Rainwater harvesting is essential for managing water and dry spells on the continent, said Malin Falkenmark, senior adviser at the Stockholm International Water Institute (SIWI).

"Green water, the hidden water in the soil ... is the key to future food production in Africa," she told the World Water Week conference in Stockholm. "Dry spells can be managed by rainwater harvesting."

The late 20th Century ‘green revolution’ in Asia was based on high-yielding crop varieties and improved irrigation methods which pushed up rice and other crop production, keeping pace with the continent's rising population.

The world's population is forecast to rise from 7.3 billion now to 9.7 billion by 2050 and 11.2 billion by 2100, with most of the growth in developing regions, particularly Africa, according to the United Nations.

Development experts have focused their efforts and investment on support for small-scale farmers and a green revolution to reduce hunger and poverty in Africa.

While Asia's massive growth in agricultural production from the 1960s to the 1990s was based on irrigation, Africa's green revolution needs to be based on catching rain before it evaporates, Falkenmark said. "The trick is to get the rain down to the soil ... where we have the roots (to) take the nutrients up to the plant," she said. "We are waiting for the green revolution in Africa."

In much of the continent, rainwater evaporates before it can recharge the rivers, and many farmers are far from rivers anyway, leaving rainwater harvesting as the only solution, Falkenmark added.

Rulers and farmers in parts of India have harvested rainwater for centuries, storing it in huge tanks for use in the dry season, and rooftop rain harvesting is becoming more popular in places with erratic rainfall or periods of drought.

World Bank economist, Claudia Sadoff, said that while the Middle East and North Africa have long suffered chronic water shortages, Africa is the only region where water insecurity is increasing, and this is slowing its economic growth. "Africa is the only region in which the risks of (inadequate) water supply and sanitation are actually increasing because the population is growing very quickly and ... the supply is not keeping pace."

Dominic Waughray of the World Economic Forum said it made economic sense to get water governance right in the context of development. "From the governments' point of view, what is really helpful is to have lots of investors who want to engage in your economy," he said. "If you get the water governance right, they'll crowd to invest."

Reporting by Magdalena Mis, editing by Alisa Tang of the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, corruption and climate change.

Photo: A farmer harvests wheat on a field in the El-Menoufia governorate, about 9.94 km (58 miles) north of Cairo April 23, 2013. REUTERS/Mohamed Abd El Ghany