Improvements to the calculation of actual evaporation from bare soil surfaces

Abstract

Evaporation of water from a saturated soil surface with ample free water is known as potential evaporation, PE, and the associated physical processes are quite well understood. However, evaporation of water from an unsaturated soil surface is known as actual evaporation, AE, and the associated physical processes are more complex and less understood. The calculation of actual evaporation is important for many geotechnical engineering applications. Soil suction and the corresponding water content at which the AE rate begins to depart from the PE rate during a drying process are re-assessed using a series of laboratory tests (i.e., thin soil section drying tests and soil column drying tests).Laboratory results show that the suction at which the actual rate of evaporation begins to depart from PE rate for soil columns (or thick soil layers) may be different than for thin soil layers. The suction at the "evaporation-rate reduction point", (ERRP) appears to be approximately 3,000 kPa for thin soil layers, but is between the air-entry value and residual soil suction for thick soil layers or soil columns. The analyses presented in this paper have resulted in the development of a methodology for the estimation of the suction corresponding to the ERRP in soil columns. Equations are also proposed to calculate the

Urban heat island modelling of a tropical city: case of Kuala Lumpur

“…The surface resistance to evaporation value (r s ) for green areas and woods was calculated as 37 s/m based on Eq. (1) given below (Fen Shu 1982;Tran et al 2015).…”

Flood-Drought Hazard Assessment for a Flat Clayey Deposit in the Canadian Prairies

“…The above equation denotes monthly evaporation by E, calibration coefficient by Ca (10.1 for this study corresponding to vapour pressure based on 24 observations of air temperature per day), monthly mean saturated vapour pressure by Vw, actual monthly mean vapour pressure by Va, monthly mean wind speed by W, elevation above mean sea level by Ae, and coefficients by α (6.21 × 10 −2 ) and β (3.28 × 10 −5 ). Finally, evapotranspiration (evaporation from soil surfaces including vegetation (Tran et al, 2015) was calculated by multiplying evaporation with a pan coefficient of 0.76 (similar to the semiarid climates of central Tunisia (Alazard et al, 2015). Figure 1 shows the climate trends of metrological parameters from 1970 through 2015.…”

Evaporation of the soil water in response to the amount of straw and evaporative demand

“…The evaporative demand of the atmosphere, caused by the combination of solar radiation, wind speed, air temperature and relative humidity (Teng et al, 2014;Zribi et al, 2015), and their variations over time, defines the higher or lower potential for soil water evaporation (Tran et al, 2016). However, this process only occurs if there is free water on the surface (Zribi et al, 2015) or if the physical-hydraulic properties of the soil do not limit the water demand caused by the weather conditions near the surface (Balwinder-Singh et al, 2014;Teng et al, 2014, Tran et al, 2016.…”

“…The evaporative demand of the atmosphere, caused by the combination of solar radiation, wind speed, air temperature and relative humidity (Teng et al, 2014;Zribi et al, 2015), and their variations over time, defines the higher or lower potential for soil water evaporation (Tran et al, 2016). However, this process only occurs if there is free water on the surface (Zribi et al, 2015) or if the physical-hydraulic properties of the soil do not limit the water demand caused by the weather conditions near the surface (Balwinder-Singh et al, 2014;Teng et al, 2014, Tran et al, 2016. In the experiment by Ward et al (2009) the lag between evaporative demand and the ability of the soil to transfer water to the surface was considered the probable cause of the low correlation between accumulated evaporation and both the air temperature and the global solar radiation.…”

“…However, this process only occurs if there is free water on the surface (Zribi et al, 2015) or if the physical-hydraulic properties of the soil do not limit the water demand caused by the weather conditions near the surface (Balwinder-Singh et al, 2014;Teng et al, 2014, Tran et al, 2016. In the experiment by Ward et al (2009) the lag between evaporative demand and the ability of the soil to transfer water to the surface was considered the probable cause of the low correlation between accumulated evaporation and both the air temperature and the global solar radiation. This occurred especially when the process was in stage II of soil water evaporation, in which the importance of physical properties is greater than those of stage I (Balwinder-Singh et al, 2014).…”