By Jennifer LaVista

Water flowing on the Colorado River near Moab, Utah. More than half of the streamflow in the Upper Colorado River Basin originates as groundwater, and a new study shows large precipitation events that occur about every 10 years are a critical source of recharge for replenishing groundwater resources.
Credit: Matthew Miller/USGS.

Large precipitation events that occur about every 10 years are a critical source of recharge for replenishing groundwater resources, according to a new study published in Water Resources Research, a journal of the American Geophysical Union.

Groundwater is a vital source of water in the western United States and will be increasingly important with continued population growth and climate variability. Understanding the role of these large recharge events in replenishing aquifers and sustaining water supplies is crucial for long-term groundwater management.

The new study is one of the first in the region to investigate the effects of climate on groundwater resources. The researchers identified and analyzed large, multi-year, quasi-decadal groundwater recharge events in the northern Utah portion of the Great Basin from 1960 to 2013. Researchers evaluated groundwater levels and climate information and identified five large recharge events with a frequency of about 11 to 13 years. Findings show these events provide a significant amount of groundwater recharge and storage across the northern Great Basin, causing water levels to rise in aquifers.

“Informed decisions for water management now and in the future rely on understanding the surface and groundwater resources within a river basin,” said Subhrendu Gangopadhyay, a civil engineer at the U.S. Bureau of Reclamation in Denver and co-author of the new study. “Understanding historical groundwater recharge provides context to better manage groundwater in the future under a variable climate.”

There has been a considerable amount of research linking climatic variability to hydrologic responses; however, most of these studies focus on surface-water resources. The implications of this work indicate if the magnitude or frequency of these recharge events change there will be significant impacts on groundwater, specifically long-term availability, use and sustainability.

“These large recharge events are vital in replenishing and maintaining groundwater storage, especially after multiple years of below average precipitation across the region,” said Melissa Masbruch, a hydrologist at the U.S. Geological Survey in Salt Lake City and lead author of the study. “Without them, groundwater resources become depleted.”

Large groundwater recharge events are characterized by above-average annual precipitation and below-average seasonal temperatures, especially during the spring (April through June). Existing groundwater flow models were then used to simulate changes in groundwater storage in several basins throughout the study area from these events.

—Jennifer LaVista is a public affairs specialist at USGS. This post originally appeared as a press release on the USGS website.