This article presents the development of distributed thermodynamic model for energy and mass balance computation between soil surface and shallow atmospheric layers and its inclusion into the hydrological model FEST–EWB (Flash–flood Event–based Spatially distributed rainfall–runoff Transformation–Energy Water Balance). This model is also thought for a synergic use of hydrological model with remote sensing data. In particular, the energy budget is solved looking for the representative thermodynamic equilibrium temperature (RET) defined as the land surface temperature (LST) that closes the energy balance equation for any pixel of basin surface. So using this approach, through the system between the mass and energy equations, soil moisture (SM) is linked to the latent heat flux (LE) and then to LST. The RET thermodynamic approach solves most of the problems of the actual evapotranspiration (ET) and SM computation. In fact, it permits to avoid computing the effective ET as an empirical fraction of the potential one. This approach, based on the RET, has been tested at field scale (10 ha) with energy fluxes and LST measured with an eddy covariance station in Landriano (Italy). Copyright © 2010 John Wiley & Sons, Ltd.