The primary ET model is based on empirically derived equations that follow the work of Kristensen and Jensen (1975), which was carried out at the Royal Veterinary and Agricultural University (KVL) in Denmark.
The primary assumption in the Kristensen and Jensen (KJ) method is Actual Evapotranspiration (AET) cannot exceed ET0. The AET is reduced primarily by insufficient water in the root zone and by the density of the vegetation. In MIKE SHE, the current moisture content in the root zone is the limiting factor for AET in a time step. The root depth defines the depth to which ET can be extracted, and the Leaf Area Index (LAI) is the measure of the density of the vegetation.
The KJ method is based on empirical equations derived from field measurements. The model generally assumes the temperature to be above freezing.