Streamflow reductions will heighten the water crisis in the Colorado River Basin.
The Science
Past research has overlooked groundwater’s impact on mountain streamflow generation, and whether groundwater will buffer or intensify streamflow losses in a warmer climate has remained unknown. To better understand groundwater and stream water interactions, researchers developed a detailed computer model of a mountain basin that stretched four hundred meters into the subsurface. The basin chosen for the study is representative of the Colorado River headwaters and contains significant weather and water monitoring infrastructure that informed model development. The model accounted for snow dynamics, vegetation water use, soil moisture, groundwater, and stream water.
The Impact
The study showed that end-of-century temperatures resulted in sharp declines in groundwater levels that were unable to recover to historical levels during wet climatic periods. In particular, warmer summers were shown to increase conifer forest water-use and lower water table elevations, which hints at the need to manage forests and groundwater together. As groundwater levels dropped, streamflow declined. This occurred because of two impacts occurring simultaneously: less groundwater moved toward streams while more stream water moved into the ground. In comparison to simulations that examined climate change in the region without accounting for groundwater declines, including declining water table levels in the analysis nearly doubled streamflow reductions and caused late summer stream flows to cease.
Summary
Groundwater interactions with mountain streams are often simplified in model projections, potentially leading to inaccurate estimates of streamflow response to climate change. Here, using a high-resolution hydrological model extending 400 m into the subsurface, the study found groundwater to be an important and stable source of historical streamflow in a mountainous watershed of the Colorado River. In a warmer climate, increased forest water use reduces groundwater recharge, resulting in groundwater storage loss. Groundwater losses were most severe during dry years and did not recover to historical levels even during simulated wet periods. Groundwater depletion resulted in no streamflow or the river becoming dry for a short period of time when precipitation was low. Expanding results across the region suggested groundwater declines will be highest in the Colorado Headwater and Gunnison basins. Our research highlights the tight connection of vegetation and groundwater dynamics and that excluding explicit groundwater response to warming may underestimate future reductions in mountain streamflow.
Contact
Eoin L. Brodie, Watershed Function SFA LRM
Lawrence Berkeley National Laboratory
Funding
Work was supported as part of the Watershed Function Science Focus Area funded by the US Department of Energy, Office of Science, Office of Biological and Environmental Research under Contract No. DE-AC02-05CH11231.
Publications
Carroll, R.W.H., et al., “Declining groundwater storage expected to amplify streamflow reductions in a warmer world ” Nature Water. 2, 419-433 (2024). [Doi: 10.1038/s44221-024-00239-0].
Model Files: https://data.ess-dive.lbl.gov/datasets/doi:10.15485/1998576
Nature, News and Views paper review: https://doi.org/10.1038/s44221-024-00243-4
Press
● Rising temperatures will significantly reduce streamflow in the Upper Colorado River Basin as Groundwater Levels Fall, New Research Shows DRI Press Release
● Colorado River Water Supply to Decrease because of Overlooked Losses Newsweek
● Climate change will reduce streamflow in the upper Colorado river basin as groundwater levels fall Smartwater Magazine
● Rising temperatures will significantly reduce streamflow in the upper Colorado river basin as groundwater levels fall Science Daily
● Climate change will reduce streamflow in the upper Colorado river basin as groundwater levels fall, study finds Phys.org
● Mystery of the disappearing snowpack. Headwaters Magazine
● Shrinking Colorado River faces another water-sapping threat – from underground, new study says. Denver Post