JWSS - Journal of Water and Soil Science

Agricultural water management studies require accurate information on actual evapotranspiration. This information must have sufficient spatial detail to allow analysis on the farm or basin level. The methods used to estimate evapotranspiration are grouped into two main groups, which include direct methods and indirect or computational methods. Basics of the indirect methods are based on the relationship between meteorological parameters, which impedes the use of these data with a lack or impairment. On the other hand, this information is a point specific to meteorological stations, and their regional estimates are another problem of uncertainty of their own. To this end, the use of remote sensing technology can be a suitable approach to address these constraints. Real evapotranspiration can be estimated by satellite imagery that has short and long wavelengths and is estimated using surface energy equations. Examples of such algorithms include SEBAL, METRIC, SEBS. Among the above mentioned algorithms, SEBAL and SEBS have been used. Among the factors of superiority of the SEBAL and SEBS algorithms, in comparison with other remote sensing algorithms, is a satellite imagery analysis algorithm based on physical principles and uses satellite simulation and requires minimum meteorological information from ground measurements or air models. 

Soil salinization is a phenomenon that threatens agricultural lands and natural areas, leading to reduced productivity, declinations of soil resources and vegetation covers, and finally, the abandonment of these areas. This study has quantified the groundwater Capillary Rise (CR) and actual Evapotranspiration (ETa) and their relationship with the soil salinity of Azadegan plain, west of Khuzestan Province. The study area has an arid climate, characterized by shallow and saline water table and a high potential evaporation rate. For this purpose, field samplings were carried out in four consecutive seasons of the year to measure salinity, soil moisture, and texture, groundwater table, and salinity at 27 scattered representative points of the study area. The CR values were estimated in different seasons of the year using UPFLOW model. Moreover, four representative Landsat satellite images were acquired to map seasonal changes of ETa through the SEBAL algorithm. Then, the effects of ETa on CR and consequent soil salinity build up were quantified in a seasonal time scale. The results showed that the average daily ETa of Azadegan plain varied from 1.55 to 7.96 mm day^-1 in different seasons which caused a capillary rise of around 1.2 to 1.5 mm.day^-1. This has led to the upward movement of 12 to 18.8 ton ha^-1  month^-1 of salts from shallow groundwater to the soil surface, which has caused surface soil salinization. Also, there was a close relationship between ETa, CR, and soil salinity parameters, which can provide insight into modeling of spatial and temporal changes of soil salinity and provision of solutions to reduce the accumulation of solutes in the soils of the study area.