Warmer winters driving fluctuations in streamflow

After examining more than 500 watersheds across the U.S., scientists have found that “altered weather patterns are impacting stream flows… with implications for flooding, drought, and ecosystems.”

Analysis of day-to-day variations in streamflow across the U.S. between 1980 and 2013 revealed that “increased winter temperatures have driven the changes, with impacts varying due to local climate and amongst snow and rain-dominated watersheds.”

“We wanted to understand how climate change has impacted the hydrological balance across the U.S. based on the observed data,” said lead researcher Dr. Abhinav Gupta, a Maki postdoctoral fellow at Desert Research Institute, “(Then) we can figure out what kind of changes we might see in the future.” 

In the study, researchers differentiated between normal variability, like seasonal changes, and longer-term trends. They also “broke down stream inputs into events that occur at different timescales, like hourly and daily (rainfall) versus monthly and annual (groundwater).” Gupta noted that streamflow statistical structure was key to understanding the composite effect of all the components.

The results show that snow-dominated watersheds across the country are now receiving more precipitation as rain than before. Short bursts of stormwater are contributing to streamflow in contrast to snow meltoff. Study authors also point out that “short-term stream inputs could also be attributed to faster snowmelt rates due to higher temperatures.”  

Researchers observed local climate influences on streamflow. Humid locales like Florida and the Pacific Northwest had decreased storm inputs. Higher temperatures caused more evaporation, and soil absorbed more rainwater. Arid watersheds experienced an “increase in the number of days each year without rainfall over the study period, as well as a significant increase in winter temperatures, making streamflow more sporadic.”

Other variables that could impact the movement of water through watersheds, like changes in forest cover or soil type were not investigated. The researchers readily asserted that more research is needed to “understand what is driving changes in streamflow.”

To read the study “Changes in streamflow statistical structure across the United States due to recent climate change” published in the Journal of Hydrology, visit DOI https://doi.org/10.1016/j.jhydrol.2023.129474.