The steps and equation to calculate SPI were followed method developed by LloydHughes
and Saunders (2002). The SPI output values are in units of standard deviation from
long-term median and provide the corresponding probabilities of occurrence of each
drought category relative to the normal probability density function. SPI values at the 3, 6
and 12 months were computed for monitoring drought at different timescales. Drought
condition were classified from SPI values into seven categories including extremely wet
(SPI was[2.0), very wet (SPI was 1.5–1.99), moderately wet (SPI was 1.0–1.49), normal.