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A low-to-no snow future and its impacts on water resources in the western United States

Abstract

Anthropogenic climate change is decreasing seasonal snowpacks globally, with potentially catastrophic consequences on water resources, given the long-held reliance on snowpack in water management. In this Review, we examine the changes and trickle-down impacts of snow loss in the western United States (WUS). Across the WUS, snow water equivalent declines of ~25% are expected by 2050, with losses comparable with contemporary historical trends. There is less consensus on the time horizon of snow disappearance, but model projections combined with a new low-to-no snow definition suggest ~35–60 years before low-to-no snow becomes persistent if greenhouse gas emissions continue unabated. Diminished and more ephemeral snowpacks that melt earlier will alter groundwater and streamflow dynamics. The direction of these changes are difficult to constrain given competing factors such as higher evapotranspiration, altered vegetation composition and changes in wildfire behaviour in a warmer world. These changes undermine conventional WUS water management practices, but through proactive implementation of soft and hard adaptation strategies, there is potential to build resilience to extreme, episodic and, eventually, persistent low-to-no snow conditions. Federal investments offer a timely opportunity to address these vulnerabilities, but they require a concerted portfolio of activities that cross historically siloed physical and disciplinary boundaries.

Key points

  • Mountain snowpacks in the western United States (WUS) have historically acted as large, natural reservoirs of water; yet, they are now harbingers of a changing climate through their signalling of a low-to-no snow future.

  • Models projecting the time horizon of low-to-no snow in the WUS lack spatiotemporal consensus due to differences in definitions, metrics, methods and regionally specific analyses.

  • Low-to-no snow will impose a series of cascading hydrologic changes to the water–energy balance, including vegetation processes, surface and subsurface water storage and, ultimately, streamflow that directly impacts water management.

  • A re-evaluation of long-standing hydroclimatic stationarity assumptions in WUS water management is urgently needed, given the impending trickle-down impacts of a low-to-no snow future.

  • Observational and modelling advances are needed to better understand the implications of a low-to-no snow future on water resources and to evaluate the trade-offs among a wide array of potential adaptation strategies that can address both water supply availability and water demands.

  • Co-production of knowledge between scientists and water managers can help to ensure that scientific advances provide actionable insight and support adaptation decision-making processes that unfold in the context of significant uncertainties about future conditions.

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Fig. 1: Spatiotemporal variability in western United States seasonal snowpack.
Fig. 2: A multiscale perspective of the mountainous hydrologic cycle.
Fig. 3: Ranges of projected twenty-first century snowpack loss.
Fig. 4: Snow disappearance based on a low-to-no snow definition.
Fig. 5: Changes in mountain environments under persistent low-to-no snow conditions.
Fig. 6: Cascading above and below ground impacts of snowpack changes.
Fig. 7: Supply and demand connections between the natural and managed WUS water systems.

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Acknowledgements

P.S.N and E.R.S.-W. acknowledge support from the Watershed Function Scientific Focus Area funded by the US Department of Energy, Office of Science, Office of Biological and Environmental Research under award no. DE‐AC02‐05CH11231. W.D.C and A.M.R. are supported by the Director, Office of Science, Office of Biological and Environmental Research of the US Department of Energy through the Regional and Global Climate Modeling (RGCM) Program under the Calibrated and Systematic Characterization, Attribution and Detection of Extremes (CASCADE) Scientific Focus Area (award no. DE-AC02-05CH11231). A.D.J., A.M.R. and J.S. are supported by the Office of Science, Office of Biological and Environmental Research, Climate and Environmental Science Division of the US Department of Energy as part of the HyperFACETS Project, A Framework for Improving Analysis and Modeling of Earth System and Intersectoral Dynamics at Regional Scales (award no. DE-SC0016605). D.R.F. is supported by the Director, Office of Science, Office of Biological and Environmental Research of the US Department of Energy under contract no. DE-AC02-05CH11231 as part of their Atmospheric System Research (ASR) Program. C.T. is supported by the National Science Foundation’s Hazard SEES program (award no. 1520847) and the National Science Foundation Critical Zone Observatory Network (award no EAR-2012821). B.J.H. is supported by the Sulo and Aileen Maki Endowment. We thank M. Anderson, S. Hatchett, S. Hubbard, C. Koven and P. Ullrich for insightful conversations and constructive comments. We are grateful to W. Grimshaw, D. Yates and Denver Water for providing GIS data on conveyance, rivers and streamflows. We also thank D. Swantek for graphic design help.

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E.R.S.-W. and A.M.R. initiated, led and contributed to all aspects of the Review. B.J.H. and L.S.H. contributed to the section on declining mountain snowpack. B.J.H., L.S.H. and W.D.C. contributed to the section on a low-to-no-snow future. C.T. contributed to the section on hydrological impacts. J.S., A.D.J., P.S.N. and L.K. contributed to the adaptation section. All authors contributed to the display items, the introduction and future directions sections, and participated in discussions, revisions and the final production of the manuscript.

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Correspondence to Erica R. Siirila-Woodburn.

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Nature Reviews Earth & Environment thanks Ben Livneh, Philip Mote and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Siirila-Woodburn, E.R., Rhoades, A.M., Hatchett, B.J. et al. A low-to-no snow future and its impacts on water resources in the western United States. Nat Rev Earth Environ 2, 800–819 (2021). https://doi.org/10.1038/s43017-021-00219-y

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