On 40 percent of the earth's land, long periods of drought with short spells of intense rainfall are the norm.

These drylands are home to millions of people, and the constant search for water can trap inhabitants into a vicious cycle of subsistence.

But in Eastern Kenya, ancient rainwater harvesting structures known as "sand dams" are being constructed to hold and filter valuable water, turning once arid land into fertile soil.

Russell Beard travels to rural Kenya to see the remarkable impact the sand dams are having on landscapes and livelihoods alike.

earthrise can be seen each week at the following times GMT: Tuesday: 2230; Wednesday: 0930; Thursday: 0330; Friday: 1630; Saturday: 2230; Sunday: 0930; Monday: 0330; Tuesday: 1630. 

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Source: Al Jazeera