Studies on water use in commercial orchards have received greater attention globally. More so because fruit tree crops rely on irrigation water which is a scarce resource, and it requires a considerable management in irrigated agriculture. (Díaz-Espejo et al. 2008, O’Connell et al. 2010, Villalobos et al. 2009). Working towards improving on-farm water management plans, the use of models to estimate evapotranspiration (ET) as a major part of crop water use in orchards has been widely adopted. Often, simple empirical models which are adjusted for local orchard characteristics are used rather than mechanistic models which are complex and require a lot of input parameters (Allen and Pereira 2009). However, mechanistic models are more suitable since they provide a degree of understanding (a causal relationship) between the controlling variables and the rate of ET, and they can be transferred to different orchard conditions. In orchard crops, water use models require three key variables; canopy size, canopy conductance, and weather variables. These variables account for; the transpiring surface, the crop resistance to transpiration when the demand and soil water are not limiting and the atmospheric demand respectively. The canopy size, byin many ways, has a significant role in determining water use in orchard crops. Apart from its direct relationship to ET, it accounts for differences in orchards such as the age of the orchard, species and/or cultivar and orchard management practices (pruning). In addition, the canopy size provides information about the seasonal dynamics of the canopy which plays a major role in estimating water use of orchard crops throughout the season. However, all orchard crops share the same difficulties in quantifying the canopy size; the degree of complexity increase with the increasing size of the canopy. Different approaches for quantifying the size of the canopy in orchard crops are depend on the objectives and convenience. Normally, radiation interception techniques, which use canopy size descriptors such as leaf area density (LAD), and leaf area index (LAI) are often used, more so because they are easily linked to ET (Fereres et al. 2012). This technique is based on the premise that radiation interception and extinction through the canopy depends on the size (leaf area, leaf distribution) of the canopy. In addition, the canopy volume, the fraction of the ground shaded by the canopy can be used in determining the size of the canopy in orchards. Alternatively, remote sensed vegetative indices such as the normalised vegetative index (NDVI) are extensively used to monitor vegetation dynamics in fruit trees. Regardless of the method used, precision and the ability to trace canopy changes throughout the season including the less dynamic such as evergreen crops is important.