"Production will deplete steadily as the climate changes more and more, and by 2015 Bangladesh, along with neighbouring countries, may be forced to look for new brand of crops," he told Reuters.

"With the changing behaviour of weather, time of rainfall has changed, drought has become more rampant while threats of more flooding also loom," Nishat said.

He said higher temperatures and concentration of carbon dioxide in the air was hurting crop output.

The water flow in the country's main rivers has also depleted, especially in summer when most food crops are sown in agrarian Bangladesh, home to more than 140 million people, mostly rice-eaters.

The supply of fish from the rivers has declined across the country, due also to the increased salinity in the rivers along the shores of the Bay of Bengal.

"The main source of water in our rivers is the upstream glaciers. The rise of temperature means these glaciers are being smaller day by day. As a result, the supply of water is being reduced," said Mozaharul Islam, a research fellow of Bangladesh Center for Advance Studies.

"It leads to drought-like situation in Bangladesh's north-western region in the dry season, affecting production of rice and wheat," he said.