Monitoring Dynamic Distribution of Surface Soil Moisture Using SMAP data in Simineh-Zarrineh Catchment (Semi-arid region), NW of Iran

Soil moisture (SM) is believed to be an impressive factor in hydrological process, agricultural productivity, and monitoring dangerous outcomes of climate changes. The present study aimed to monitor and recognize the pattern of spatial and temporal variation of SMAP soil moisture in five subcatchments of Simineh-Zarrineh catchment in northwest of Iran from 2015 to 2017. Precipitation data of 35 meteorological stations and 287 soil moisture points were derived from the SMAP and used to monitor SM variations in the time scale. The results indicated that the SM variations are subject to precipitation variations throughout the monthly scale in the catchment. In all the seasons of this period, SM was found to have a decreasing trend from north to south of the catchment. On the contrary, no such constant pattern was observed from east to west. Oscillation SM patterns in this period were completely coordinated with the precipitation pattern. The determination coefficient between monthly SMAP soil moisture and precipitation for each subcatchment was 0.9, 0.83, 0.7, 0.84, and 0.71 for Bokan, Saqqez, Takab, Saeinqaleh, and Miandoab subcatchments, respectively. Spatial variability of standard deviation for SM values was used to find the amount of deviation from the average value during dry and wet seasons . The results revealed that in the seasonal scale, northwestern (0.067 to 0.069 cm3.cm3) and eastern parts (0.057 to 0.061 cm3.cm3) of the study area had higher values of the SM standard deviations in autumn. Additionally, according to the findings, a high value of standard deviation was observed in autumn because of irregular precipitation events and fluctuation of the temperature.