Modeling tools take an increasing place in the field of water supply monitoring investigations. A energy balance model, based on the 3-D description of plants at leaf level, is used to simulate cotton crop leaves temperature variability according to crop water status (Dauzat el al., 2001, In press). Model validation gives good results for homogeneous canopies. For heterogeneous crops, a systematic underestimation is observed, due to strong thermal soil effects. Also, the model is being implemented with a bare soil compartment to account for soil temperature and heart exchanges with the crop. Once validated, this approach will permit to interpret accurately crop temperature variability, to better estimate water status. Hence, it will be possible to test the Iimits of existing crop water status indexes based on temperature measurement, and determine the ways to be investigated to improve or perform such techniques.