Effects of temporal resolution of river routing on hydrologic modeling and aquatic ecosystem health assessment with the SWAT model

Authors: QUI, H. - University Of Wisconsin; QI, J. - University Of Maryland; LEE, S. - University Of Seoul; Moglen, Glenn; McCarty, Gregory; CHEN, M. - University Of Wisconsin; Zhang, Xuesong

Submitted to: Environmental Modelling & Software
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2022
Publication Date: 10/26/2022
Citation: Qui, H., Qi, J., Lee, S., Moglen, G.E., Mccarty, G.W., Chen, M., Zhang, X. 2022. Effects of temporal resolution of river routing on hydrologic modeling and aquatic ecosystem health assessment with the SWAT model. Environmental Modelling & Software. 145:105232. https://doi.org/10.1016/j.envsoft.2021.105232.
DOI: https://doi.org/10.1016/j.envsoft.2021.105232

Interpretive Summary: Watershed models are widely used to study hydrological processes and assess their responses to anthropogenic and natural drivers. The USDA Soil and Water Assessment Tool (SWAT) model often uses a daily time step for river routing for watershed assessment. We modified the river routing code of the SWAT model to examine the effects of river routing time steps (from 1 minute to 1 day) on the model simulations of streamflow, stream water depth, and water storage in river networks in the Choptank River Watershed. We found that using 1 day as the river routing time step can lead to unrealistically low stream water depth and water storage and cause large bias in assessment of hydrologic connectivity and aquatic ecosystem health. We recommend taking a time step that is shorter than 1 hour, while recognizing that the appropriate time step depends on actual watershed size and local conditions. The results presented here will benefit future watershed model development and application to support real world decision making.

Technical Abstract: Watershed models are widely used to study hydrological processes and assess their responses to anthropogenic and natural drivers. To ensure model fidelity, diagnosing key uncertainties associated with model simulations and identifying potential solutions has been recognized as an important topic in watershed model applications. Here, we investigate how the temporal resolution of river water routing within the Soil and Water Assessment Tool (SWAT) model can affect simulated riverine hydrological processes, including streamflow discharge and water storage and depth in reaches, and derived ecological indicators to assess integrity of aquatic ecosystems. We conducted numerical experiments in two watersheds in the Northeastern U.S. to execute the SWAT model’s variable storage coefficient river routing method with six different time steps ranging from 1 minute to 1 day for the period between 2001 and 2018. We found that SWAT simulated stream discharge largely stabilize with different time steps, whereas the stream water storage and depth vary greatly. Those simulation results lead to dramatic difference in calculated Dendritic Connectivity Index (DCI), which is a widely used indicator for assessing hydrologic connectivity and aquatic ecosystem health. In addition to streamflow, our results clearly show that model simulations of riverine water storage and depth should be examined carefully to ensure reliable watershed modeling, particularly for studies aimed to assess hydrologic connectivity and aquatic ecosystem health. We recommend taking a time step that is shorter than 1 hour, while recognizing that the appropriate time steps depend on actual watershed size and configuration. We anticipate the results present here will benefit future watershed model development and application.