A recently released 2020 Nebraska Groundwater-Level Monitoring Report shows that groundwater levels increased across most of Nebraska from January 2019 to January 2020.
According to Aaron Young, a geologist with the University of Nebraska–Lincoln’s School of Natural Resources and lead author of the report, during that period, 159 of 163 weather stations across Nebraska measured more precipitation than the 30-year normal. But in Cherry County, he said 212% of normal precipitation fell.
Young said the rain, snow and ice surpluses from 2019 were reflected in thousands of well measurements taken across much of Nebraska in early 2020, beneath which nearly three-quarters of the total volume of the High Plains Aquifer lies. In total, 4,970 wells were measured across Nebraska last spring, and there was an average increase of 1.58 feet in them statewide.
“An average rise of 1.58 feet statewide is pretty significant,” Young said.
Groundwater-level rises were recorded in 79% of the wells measured, with 55% of the wells recording an increase of more than a foot of water.
But precipitation can be erratic in Nebraska. In 2019, Grand Island experienced nearly 40 inches of precipitation. In 2020, Grand Island received 22.98 inches of precipitation as much of the state was suffering drought conditions.
According to a recent study by the U.S. Department of Agriculture Research Service and the University of Arizona, dry periods between rainstorms have become longer and annual rainfall has become more erratic across most of the western United States during the past 50 years.
The study found that against the backdrop of steadily warming temperatures and decreasing total yearly rainfall, rain has been falling in fewer and sometimes larger storms, with longer dry intervals between. Total yearly rainfall has decreased by an average of four inches over the last half century, while the longest dry period in each year increased from 20 to 32 days across the West.
Extreme droughts are also occurring more often in the majority of the West according to historical weather data as there has been an increase in the year-to-year variation of both total rainfall amounts and the duration of dry periods.
The report said that the rate of increasing variability of rainfall within each year and between years also appears to be accelerating, with greater portions of the West showing longer drought intervals since 2000 compared to previous years.
Exceptions to these drought patterns were seen in Washington, Oregon and Idaho and the Northern Plains region of Montana, Wyoming, and the most western parts of North and South Dakota.
In these regions, the researchers found some increases in total annual rainfall and decreases in drought intervals.
Together, these changes support what models have predicted as a consequence of climate change: a northward shift in the mid-latitude jet stream, which brings moisture from the Pacific Ocean to the western United States.
In Nebraska, many of the groundwater level decreases in the latest report were recorded in wells located near the Missouri River or in Dawson County, which is located along the Platte River.
Young said that in 2019, those water levels were measured at or near the peak stage of spring flooding, meaning that even though groundwater totals remained robust in those areas when they were measured in early 2020, the measurements had nowhere to go but down.