A survey on the effect of drought on environmental indices derived from the MODIS data over the 2001-2019 period (Case study: Rangelands of Isfahan province)

Regarding the heavy damage of droughts to plant communities and soil moisture, the present study aimed to derive the SPEI drought index using the climatic data, temperature and rainfall, and to calculate the EVI vegetation cover and CWSI soil moisture indices through satellite data processing. Then variations of the indices and their correlation with drought was addressed. Looking at the trend of drought variations in Isfahan province shows a frequent drought over a 19-year period. The most severe droughts happened in 2001, 2008, and 2010 at which the minimum indices vegetation cover and soil moisture were observed. The trend of the variations of SPEI, EVI, and CWSI revealed their ascending trend by 88.54%, 13.14%, and 90.72% and their descending trend by 2.93%, 78.33%, and 9.28%, respectively. Out of the increases of the indices, 6.93%, 6.32%, and 63.56% were significant at the P < 0.05 level, respectively. Out of all decreases, 0.33%, 7.45%, and 8.75% were significant at the same level, respectively. The test of the correlation of SPEI index with soil moisture and vegetation cover indices indicated that the effect of SPEI on these two indices was positive across 87.23% of the province and negative across 56.56%. As a result quantity and quality of the vegetation cover and soil moisture have declined. The information produced by these climatic data and satellite imagery can considerably help policymakers and planners to cope with the drought and its impacts on vegetation cover and soil moisture.