Two-thirds of the world's population are expected to live in cities by 2050, and that's driving a need for urban agriculture.

Rooftop farms and vertical gardens could prove crucial in fighting hunger in urban areas, according to new research released this week from Arizona State University.

Associate professor Matei Georgescu is co-author of the paper. He said urban farms and vertical gardening reduce the urban heat island effect.

Georgescu said urban farms can lower flooding risks and help to keep water in dry areas, according to his findings. With roughly 5 million acres, he said the U.S. has more urban area available than any other country.