SWAT+ versus SWAT2012: Comparison of Sub-Daily Urban Runoff Simulations

Abstract

Abstract. The current FORTRAN code of SWAT (SWAT2012) is being rebuilt to ease new model and module development by incorporating object-oriented programming techniques into defining spatial objects and calculating variables. SWAT+, the new SWAT code, is expected to offer flexible watershed representation with linked spatial objects. Ideally, SWAT+ produces outputs that are comparable to SWAT2012, if not identical, when the two versions of SWAT are set with the same input for a watershed. However, the drastic restructuring of the source code may cause unexpected results in the output, especially when compared with the current SWAT2012 model that has a long history of model validation. In this technical note, we compare sub-daily, daily, and monthly hydrographs provided by SWAT2012 and SWAT+ that were prepared for a small urban watershed in Austin, Texas. The model parameters were calibrated to 15 min and daily runoff observed in the watershed. SWAT+ was on par with SWAT2012 in predicting streamflow at daily and monthly scales. However, the HRU-level flow routing scheme newly added to SWAT+ created multiple peaks in the sub-daily hydrographs, suggesting a need to further improve the water transport simulation strategies. This technical note provides ideas of how SWAT+ is organized and if a SWAT modeler can maintain consistency in modeling results when shifting from the original code to the new code. In addition, this technical note discusses the potential for improved SWAT+ modeling. Keywords: Model calibration, Storm event, Sub-daily simulation, SWAT, Urban watershed.