The METRIC algorithm (Allen et al., 2007) was applied to a Landsat 5 image to assess the range of vegetation cover (measured as Normalised Difference Vegetation Index; NDVI), and rates of evapotranspiration (ET), of major horticultural crops grown in the Sunraysia Irrigation Region of SE Australia. The image represented the period of maximum foliage cover of horticultural crops grown in the Region. The range in mid-season NDVI of almond, grape and citrus crops almost matched the whole-of-season range reported for broad-acre irrigated annual crops grown in Idaho, USA. Alfalfa reference ET (ETr) constituted the upper limit to ET rate seen in Sunraysia crops. The range of ET and NDVI observations in this study therefore complied with limits on ET and NDVI seen in irrigated crops in Idaho, USA. ET-NDVI relationships seen in USA crops appear to provide a useful reference framework for well-watered irrigated crops in cases where ETr is the upper limit on ET. ET rates in Sunraysia crops were strongly related to NDVI. The dependence of ET rates on NDVI, combined with the large range in NDVI, meant that irrigation water requirement varied widely within and between crop types in the Sunraysia region: results support the use of NDVI measures to account for site-specific differences in crop water requirement attributable to vegetation cover. Findings suggest that satellite-based METRIC methods of ET estimation may be used to formulate region- and crop-specific estimates of the crop coefficients (Kcb, Ke, and Kc) required for optimal irrigation water management of horticultural crops.
