NDVI reflects changes in chlorophyll content and vegetation amount and has proved to be useful tool for studying vegetation cover change and amount in semiarid and arid environments (Weiss et al, 2004; Fensholt and Sandholt, 2003). VWI can provide valuable information on vegetation and soil water stress and detecting drought status. When combined
with normalized difference vegetation index, the indices can give reliable information on water availability, drought status, vegetation vigour and phenology (Bajgiran et al., 2009).