SINGAPORE (Reuters) - Increased melting of glaciers and snow in the Himalayas and Tibetan Plateau threatens the food security of millions of people in Asia, a study shows, with Pakistan likely to be among the nations hardest hit.
A team of scientists in Holland studied the impacts of climate change on five major Asian rivers on which about 1.4 billion people, roughly a fifth of humanity, depend for water to drink and to irrigate crops.
The rivers are the Indus, which flows through Tibet and Pakistan, the Brahmaputra, which carves its way through Tibet, northeast India and Bangladesh, India's Ganges and the Yangtze and Yellow rivers in China.
Studies in the past have assumed that a warmer world will accelerate the melting of glaciers and snow in the Himalayas and Tibetan Plateau, which act like water towers, the study published in the latest issue of the journal Science says.
But a lack of data and local measurement sites has hampered efforts to more precisely figure out the magnitude of climate change impacts on particular countries, the numbers of people affected in coming decades and the likely effects on crops.
The issue is crucial for governments to assess the future threats from disputes over water, mass migration and therefore political risk for investors.
Lead author Walter Immerzeel and his team conducted a detailed analysis looking at the importance of meltwater for each river, observed changes to Himalayan and Tibetan glaciers and the effects of global warming on the water supply from upstream basins and on food security.
Immerzeel, a hydrologist at Dutch consultancy FutureWater and Utrecht University, said he believed his team was the first to use a combination of computer modelling, satellite imagery and local observations for all major Asian basins.
They found that meltwater was extremely important for the Indus basin and important for the Brahmaputra basin, but played only a modest role for the Ganges, Yangtze and Yellow rivers.
The Brahmaputra and Indus basins are also most susceptible to reductions of flow because of climate change, threatening the food security of an estimated 60 million people, or roughly the population of Italy.
"The effects in the Indus and Brahmaputra basins are likely to be severe owing to the large population and the high dependence on irrigated agriculture and meltwater," the authors say in the study.
For the Yellow River in northern China, the reverse appeared true with climate change likely to lead to more rainfall upstream, which, when retained in reservoirs, could benefit irrigation downstream.
The findings are a warning signal for Pakistan in particular whose growing population of 160 million people is heavily dependent on the Indus to grow wheat, rice and cotton from which the nation earns hard currency.
Immerzeel said adaptation was crucial.
"The focus should be on agriculture as this is by far the largest consumer of water," he told Reuters in an email interview.
"You could think of measures such as different crop varieties which are less water consuming, different water management, or by providing economic incentives to farmers to use less water." (Editing by Nick Macfie)