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Vegetation indices have been developed to characterize and extract the Earth's vegetation cover from space using satellite images. In order to detect vegetation changes, usually temporal images are independently analyzed or vegetation index differencing is implemented. A review on previous studies reveal  that extracting vegetation cover or vegetation changes usually NDVI and EVI are used  in spite of developing several vegetation indices. Therefore, the main objective of this study is to compare and investigate the applicability of these indices in detection of vegetation changes in different climate and environmental conditions. In so doing, several test sites in Malaysia, Iran and Italy with different environmental conditions including Tropical, Subtropical and Mediterranean were selected.Then, index differencing method using temporal Landsat-7 ETM+ and Landsat-8 OLI images belonging to the years of 2001 and 2014 were applied. In order to evaluate the accuracy of the output maps, confusion matrix was made to calculate overall accuracy and kappa index. Subsequently, commission and omission errors were calculated to assess nature of the errors in the results. Accuracy assessment analysis indicated that the results of EVI in some of the test sites were acceptable excluding all test sites with variety of weather and environmental conditions, NDVI  which provided higher accuracyoutcomes in detection of vegetation changes.

 

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Investigating the sustainability of vegetation changes is one of the most important issues of vegetation management in the direction of sustainable development. It is necessary to conduct studies in this regard to select appropriate management for greater compatibility with new conditions. In this research, changes in the vegetation dynamics trend of Fars province were studied using the NDVI index obtained from MOD13Q1 during the period 2001 to 2017. Mann-Kendall and Thiel-Sen tests in the Earth Trends Modeler of TerrSet software and the Hurst index in the ArcGIS software were calculated, then the results were combined with each other. Theil-Sen trend for statistical analysis of the changes slope, and Mann-Kendall test to determine the significance of these changes are a new approach to investigate the NDVI time series data analysis process. Overlaying the results of the trend analysis and Hurst index, the future sustainability in the NDVI changes was also calculated. According to the analysis of the Horst index, the trend of vegetation changes in the future is contrary to the changes that have taken place in the past.. In addition, the results of total trend analysis indicate that plant growth in mountainous areas continuously improves at a higher rate than the plains. Finally, the results of analyzing the Horst index and the process of vegetation changes showed that the highest number of pixels is for the month of May with 41.1% located in Class B. Class B represents that the rehabilitation trend has replaced the degradation trend in the region  and this trend will not continue in the future. This month, the northern and southern strips of the province have a maximum value.

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Today, one of the most important issues in economic, social planning and future decisions in an area is the awareness of vegetation rates and its spatio-temporal variations. The purpose of this research is to investigate vegetation changes in Central Zagros using MODIS Terra satellite data with spatial resolution of 250 m (2001 - 2018) and NDVI index. At the same time, DEM and DSM models and bilinear interpolation method were used to resampling. These data were processed to analyze vegetation changes in the interior and exterior of anthropogenic activities in the Central Zagros. The results showed that the NDVI index has increased in these altitudes and within mountain passes and valleys and in areas and lowlands adjacent to the slopes to the southwest, especially the Khuzestan plain. At the same time, the temporal trend of vegetation changes in the Central Zagros shows the increase of the NDVI index in this period. In the Central Zagros in January, the vegetation index at low altitudes, especially towards the Khuzestan plain, has a significant increase compared to higher altitudes; Therefore, nomads migrate to winter settlements. Meanwhile, in May, it is possible to establish nomads at higher altitudes and use high rangelands, resulting in nomadic summer migration. Spatial changes of vegetation within the interior and exterior of human activities showed that the increase of the average positive part of the vegetation index within the 5 km around of the cities is due to the expansion of gardens, agriculture and green area in this region. The relatively noticeable trend outside of that is also caused by temperature changes and the general trend of increasing vegetation index in central Zagros. The increase in the vegetation index in the 1km around of the communication roads and villages, as well as the areas outside it, can be related to the increase in temperature due to global warming and the reduction of winter snow-covers and due to the expansion of fields and gardens around the villages, roads and green area created in the around of roads and villages.