Estimation of Daily Evaporation from Shallow Groundwater Using Empirical Models with a Temperature Coefficient

摘要

Shallow groundwater evaporation (E-g) is a major component of the hydrological cycle, especially in semiarid and arid locations. Empirical methods are commonly used to estimate E-g. However, most of these methods can only weakly represent E-g variations along the soil depth and do not consider the energy driver. In this paper, a temperature coefficient was proposed and incorporated into two preferred empirical models to characterize the impacts of soil temperature and air temperature lags on E-g. The method was evaluated using in situ daily data obtained from nonweighing bare soil lysimeters. The results indicated that the models that considered the temperature gradient variable (T) conformed to the changes in the actual E-g values with depth more appropriately than the original models, accompanied by 4.3%-8.8% accuracy improvements overall. Shallow groundwater evaporation E-g was found to be influenced by the water table depth (H), T, and pan evaporation (E-0) in descending order, and strong interactions were found between H and T. Moreover, the impact of precipitation on E-g was investigated; measurements from dry days without precipitation revealed the actual E-g process, the relative errors in the cumulative E-g values derived at different depths demonstrated a positive relationship with infiltration recharge, and the errors related to precipitation induced 6.7%-8.3% E-g underestimations. These results contribute to a better understanding of evaporative losses from shallow groundwater and the typical E-g situation that occurs simultaneously with recharge, and they provide promising perspectives for corresponding integrated hydrologic modeling research.