The article "Human-Induced Changes in the Hydrology of the Western United States" by Tim P. Barnett, David W. Pierce, Hugo G. Hidalgo, Celine Bonfils, Benjamin D. Santer, and others, presents a regional, multivariable climate change detection and attribution study focusing on the western United States. The study uses a high-resolution hydrologic model forced by global climate models to analyze changes in river flow, winter air temperature, and snow pack between 1950 and 1999. The results indicate that up to 60% of these climate-related trends are human-induced, robust to perturbations in study variates and methods. The findings suggest a significant crisis in water supply for the western United States, as the region experiences shifts in mountain precipitation, earlier snow melt, and associated changes in river flow, exacerbated by warming conditions. The study employs a multivariable detection and attribution (D&A) methodology to demonstrate that the observed low-frequency changes in the hydrological cycle are primarily due to human-caused climate changes from greenhouse gases and aerosols. The results are consistent with the anthropogenic model runs, indicating a detectable and attributable signature of human effects on western hydrology.The article "Human-Induced Changes in the Hydrology of the Western United States" by Tim P. Barnett, David W. Pierce, Hugo G. Hidalgo, Celine Bonfils, Benjamin D. Santer, and others, presents a regional, multivariable climate change detection and attribution study focusing on the western United States. The study uses a high-resolution hydrologic model forced by global climate models to analyze changes in river flow, winter air temperature, and snow pack between 1950 and 1999. The results indicate that up to 60% of these climate-related trends are human-induced, robust to perturbations in study variates and methods. The findings suggest a significant crisis in water supply for the western United States, as the region experiences shifts in mountain precipitation, earlier snow melt, and associated changes in river flow, exacerbated by warming conditions. The study employs a multivariable detection and attribution (D&A) methodology to demonstrate that the observed low-frequency changes in the hydrological cycle are primarily due to human-caused climate changes from greenhouse gases and aerosols. The results are consistent with the anthropogenic model runs, indicating a detectable and attributable signature of human effects on western hydrology.