Hydro logical drought monitoring using SDI and GRI indicators In the watershed of Azam Herat, Yazd province

Drought is a natural and repetitive phenomenon. In this study, using SDI and GRI indicators, the hydrological drought condition was evaluated and compared with meteorological drought indicators.
In the MATLAB environment, the GRI index was determined. According to the results, the GRI index during the statistical period (1981-2015), the maximum drought severity was -73.25, and the maximum duration of drought was 79 months.
These values are higher than the SDI index in the same time scale and the common statistical period.
The Frequency of different groups of GRI indicator in the 35-year statistical period showed that normal drought had the highest percentage of abundance.
The SDI index has the highest maximum continuity in the low-level time scales compared to the drought indicators of the meteorology. Frequency of drought groups was calculated based on an SDI index for the statistical period for different time scales.
The results of this study showed that SPEI on 24 and 48 months scale with 3 month delay have the highest correlation with GRI which showed the impact of meteorological drought after two years has more effect on groundwater resources.
Knowing the time interval between the occurrence of meteorological drought as main cause of coming drought that could help planners and managers to take the necessary management measures to cope with the drought caused by a shortage of water resources including surface and groundwater.