Zhengyu Liu and M. Notaro

Center for Climatic Research, UW–Madison

On the cause of abrupt ecosystem collapse in Northern Africa during the Holocene: Climate variability vs. vegetation feedback

Room 811 AOSS, Monday, March 12, 2007, 3:30 PM

Abstract

The abrupt desertification over northern Africa in the mid–Holocene is studied in coupled climate–terrestrial ecosystem models. A new mechanism is proposed for the abrupt collapse. In contrast to the previous mechanism that relies on a strong positive vegetation feedback and the resulted multiple equilibrium, our mechanism proposes that the abrupt desertification is caused by low frequency climate variability, in the absence of strong positive vegetation feedback and multiple equilibrium. The vegetation feedback on climate is further studied using two independent assessment methods: one statistical method and a direct dynamic model simulation. It is found that Northern Africa vegetation cover exerts a negative feedback on annual rainfall in the mid–Holocene, with the negative feedback diminishing towards the present. The model negative feedback is associated with the competition between transpiration and bare ground evaporation. Implications of the model simulation on the observations are also discussed.