Report: Developing Nations Need To Diversify Water Supplies

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IWMI and its research partners estimate that up to 499 million people in Africa and India can benefit from improved agricultural water management. Even though there has been a spate of dam building, especially in poorer nations, many rural people still depend on the rain. In Asia, 66 percent of the total cropped area is rain fed, and in sub-Saharan Africa it is 94 percent.

While big dams offer real benefits, too often the environmental and human impact is not well studied, the report says. Dams can result in millions of displaced people and affect livelihoods of those living downstream, especially if they depend on a certain level of river flow. Creating large pools of standing water - as with a dammed river - can also create breeding grounds for mosquitoes that spread malaria.

To help address these problems, the IWMI study advocates giving more weight to a wide range of small-scale storage projects.

The group says field studies in different semi-arid environments, for example, have proven the effectiveness of using small planting basins to "harvest" water, together with targeted use of fertilizer. In Zimbabwe, such basins have been shown to boost corn yields, even when rainfall is less abundant, while in Niger, they have permitted three- or four-fold increases in millet yields.

In the northeast of India's Rajasthan State, the construction of about 10,000 water harvesting structures-intended mainly to recharge groundwater-allowed for irrigating about 14,000 hectares (34,600 acres) benefiting some 70,000 people. Previously, farmers had too little water to produce vegetables and other cash crops. The construction of more than 90,000 underground water storage tanks in China is benefiting a million farmers.

The results aren't always rosy. In Ethiopia, for example, one study showed groundwater wells and small dams reduced poverty by 25 to 50 percent. But another analysis in the country's Amhara region found that most of the approximately 4,000 water harvesting ponds constructed from 2003 to 2008 were no longer working, mainly because of poor site selection, technical failures and weak community involvement in maintenance.

"None of these options is a panacea," said McCartney. "They all have pros and cons, which depend on their inherent characteristics, on the way they are planned and managed, and on the conditions at specific sites."