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چکیده
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Soil moisture is an important variable in evaporation and plant transpiration processes and is the limiting factor for Photosynthesis. Therefore, it can be used for irrigation scheduling and crop yield forecasting. Despite the importance of soil moisture, land surface soil moisture observations are not enough for climatological and hydrological analysis, mainly due to the high cost and spatial insufficient coverage. In such condition, determination of soil moisture by remote sensing can be a good alternative for filling the gaps of land surface measurement. Therefore, one of the best data source for soil moisture is remote sensing technique. In this research, we present the trend analyses of 35 years (1979-2013) monthly remote sensing soil moisture time series based on European Space Agency's (ESA) combined soil moisture data with 25km resolution over Iran (40 - 65 E, 25- 45 N). We depict regions, which have become wetter or drier over 35 years based on long-term trend. We also compare soil moisture with the normalized difference vegetation index (NDVI) trends to find out how does soil moister changing effect on vegetation. GIMMS NDVI (growth seasonal) time series that derived from NOAA AVHRR data and MODIS gridded NDVI dataset (monthly) was applied. We use modified Man-Kendall method to do trend analyses. In most parts of Iran, soil moisture trend is negative that are significant in only 38 percent of areas. NDVI trend is negative in the central and small parts of the western and positive in the northern and southeast. NDVI trend is significant in 29 percent of area. We concluded that soil moisture and NDVI trend are not harmonic over Iran.
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