Williams et al. (2026) Carbon emissions exacerbating the Western US water crisis

Identification

• Journal: Communications Earth & Environment
• Year: 2026
• Date: 2026-08-25
• Authors: Emily L Williams, John T. Abatzoglou, Carly A. Phillips, Mohammad Safeeq, Shaina Sadai, O. Chegwidden, Angel Santiago Fernandez‐Bou, L. Delta Merner, J. Pablo Ortiz‐Partida
• DOI: 10.1038/s43247-026-03900-6

Research Groups

• Sierra Nevada Research Institute, University of California, Merced, CA, USA.
• Management of Complex Systems Department, University of California, Merced, CA, USA.
• Union of Concerned Scientists, Cambridge, MA, USA.
• Civil and Environmental Engineering, University of California, Merced, CA, USA.
• Five College Associate, Amherst, MA, USA.
• CarbonPlan, San Francisco, CA, USA.

Short Summary

This study quantifies the impacts on western US water resources attributable to the Carbon Majors' emissions since 1950. The results show that these emissions have led to a reduction in snowpack and streamflow, an increase in irrigation demand, and a widening seasonal gap between water supply and demand.

Objective

• Investigate the contribution of the Carbon Majors' emissions to changes in western US water resources.
• Compare the attribution approach with the proportional approach for estimating impacts on water supply, water demand, and groundwater.

Study Configuration

• Spatial Scale: Western United States (WUS), focusing on three variables: April 1st snow water equivalent (SWEApr1) and warm season streamflow (streamflowwarm) on the supply side, and annual total irrigation demand on the demand side.
• Temporal Scale: Past decade (2014–2024).

Methodology and Data

• Models used: Source-to-impact attribution approach, leveraging estimates of ΔGMT forced by Carbon Majors emissions versus ACC from previous work.
• Data sources: High-resolution meteorological data, pattern scaling results, and off-line modeling.

Main Results

• Emissions traceable to the Carbon Majors since 1950 (CM1950) have led to a 15% (~35 km3 per year) reduction in April 1st SWEApr1 across the WUS over the past decade.
• CM1950 has reduced warm season streamflow by 6% (~15 km3 per year) and increased irrigation demand by 2.4% (~0.89 km3 per year).
• The changes have widened the seasonal gap between water supply and demand, with decreased streamflow and increased irrigation demand during the warm season.

Contributions

• This study provides a source-to-impact attribution analysis of the impacts on western US water resources attributable to the Carbon Majors' emissions since 1950.
• The results highlight the importance of considering the nonlinearity in the changes in water supply and demand variables in response to ΔGMT.

Funding

• Not specified.

Citation

@article{Williams2026Carbon,
  author = {Williams, Emily L and Abatzoglou, John T. and Phillips, Carly A. and Safeeq, Mohammad and Sadai, Shaina and Chegwidden, O. and Fernandez‐Bou, Angel Santiago and Merner, L. Delta and Ortiz‐Partida, J. Pablo},
  title = {Carbon emissions exacerbating the Western US water crisis},
  journal = {Communications Earth & Environment},
  year = {2026},
  doi = {10.1038/s43247-026-03900-6},
  url = {https://doi.org/10.1038/s43247-026-03900-6}
}