Nonlinear dynamics in a coupled vegetation-atmosphere system and implications for desert-forest gradient

Abstract

Although the global vegetation distribution is largely controlled by the large-scale climate pattern, the observed vegetation-rainfall relationship is also influenced by vegetation feedback and climate variability. Using a simplified coupled atmosphere-vegetation model, this work focuses on the effects of these on the gradient of desert-forest transition. A positive feedback from interactive vegetation leads to a wetter and greener state everywhere compared to a state without vegetation. As a result, the gradient in vegetation and rainfall is enhanced at places with moderate rainfall. Climate variability is found to reduce vegetation and rainfall in higher rainfall regions, while enhancing them in lower rainfall regions, thus smoothing out the desert-forest gradient. This latter effect is due to the nonlinear vegetation response to precipitation and it is particularly effective in the savanna regions. The analyses explain results from a three-dimensional climate model. The results suggest that in a varying environment, vegetation plays an active role in determining the observed vegetation-rainfall distributions.