The UN food agency on Thursday warned climate change will restrict the availability of water for farming in decades to come, including in the Mediterranean region, and urged governments to take action.

A report by the Food and Agriculture Organisation (FAO) said climate change will reduce river runoff and aquifer recharges, adding that the loss of glaciers "will eventually impact the amount of surface water available."

The report said that in Asia "large areas of irrigated land that rely on snowmelt and mountain glaciers for water will also be affected."

"Heavily populated river deltas are at risk from a combination of reduced water flows, increased sanity and rising sea levels," it added.

FAO also found that while increased temperatures will lengthen the growing season in northern temperate zones they will reduce it almost everywhere else, leading the yield potential and water productivity of crops to decline.

It said governments should improve the ability of countries to measure their water resources, as well as encourage farmers to change their cropping patterns to allow earlier or later planting and reduce their water use.

"Farm size and access to capital set the limits for the scope and extent of adaptation and change at farm level," the report said.