Characteristics and driving factors of potential evaporation over saturated bare soil and open water surface

Evaporation from saturated bare soil is the basis for estimating actual evaporation rate, although it is often substituted with open-water evaporation in practical applications. Systematic monitoring and driving factor analysis on the differences in evaporation between saturated bare soil and water surfaces remain insufficient. In this study, evaporation differences between saturated bare soil and water were investigated based on high-frequency field measured data from lysimeters. Combined with the energy balance and vapor transport mechanisms of the evaporation process, we analyzed the driving factors of evaporation differences between these two water-sufficient media using sensitivity analysis and machine learning methods. The results indicated that annual evaporation from saturated exposed sand was higher than that from water, with a 21% increase during the summer. The surface energy balance equation coupled with surface temperature, as well as the vapor transport model can quantitatively resolve the observed evaporation differences. It was found that the discrepancy in evaporation from the two surfaces was caused by differences in responses to temperature. Specifically, evaporation from exposed saturated soil was dominated by rapid responses to temperature, while evaporation from open water resulted from thermal inertia and heat-capacity buffering. Additionally, both temperature and heat flux were critical determinants of differences in evaporation from water-saturated media and the accurate calculation of potential evaporation rates at the sub-daily scale.