“…Drought indices are particularly useful for monitoring the impact of climate variability on vegetation because the spatial and temporal identification of drought episodes is extremely complex. A number of drought indices, including meteorological (Wilhite and Glantz, 1985), remote sensed, hydrological and other indicators, have been used to measure drought impacts (Palmer, 1965(Palmer, , 1968Gibbs and Maher, 1967;Shafer and Dezman, 1982;Kogan, 1990Kogan, , 2002McKee et al, 1993;Keyantash and Dracup, 2004;Bhuiyan et al, 2006;Yagci et al, 2011;Zhou et al, 2012;Du et al, 2013;Yang et al, 2013;Abbas et al, 2014;Nichol and Abbas, 2015). Traditional methods of drought assessment and monitoring rely on rainfall data (e.g., the Palmer drought severity index (PDSI) and Standardized Precipitation Index (SPI)).…”