French architect firm designs a sustainable vertical city to be installed in the Sahara desert

The arid expanses of the Sahara desert could be transformed within a decade, according to French architecture company OXO.

The Parisian firm has proposed building a futuristic mixed-use tower in the world's biggest desert. The tower's design is based on renewable resources like rainwater collection, solar power and geothermal energy to make it an entire sustainable city in one building.

French-Moroccan architect Manal Rachdi is behind the 450 meter tower design, which would have a floor area of 780,000 square meters (approximately 840000 square feet).

The design is conceptual and has not yet been commissioned. Rachdi said his motive was to think about new ways of urbanising 'hostile' environments such as the Sahara.

"We tried to think of a concept which enables us to create not a building but a vertical city in the desert. It's a place which is hostile and where it's difficult to live so we created this tower including a kind of protective shell," he said.

More than 20 percent of the floorspace is designed for offices, while a hotel and 600 housing units would be created on another 50 percent of the available floorspace. The aim of the tower is to house a whole city, its designer explained.

"The idea is to make a city out of this tower. A city includes many things. The idea is to obtain a building combining different programs including housing units adjacent to offices of course. There is a museum, an meteorological observatory on the Sahara, there are libraries, gyms, pools. The idea was really to offer a sufficient number of programs to be able to remain self-sufficient and not to have to rely on other buildings or have to create new ones," said Rachdi.

The harsh desert environment is kept at bay in the design, with a central inner tower covered in plants to serve as a vertical garden.

"The consequence is that we recreate a livable and green ecosystem inside the tower, which otherwise could not exist in the middle of the Sahara," explained Rachdi.

OXO's desert tower incorporates shades and natural ventilation to help control the temperature. The geothermal technology proposed sees the rainwater collected being injected underground where heat from the earth would turn it into steam to generate energy.

Rachdi said the tower's use of sustainable technologies would make the vertical city very efficient, including using some of the rainwater collected for the irrigation of the vertical garden, despite the parched proposed location.

He described his design as an 'ecosystem'.

"When you get closer and you get in -like here-, you can see large water basins which refresh the air and refresh the space and then you enter in this inner space which is the second tower, a large vertical park , a large vertical forrest which has developed inside the building. Then, you get to spaces aimed to become offices, large landscape offices where nature is present. It comes from this large patio where we created an ecosystem," he said.

The Sahara desert is expanding southward at a rate of 48 km (30 miles) a year, forcing whole communities to migrate and pushing them on to land occupied by other groups, researchers said in a 2011 study.

Summer temperatures in the desert can top 45 degrees Celsius (116 Fahrenheit) and it is currently one of the most sparsely populated regions of the world, with around 4 million people living there, many nomadic.

The French architects envisage work starting on the project in 2025, with construction phased over 50 years.