Evaluation of desertification in Qazvin Plain using Sentinel 2 images and spectral indices and degree of desertification (DDI)

Desertification is one of the factors that seriously threatens semi-arid areas. Climate changes and human activities in recent years have intensified this phenomenon. In this research, Sentinel 2 images in 2023 have been used to evaluate desertification in Qazvin Plain. At first, TGSI, albedo, NDVI and MSAVI indices were extracted. Then, for linear regression analysis, different combinations of indices were considered and Pearson correlation relationship was established between NDVI and albedo, MSAVI and albedo, TGSI and albedo, TGSI and MSAVI indices. Then, by using the regression relationships between NDVI-albedo and MSAVI-albedo, DDI desertification degree index was estimated. Finally, the map of desertification was drawn for the entire studied area in five classes: very severe, severe, moderate, low and very low. The obtained results showed that there is a negative correlation between albedo and MSAVI and NDVI indices, and a positive correlation between this index and TGSI. MSAVI-albedo combination has the best correlation coefficients with a value of -0.417 and the lowest correlation is estimated at 0.33 between albedo and TGSI. According to the DDI index, the desertification situation in the region has been in the alarming range. In fact, based on the albedo ratio with the MSAVI index, 55.6% of the region is classified as very severe desertification. While only 1.9% was very low in the area of desertification. According to albedoNDVI ratio, 68% of the region is in a very severe desertification state. The values obtained for the two models are very close to each other and similar estimates have been obtained in the estimation of extreme and very low values. Investigations showed that the studied area has been severely affected by desertification.