A number of hamlets in the foothills of Arunachal Pradesh and upper Assam have disappeared under water in the last few decades with climate change causing rivers to migrate from their route, experts say.
Many such cases of inundation were initially described as flash floods by the administration, but gradually it has emerged that rivers like Bikram, Ranga, Bogi, etc, originating from the Arunachal mountains have actually changed their course due to long spells of high intensity rainfall.
A number of small villages like Hatkhola, Kapisala, Tenga, Bango and Vikram Chapori in Assam's Lakhimpur and Dhemaji district and Papum Pare district in Arunachal have been among the worst affected as a number of settlements have gradually submerged under water, this visiting correspondent found.
An analysis of geological data shows that in some places the rivers have changed their course by 300 metres while in other areas the change was as high as 1.8 km in between 1963 and 2009.
"As a result, parts of some villages have gone under water while in other cases the entire villages have simply vanished," points out geologist SK Patnaik of Arunachal's Rajiv Gandhi University.
A study under climate change fellowship by the New Delhi -based Centre for Science and Environment (CSE) shows that this has not rendered hundreds of people homeless but also damaged agricultural fields and the rich biodiversity of this north-eastern state.
Although the total rainfall hasn't changed much all these years, yet there has been an unprecedented increase in the duration and intensity of rainfall as well as cloudbursts in the Eastern Himalayas, explains Dr Prasanna K Samal, scientist in-charge at the G B Pant Institute of Himalayan Environment and Development in Itanagar.
As the river channel gets more rainwater supply, it discharges excess water and sediments on reaching the plains. Often it leads to rivers changing its course.
"Under normal climatic conditions, rainfall would have been well-distributed throughout the year. Now due to climate change, the pattern has changed. It has become erratic," says geologist Patnaik who is studying the impact of climate change in the state.
Two extremely intense cloudbursts of unprecedented intensity in Arunachal Pradesh were recorded in 2008 and 2010 produced devastating flash floods causing many deaths and enormous loss to forests and agricultural land.
The rainfall of Arunachal Pradesh is amongst the heaviest in the country receiving more than 3500 mm in a year.
"Perusal of available events leads one to believe that the instances of flash floods due to cloudbursts and excessive rainfall are on the increase in the Himalayan states of India.
However, no such evaluation can be made since insufficient numbers of events are recorded," says a report from International Centre for Integrated Mountain Development (ICIMOD).
Manoj Kumar, scientist at ICAR (Indian Council of Agricultural Research) in Meghalaya opines that with the river-feeding Himalayan glaciers receding, water stress will increase in the Brahmaputra basin.
The state action plan on climate change admits that flood is a recurring phenomenon in the state due to high precipitation and an estimated 8155 sq km area of the state is flood prone.
Besides the visible impact on human life, a number of endangered, endemic and threatened floral and fauna species with restricted distribution and narrow habitat ranges are also at risk due to this inundation.
As one of the world's 18 biodiversity hotspots, Arunachal possesses India's second highest level of genetic resources.