AVERAGING HYDRAULIC PROPERTIES FOR EVAPORATION IN HETEROGENEOUS SOILS

Hydraulic properties at large grid resolution are required in large-scale hydrologic and global circulation models. In this study, we examine the appropriateness of using simple averaging schemes (arithmetic, geometric and harmonic means) of hydraulic parameters in representing large scale transient evaporation in heterogeneous soils. The main objectives are to investigate how the time frame of hydrologic processes affects the performance of averaging schemes and how the hydraulic parameter correlation and variability impact the performance of averaging schemes. The average cumulative evaporation in the heterogeneous soils is quantified through multiple realizations of local scale evaporation processes. The suitability of using the simple averaging schemes to represent the heterogeneous evaporation processes is quantified by the difference between the cumulative evaporation based on the simple averaging schemes and the average cumulative evaporation. In general, all averaging schemes produce large deviation from average evaporation at early stage. Relative errors based on the simple averaging schemes of hydraulic parameters are larger for initially wetter conditions. The appropriateness of different averaging schemes also depends on the correlation between the hydraulic parameters.