Impact of ambient conditions on evaporation from porous media

• Published in: Water resources research 2014-08, Vol.50 (8), p.6696-6712
• Main Authors: Ben Neriah, Asaf, Assouline, Shmuel, Shavit, Uri, Weisbrod, Noam
• Format: Article
• Language: English
• Subjects: Air temperature; Ambient temperature; drying porous media; Evaporation; Evaporation rate; High temperature; Mass transfer; Porous media; Relative humidity; soil; Temperature; Vapor pressure
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1002/2014WR015523

The complexity of soil evaporation, depending on the atmospheric conditions, emphasizes the importance of its quantification under potential changes in ambient air temperature, Ta, and relative humidity, RH. Mass loss, soil matric tension, and meteorological measurements, carried out in a climate‐controlled laboratory, were used to study the effect of ambient conditions on the drying rates of a porous medium. A set of evaporation experiments from initially saturated sand columns were carried out under constant Ta of 6, 15, 25, and 35°C and related RH (0.66, 0.83, 1.08, and 1.41 kPa, respectively). The results show that the expected increase of the stage 1 (S1) evaporation rate with Ta but also revealed an exponential‐like reduction in the duration of S1, which decreased from 29 to 2.3 days (at Ta of 6 and 35°C, respectively). The evaporation rate, e(t), was equal to the potential evaporation, ep(t), under Ta = 6°C, while it was always smaller than ep(t) under higher Ta. The cumulative evaporation during S1 was higher under Ta = 6°C than under the higher temperatures. Evaporation rates during S2 were practically unaffected by ambient conditions. The results were analyzed using a mass transfer formulation linking e(t) with the vapor pressure deficit through a resistance coefficient r. It was shown that rS1 (the resistance during S1) is constant, indicating that the application of such an approach is straightforward during S1. However, for evaporation from a free water surface and S2, the resistances, rBL and rS2, were temperature‐dependent, introducing some complexity for these cases. Key Points Cumulative evaporation during S1 was higher in low temperature The evaporation characteristic length, LC, decreases linearly with temperature The resistance coefficient is constant in S1 and change with T for S2 and ep