Models for calculating phreatic evaporation from bare soil in Tarim Basin

This paper is designed to study the laws of phreatic evaporation and improve the understanding to the ultimate rate and depth of phreatic evaporation. By analyzing the control conditions for establishing empirical formulae of phreatic evaporation, the calculation models for calculating the phreatic evaporation from bare land have been developed, which was based on the experimental data of phreatic evaporation on bare land at the Akesu Water Balance Experimental Station in Tarim Basin from 1990 to 1996. The results show that (1) developed calculation models are accord with the control conditions; (2) as for a given depth of groundwater table, the relation of phreatic evaporation and water surface evaporation is nonlinear and the phreatic evaporation is close to the ultimate rate when water surface evaporation reaches the infinity great; (3) the threshold of groundwater depth doesn’t exist theoretically. With the reasonable construction, these models overcome the shortcomings that the phreatic evaporation is overestimated when atmosphere evaporation capacity is higher, and the phreatic evaporation increases linearly along with the water surface evaporation increases. The test results show that the calculation accuracy of the models is high and it can be applied to calculate phreatic evaporation in similar regions.