Effects of climate change including the melting of Himalayan glaciers threaten water and food security for more than 1.6 billion people living in South Asia, according to a study released Wednesday. India, Bangladesh, Afghanistan, and Nepal will be most vulnerable to falling crop yields caused by glacier retreat, floods, droughts and erratic rainfall, said the study financed by the Asian Development Bank. «South Asia's vulnerability to climate change has extremely serious implications for agriculture and therefore food security,» Kunio Senga, the ADB's director general for South Asia, told a news conference in the Nepalese capital, Katmandu, according to a report of The Associated Press.