Demise of the Decapolis

Desertification and land deterioration are severe threats to the desert fringes and Mediterranean ecosystems, endangering not only food production, but also water supply and landscape stability. These areas host 30% of the world population with the strongest growth rates, and are characterised by numerous ancient ruins. While it is usually assumed that desertification is a result of unwise land use, climate variations may also lead to an advance of the desert. Can mitigation measures compensate for the expected negative impact of global warming? Human and natural factors are connected in feedbacks, which makes it difficult to describe cause-and-effect relationships. A key for predicting the impact of global warming is understanding historic desertification, since the investigation of the past allows to better separate the roles of man and climate. These questions were investigated in the Decapolis region in northern Jordan, an area in the transition zone between the Arabian desert and the Mediterranean climate belt. No evidence could be found for historic desertification due to land use: Environmental change was mainly related to climate variations.