Drought is a natural and complex phenomenon which occurs in all areas. According to drought damages and its impacts, drought monitoring is necessary. The aim of this study was examine the possibility of drought monitoring using climate-based standardized precipitation index (SPI) and also remotely-sensed drought indices perpendicular drought index (PDI), modified perpendicular drought index (MPDI) and temperature-vegetation dryness index (TVDI) in Khorasan Razavi province with anarea about 12842 Km 2 . The data used in this study were MODIS Level 1B data (three images in a month) from 2003 to 2013. First, Level 1B data were pre-processed and the PDI, MPDI and TVDI indices were calculated. To investigate the effect of land use land cover on the indices, agricultural and urban areas were, removed from images, and then minimum, maximum and mean valued of the indices were extracted before and after masking these land-use. Monthly precipitation data from 42 rainfall stations 30 years period were used to calculated SPI, at five different time scales including, 1, 3, 6, 9 and 12 months. In the next step, SPI maps were spatially create by kriging technique and their minimum, maximum and mean values were extracted and regressed against satellite-based indices. Soil moisture in the 0-15 and 15-30 cm layer of soil depth were used to validate PDI, MPDI and TVDI indices. The correlation between SPI and image indices showed that PDI and MPDI had the highest correlations with 6- months SPI (R 2 = -0.95, R 2 = -0.96 ) and TVDI’s relationship was about (R 2 = - 0.47) With 3- month SPI. After removing agricultural and urban land uses the correlations were increased up to Strong relationships ranging from 0.81 to 0.92 between PDI, MPDI and TVDI and field –based soil moisture data revealed that these image- based indices are good predictors of drought in the region. Overall, the results showed that both the PDI and MPDI are appropriate indicators of soil moisture and vegetation cover and they can be used as an adjunct to SPI in drought assessment and monitoring at regional scales. Key words : Drought monitoring, PDI, MPDI,TVDI, SPI, Khorasan Razavi province
