- The effects of mesoscale circulations induced by soil moisture heterogeneities are studied to assess the impact that the coupling of the land surface and the planetary boundary layer has on the rainfall and soil moisture dynamics at different scales. Our goal is to single out the most important physical mechanisms which affect the behaviour of the land-atmosphere system at the mesoscale leading to a dynamical evolution which shows the same features at different scales both in space and time. In particular we aim to understand if any hypothesis of self-organization in the system can find its rationale in the mesoscale soil-atmosphere coupling. The main mechanisms of interaction have been simulated through a cellular automata model which incorporates in a soil water balance both the local and the large scale phenomena. Fractal features are shown to emerge in the simulated hydrological fields as an effect of the land-atmosphere coupling and this suggests the possible occurrence of self-organization. Some comparisons with real data tend to support such a hypothesis.