Tiger, tiger... burning bright?

In the four Sunderban maps seen here, only the RCP 6.5 scenario by 2050 shows some land left for tigers (in red, yellow and green). In other three maps, hardly any land is left as the entire area is under water (shown in blue). 

Jamespur, Satjelia, Dayapur, Sonaga, Lahiripur — residents of these tiny villages in the Indian part of Sundarbans have lived with the Royal Bengal Tiger over the years. A common tale in this part of West Bengal is how scores of villagers have lost their near and dear ones to the enigmatic predator that lords over the world’s largest mangrove habitat. Ditto is the experience of villagers staying in the Bangladesh part of the swampy forest.

The threat of encountering the marauding tiger is now set to worsen for Sundarbans villagers, in both countries, as the big cats are on the verge of losing their last bastions, courtesy climate change. A new study predicts that the combined effect of climate change and sea level rise would lead to the loss of tiger population due to the destruction of tiger habitat in Sundarbans by 2070. The decline in numbers may be visible by 2050.

The Bangladesh Sundarbans covers an area of 6,017 sq km, which is nearly 60% of the total area of the Sundarbans (remaining 40% is in India). Besides the feline beast, at least 334 species of plants, 48 mammals, 59 reptiles, eight amphibians and 315 bird species were recorded in Bangladesh Sundarbans. While climate change had caused alterations in vegetation, salinity and sedimentation in the Sundarbans, scientists have now presented the first evidence on the looming threat hanging over the most famous occupants of the delta.

Sharif A Mukul, an environmental scientist at the Independent University, Dhaka partnered with researchers from Australia, New Zealand and the US to look at the future of the globally endangered Bengal tiger in its habitat. They chose Intergovernmental Panel on Climate Change’s two climatic scenario — RCP or Representative Concentration Pathways 8.5 and 6.0 — to look at the future.

While RCP 8.5 is a substantially carbon dioxide rising pathway, RCP 6.0 is an intermediate pathway. Under RCP 6.0, Sundarbans is also likely to witness 30 cm rise by 2050 and 60 cm by 2070 while in the RCP 8.5 scenario, the corresponding figures would change to 40 and 80 cm respectively. This is significant because the mean elevation of most of the Sundarbans is less than one metre above sea level making it highly vulnerable to sea level rise.

Of the total area of Bangladesh Sundarbans, almost 30% comprised a complex network of rivers and streams of varying depth and width. The elevation of most of the Sundarbans varies from 0.5-3.0 metres with nearly 70% of the area under one metre from the sea level. A majority of the vegetation is inundated by water twice a day during regular tidal flooding and the salinity level also varies between the east and the west.

Submerged habitat

To their utter horror, the scientists found only the RCP 6.0 scenario showed some habitat left for tigers by 2050. In all other three cases, barely any land is left. Under the RCP 8.5 scenario, the entire Bangladesh Sundarbans will be under water by 2070, leading to disappearance of the tigers from their most famous home.

“The projected habitat loss due to climate change will be 49.7% and 96.2% respectively by the year 2050 with IPCC’s RCP 6.0 and RCP 8.5 scenario. A complete loss of habitat is likely to happen only due to climate change by 2070 with RCP 8.5 scenario. Although sea level rise continues to threaten the existence of Bengal tiger habitats in the area, the effect will be not as be pronounced as climate change. Due to the combined effect of climate change and sea level rise, there will be no remaining Bengal tiger habitat in the Sundarbans by 2070,” researchers reported in the journal Science of the Total Environment in April.

Asked whether the findings would hold water for Indian part of the Sundarbans, Mukul said, “Our study findings are applicable for both part of the Sundarbans, as they both share similar climatic, geographic and environmental settings. Already salinity level changes in places within Sundarbans, vegetation composition (tree species) are altering too.”

In near future, most of the suitable Bengal tiger habitats will be confined within or in the periphery of the Sundarbans, which is closer to the Indian part of the Sundarbans and has relatively greater salinity than the rest of the forest. Dominated by Goran tree (Ceriops decandra), the area is also quite far from human settlements and, thereby, less prone to anthropogenic disturbance. Surprisingly, it is also one of the lower elevation zones.

However, even the West Bengal refuge is only up to 2050. If the situation continues to persist, that habitat too would disappear by 2070.

“Right now, the food is alright but if we can’t control illegal hunting of deer and other animals, there might be a problem in the near future (apart from climate change). With rising sea level and shrinking fresh water source and suitable vegetation, the tiger may move closer to the human settlement which will lead to more human-tiger conflict in the area,” Mukul told DH.

Of course, there are several if and buts in such modelling studies. But notwithstanding such uncertainties, there is no denying the seriousness of the threats.

Of the eight subspecies of tiger, three — Panthera tigris balica; Panthera tigris virgata; Panthera tigris sondaica — are already extinct while the rest — Indo Chinese tiger, South China tiger, Siberian tiger and Sumatran tiger — are either endangered or critically endangered.

The Bengal tiger, Panther tigris tigris, represents the largest remaining population (about 67%) of wild tigers spread over Bangladesh, Bhutan, India, Nepal, and Myanmar.

Jumbos in trouble, too

The warning from Mukul and his co-workers comes weeks before the publication of a UN report that red-flags the vanishing risks to one million of the world’s species, some as soon as within the next few decades. The top threat to species on land due to humans is habitat loss.

The tiger study coincides with another study that shows wild elephants may disappear from many parts of Karnataka and other southern states within decades owing to habitat loss.

India would experience nearly 42% loss in elephant habitats as climate change will compel the pachyderms to travel to higher altitudes for better water availability, according to the second study carried out by researchers from India and Europe.

“Climate and land use changes will lead to the disappearance of elephant habitat, and local extinction of elephants in human dominated areas in the eastern part of central and southern India. This includes the Eastern Ghats, which are an important, although fragmented, habitat for elephants. This would lead to local extinctions of elephants in those areas,” lead author of the study Rajapandian Kanagaraj from National Museum of Natural Sciences, Madrid told DH.

“In 2017, a drought decreased the elephant population in Tamil Nadu. The phenomena described in the study are already at work,” said Jean-Philippe Puyravaud from Sigur Nature Trust, Tamil Nadu and one of the co-authors of the paper.