Since soil moisture and vegetation cover are the most important parameters effecting drought, analyses of the vegetation fraction and soil spectral signature, especially in the red and infra red bands, are essential in drought estimation. In this study, the Perpendicular Drought Index (PDI), Modified Perpendicular Drought Index (MPDI) and Vegetation Supply Water Index (VSWI) have been used for drought assessment in arid regions in Central Iran during a time interval of four years (1999-2002). To do this, ETM+ images of LANDSAT 7 for the years 1999 and 2002 and the rainfall statistics for 23 years have been used. Analysis of vegetation cover using vegetation indices demonstrated that in arid regions, changes in vegetation cover were best mapped using a SAVI2 index. The results of MPDI indicated that drought has increased in the rangelands of the study area because of a decrease in seeding of the rangeland and vegetation fraction. PDI showed that the severity of the drought has decreased due to an increase in rainfall in 2002.