Studies of stream flow generation and routing typically focus on single events such as rainfall impulses to characterize whole-watershed response, scientists said. But in the new study, led by Steven Wondzell of the Olympia Forestry Sciences Laboratory at the U.S. Forest Service's Pacific Northwest Research Station, researchers discovered seasonal changes in daily fluctuations in flow volume at the watershed's mouth can be explained by transport of evaporation and transpiration, or ET, generated signals down the stream network.

Wondzell and colleagues found when stream flow velocity is high, ET-generated signals tend to reach the stream gauge in phase, reinforcing the signals and producing strong daily fluctuations. As flow velocity slows during the summer, ET-generated signals become increasingly out of phase, which masks discharge fluctuations.

The researchers -- including Michael Gooseff of Pennsylvania State University and Brian McGlynn of Montana State University -- concluded the pattern of naturally produced fluctuations in discharge could be used to analyze the ecology and hydrology of whole watersheds.

The study is detailed in the journal Geophysical Research Letters.