OSLO, March 20 (Alister Doyle/Reuters) - The United Nations should promote hydro-diplomacy to defuse any tensions over water in regions like the Middle East and North Africa where scarce supplies have the potential to spark future conflicts, experts said on Sunday.

They said the UN Security Council should work out ways to bolster cooperation over water in shared lakes or rivers, from the Mekong to the Nile, that are likely to come under pressure from a rising world population and climate change.

The Middle East and North Africa are the regions most at risk of conflict over scarce water supplies, they said, but history shows water wars are very rare.

We think that water is an issue that would be a appropriate for the UN Security Council, Zafar Adeel, chair of UN-Water, told Reuters ahead of a meeting of experts in Canada this week to discuss water and security.

UN studies project that 30 nations will be water scarce in 2025, up from 20 in 1990. Eighteen of them are in the Middle East and North Africa, with Libya and Egypt among those added to the 1990 list that includes Israel and Somalia.

Water scarcity is when each person has access to 1,000 or fewer cubic meters of water a year.

UN-Water coordinates water-related activities of all UN agencies. March 22 is World Water Day in the UN calendar.

The world's top ranked water conflict hotspot is the Arab region, comprised of the Middle East and North Africa, according to a statement about the March 21-23 talks in Toronto.

Adeel said the UN should try to promote past traditions of rivals cooperating over supplies in a form of hydro-diplomacy.
              
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We have a whole history of cases where...even countries at war have used water almost as a neutralizing element, he said.

India and Pakistan, for instance, cooperated to share supplies in the Indus River even during conflicts in 1965 and 1971.

There are clear advantages in cooperation, former Canadian Prime Minister Jean Chretien, who will be a co-chair of the meeting in Toronto, told Reuters.

Water will become an ever more important issue, he said, adding that the talks would look at cases such as the River Jordan, with rival demands by Israelis, Palestinians, Jordanians and Syrians.

Experts say the only documented case of a water war was about 4,500 years ago when the city-states of Lagash and Umma went to war in the Tigris-Eurphrates basin.

Apart from that example, water has never been the principal cause of two states going to war, Fabrice Renaud, of the UN University's Institute on the Environment and Human Security, said in a statement.

Even so, Adeel said that stresses on water supplies due to global warming and a rising population -- which is set to grow to 9 billion by 2050 from 7 billion in 2011 -- could heighten the risk of future conflicts.

Forty percent of the world's population live within 263 international river basins, from the Amazon to the Jordan.

Chretien is among 37 former national leaders in the InterAction Council, who will meet in Canada in May to discuss water and security after this week's preparatory talks.

(Editing by Kate Kelland)