Calculation of land subsidence and changes in soil moisture and salinity using remote sensing techniques

Among the Iranian plains which have experienced land subsidence, there is an indicator, in addition to its high rate of subsidence, soil salinity, and proximity to the centers of population, transportation routes, and infrastructures in Varamin plain, which has raised serious concerns about this center of land subsidence. Excessive use of groundwater and aquifers and lack of optimal cultivation patterns decrease soil fluidity, leading to land subsidence, increased soil salinity, and reduced surface moisture and soil moisture to a depth of 1-2 m. The subsidence phenomenon also disrupts water storage in underground aquifers, making it difficult to reduce the volume of the reservoir and break the soil layers and fill the pores of the water sediment into the lower layers, and store water in the reservoirs. It cannot reach the underground, which is one of the main reasons for the decrease in soil moisture and the increase in soil salinity. In this study, the changes in the land subsidence during the 2014-2020 time period, were evaluated by Sentinel-1 satellite imagery and SNAP software. The soil electrical conductivity, soil surface moisture content, and soil moisture content in the depth of 1-2 m were calculated by Sentinel-2 satellite imagery, Landsat 8 satellite, and FLDAS data in the GEE platform, respectively. The results showed that the increase in land subsidence has raised soil salinity covering area and its intensity. As a result, moisture reduction is observed in different depths in recent years.