Potential Evaporation, PE, from soils is defined as the water loss through evaporation from a saturated soil surface with ample water. The calculation of Actual Evaporation, AE, is required when calculating water balance for near-ground-surface engineered situations. AE can be less than PE for a number of reasons. It has been noted that the rate of evaporation begins to depart from the potential rate of evaporation during drying process at distinct soil suction values that are related to the soil-water characteristic curve, SWCC. This paper mainly focuses on re-assessment of soil suction and the corresponding water content at which the actual rate of evaporation begins to depart from potential rate of evaporation during drying process using a series of the laboratory data collected from the research literature. It is found that the value of suction at evaporation-rate reduction point appears to be approximately 3,000 kPa for thin soil sections regardless of the soil texture. However, the soil suction appears to be between the air-entry value and residual soil suction for evaporation from soil columns. An empirical equation has been proposed for the determination of the soil suction at the evaporation-rate reduction point in soil columns. Equations are also proposed to calculate the coefficient of surface moisture availability, the vapour pressure and surface resistance at the soil surface.
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