Major rivers of the world, including the Ganga and Brahmaputra, are facing a big human onslaught, a point to note ahead of the climate change summit in Copenhagen in December.
The areas drained by the Ganga (2,510 km) and Brahmaputra (960 km in India) in India are getting regularly submerged due to the construction of dams and canals, and rising sea levels.
The Ganga and Brahmaputra river basins are important to India because they support close to 40 per cent of India’s agricultural production and some of the unique bio-diverse hot spots.
Any change in the water flow systems of these rivers could result in a 15-20 per cent fall in India's farm production, a source of livelihood of around 400 million people. The two rivers play a major part in 25 per cent (more than 50 million tonnes) of India’s agricultural production.
Not only humans, even nature will face the music as the two river basins support 30 per cent of Indian bio-diversity, especially in the upstream Himalayan region.
Similar has been the case of 22 other large rivers of the world like the Irrawady in Myanmar and the Mekong in Indo-China, whose deltas (landmasses formed at the mouths of the rivers) are critically threatened.
The University of Colorado, in the central United States, has published this finding in the journal Nature Geo Science.
The study highlights a two-way process. On the one hand, pebbles and silt brought in through man-made canals are obstructing the flow of the rivers, causing an elevation in their level and the consequent overflowing of the banks.
And the rise in the sea level, due to the melting of glaciers, is blocking what might have flowed into the sea, leading to rivers remaining laden with impurities. "This phenomenon is called the extension of the salt wedge and it will salinate the groundwater of Kolkata and turn agricultural lands barren in adjoining rural belts," said Pranabes Sanyal, head of the School of Oceanographic Studies in Kolkata’s Jadavpur University, in his recent study of the impact of rising levels of the Bay of Bengal on the Ganga. Sea levels in some parts of the Bay of Bengal are rising by 3.14 mm annually against a global average of 2 mm, threatening the low-lying areas of eastern India.
Around the world, about 500 million people living in major river deltas are likely to be hit by this process, causing more frequent floods.
“Our data analysis … clearly shows that human activity has fastened
the process of the sinking of deltas and has caused increase in the frequency of severe floods,” said the lead author James Syvitski, dean, department of earth sciences, Colorado University.
Syvitski is directing a $4.2 million effort funded by the National Science Foundation to model large-scale global processes like erosion and flooding.
In India, studies have shown that the severity of floods in river deltas has also increased by 3-5 per cent in the last few years.
“Disturbances caused in the hydro-geological structure of a particular river basin can increase the frequency of floods,” said S.P. Gautam (54), chairperson of the Central Pollution Control Board, who contended that no research has been done in India on the impact of human activity on the rivers’ hydro-geological structures.
In such a situation, Indian scientists say there would be more human loss on account of sudden flash rains, especially during monsoons. The Indian Institute of Tropical Meteorology has found that in the past 50 years, the prevalence of sudden flash rains has increased.
“There are already 7,000 environmental refugees in the Sunderbans (close to 100,000 people live in the Sundarban islands) and the numbers can only increase with the sea devouring more islands as a result of global warming," said Sanyal.