Associated with the leaf-transpiration process, a phenomenon known as evaporative cooling occurswhereby heatis dissipated by water vaporloss from the stomata. With lower transpiration levels, the evaporative-cooling process is significantly reduced,raising the leaf temperature (Tleaf) typically several degrees above the air temperature (Jones, 1999; Jones et al., 2002; Araus et al., 2008; Fuentes et al., 2012). These relationships establish the basis monitoring the crop–water based on leaf/canopy temperature, since any situation that causes a partial closing of the stomata (for example by a more or less prolonged water-stress situation) will result in a significant rise in leaf temperature. Therefore,Tleaf can be used as an indicator of the degree water stress with the advantage that it can be remotely measured and in plants of different sizes under field as well as controlled conditions.