea-level rise has been accelerating as a consequence of the combinations of the effects of climate change and rate of subsidence. Further, rate of subsidence has partially been lessening with the simultaneous effect of the accumulation of sediments. rate of sediment accumulation differs in the Sunderbans having ≤ 5 mm/yr for the western Sunderbans, 1 – 4 mm/yr for the eastern Sunderbans and 2 – 4 mm/yr for the central Sunderbans whereas average rate of subsidence of the Sunderbans is 5.2 ± 1.2 mm/yr, which includes 0.8 mm/yr of eustatic sea-level rise as reported by Till J.J. Hanebuth in 2013. IPCC (Inter-governmental Panel for Climate change) working group II advises for mitigation and adaptation as complimentary components in order to response and take strategy for sea-level rise due to climate change.

Sunderbans region, once collapsed, probably caused by a major catastrophic cyclone storm surge in 1699 A.D. reported for the Sunderbans by SAARC Meteorological Research Centre (1998), which had at least 50,000 casualties. It is considered by the scientists that the cyclonic storm-hit human habitation zone has gradually been covered by the mangroves from that time period as supported by the evidence of tree trunks found in the 230 – 240 cm depth of the excavated ponds and were existed in about 360 years before present as dated and supported by 14C ages. The catastrophic cyclonic storm of 1699 devastated Sunderbans resulting several drastic effects, whereas, sea-level rise has slow but steady impact on the deltaic plains of the Bengal Basin vulnerable to climate change of Sunderbans.

Sea-level rise and land subsidence have adverse effects on the nutrient availability and resist development and production in the floral assemblages in Sunderbans. As a result, nutrient cycle can create immediate and impressive changes in the mangroves vegetation. Along with nutrient cycle, salinity intrusion, as controlled by climate change and sea-level rise, affects the productivity and growth of mangrove forests. Mangrove vegetation is more luxuriant in lower salinity areas due to sea-level rise, though the sea-level rise leads to the permanent inundation upon the mangrove patch. As a consequence, breathing roots (pneumatophores) has been submerged as a result of the mangrove degradation through reduced respiration. Naturally mangrove patches start moving towards natural levee and river flood plains for its regeneration which obstructed by the construction of embankments, dam and dikes. The embankments, dam and dikes are thrown up as a protection against inundation or intrusion of saline water of flood tidal flow. In this way, loss of mangroves occurs due to lack of habitat for regeneration. Inundation of water due to sea-level rise spreads over the areas of even human habitation zone. The embankments surrounding human habitation areas are supposed to be shifted towards land year by year due to increasing waters for sea-level rise. Only the planned adaptation, along with more options and greater possibilities for offering incentives by the government would reduce the vulnerability to climate change. Enhanced adaptive capacity for mitigation of adverse effects of the climate change particularly in the human habitation are based on  some activities like improving infrastructure, improving access to resources, reducing poverty, lowering inequities of resources and wealth among islanders, manifestation of education and information, broadening institutional capacity and efficiency. If such activities don’t work well, it can result maladaptation, warned by Working Group II of IPCC, the kind of activism advocating the consequence of climate change of force for achieving big ends.

Feb 10, 2019

Gautam Kumar Das

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