Evaluation of simple to complex parameterizations of bare ground evaporation

Abstract

Integrated hydrologic models coupled to land surface models link water and energy movement among the subsurface, land surface, and atmosphere. These connections are especially important when estimating a complex, nonlinear process like evaporation. A comprehensive sensitivity study of an evaporation parameterization was conducted using the integrated ParFlow-Common Land Model (PF-CLM). Estimates of ground evaporation using three forms of the same equation, two simplified closed-form solutions and one fully-coupled PF-CLM equation, are systematically compared. The parameterizations vary in complexity, coupling strength, and nonlinearity. Forcing data from three climate regions (alpine, plains, and tropical) are used to compare estimates of bare ground evaporation across all three formulations, thus exploring the process and coupling sensitivity in a novel way. The overall behavior of ground evaporation is consistent throughout the year for all parameterizations, but magnitudes vary with respect to parameterization complexity during energy-limited and water-limited times of the year. A relationship between ground evaporation and ground temperature is shown to exist across all climates and aggregate by pressure, wind speed, and air temperature in the plains climate. Furthermore, results show how increasing complexity through the addition of land surface conditions, atmospheric conditions, and atmospheric stability uniquely compound to influence the relationship between bare ground evaporation and subsurface pressure. Identification of sensitive interactions and unique relationships is necessary to further understand and predict hydrologic processes like evaporation.