Loss of land through desertification and drought costs up to five percent of world agricultural gross domestic product (AGDP), or some $450 billion (340 billion euros), every year, said a study presented at a UN conference Tuesday.

Each year an area roughly three times the size of Switzerland is lost through soil degradation, it said, as 870 million people suffer from chronic hunger.

Between four and 12 percent of Africa's AGDP is lost due to degraded land annually, and in Guatemala the figure is 24 percent, the report said.

In Uzbekistan, food yields have declined by 20-30 percent due to deteriorated land, while in East Africa nearly 3.7 million people need food assistance as a result of the drought of 2011, it said.

The study, a summary of published research, was presented at the opening of a four-day conference in Bonn of the UN Convention to Combat Desertification (UNCCD).

It is the most detailed exploration of the economic cost of degraded and desertified land since 1992, the UNCCD said.

At that time, the direct annual cost was estimated at $42 billion.

"For current estimates, the best guess is $450 billion per year as a result of land degradation, drought and desertification and loss in fertile soil," said Walter Ammann, head of Global Risk Forum Davos, which promotes debate on issues of world risk.

"For example, Bangladesh is losing two percent of its fertile soil on an annual basis," Ammann said in a phone interview from the former West German capital.

"If you calculate this on a linear basis, then in 50 years' time, Bangladesh will have no fertile soil available."