Decreased flow projected for Southwest streams by end of century — @USGS #ColoradoRiver #COriver #RioGrande #aridification

Graphs showing water-year time series of basin-mean, annual-mean (A) precipitation (millimeters per year), (B) temperature (degrees Celsius), (C) April 1 snow water equivalent (millimeters), (D) surface albedo, (E) surface net radiation (watts per square meter), (F) evapotranspiration (millimeters per year), and (G) discharge per unit area (millimeters per year). Blue curves represent estimates from observations, and grey bands represent ensemble range of model outputs. Black line represents least-squares linear fit.(Credit: Paul (Chris) Milly, USGS)

Here’s the release from the USGS:

Streamflow in the Southwestern U.S. is projected to decrease by as much as 36–80% by the end of this century, reports a new study by the U.S. Geological Survey. Decreases of this magnitude would challenge our ability to meet future water demand in this region and could jeopardize compliance with interstate and international water-sharing agreements.

The study projects streamflow for the seven major river basins that comprise the U.S. Southwest, including the Colorado River and Rio Grande basins. Projections were done for three 30-year intervals starting in 2020 using seven different climate models, two greenhouse gas concentration scenarios, and a streamflow model. The maximum projected decreases for the river basins range from 36 to 80%. Some increases are projected as well, mostly during the next 30 years. However, most models suggest that substantial water stresses in the region are likely by about 2060.

Streams in the region provide water for drinking, agriculture, hydroelectric power, recreation, and ecosystems. Water-supply shortages would affect all uses and would affect interstate and international water-sharing agreements. Decreases in streamflow in key areas for interstate and international water sharing agreements show potential declines up to 62%, putting agreement compliance at risk.

The results of this study, reached using an entirely different approach, are consistent with and support those of a recent USGS study that investigates how declining snow cover is playing a key role in decreasing the flow of the Colorado River.

Citation: Miller, O.L., Putman, A.L., Alder, J., Miller, M., Jones, D.K., Wise, D.R., 2021. Changing climate drives future streamflow declines and challenges in meeting water demand across the southwestern United States. Journal of Hydrology X, 11: 100074. DOI:

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