Surveying of Spatial and Temporal Variability of Surface Soil Moisture using SMAP L4 Products in Iran

Despite the important role of soil surface moisture in the management of water and soil resources, unfortunately in Iran, there is no national network for monitoring soil moisture and the spatial distribution of measuring stations is limited. Therefore, in the present study, an attempt was made to extract and analyze the spatial and temporal distribution maps of soil moisture from SMAP products during the period 2015 to 2021 in Iran. The results showed that the average 7-year soil moisture at a depth of 5 cm in Iran varies between 0.005 to 0.5388 m3/m3, and the temporal average of soil moisture is 0.137 m3/m3. Evaluation of monthly average soil moisture maps by SMAP showed that the highest and lowest long-term average soil moisture in February and August occurred at 0.192 and 0.079 m3/m3, respectively. The spatial assessment also shows that the highest average annual soil moisture values are concentrated in the northern and western regions, and the lowest values are concentrated in the central and southeastern regions. Evaluation of the results based on the provincial scale shows the highest average annual soil moisture in the provinces of Gilan, Mazandaran, Kohgiluyeh and Boyer-Ahmad, and Alborz, respectively 0.294, 0.243, 0.216, and 0.209 m3 / m3. While the lowest values in Sistan and Baluchestan, South Khorasan, and Yazd provinces are 0.076, 0.091, and 0.096 m3 / m3, respectively. The results of this study can help the management of soil and water resources by knowing the amount of soil moisture in different areas.