Impact of climate change on river deltas and other coastal areas in India

The effects are most visible in the Sunderbans. Literally the 'beautiful forest', these wetlands at the mouths of the Ganga and Brahmaputra river systems are among the largest mangrove forests in the world. About 62% of this area of some10000sq km lies in Bangladesh but there is a significant Indian portion in the state of West Bengal. Two hundred years ago, the area extended to nearly 17000 sq km. This region is an important wildlife habitat and one of the last remaining refuges of the Bengal tiger with a population estimated at just around 500 of these magnificent mammals. It is also home to spotted deer, crocodiles, various species of snakes, birds and aquatic species. On account of this, the Sunderbans in both countries have been included in the list of important sites designated by the Ramsar convention on the conservation of world wetlands.

The entire land is undergoing a very slow tilt toward the east due to tectonic movement which is a cause of subsidence. In addition, the part facing the Bay of Bengal is susceptible to seasonal ocean currents, tides, waves, winds and cyclonic storm surges which can cause rapid erosion on the one hand and deposition on the other. Heavy annual rainfall and the flow of river waters also keeps a large proportion of the ground partially or completely submerged much of the year. Local human activities accompanying an ever increasing population over a few centuries (and greatly accelerated in the last few decades) have included damming, diversion of fresh water, dredging, sand quarrying, construction as well as felling of mangroves, poaching, overfishing, discharge of effluents and attempts at reclamation. The reduction of natural vegetation, particularly the mangroves has reduced the deposition of sediment and accelerated erosion apart from removing an important protection against flood waters and high waves.

By far, the biggest threat in the long run is the rise in sea level due to global warming as well as increasing rainfall in the region. The last thirty years has seen the loss of some 81 square kilometers of land. Old maps record 102 islands on the Indian side, 52 of them inhabited by a total of 1800000 people. Of these two, named Suparibhanga and Lohacharra have already disappeared and cannot be located even with sophisticated satellite imaging, rendering some 10000 inhabitants environmental refugees. A further 100000 residing on twelve islands in the west of the estuary face a similar fate in the next few years. One of these islands is Ghoramara, a large piece of land which has shrunk to a tiny mudbank over the last quarter century. Most of those who dwelt here have moved out to nearby Sagar and it is only a matter of a few years at the most before the few who are left are forced to follow suit as the remaining land is swallowed up by the sea. But Sagar itself is diminishing in area due to erosion. Those who have been turned into environmental refugees lead a precarious existence with the bare amenties provided by the government which are highly inadequate for the number of people involved. They are often forced to eke out a livelihood through dangerous, unhealthy and environmentally destructive practices such as scouring mudflats for prawn spawn.

All this is only the beginning. Since the 1880s, world temperatures have increased by 0.8 degrees Celsius. This is primarily due to a 36% increase in carbon dioxide in the atmosphere as well as substantial increase in other greenhouse gases such as methane, NO2 and CFCs. While there is no clear agreement on the quantum of warming predicted, expectations are broadly to the tune of 0.5-2 degrees Celsius by the year 2030. There is little hope of achieving the 50% or more cut in global carbon emissions before a threshold is crossed in the next decade and a 1-7 degree rise by 2070 is very likely. This translates into a rise in sea levels of 3-16 cm in the next two decades and up to 50 cm by 2070. By 2100 this could be well over 60cm. Mitigation in the form of barriers are can at best provide a very limited and temporary solution and that too at high cost.

While the case of the Sunderbans (classified as extremely vulnerable) has been well documented in scientific literature as well as the media, a fairly similar situation prevails in the rest of the deltas in peninsular India – the Mahanadi, Godavari, Krishna and Cauvery. Of these, the Krishna delta has been identified as highly vulnerable while the rest are moderately so. One aspect of climate change is the increase in the frequency or intensity of the tropical cyclones that hit these areas. This together with the denser population and environmental degradation makes for far higher human and economic losses and slower and less complete recovery from these natural disasters. The recent havoc caused by Cyclone Nargis in Myanmar and parts of Bangladesh are a grim reminder of this risk. Even in years without such storms, the impact of climate change will be felt as in the Sunderbans through erosion and flooding, apart from intrusion of saltwater into freshwater bodies and aquifers affecting irrigation, drinking water and industrial water supplies. Water and vector borne diseases are also likely to increase. Loss of biodiversity through habitat destruction and other factors will also be significant.

The maritime impacts of global warming will be felt not only in the deltas but other coastal areas as well. Estuaries, lagoons and backwaters will experience an increase in water level and salinity due to rising sea levels. This would in turn affect brackish water species and the fisheries that depend on them. Navigation could also be affected by changing coastlines. The rising ocean would swallow up large tracts of land which have importance – ecological, economic and cultural. Millions of people living in these areas would be displaced. States like Kerala and Goa would be particularly hard hit. Several cities including three of the metros are in the danger zone and would be threatened by rising water and storms. The possibility of Mumbai, Chennai and Kolkata having to be partly or even completely abandoned are horrendous to contemplate.

Where would the crores of displaced city dwellers go to? Most parts of the already overpopulated country would already be reeling under other effects of climate change such as heat waves, droughts, famine and disease. The influx of millions of displaced persons could, among other problems lead to huge social tensions and conflict making it extremely difficult for the government to maintain law and order. The economic burdens could also stretch national resources to the breaking point and undoing all the great strides we take pride in. With all countries suffering these effects, little international aid would be available. How long the changed conditions would last, if they would be reversible at all or what sort of equilibrium would finally be reached are big unknowns.

At the cost of sounding pessimistic, one can only say, 'Be prepared for the worst.'

• References