STOCKHOLM (AFP) - Climate change poses a serious threat to essential water resources in the Himalayan region putting the livelihoods of 1.3 billion people at risk, experts said Thursday. The mountainous region, home to the world's largest glaciers and permafrost area outside the polar regions, has seen rapid glacial melting and dramatic changes in rainfall, experts at the World Water Week conference in Stockholm said. "Himalayan glaciers are retreating more rapidly than anywhere else in the world," said Mats Eriksson, programme manager for water and hazard management at the International Centre for Integrated Mountain Development. Although high altitudes, remoteness and cooperation difficulties between countries in the region have made it difficult to conduct comprehensive studies, Eriksson said it was obvious "the region is very strongly affected by climate change." "The glaciers' retreat is enormous - up to 70 metres per year," he told AFP. Xu Jianchu, who heads the Centre for Mountain Ecosystem Studies in China, pointed out that temperatures on the Tibetan Plateau for instance were increasing by 0.3 degrees Celsius each decade. "That's double the worldwide average," he said. This has a large impact in a region where melting glaciers and snow account for about 50 percent of the water that flows down mountains, feeding into nine of the largest rivers in Asia. The Himalayas stretch across China, India, Nepal, Pakistan, Myanmar, Bhutan and Afghanistan, and the mountain range thus constitutes a major source of water for some of the most populous parts of the planet. Eriksson and other experts said the region covers 1.3 billion people. "Snow and glacial ice melting provide a very important source for fresh water for irrigation, energy and drinking water downstream," Xu said. Glaciers hold numerous capacities to store water, so although water levels initially rise as the ice melts, in the long term their disappearance leads to less available water downstream. "Livelihoods will be severely affected by this," Eriksson said. At the same time as glaciers are melting, scientists say precipitation patterns in many parts of the Himalayas are changing dramatically, serving up more rain in the monsoon periods and less in dry seasons. "The drier areas are becoming drier, while the wetter areas are becoming wetter," said Rakhshan Roohi of the Water Resource Research Institute in Pakistan. Eriksson said changes had been especially felt in the drier western part of the Himalayas. On top of the more uncertain harvest conditions, which are prompting many people to migrate, farmers and others also face a growing number of natural disasters like flash floods and bursting glacier lakes. "Maybe before your district was suffering from one flash flood every season, and that was perhaps what people managed to cope with. But if you get three or four or five flash floods, maybe that's too much. The question is how much more can people tolerate without losing their basis for livelihood," Eriksson said. The Himalayan mountains does not produce much of the greenhouse gases that are so drastically altering its ecosystem, and in fact functions as a carbon sink, capturing carbon dioxide to mitigate global warming. Xu however cautioned that increased glacial melting means the captured CO2 will seep back into the atmosphere. "This will transform the carbon sink into a carbon source ... more soil carbon will be released with the melting of glaciers and permafrost," he said.