فهرست مطالب حمید غفاریان

Drought monitoring is critical for early warning of drought hazard. This study  is  attempted to develop remote sensing drought monitoring index (VDI), based on Accuracy of different bands of Moderate Resolution Imaging Spectroradiometer data MODIS, VDI focuses about the vegetation water stress. Spectral studies have demonstrated that due to the large absorption by leaf water, shortwave infrared reflectance (SWIR) is negatively related to leaf water content. Being sensitive to leaf water content, SWIR is widly utilized to construct various remote-sensing indices for example VDI for reflecting vegetation water content, . In this study, Vegetation Drought Index (VDI) was evaluated Based on the sensitivity rate to moisture by shortwave infrared reflectance bands SWIR 5 and 6 (VDI5 and VDI6). The data included the MODIS sensor images from Terra satellite in a period of nineteen years from 2000 to 2018 and Precipitation data are obtained from the Global Land Data Assimilation System (GLDAS), in Sistan & Balouchestan Province, Pearson correlation coefficient was used to evaluate the accuracy of the Drought spatial distribution maps calculated based on the two bands.Results indicate high significant correlation rate between VDI6 and Precipitation data . Study also showed that shortwave infrared band 6 (SWIR) is more sensitive to agricultural drought than band 5,in Sistan and Baluchestan province . The study recommends  to use VDI index with and 6 for better early detection and monitoring of agricultural drought in operational drought management programmes.

Monitoring the spatial and temporal variations of evapotranspiration is crucial for irrigation management and the crop water requirement, especially in arid and semi-arid areas. The purpose of the present study is to estimate the actual evapotranspiration using the SEBAL algorithm and compare it with the FAO 56 standard evapotranspiration to determine pistachio orchards under drought stress in Yazd province. To do so, Landsat 8 satellite images time series with 15 images in 2015 were used. At first, actual evapotranspiration was calculated in 15 days of pistachio phenology and then by summation of evapotranspiration in 15 days, total evapotranspiration was determined in four main stages of pistachio phenology covering the whole period of annual growth. The FAO 56 standard evapotranspiration was also obtained by using the KC-NDVI relationship as the standard for comparing with actual evapotranspiration. Based on the results, SEBAL algorithm has an acceptable capability to determine the evapotranspiration rate in the study area. However, due to lack of valid Lysimeter data in the study area, It was not possible to validate the results of the SEBAL algorithm. But comparing the results with the FAO 56 standard method showed that the two methods are in good agreement with each other. In average, the coefficient determination, RMSE and MAE between the results of SEBAL algorithm and FAO KC-NDVI approach were 0.8, 16.7 mm and 14.5 mm, respectively, for the 15-day of pistachio phenology stages. The average of actual and standard evapotranspiration rates during a pistachio growing season at the study area were 950 and 1086 mm, respectively. Comparison of actual and standard evapotranspiration shows that in most of the study area actual evapotranspiration is lower than standard conditions.

Phenology is the study of the occurrence of repeatable plant life events in relation to living and non-living factors. The phenology reflects the response and adaptability of ecosystems to climate change. Phonological study can be used to regulate livestock grazing management programs at rangeland, various agricultural activities, and etc. In order to study the effect of height and temperature on plant phenological processes, harmonic analysis of time series satellite observations was used. In this study, the 8-day products of the NDVI indices of MODIS sensor (namely MOD09Q1) with a spatial resolution of 250 m was used. First, the HANTS algorithm was used to decompose the one-year NDVI MODIS products time series to thier Fourier Series components (the amplitude and phase images). Then, the correlation of each of these components with respect to height and temperature were investigated in Shirkoh area of Yazd province. According to the results, with 1 centigrade decrease in the average spring temperature, which occurs with elevation, there were a delay of 6.6 days in annual cycles and 3.9 days in the 6-month cycles of the NDVI time series, respectively. These results indicate that a delay of 6.3 days was observed in phenological processes and plant starting growth time in plant with annual growth periods and a delay of 3.9 days in plants with seasonal and six-month growth stages. Accordingly, the results of the HANTS algorithm and the Fourier series analysis can be very effective in understanding the effects of climatic factors on phenological processes and the onset of plant growth.