Behnaz Asefjah; Yahya Esmaeilpour; Ommolbanin bazrafshan; Hossein Zamani
Abstract
The past decade has seen a major revolution in vegetation monitoring using satellite imagery, resulting in quantitative indicators of vegetation with a professional processor in a web-based interactive development environment. In this study, using MOD13A1 and MOD13Q1 products of Modis sensor, the trend ...
Read More
The past decade has seen a major revolution in vegetation monitoring using satellite imagery, resulting in quantitative indicators of vegetation with a professional processor in a web-based interactive development environment. In this study, using MOD13A1 and MOD13Q1 products of Modis sensor, the trend of temporal and spatial changes of NDVI and EVI indices in Fars province in a period of 16 days from 2000 to 2020 was coded and processed monthly in Google Earth engine system. The results of this study showed that the average index of NDVI index is from minimum 0.11 to maximum 0.495 and the average index of EVI index is 0.1. According to the results obtained in this survey, in all the years from 2000 to 2020 in January, NDVI and EVI values had the highest values compared to other months, so that in January 2019 and January 2020, the highest EVI values averaged 0.22 and the NDVI values Was estimated to be 0.18. The lowest monthly average values of both indices occurred between 2000 and 2005, which indicates that the vegetation has been severely degraded during these years. The results of spatial changes using EVI index showed that the level of vegetation in Fars province in different months varied from 10,000 square kilometers to 22,000 square kilometers and from the perspective of NDVI index from 15,000 square kilometers to 30,000 square kilometers.
Setareh Bagheri; Reza Tamartash; Mohammad Jafari; Mohammad Reza Tatian; Arash Malekian
Abstract
Plain ecosystem is highly vulnerable to environmental changes, and drought is the most famous ecosystem change driver that is difficult to identify after its occurrence. In this research, to study the slope of vegetation changes against drought, the NDVI index of MODIS images and the SPI index from 2001 ...
Read More
Plain ecosystem is highly vulnerable to environmental changes, and drought is the most famous ecosystem change driver that is difficult to identify after its occurrence. In this research, to study the slope of vegetation changes against drought, the NDVI index of MODIS images and the SPI index from 2001 to 2016 were used and the map of vegetation changes against drought with five drought stress classes included very low classes, Low, moderate, high and very high, so that a suitable assessment of the drought can be made at specified time scales. The results of slope pattern of spatial change of vegetation against drought showed that across the plain vegetation changes have declined, and from east to west of Qazvin plain, the slope of vegetation changes and land susceptibility to drought have been reduced. So that the most percentage of area in a one-month drought related to the drought class is very low, but in droughts of 3, 6, 9, 12, 24 and 48 months, the highest percent of the area belonged to moderate and high drought classes. The results of this study, the determination of the level of vegetation changes in against drought in the past years and prediction of these changes in the future years, can be used in the planning and optimal use of resources, control changes in the future.
Ahmad Gillvare; Gholamreza Zehtabian; Hassan Khosravi; Hossein Azarnivand; Salman Zare
Abstract
Due to the importance of vegetation cover in these areas, the aim of this study was to investigate the effect of drought, on vegetation of HablehRood watershed.Initially, NDVI index obtained from MODIS sensor was used to study vegetation cover and then SPI index based on rainfall data of two basins in ...
Read More
Due to the importance of vegetation cover in these areas, the aim of this study was to investigate the effect of drought, on vegetation of HablehRood watershed.Initially, NDVI index obtained from MODIS sensor was used to study vegetation cover and then SPI index based on rainfall data of two basins in two arid and semi-humid climates was used for drought assessment (2001-2018) using image processing methods. The results showed that during this 18-year period, 53% of the region had droughts on average. Also during the period 2001-2003, drought was more severe than other periods (2003-2018). In addition, the highest vegetation index occurred in 2005, indicating that vegetation was affected by rainfall fluctuations in the region. The correlation matrix between the three indices indicated that NDVI had the same correlation with SPI and annual rainfall. The results of this correlation in dry and semi-humid climates showed that the correlation was 0.38 and 0.25, respectively. These results indicate that this relationship is positive and robust in different climates of a region؟. On the other hand, drought class is mainly located in dry and semi-humid climates, with 55.55% and 50% in relatively normal drought class, respectively. Based on the above, it can be concluded that using remote sensing data can monitor the response of semi-humid and dry arid ecosystems to climate change. The study also showed that arid and semi-arid regions are highly susceptible to climate change and human anomalies. Therefore, the destruction of these lands will have many environmental and economic consequences.
Leila Yaghamei; Reza Jafari; Saeed Soltani; Hasan Jahanbazi
Abstract
Snow is one of the effective fators on vegetation rate and function in mountainous areas. The aim of this study was to investigate the impact of snow cover area index and snow cover duration index on two declining and dominant plant species including Astragalus adscendens and Quercus brantii in Chaharmal ...
Read More
Snow is one of the effective fators on vegetation rate and function in mountainous areas. The aim of this study was to investigate the impact of snow cover area index and snow cover duration index on two declining and dominant plant species including Astragalus adscendens and Quercus brantii in Chaharmal and Bakhtiari Province from 2003 to 2016. For this purpose, Normalized Difference Snow Index (NDSI) and Normalized Difference Vegetation Index (NDVI) were extracted from MODIS satellite images and compared using Pearson analysis in forest decline regions (Barz, Seveh, Helen and control area) and in rangeland decline regions including Astragalus adscendens decline and control areas. Results showed that about 32% of the snow cover in the study area has been reduced, although a constant trend was not observed. The studied snow indices showed the highest relationships with rangeland and forest vegetation cover in March. The decline region of Astragalus adscendens had the maximum relationship with the snow cover area (R>0.70) and snow cover duration (R>0.71) in March. According to the findings, snow precipitation in late winter season and its duration is more effective on the rangeland Astragalus adscendens species than forest vegetation cover and this pecies can be more sensitive to decline in case of snow reduction.
mojtaba jannatrostami; mohammad rahimi; hassan kaboli
Abstract
Most of the studies on dust storms are concentrated in the western-eastern provinces of the country and less research has been done in other parts of Iran. In this research, some of the southern plains of Alborz; which have the potential to produce dust were selected. Daily data of 18 meteorological ...
Read More
Most of the studies on dust storms are concentrated in the western-eastern provinces of the country and less research has been done in other parts of Iran. In this research, some of the southern plains of Alborz; which have the potential to produce dust were selected. Daily data of 18 meteorological stations with long-term statistical period from 2008 to 2017 and to calculate the indicators of agricultural drought, MOD13Q1 and MOD11A1 products were used in the same period. Standardized precipitation index and standardized precipitation-evapotranspiration index were calculated and from the dust hourly meteorological codes, the experimental dust storm index was obtained. Then the relationships between climatic indices, vegetation and experimental index of dust storm were investigated using Pearson correlation and multivariate regression statistical method. The highest frequency of DSI index during 10 years is related to Imam Khomeini station with a value of 30.5 and the lowest is Taleghan station with 0.05. The Year-on-year changes in the dust index show that in the early years, the central and southeastern parts of the region were affected by dust storms, and sudden decrease had a significant effect on the results and reduced the long-term trend. The highest and the lowest correlation is respectively wind speed and Temperatur .Regarding the results of monthly multivariate regression, are somewhat variable in different months of the year, so that the effect of climatic elements and vegetation changes in different months, in general wind speed, TCI and SPEI have the most important effect on increasing
Leila Fazel Dehkordi; Hossein Azarnivand; Mohammad Ali Zare Chahouki; Farhad Mahmoudi Kohan; Shahram Khalighi Sigaroudi
Abstract
To identify an appropriate index for monitoring and evaluation of drought, rainfall data obtainedfrom meteorological stations of Ilam Province from 2000 to 2011 and MODIS satellite images with16-day intervals were collected and processed. The Standardized Precipitation Index (SPI) wascalculated based ...
Read More
To identify an appropriate index for monitoring and evaluation of drought, rainfall data obtainedfrom meteorological stations of Ilam Province from 2000 to 2011 and MODIS satellite images with16-day intervals were collected and processed. The Standardized Precipitation Index (SPI) wascalculated based on rainfall data; therefore, the rainfall data were used for measuring SPI andsatellite images were used for calculating NDVI. Also, the percentages of canopy cover in rangetypes were selected from the information of the National Evaluation of rangelands in differentclimatic zones. The correlation between SPI and NDVI and also canopy cover and NDVI wasexamined. The relationship between vegetation index (NDVI) and SPI was determined byregression. The results of SPI showed that in 2000 a severe drought and in 2006 a medium wetoccurred in rangelands of Ilam Province. NDVI value variations have as well confirmed it. Theresults showed that NDVI and life form (annual forb and annual grass) has the highest percentage ofcorrelation. Also examining of result showed that most correlation of SPI and NDVI was in 3 and 6-months intervals. Evaluation of regression models performance in range types described thatmodels in 3 and 6- months intervals was suitable for monitoring drought. The result of regressionconfirmed that NDVI was an appropriate index for monitoring and assessment of drought.
