An experimental study, taking place in the semi-arid region of Cariri in Northeast of Brazil, is intended to measure the irradiative budget, the soil moisture budget and the energy budget in a vegetated cover soil at the plot scale to perform an heat and water transfers model in the soil vegetation atmosphere continuum. The experiment has been carried on from July 2001 to December 2003. The soil is narrow, a Bruno não cálcico type, i.e. a brown sandy loam soil. The vegetation is sparse, made of shrubs of 2,5m to 3m heigh, called “Caatinga”. It is compound of cactácea, broméliaceae and others vegetations with very little sheets. Vegetation islands alternate with bare soil. The experimental results show that main results: The sensible heat fluxes and the latent heat fluxes are controlled by a free convection process between soil and canopy, which results from both high surface temperature due to a very low thermal diffusivity and high in-vegetation temperature due to vegetation transpiration control (Silans et al., 2003). Só evaporation rate is relatively low along a drying period and soil moisture shows a very particular pattern. Soil moisture has been measured by a TDR probe at 5cm depth. To explain these results an heat and mass transfer model in the soil – vegetation – atmosphere – continuum has been developed and a sensibility study to the thermal diffusivity is shown. The model uses, in the soil, the coupled equations of energy and water (liquid and vapor) transfers in porous media proposed by Milly (1982) and modified by Silans et al. (1989). At the soil interface with the air between soil surface and vegetation canopy, fluxes are modelized by the free convection equations proposed by Jacob e Verhoef (1997) and the Bowen ratio. Because of difficulties to disaggregate liquid radiation in vegetated soil and bare soil liquid radiationxs components, the measured in-vegetation temperature and air specific humidity are input as upper boundary condition. The lower in-soil boundary condition is of the first kind for the energy transfer equation, this is a daily constant temperature and of the second kind for water transfer, this is a null flux as stones at 50 cm depth limit the soil depth. The model uses the finite volume techniques with an explicit scheme for time integration, with an irregular one dimension vertical grid. Results of simulations show a low evaporative rate as was measured and a soil moisture pattern at 5 cm depth quite similar to the measured one, but surface temperature and daily soil moisture amplitude are sensible to the thermal diffusivity. Then the role of the thermal control by soil layer on soil moisture and evaporation rate is demonstrated. However soil thermal diffusivity is difficult to obtain by in-situ measurement and may show a great spatial variability which needs to be investigated.