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.

The safety of our drinking water is often taken for granted, but a recent study from Washington University in St. Louis reveals that even seemingly harmless substances can pose significant risks when combined during the treatment process. Inactive ingredients in agricultural products, such as herbicides and fertilizers, have long been considered inert and thus, non-threatening to human health. However, researchers Jean Brownell and Kimberly Parker have discovered that these chemicals can be converted into hazardous byproducts known as nitrosamines during water disinfection.

Brownell’s investigation found that amines, used as stabilizing agents in herbicides to increase solubility and reduce drift, may be more important than active agents in herbicides when it comes to forming DBPs linked to various health risks. The study suggests that these inactive ingredients could enter the environment at rates similar to precursors from pharmaceuticals, which is a significant concern given their potential impact on water treatment processes.

The implications of this research are far-reaching and require immediate attention. As agricultural practices change, it’s essential to reevaluate our assumptions about herbicide use and its effects on drinking water quality. Brownell’s analysis confirms that shifting trends in herbicide formulation and use necessitate a closer look at nitrosamine precursors. These studies need to be done at specific locations and times of year to account for variations across space and time, which can be large and impactful.

The importance of collecting and sharing high-quality data from farmers and agencies across regions cannot be overstated. This information is crucial for developing consistent best practices for water and food safety. As Parker noted, “This paper raises questions that require more work to find answers.” Indeed, it does, but the potential consequences of inaction are too great to ignore.

The time has come to rethink our assumptions about agricultural runoff and its impact on drinking water quality. We need to evolve our studies and question our assumptions to ensure what we’re assuming is either truly generalizable or alternatively, needs to be applied to local areas. The future of our health and safety depends on it.