Some climate models project more rainfall in the West
While most recent research suggests that the Colorado River will be depleted well beyond current demands as global temperatures increase, there may be one small bright spot on the horizon. Even if runoff from snow declines, groundwater replenishment in the basin may hold stead under projected increases in precipitation, the U.S. Geological Survey and U.S. Bureau of Reclamation found in a new study.
“You can’t manage what you don’t measure,” said Fred Tillman, lead author and USGS scientist. “These results are the first step in understanding the quantity of groundwater we can expect in the Upper Colorado River Basin; however, further studies are needed to help more accurately forecast future groundwater availability.”
The Colorado River is a critically important source of water for more than 35 million people in the United States and 3 million people in Mexico. As much as half the water flowing in the rivers and streams in the Upper Colorado River Basin originates as groundwater. Understanding how much groundwater is available and how it’s replenished is important to sustainably manage both groundwater and surface water supplies in the Colorado River basin now and in the future.
In the new study, USGS and Reclamation scientists estimated projected changes in groundwater recharge for the Upper Colorado River Basin from recent historical (1950–2015) through future (2016–2099) time periods using climate projections and a groundwater-recharge model.
Simulated future groundwater recharge through 2099 is generally expected to be somewhat greater than the historical average in most decades due to an anticipated wetter future climate in the basin under the most advanced climate modeling projections. Groundwater resources are replenished through increases in precipitation, which may offset reductions from increased temperatures. The full report is available online in the journal Geophysical Research Letters.
But researchers urged caution interpreting the results because a few of the models suggested decreased future recharge relative to the historical climate period.
“Future estimates of groundwater recharge are compounded by the large-scale of the Upper Colorado River Basin and the uncertainties of future climate projections,” said Reclamation co-author Subhrendu Gangopadhyay.
“Given these uncertainties, multiple-future water supplies scenarios are used to inform Reclamation’s water management and planning within the Upper Colorado River Basin,” Reclamation’s Upper Colorado Region Water Resources Manager Malcolm Wilson added.