Comparison of fuzzy method and Integrated Desertification Index (IDI) in assessing the intensity of desertification in Torbat-e-Heydariyeh of Khorasan Razavi province with emphasis on vegetation indices

In this study, the efficiency of two fuzzy methods and the integrated desertification index in Torbat-e-Heydariyeh, Khorasan Razavi province, have been compared using enhanced vegetation indices, vegetation condition index, salinity index, synthetized drought index, and temperature index for 2000 and 2020. The indices were normalized using maximum-minimum and fuzzy methods and weighted by analytical hierarchical method (AHP). Next, by weighted overlay combination and IDI method, the intensity of desertification was determined. The results showed that in the fuzzy method, 45% (1676 Km2) of the region suffers from severe and very severe desertification, and a major section (ie 55%, 2048 sq. Km) has mild and moderate intensity. In comparison, in the IDI method, no area fell into the very severe class, but at the same time, 67% (2496 Km2) of the total area fell into the extreme class. Accordingly, although the two methods have classified the area at risk of desertification, but this classification in the fuzzy method has been much stricter than the IDI method. The IDI method tends to overestimate desertification conditions. The comparison between the measured field data and similar values ​​in the obtained maps showed that the IDI method (kappa index of 0.73) was more compatible with the ground truth than the fuzzy method (kappa index of 0.54). Therefore, it can be concluded that the IDI method, although more efficient, has also overestimated the desertification in the region. Finally, this method is proposed to evaluate desertification in the region against the fuzzy method.