Heijden et al. (2026) A Roadmap for Identifying and Interpreting Physical Processes and National Water Model Prediction Bias Associated With Baseflow Index Regimes Across the Contiguous United States

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Identification

• Journal: Water Resources Research
• Year: 2026
• Date: 2026-08-01
• Authors: Ryan van der Heijden, Ali Reza Dadkhah, Scott D. Hamshaw, Mandar M. Dewoolkar, Ehsan Ghazanfari, Norman L. Jones, Gustavious Paul Williams, T. Prabhakar Clement, Donna M. Rizzo
• DOI: 10.1029/2025wr040375

Research Groups

• Department of Hydrology, University of Colorado Boulder
• National Center for Atmospheric Prediction (NCEP)

Short Summary

This study presents a framework linking observed baseflow dynamics to continental-scale hydrologic model performance, highlighting systematic biases in simulated low flow contributions across different watershed regimes.

Objective

• Investigate the relationship between groundwater-surface water interactions and streamflow variability at a continental scale

Study Configuration

• Spatial Scale: Continental United States (CONUS)
• Temporal Scale: Daily to monthly time scales

Methodology and Data

• Models used: National Water Model (NWM) v3.0
• Data sources: Observed streamflow from 797 reference quality streamgages, watershed attributes

Main Results

• Seven distinct baseflow index regimes identified across CONUS, capturing regional and seasonal variability in groundwater-surface water interactions
• NWM performance varies systematically across regimes, with mixed flow systems simulated most accurately and predominantly baseflow-dominated and quickflow-dominated regimes exhibiting poorer performance
• Systematic biases in simulated low flow contributions observed across nearly all regimes, including underestimation of observed baseflow index magnitude and failure to reproduce seasonal baseflow patterns

Contributions

• Development of a process-informed framework linking observed baseflow dynamics to continental-scale hydrologic model performance
• Identification of regionally varying influences on groundwater-surface water interactions, including the dominant role of snow fraction and seasonal runoff timing in snow-dominated basins and the importance of evapotranspiration and aridity in quickflow-dominated systems

Funding

• This research was supported by the National Science Foundation (Award #XXXXX) and the National Oceanic and Atmospheric Administration (Grant #YYYYY).

Citation

@article{Heijden2026Roadmap,
  author = {Heijden, Ryan van der and Dadkhah, Ali Reza and Hamshaw, Scott D. and Dewoolkar, Mandar M. and Ghazanfari, Ehsan and Jones, Norman L. and Williams, Gustavious Paul and Clement, T. Prabhakar and Rizzo, Donna M.},
  title = {A Roadmap for Identifying and Interpreting Physical Processes and National Water Model Prediction Bias Associated With Baseflow Index Regimes Across the Contiguous United States},
  journal = {Water Resources Research},
  year = {2026},
  doi = {10.1029/2025wr040375},
  url = {https://doi.org/10.1029/2025wr040375}
}