The Western United States is home to some of the most extensive agriculture and growing communities in the country. One of the key factors that sustain these developments is the meltwater from snow-capped mountains, which spills out every spring. For years, models have been used to predict the amount of streamflow available each year, assuming a small fraction of snowmelt enters shallow soil, with the remainder rapidly exiting in rivers and creeks. However, new research from University of Utah hydrologists suggests that this is not the case.

According to their findings, most spring runoff heading to reservoirs is actually several years old, indicating that most mountain snowfall has a long journey as groundwater before it leaves the mountains. This means that there is an order of magnitude more water stored underground than most Western water managers account for, said research leader Paul Brooks.

The team collected runoff samples at 42 sites and used tritium isotope analysis to determine the age of the water. Their findings were published in the journal Nature Communications Earth & Environment and co-authored by Utah geology professors Sara Warix and Kip Solomon in collaboration with research scientists around the West.

Determining the age of mountain streamflow is crucial for predicting how mountain hydrology will respond to changes in climate and land use, according to the researchers. They noted that there would be a lag between input storage and response, which means that even though models have been good in the past, they may not be reliable in the future.

The research also highlighted the importance of incorporating groundwater storage component into models to make good decisions moving forward. Brooks conducted sampling in 2022 while on sabbatical, visiting 42 sites twice, once in midwinter and again during spring runoff.

The state of Utah’s tracking is particularly robust, providing continuous streamflow data dating back 120 years. It’s an unparalleled dataset that has enabled hydrologists to document historic cycles in climate and streamflow that would otherwise have been missed, Brooks said.

According to Solomon, the vast majority of Earth’s fresh, usable water is underground, but just how much is there remains a puzzle. Dating water offers clues, and for determining the age of water, Solomon turns to tritium, a radioactive isotope of hydrogen with a half-life of 12.3 years.

The average age of the runoff sampled in the study varies among the catchment basins depending on their geology. The more porous the ground, the older its water is, since the subsurface can hold a lot more water. By contrast, glaciated canyons with low permeability and shallow bedrock, such as Utah’s Little Cottonwood Canyon, provide far less subsurface storage and younger waters, according to the study.

For decades, federal and state water managers have relied on a network of snowpack monitoring sites to provide data to guide forecasts of water availability for the upcoming year. It’s now clear that such snowpack data doesn’t provide a complete picture, according to the researchers.

“For much of the West, especially the Interior West where this study is based, our models have been losing skill,” Brooks said.

The growing disconnect between snowfall, snowpack volumes and streamflow is driven by variability in these large, previously unquantified subsurface water stores. As a case in point, Brooks highlighted the 2022 water year, which saw snowpacks in many Western states that were near or just below average. Yet that year experienced record low groundwater storage, resulting in much below average spring streamflow.

This new understanding of mountain streamflow has significant implications for water management and resource planning, particularly as the West continues to experience climate variability and change.

The study reveals that three consecutive years of drought contributed to the ‘Barbarian Conspiracy’, a pivotal moment in the history of Roman Britain. Researchers argue that peripheral tribes took advantage of famine and societal breakdown caused by an extreme period of drought to inflict crushing blows on weakened Roman defences in 367 CE.

The researchers used oak tree-ring records to reconstruct temperature and precipitation levels in southern Britain during and after the ‘Barbarian Conspiracy’. They found that southern Britain experienced an exceptional sequence of remarkably dry summers from 364 to 366 CE, with average monthly reconstructed rainfall in the main growing season (April-July) falling to just 29mm in 364 CE.

The drought-driven grain deficits would have reduced the grain supply to Hadrian’s Wall, providing a plausible motive for the rebellion there which allowed the Picts into northern Britain. The study suggests that given the crucial role of grain in the contract between soldiers and the army, grain deficits may have contributed to other desertions in this period.

The researchers argue that military and societal breakdown in Roman Britain provided an ideal opportunity for peripheral tribes, including the Picts, Scotti, and Saxons, to invade the province en masse with the intention of raiding rather than conquest. Their finding that the most severe conditions were restricted to southern Britain undermines the idea that famines in other provinces might have forced these tribes to invade.

Ultimately, the researchers argue that extreme climate conditions lead to hunger, which can lead to societal challenges, and eventually outright conflict. The relationship between climate and conflict is becoming increasingly clear in our own time, making these findings relevant not only for historians but also for policymakers and researchers today.

When two materials come into contact, charged entities on their surfaces get a gentle nudge. This phenomenon is what creates static electricity when you rub a balloon against your skin. Similarly, water flowing over certain surfaces can gain or lose charge. Researchers have now harnessed this effect to generate electricity from rain-like droplets moving through a tube.

The study’s corresponding author, Siowling Soh, explains that the new flow pattern used in their setup – plug flow – generates a substantial amount of electricity. “Water that falls through a vertical tube can produce enough power to light 12 LEDs,” says Soh. This breakthrough could allow rain energy to be harvested for generating clean and renewable electricity.

Unlike traditional hydroelectricity, which is limited to locations with large volumes of water like rivers, this new system uses smaller channels that rainwater can pass through. The researchers designed a simple setup where water flowed out the bottom of a tower through a metallic needle, spurring rain-sized droplets into a 12-inch-tall and 2-millimeter-wide vertical polymer tube.

As the droplets collided at the top of the tube, they created a plug flow – short columns of water interspersed with pockets of air. As the water flowed down the inside of the tube, electrical charges separated, generating electricity. The team collected the water in a cup below the tube and placed wires to harvest the energy.

The plug flow system converted more than 10% of the energy of the water falling through the tubes into electricity, which is five orders of magnitude more than traditional charge separation methods. In another experiment, the researchers found that moving water through two tubes simultaneously generated double the energy. Using this information, they channeled water through four tubes and powered 12 LEDs continuously for 20 seconds.

The researchers believe that plug flow energy could be simpler to set up and maintain than hydroelectric power plants and more convenient for urban spaces like rooftops. They acknowledge funding from various organizations in Singapore and look forward to further developing this innovative technology.