But, reliable aridity indices could not be developed until long time series from instruments and global vegetation maps were available. Thus, aridity indices are a product of the twentieth century (Dzerdzeevski, 1963, Hare, 1977, Tsakiris and Vangelis, 2005 and Livada and Assimakopoulos, 2007). The calculation of these indices includes the input of evapotranspiration data, estimated by the equation Penman–Monteith (Allen et al., 1998). But, necessary data that must be imported in the equation are soil and atmospheric data, such as solar radiation and soil heat flux, data which are collected with difficulty in most areas of the world