Advancing the science of headwater streamflow for global water protection


Abstract

The protection of headwater streams faces increasing challenges, exemplified by limited global recognition of headwater contributions to watershed resiliency and a recent US Supreme Court decision limiting federal safeguards. Despite accounting for ~77% of global river networks, the lack of adequate headwaters protections is caused, in part, by limited information on their extent and functions—in particular, their flow regimes, which form the foundation for decision-making regarding their protection. Yet, headwater streamflow is challenging to comprehensively measure and model; it is highly variable and sensitive to changes in land use, management and climate. Modelling headwater streamflow to quantify its cumulative contributions to downstream river networks requires an integrative understanding across local hillslope and channel (that is, watershed) processes. Here we begin to address this challenge by proposing a consistent definition for headwater systems and streams, evaluating how headwater streamflow is characterized and advocating for closing gaps in headwater streamflow data collection, modelling and synthesis.

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Fig. 1: Percentage of headwater streams by length in level 4 HydroBASINS across the globe using the MERIT Hydro-based stream network (with a 5 ha drainage threshold) as used in the Hydrography90m global hydrography dataset.
Fig. 2: Comparing observed and predicted headwater flows with those of larger rivers, with flows normalized by area.
Fig. 3: Percentage of headwater streams by length in US Geological Survey Hydrologic Unit Code (HUC)12 watersheds across the conterminous United States.
Fig. 4: Percentage of US Geological Survey (USGS) stream gauges across the conterminous United States with at least 5 years of recent data (2018–2023) that are considered headwaters, as operationally defined by Strahler stream orders 1 and 2, based on the NHDPlus High Resolution (V2) dataset.
Fig. 5: Simple conceptualization of data availability balanced against hydrological process heterogeneity at different scales of flow regime modelling.

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Acknowledgements

This work developed from discussions at the Headwater Modeling Research Working Group, held at the John Wesley Powell Center for Analysis and Synthesis, funded in kind by the US Geological Survey and directly by US Environmental Protection Agency’s Office of Research and Development. We thank E. D’Amico for graphical assistance and K. Fritz and B. Johnson for helpful feedback. Some data were provided by the H.J. Andrews Experimental Forest and Long Term Ecological Research (LTER) programme under the NSF grant LTER8 DEB-2025755. The views expressed in this Perspective are those of the authors and do not necessarily reflect the views or policies of the US EPA. Any use of trade, firm or product names is for descriptive purposes only and does not imply endorsement by the US Government.

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Golden, H.E., Christensen, J.R., McMillan, H.K. et al. Advancing the science of headwater streamflow for global water protection.
Nat Water (2025). https://doi.org/10.1038/s44221-024-00351-1

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  • Received: 22 February 2024

  • Accepted: 06 November 2024

  • Published: 02 January 2025

  • DOI: https://doi.org/10.1038/s44221-024-00351-1


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