Tampa (AFP) - Installing massive wind and solar farms in the Saharan desert could slow global warming, and also give a small but beneficial boost to rain in the dry African region, researchers said Thursday.

The study in the journal Science used computer modeling to simulate the effect of covering 20 percent of the largest desert on the planet in solar panels and installing three million wind turbines there.

A solar and wind farm of that size -- more than 3.5 million square miles (nine million square kilometers) -- would be "at a scale large enough to power the entire world," said the report.

Overall, researchers found that any changes in the African desert climate resulting from wind and solar power installations would be positive, because more plants would grow near where the farms are placed.

Together, according to model simulations, the wind and solar farm effect boosted average rain across the entire Sahara from 0.24 millimeters per day to 0.59 mm per day.

The effect was not uniform across the vast desert, with the most substantial rain increase occurring in the Sahel, a semi-arid region extending from Senegal to Sudan, where residents could see 200 to 500 mm more rain per year, or about 1.12 mm per day near the wind farms.

This would be "large enough to have major ecological, environmental, and societal impacts," said the report.

- More plants, more grazing -

"The vast majority of the Sahara would remain extremely dry," said co-author Daniel Kirk-Davidoff, an adjunct associate professor at the University of Maryland.

But more rain along the southern edge of the Sahara would lead to more plant growth, "which would allow for more grazing," he told AFP in an email.

"It is hard to imagine that this would be a bad thing from the point of view of human communities there."

The reason for the change has to do with the way wind farms bring in warmer air from above, particularly at night, a process which can increase evaporation and plant growth.

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This warm air exchange can also double the amount of daily precipitation.

Meanwhile, dark-colored solar panels reduce the amount of surface light that is reflected from the Earth, slightly raising temperatures and also triggering more precipitation.

Previous studies have found that wind and solar farms can introduce significant changes in climate at the continental scale by creating rougher, darker land surfaces.

But this study is the first to incorporate how vegetation would change as a result, said lead author Yan Li, a postdoctoral researcher at the University of Illinois.

"The lack of vegetation feedbacks could make the modeled climate impacts very different from their actual behavior."

Researchers also pointed out that any hikes in temperature from solar and wind farms would be limited in geographic area and scope, unlike fossil fuel emissions which continually build in the atmosphere and raise warming over time.

"The increase in rainfall and vegetation, combined with clean electricity as a result of solar and wind energy, could help agriculture, economic development and social well-being in the Sahara, Sahel, Middle East and other nearby regions," said co-author Safa Motesharrei, a researcher at the University of Maryland.