Evaporation between saturated bare soil and water – an analysis based on field observations and energy balance consideration

Accurate estimation of evaporation rate in bare soil is of great significance for hydrogeological processes in arid regions. Potential evaporation has been regard as a standard to estimate the actual evaporation rate. In applications, evaporation rate in the saturated bare soil (PE_s) is often replaced by water evaporation rate (PE_w). Whether this simplification is adequate needs to be verified. This research is based on the measured potential evaporation rates (by lysimeters) and meteorological elements. The results show that PE_s is higher than PE_w on a yearly scale, and the differences are more obvious especially in spring and summer. In summer, PE_s is greater than PE_w at day but smaller at night. Besides, the curve of PE_w lags behind PE_s. Detailed analyses of evaporation dynamics over fully saturated bare sandy soils and water surface are provided by energy balance considerations. PE dynamics are mainly governed by available energy (R_n−G_s/N_w). Compared with water, the existence of solid particles in the saturated bare soil results in a smaller albedo and heat capacity, which has a further influence on R_n and G_s. Available energy for the saturated bare sandy soil is higher than that of water (R_n,s−​​​​​​​G_s>R_n,w−​​​​​​​​​​​​​​N_w), resulting in a higher rate for PE_s. The peak value of G_s exists earlier than N_w, leading to lag of PE_w behind PE_s. This research provides a theoretical basis for accurate calculation of the actual evaporation rate and groundwater resources.