Of the 16 countries listed as being at "extreme" risk from climate change over the next 30 years, five are from South Asia, with Bangladesh and India in first and second places, Nepal in fourth, Afghanistan in eighth and Pakistan at 16th.
The Climate Change Vulnerability Index, compiled by a British-based global risks advisory firm, Maplecroft, is intended as a guide for strategic investment and policymaking.
The barometer is based on 42 social, economic and environmental factors, including the responsiveness of government, to assess the risk to population, ecosystems and business from climate change.
South Asia is especially vulnerable because of changes in weather patterns that result in natural disasters, including floods in Pakistan and Bangladesh this year that affected more than 20 million people, Maplecroft said.
"There is growing evidence climate change is increasing the intensity and frequency of climatic events," the firm's environmental analyst, Anna Moss, said.