Increasingly?erratic rainfall patterns related to climate change pose a major threat to food security and economic growth, water experts said yesterday, arguing for greater investment in water storage.

In a report by the International Water Management Institute, experts said Africa and Asia were likely to be hardest hit by unpredictable rainfall, and urged policy makers and farmers to try to find ways of diversifying sources of water.

The IWMI research estimates that up to 499 million people in Africa and India could benefit from improved agricultural water management.

"Just as modern consumers diversify their financial holdings to reduce risk, smallholder farmers need a wide array of 'water accounts' to provide a buffer against climate change impacts," Matthew McCartney, a hydrologist at IWMI, said in a statement.

"That way, if one water source goes dry, they'll have others to fall back on."

The UN panel of climate experts has projected more extreme weather such as droughts, floods and heat waves this century due to global warming.

The report said around 66 percent of agriculture in Asia is dependent on rainfall despite a great expansion in irrigation in recent decades.

In sub-Saharan Africa, the proportion is even greater at 94 percent, it said. These regions have the least developed water storage infrastructure.

The report cautioned against over-reliance on single solutions such as big dams, and said an integrated approach combining large- and small-scale storage was a better strategy.

It suggested the use of water from natural wetlands, water stored in the soil, groundwater and water collected in ponds, tanks and reservoirs.

"For millions of people dependent on rain-fed agriculture, reliable access to water can make all the difference between chronic hunger and steady progress toward food security," McCartney added.

"Even small amounts of stored water, by enabling crops and livestock to survive dry periods, can produce large gains in agricultural productivity and in the wellbeing of rural people."

The IWMI is funded by the Consultative Group on International Agricultural Research, a partnership of governments, donors and international organizations.

It said, in response to increased demand for food and power supplies, many developing countries have recently invested in large dams.

The benefits of these projects in terms of storing water for crop irrigation were clear, it said, "but so are the adverse social and environmental impacts."