Do Model Results Vary under Different Routing Algorithms Based on a Distributed Ecohydrological Model?

Although several flow routing (FR) algorithms are developed for hydrological modeling, it is still uncertain how the selection of algorithms may affect model results. This study aims to explore the similarity and dissimilarity in model results among different FR algorithms characterized by single flow direction (SD) and multiple flow direction (MD). The Coupled Hydro-Ecological Simulation System (CHESS) was incorporated with six different FR algorithms (D8, D infinity, MD infinity, MD8, MFD-md, and RMD infinity) and then applied for modeling ecohydrological processes for a semiarid mountainous watershed in the western United States during 1991-2012. Comparisons were made between the model results at the catchment and the grid scale. After slightly adjusting one of the most sensitive soil parameters, all algorithms behave similarly in simulating stream hydrographs. When averaged for the watershed, the modeled ecohydrological variables mostly do not differ significantly (<5%) among the six FR algorithms. Nevertheless, the simulated ecohydrological variables are spatially more autocorrelated under the more dispersive MD algorithms. In addition, there exist significant (>5%) cell-level differences in modeled soil moisture among different FR algorithms, with propagated influences on the simulated evapotranspiration and vegetation growth variables. In hillslopes, the cell-level differences in model results tend to increase significantly as the flows move to the streams. Overall, this study proves that the watershed-level differences in model results among FR algorithms are low after model calibration, while significant differences still occur at the cell level. Thus, observational data are essential for testing which routing algorithm captures better the reality of local ecohydrological processes. Significance StatementThe consideration of flow routing is essential for accurately simulating land surface ecohydrological processes. However, less is known about how the selection of flow routing algorithms may affect the model results. Based on model experiments, we found that the model results under different algorithms do not significantly differ from each other when averaged for the watershed. However, significant differences in model results exist at the individual cell level. These findings are useful for guiding future modeling-related research and also suggest the importance of field studies for testing which routing algorithm can better represent local ecohydrological processes.