New method for calculating soil surface evaporation considering effect of wind speed

Soil surface evaporation is one of the main processes in the soil-atmosphere interaction. Since it is highly related to meteorological factors and soil properties, the determination of evaporation from soil surface remains a challenge, and the key point is to determine the critial water content where the evaporation changes from constant rate stage into falling rate stage. To investigate the effect of wind speed on soil evaporation, a climate control apparatus is newly developed, with a feature of completely controlling air temperature, relative humidity and wind speed. 12 climatic conditions are applied to 3 kinds of soil specimens to carry out the evaporation tests. The results show that a lower aerodynamic resistance always leads to a higher critical water content, only the water content cannot allow an accurate estimation, and the additional variables accounting for soil texture and wind speed must be included as well. Moreover, a simple approach to parameterizing the evaporation is presented by using the water content of top 1-cm layer as a variable and considering the effect of soil texture and wind speed.