A model for soil-vegetation-atmosphere interactions

We study the interaction between atmosphere, soil moisture, and vegetation inwater-limited environments with significant water recycling, and introduce asimple process model including some of the main feedbacks active in the system. In ourmodel, the soil-vegetation-atmosphere dynamics display two stable states for realisticvalues of the synoptic moisture convergence flux. Starting from low soil moisture and/orlow vegetation cover, the system reaches a dry and hot state, whereas it reaches a wetand cool state when starting from higher initial values of soil moisture and of vegetationcover. The role of synoptic perturbations is investigated by inserting a stochastic inputof moisture: in this case, a bimodal distribution of soil moisture is obtained. We explorethe difference between the dynamics of natural vegetation, capable of adjusting itsareal extent to variations in soil moisture, and cultivated vegetation, whose areal extentcannot vary. The model results indicate that the presence of natural vegetation increases theprobability of reaching a wet/cool state with respect to the case of cultivated plants.