Walther, J., 1924, Das Gesetz der Wüstenbildung in Gegenwart und Vorzeit, Leipzig, Verlag Quelle & Meyer, 421pp.Īggradation Alluvium Coulee, Coulee Cliff, etc. F., 1957, Arroyos and the semiarid cycle of erosion, Am. A., 1961, Effect of sediment characteristics on erosion and deposition in ephemeral-stream channels, U.S. This paper quantifies thresholds in ephemeral streams and evaluates how they are affected by rainfall and watershed properties. Pardé, M., 1933, Fleuves et rivières, Paris, Coll. IRES dominate surface runoff in semiarid areas of Mediterranean Europe (Cushing et al., 1995. F., 1962, Formation and deposition of clay balls, Rio Puerco, New Mexico, U.S. P., 1964, Fluvial Processes in Geomorphology, Chs. P., 1956, Ephemeral streams-Hydraulic factors and their relation to the drainage net, U.S. G., 1962, Transmission losses in ephemeral stream beds, J. A., 1961, Sediment sources and drainage basin characteristics in upper Cheyenne River basin, U.S. F., 1961, Influence of riparian vegetation on channel shape, U.S. (President Joe Biden’s administration is now reviewing those exclusions.) Such streams can seem inconsequential, Wohl says, but, “If you start chopping off the first joint of each finger, you’re going to lose functionality in your hand pretty fast.Bryan, Kirk, 1922, Erosion and sedimentation in the Papago Country, Bull. Many such streams were excluded from federal environmental laws under former President Donald Trump’s administration. Others say the results highlight the need for stronger legal protections for intermittent tributaries that form the headwaters of many rivers. “We should have many more gauges in small streams,” says Albert Ruhi, a freshwater ecologist at the University of California, Berkeley. They may have a well-defined channel and they typically lack the biological, hydrological, and physical characteristics commonly associated with intermittent or continuous conveyances of water. “I definitely didn’t expect the pattern to be so regionally clear.”īroader monitoring of intermittent streams would help researchers and policymakers better understand the sometimes subtle impacts that climate change is having on water quantity and quality, scientists say. Ephemeral streams are features that only carry stormwater in direct response to precipitation. But a warming climate appears to be “the overarching organizer” of the shifts, Zipper says. In some cases, human activities such as operating dams, irrigation, and groundwater pumping could be contributing to dewatering. One possible reason: Winters are warmer and shorter, meaning frozen landscapes thaw earlier, allowing streams to flow. In contrast, in the northern United States ephemeral rivers are now flowing longer. But even in the Southeast, which is relatively wet, streams are drying earlier and staying dry longer. The drying trend is clearest in arid regions, such as the Southwest. It also has implications for water quality, as microbes in damp sediments can remove nitrogen pollution even after the last puddles have disappeared. “Just because the channel is dry does not make it biologically dead,” says river scientist Ellen Wohl of Colorado State University. That is bad news for the many plants and animals that time their reproduction to the availability of water, especially in deserts. At some 7% of gauges, dry periods expanded by 100 days or more. Some now shrivel earlier in the year and remain dry for longer, for example, or they dwindle more quickly than before. More than half of the gauges showed changes in the streams’ flow patterns since 1980. Still, the analysis revealed some eye-opening regional shifts, says Sam Zipper, one of the authors and an ecohydrologist with the Kansas Geological Survey. The sample covered just a small fraction of intermittent streams, the authors note, and left out some states, such as Nebraska and Maine, that don’t have any long-term gauges on these streams. Most of the gauges were on small waterways in river headwaters, but a few tracked large rivers that are intermittent in places, such as the Rio Grande, which flows sporadically in New Mexico and Texas. The findings, reported last month in Environmental Research Letters, come from a study of data collected between 19 by flow gauges on 540 intermittent streams around the United States. “That’s really shocking,” says Sarah Null, a watershed scientist at Utah State University. Some are dry for 100 days longer per year than in the 1980s. Now, a study has found that ephemeral streams across the continental United States have become less reliable over the past 40 years, likely as a result of climate change. They help purify surface water and provide crucial habitat for creatures such as the Sonoran Desert toad, fairy shrimp, and Wilson’s warbler. But these intermittent streams are everywhere, making up more than half of Earth’s waterways. Small streams that dry up for part of the year are easy to overlook.
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