زمانیده از سریستفا ااهی باش گیند پوشیل رو تحل/ ... ضی دستی مرت گردی وران همکا 135 Print ISSN: 2322-2069 Online ISSN: 2322-2794 Journal of Water and Soil Conservation Vegetation trend analysis using NDVI time series of Modis satellite in the northeast of Iran Morteza Dastigerdi 1 , Mehdi Nadi *2 , Mahmoud Raeini Sarjaz 3 , Khadijeh Kiapasha 4 1. M.Sc. Student of Agrometeorology, Dept. of Water Engineering, Sari Agricultural Sciences and Natural Resources University, Sari, Iran. E-mail: mortezadastigerdi@gmail.com 2. Corresponding Author, Assistant Prof. of Agrometeorology, Dept. of Water Engineering, Sari Agricultural Sciences and Natural Resources University, Sari, Iran. E-mail: m.nadi@sanru.ac.ir 3. Professor of Agrometeorology, Dept. of Water Engineering, Sari Agricultural Sciences and Natural Resources University, Sari, Iran. E-mail: raeini@yahoo.com 4. Ph.D. Graduate of Forestry Sciences, University of Tehran, Tehran, Iran. E-mail: kh.kiapasha@alumni.ut.ac.ir Article Info ABSTRACT Article type: Research Full Paper Article history: Received: 05.10.2022 Revised: 06.10.2022 Accepted: 06.15.2022 Keywords: Mann-Kendall, MODIS-NDVI, Time series, Trend analysis, Vegetation change Background and Objectives: Vegetation is very important in providing organic matter, regulating the carbon cycle and exchanging energy at the surface. In recent years, climate change and global warming have created frequent events such as floods, high temperatures and droughts that can damage terrestrial ecosystems. Weather fluctuation due to climate change directly affects vegetation growth, on the other hand, vegetation respond to climate change by regulating water, energy exchange, and carbon dioxide concentrations. Materials and Methods: In this study, which was conducted to investigate the trend of vegetation changes in the study area during the period 2001-2018, 16-day combined time series data of MODIS-NDVI called MOD13Q1 with a spatial resolution of 250 meters was used. In this study in order to investigate the significance trend of vegetation cover, the non-parametric Mann-Kendall method was taken. Also the relationship between vegetation changes and altitude was investigated. Results: Of the total area of the study area, 52% of the area had a decreasing trend of vegetation and the rest showed an increasing trend of vegetation, although a significant decrease in vegetation at the level of 5 and 1% occurred in 36% and 32% of the area, respectively. Also, 31 and 26 percent of the study area had a significant increase in vegetation at the level of 5 and 1 percent. In the study of the relationship between Z-Kendall statistic and height, the results showed that with increasing the height of Z-Kendall statistic increases and the correlation coefficient of height with Z-statistic is about 0.62. It seems that significant positive trends in vegetation occur at higher altitudes and significant negative trends in vegetation occur at lower altitudes. 99% and altitudes of 670 and 840 were obtained for the negative trend of 95 and 99%. In other words, at altitudes above 2030 and 1860, the trend of vegetation changes is positive and at altitudes below 670 and 840 meters, the trend of vegetation changes is significantly decreasing. Conclusion: The results of this study showed a significant trend of greening at altitudes of more than 2030 meters in the region. It seems that with the increase of temperature due to climate change at elevated area,