Evaluating Enhanced Hydrological Representations in Noah LSM over Transition Zones: Implications for Model Development

Quantitatively, calibrated DV and GW show only slight improvement in the skill of the model over calibrated STD. Then, multiple model realizations are compared to explicitly account for parameter uncertainty. Model performance, robustness, and fitness are quantified for use across varied sites.

The authors show that the least complex benchmark LSM (STD) remains as the most fit version of the model for broad application. Although GW typically performs best when simulating evaporative fraction (EF), 24-h change in soil wetness (∆W30), and soil wetness, it is only about half as robust as STD, which also performs relatively well for all three criteria. GW's superior performance results from bias correction, not from improved soil moisture dynamics.

DV performs better than STD in simulating EF and ∆W30 at the wettest site, because DV tends to enhance transpiration and canopy evaporation at the expense of direct soil evaporation. This same model structure limits performance at the driest site, where STD performs best. This dichotomous performance suggests that the formulations that determine the partitioning of LE flux need to be modified for broader applicability.

Thus, this work poses a caveat for simple "plug and play" of functional modules between LSMs and showcases the utility of rigorous testing during model development.