Predicting evaporation from moist, cracked soil, based on near‐surface wind speed, crack width and crack distance

Abstract

AbstractEvaporation from both cracked and uncracked soil surfaces under moist conditions was measured as a function of near‐surface wind speed, with wind speeds ranging between 0 and 5 ms−1. Crack aperture width and distance between neighbouring cracks ranged from 2 to 20 mm and 40 to 120 mm, respectively, while crack depth was kept constant at 50 mm. Experiments were carried out in a wind tunnel with a 1 m × 1 m × 2.5 m test section, using large‐scale (50 cm diameter, 15 cm depth) soil samples. Sixty‐six combination of crack properties and wind speed were considered. Resulting evaporation data were used to assess the shape of the relationships between evaporation rate, wind speed conditions and crack properties. A semiempirical model for estimating evaporation from cracked soil, as a function of wind speed, crack width and crack distance, given evaporation as a function of wind speed from uncracked soil, was developed. Results showed that evaporation from cracked soil under moist conditions increased by 60%–65% compared to uncracked soil, for the wind speed and crack properties given above. Evaporation from crack apertures was up to eight times higher than from an uncracked surface under the same wind conditions. Results further indicated that for constant wind speed and crack distance, there exists a crack width at which evaporation from the soil is at maximum. The semiempirical model based on exponential and power function relationships, was able to very closely match the experimental data and is further expected to be able to approximate evaporation under natural conditions.Highlights Near‐surface wind speed is strongly affected by presence of cracks Cracking in moist soils can increase evaporation up to 65% over uncracked soil There exists an intermediate crack width at which evaporation is at a maximum Evaporation may be estimated based on wind speed and crack properties