monitoring agricultural drought in iran using time series of vegetation health index

In this study, in order to examine the severity of drought risk in iran during 18-year period (2001-2018), we used rain meteorological data of 176 synoptic meteorological stations, ground surface temperature product (mod11c3) and vegetation product (mod13c2) of moderate resolution imaging spectro radiometer (modis). the study results show that the highest drought severity occurred in 2001 and 2003, in 2001 in spring 85.8% and in the summer of 2003, 93.8% of the country was affected by different degrees of drought. during the 18-year period, the highest percentage of drought was related to mean (45.3%), mild (25%), and severe (8.9%) classes, and no drought (20.79%), respectively. the results indicate that in the whole country, there is no severe drought region in the studied period. according to the map of the rainy regions, iran’s rainfall is highly dependent on the roughness, latitude and frequency of the arrival of synoptic systems in the region. the spatial rainfall map in iran is well suited to vhi drought maps. the regions that receive less than 100 mm of rainfall represent the real deserts of the country. in these regions, severe drought conditions occur. the rainy regions between 100 and 200 mm, in terms of drought conditions, are in the mean class of drought. the rainy regions with a range of 200 to 300 mm are in the mild class of drought and rainy regions with more than 300 mm are usually not affected by drought stress.