Elham Rafiei Sardooi; Mina Eghtedarnejad; Shapour Kohestani
Abstract
Since that the traditional methods are based on meteorological station data and more investigate meteorological drought, hence, the application of remote sensing techniques and satellite images have been considered as a useful tool for monitoring of agricultural drought. In this study, the relationship ...
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Since that the traditional methods are based on meteorological station data and more investigate meteorological drought, hence, the application of remote sensing techniques and satellite images have been considered as a useful tool for monitoring of agricultural drought. In this study, the relationship between the meteorological drought index (SPI) and remote-sensing-based indices (VCI, TCI and VHI) has been studied in Bam plain. In this regard, using Terra satellite images (Modis sensor) and precipitation data of synoptic and rain gauge stations in the study area, the occurred changes were detected over the 15-year period. In this study, with respect to high temporal accuracy and spectral coverage and accessibility, MOD13A3 and MOD11A1 products extracted from MODIS sensor were used during 2009 to 2023. Then, indices of VCI, TCI and VHI were compared with Standard Precipitation Index (SPI). The results of drought mapping with the SPI index during 2010 to 2024 showed that the drought severity has increased from north to south in the study area. So that, extremely drought is detected in the southern regions of the plain and extremely wet is detected in the northern regions. The annual correlation coefficient between SPI, VCI and SPI indices is 0.70 and 0.53, respectively. It shows high significant positive correlation at level of 0.05. The correlation coefficient between SPI and TCI is 0.11 which shows a weak correlation but significant positive at level of 0.05. Therefore, VCI and VHI Indices have more correlation with annual precipitation and have acceptable results compared with TCI Index.
vahideh moradzadeh; Ardavan Ghorbani; Leila Nemati Sham-Asbi; Mehdi Moameri; Zeinab Hazbavi; Ali Teymourzadeh; Behzad Behtari
Abstract
Rangelands, as natural ecosystems, play a significant role in maintaining carbon balance of the environment. This study aimed to Identification of Carbon Sequestration Patterns under the Influence of Climatic, Soil, and Topographic Factors in the Rangelands of Northern Sabalan, located in Meshginshahr ...
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Rangelands, as natural ecosystems, play a significant role in maintaining carbon balance of the environment. This study aimed to Identification of Carbon Sequestration Patterns under the Influence of Climatic, Soil, and Topographic Factors in the Rangelands of Northern Sabalan, located in Meshginshahr County. Soil sampling was conducted in two types of vegetation cover- grassland and shrubland- across four main geographical directions and at two soil depths (0–15 and 15–30 cm). Data were collected for 24 different soil properties. To perform statistical analyses, the normality of the data was first assessed, followed by a one-way analysis of variance (ANOVA) and Duncan’s multiple range test to compare the mean values of different properties between grasslands and shrublands. Principal Component Analysis (PCA) was also used to evaluate data structure. The results revealed that clay content, silt, organic carbon, particulate organic carbon, total nitrogen, and soil carbon sequestration were significantly higher in grasslands than in shrublands (p<0.01). In contrast, sand content, pH, and electrical conductivity were significantly higher in shrublands than in grasslands (p<0.01). The northern slope exhibited higher levels of clay, silt, organic carbon, and carbon sequestration compared to the southern slope. Additionally, increasing soil depth led to decreases in organic carbon, total nitrogen, and carbon sequestration. PCA showed that the first two components explained 36.30% of the total variance. Sand content, precipitation, and organic carbon having the highest correlation with the first component, while slope percentage and litter showing the strongest correlation with the second component. These findings indicate that soil physical and chemical properties- particularly those affected by climatic gradients and topography- significantly influence carbon sequestration.
Sirous Shamshiri; Bijan Azad; Majid Karimpourrihan
Abstract
Drought is among the most severe climatic hazards in arid and semi-arid regions, and its increasing intensity and frequency in recent decades have substantially impaired the structure and functioning of terrestrial ecosystems. Nevertheless, field-based evidence on drought impacts on woody vegetation ...
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Drought is among the most severe climatic hazards in arid and semi-arid regions, and its increasing intensity and frequency in recent decades have substantially impaired the structure and functioning of terrestrial ecosystems. Nevertheless, field-based evidence on drought impacts on woody vegetation in dryland ecosystems, particularly with respect to vegetation density dynamics, remains limited. This study aimed to assess the effects of drought, using the standardized drought indices SPI and PNPI, on density variations of two woody species, Acacia ehrenbergiana Hayne and Ziziphus spina-christi, in the Espakeh Plain, Sistan and Baluchestan Province, Iran. Furthermore, transformed drought index time series were employed to investigate temporal lags in species density responses to wet and dry periods. The results demonstrated that density differences of both species between wet and dry periods were statistically significant, and that vegetation density variations exhibited a strong correspondence with the transformed SPI index. Time-series analysis revealed a lag of one to two years in density responses following wet and drought events, with the lowest densities of both species occurring one to two years after the most severe drought. Based on the SPI index, Spearman correlation coefficients between vegetation density and wet and dry periods were 0.62 and 0.96 for A.ehrenbergiana, and 0.88 and 0.74 for Z.spina-christi, respectively. In contrast, the PNPI index showed limited explanatory power for A.ehrenbergiana, likely due to differences in the computational frameworks of the drought indices applied in this region. Overall, drought resulted in a significant decline in the density of both species in the study area, with A.ehrenbergiana and Z.spina-christi densities decreasing from 17.33±7.22 and 8.44±4.51 to 8.66±4.78 and 5.11±3.32 individuals per hectare, respectively. Given the greater vulnerability of Z.spina-christi to drought stress, the development and implementation of climate-adaptive management strategies are essential to ensure its conservation and long-term persistence.
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 ...
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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.
samaneh Mohammadi Moghaddam; Abolfazl Mosaedi; Mohammad Jankju; Mansour Mesdaghi
Abstract
Although precipitation is the most important factor which effects rangeland production, but there is little information on the relationship between production and the interactions of climatic factors and specially drought indices. .In this research, the relation between production and climatic ...
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Although precipitation is the most important factor which effects rangeland production, but there is little information on the relationship between production and the interactions of climatic factors and specially drought indices. .In this research, the relation between production and climatic factors of rainfall, temperature, evapo- transpiration, and as well as drought indices of Standardized Precipitation Index )SPI) and Reconnaissance Drought Index (RDI) were investigated in Noudoshan Rangelands.Then the data with 33 variables were generated for different time periods of one to four months based the years of available production data. PCA was employed to decrease the number of variable and based on further component analysis, some variable were selected. To find the relation between production and climatic factors, regression analysis was used. Finally, the model with least IPE was selected as preferred model. By comparison equations based on rainfall, temperature, evapo- transpiration, and drought indices, the model resulted from RDI, selected as preferred range production estimator (R=0.969, MARE=0.111).
Maryam Azarakhshi; Behnoush Farokhzadeh; Mohammad Mahdavi; Hossein Arzani; Hassan Ahmadi
Abstract
Iran is located in dry belt of the earth and always involved with drought in different sections. Drought has already caused many losses to natural plant cover, agriculture and human society. For drought monitoring, we can use some drought indecies. In this research, the Standard Index of Annual Precipitation)SIAP),Sandardized ...
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Iran is located in dry belt of the earth and always involved with drought in different sections. Drought has already caused many losses to natural plant cover, agriculture and human society. For drought monitoring, we can use some drought indecies. In this research, the Standard Index of Annual Precipitation)SIAP),Sandardized Precipitation Index (SPI) and Palmer Drought Severity Index (PDSI) were used for assessment of drought effects on rangeland plant production. The research area is located in Qom province that contains eight rangeland sites. Plant production and soil factors were measured in rangeland readiness period from 1997-1998 to 2005-2006 annualy. Regression techniques were used between drought indices and total production and also production of different vegetation forms in seven time scales (early March to late July (growth season) and early February to late July (growth season and the previous month), March to June, March to May, March to April and March (start of growth season). The best drought index was then selected based on the highest correlation coefficient and lowest standard error. The result showed that the best drought indices in Qom rangelands are SPI-3, PDSI, SPI-24 and SPI-6, respectively. Also the most significant time step was resulted growth season and specially early stage of growth season.
S. Saadati; S. Soltani; S. eslamian
Volume 62, Issue 2 , October 2009, , Pages 257-270
Abstract
Drought is universal phenomenon that can occur everywhere and can cause harmful impacts on human beings and natural ecosystems. Thus, it is very important to study drought character ristics part of for water resources management. In this study, the Standardized Precipitation Index (SPI) is used for drought ...
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Drought is universal phenomenon that can occur everywhere and can cause harmful impacts on human beings and natural ecosystems. Thus, it is very important to study drought character ristics part of for water resources management. In this study, the Standardized Precipitation Index (SPI) is used for drought frequency analysis in Isfahan province. After collecting the precipitation data in the province stations and removing those stations with incomplete data, frequency analysis of drought was carried out by 12-month SPI time series scale end of March. Then, the maps of drought return periods were prepared and analyzed by SURFER software. These maps show that moderate and severe drought with long return period mainly in the west the province and extreme drought events in the east and north east of the province with short return periods which indicate high sensitivity and the necessity for suitable managing programs to deal with the problem of drought.
