OSLO (Reuters) - The main impact of climate change will be on water supplies and the world needs to learn from past cooperation such as over the Indus or Mekong Rivers to help avert future conflicts, an expert said on Sunday. Desertification, flash floods, melting glaciers, heatwaves, cyclones or water-borne diseases such as cholera are among the impacts of global warming inextricably tied to water. And competition for supplies might cause conflicts. The main manifestations of rising temperatures...are about water, said Zafar Adeel, chair of UN-Water which coordinates work on water among 26 UN agencies. It has an impact on all parts of our life as a society, on natural systems, habitats, he told Reuters in a telephone interview. Disruptions may threaten farming or fresh water supplies from Africa to the Middle East. Therein lies the potential for conflicts, he said. Shortage of water, such as in Darfur in Sudan, has been a contributing factor to conflict. But Adeel said that water had often proven a route for cooperation. India and Pakistan have worked to manage the Indus River despite border conflicts and Vietnam, Thailand, Laos and Cambodia have cooperated in the Mekong River Commission. Water is a very good medium (for cooperation). Its typically an apolitical issue that can be dealt with, said Adeel, who is also Director of the UN Universitys Canada-based Institute for Water, Environment and Health. Regions likely to become drier because of climate change include Central Asia and northern Africa. Up to 250 million people in Africa could suffer extra stress on water supplies by 2020, according to the UN panel of climate experts. There are many more examples of successful transboundary cooperation than conflict over water, said Nikhil Chandavarkar, of the UN Department of Economic and Social Affairs and Secretary of UN-Water. We are trying to take the examples of good cooperation - the Mekong, the Indus are examples. Even where there were hostilities in the surrounding countries the agreements did function, he told Reuters. Adeel said that water should have a more central role in debates on food security, peace, climate change and recovery from the financial crisis. Water is central to each of these debates but typically isnt seen as such, he said. And efforts to combat global warming will themselves put more strains on water because of rival economic demands - such as for irrigation, biofuels or hydropower. Adeel noted efforts to manage water supplies by counting how much water goes into products - from beef to coffee. One study showed that it took 15,000 litres to produce a pair of blue jeans, he said. Making industries aware of water use could help shift to conservation. He said the world might reach a millennium goal of halving the proportion of people without access to safe water by 2015 but was failing in a related target of improving sanitation. About 2.8b people lack access to basic sanitation.