Aridification of Colorado River Basin's Snowpack Regions Has Driven Water Losses Despite Ameliorating Effects of Vegetation

Journal Article · 20 July 2023 · Water Resources Research

DOI: https://doi.org/10.1029/2022WR033454 · OSTI ID:1991643

Bass, Benjamin  ^[1]; Goldenson, Naomi  ^[1]; Rahimi, Stefan  ^[1]; Hall, Alex ^[1]

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1. Department of Atmospheric and Oceanic Sciences University of California Los Angeles CA USA

Abstract The Colorado River Basin is an important natural resource for the semi‐arid southwestern United States (US), where it provides water to more than 40 million people. While nearly 1.5°C of anthropogenic warming has occurred across this region from the 1880s to 2021, climate models show little agreement in the precipitation change during the same historical period, with no trend in the mean of the latest (sixth) generation of Global Climate Models. As such, here we focus on how the CO ₂ increase and associated anthropogenic warming over the historical period has impacted runoff across the Colorado Basin. We find that the Colorado Basin's runoff over the historical period has decreased by 8.1% per degree Celsius of warming (°C ⁻¹ ). However, the magnitude of this sensitivity is reduced to 6.8% °C ⁻¹ when considering vegetation response to historical CO ₂ . For present‐day conditions, this translates to runoff reductions of 10.3% due to anthropogenic increases in both temperature and CO ₂ since 1880. We demonstrate that Colorado Basin's natural flow has been decreased by roughly the storage of Lake Mead during the 2000–2021 megadrought due to this long term anthropogenic influence, suggesting the basin's first shortage in 2021 would likely not have occurred without anthropogenic warming. We further show warming has led to disproportionate aridification in snowpack regions, causing runoff to decline at double the rate relative to non‐snowpack regions. Thus, despite only making up ∼30% of the basin's drainage area, 86% of runoff decreases in the Colorado Basin is driven by water loss in snowpack regions.

• Sponsoring Organization: USDOE
• OSTI ID: 1991643
• Journal Information: Water Resources Research, Journal Name: Water Resources Research Journal Issue: 7 Vol. 59; ISSN 0043-1397
• Publisher: American Geophysical Union (AGU)Copyright Statement
• Country of Publication: United States
• Language: English