An experimental study has been carried on in the semi-arid region of Cariri in Northeast of Brazil. The experiment 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. A numerical heat and mass transfer model in the soil – vegetation – atmosphere continuum shows the important role of the soil thermal diffusivity on the redistribution moisture process in the soil and on the soil evaporation rate. To estimate the soil thermal diffusivity x soil moisture relationship for this soil, three published methods have been used and their application to this soil case is discussed in this communication. The three methods are namely the Harmonic (HM) method (Horton et al., 1982), the Nashar (NS) method (Horton & Nashar, 1989) and the CLTM method (Silans et al., 1996). The HM method is based on the daily periodic assumption. A Fourier series with eight harmonics describes the measured soil temperature at the soil surface, then an analytical solution for the heat conduction equation is derived. The solution depends only on the thermal diffusivity value if constant thermal properties, namely thermal conduction and specific heat capacity are assumed to be constant in time and space. So the thermal diffusivity is obtained by the minimization of a mean quadratic error between the measured and calculated temperature at a determined depth. The NS method uses only a one harmonic Fourier series for surface temperature but allows estimating a non constant vertical soil thermal diffusivity using the temperature profile measurements. CLTM method is based on a corrected Laplace Transform analytical method and does not need the periodicity assumption, so the constancy of thermal properties in the vertical profile can be used in only few hours which can be easily verify in practice. This method shows the more consistent results and is very performing in semi-arid conditions. In this experiment a very low thermal diffusivity has been found. It varies between 2,4E-8 to 5,6E-8 m²/s.