Soil moisture provides the physical link between soil, climate and vegetation. It increases via the infiltration of rainfall and decreases through evapotranspiration, run-off and leakage, all these effects being dependent on the existing soil moisture level. During wet periods, soil moisture tends largely to be driven by the topography, while evapotranspiration has more influence in dry periods. In this talk, I will describe models for soil moisture dynamics in which marked Poisson processes are used to model the temporal process of rainfall input to the soil moisture dynamics, first at a fixed location and then over a spatial region. In these models, precipitation input is instantaneous so that, in the spatial-temporal version, rain storms have a spatial extent but no temporal duration. In a generalisation, storms are allowed to have both spatial and temporal extents. Losses due to evapotranspiration depend on vegetation cover and the models allow for variable, and possibly random, vegetation processes. In the spatial-temporal models, random-radius circular tree canopies are assumed, located in a homogeneous Poisson process over the region. Under arid/semi-arid conditions, many transient and equilibrium properties of these models can be determined analytically and used for comparison with data on soil moisture dynamics. Valérie Isham - University College, London Bande son disponible au format mp3 Durée : 48 mn