2025-02-13 カリフォルニア大学サンタバーバラ校 (UCSB)
＜関連情報＞
- https://news.ucsb.edu/2025/021755/predicting-seasonal-changes-river-networks
- https://www.science.org/doi/10.1126/science.ado2860
- https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL081799
アメリカ全土における流路網の長さの変化 Variability of flowing stream network length across the US
Jeff P. Prancevic, Hansjörg Seybold, and James W. Kirchner
science Published:13 Feb 2025
Editor’s summary
Ephemeral streams flow only sporadically and are dry the rest of the time. How much does their coming and going affect overall stream network length? Prancevic et al. used a semimechanistic model combined with stream gauge measurements and topographical data to estimate the variability of stream network length across the entire contiguous United States. This approach allowed them to conclude that the median US stream network is six times longer during annual high-flow conditions than during annual low-flow conditions. —Jesse Smith
Abstract
The aggregate length of flowing streams in a drainage network lengthens and shortens as landscapes become wetter and drier. However, direct measurements of stream network variability have been limited to a handful of small drainage basins. We estimated the variability of stream network length for 14,765 gauged basins across the contiguous United States using measured streamflow distributions and topography-based estimates of how sensitive each stream network is to changing landscape wetness (the network’s elasticity). We find that the median US stream network is five times longer during annual high-flow conditions than during annual low-flow conditions. Stream networks are more dynamic in some regions than in others, driven by regional differences in both hydroclimatology and the networks’ elasticity in response to hydroclimatic forcing.
地形による流路の伸縮の制御 Topographic Controls on the Extension and Retraction of Flowing Streams
Jeff P. Prancevic, James W. Kirchner
Geophysical Research Letters Published: 01 February 2019
DOI:https://doi.org/10.1029/2018GL081799
Abstract
Flowing stream networks extend and retract as their surrounding landscapes wet up and dry out, both seasonally and during rainstorms, with implications for aquatic ecosystems and greenhouse gas exchange. Some networks are much more dynamic than others, however, and the reasons for this difference are unknown. Here we show that the tendency of stream networks to extend and retract can be predicted from down-valley changes in topographic attributes (slope, curvature, and contributing drainage area), without measuring subsurface hydrologic properties. Topography determines where water accumulates within valley networks, and we propose that it also modulates flow partitioning between the surface and subsurface. Measurements from 17 mountain stream networks support this hypothesis, showing that undissected valley heads have greater subsurface transport capacities than sharply incised valleys downstream. In catchments where broad valley heads rapidly transition to sharply incised valleys, subsurface transport capacity decreases abruptly, stabilizing stream length through wet and dry periods.
Key Points
- Some flowing stream networks lengthen dramatically as their catchments become wetter, whereas others change much less
- This tendency for networks to extend and retract can be predicted from down-valley changes in slope, drainage area, and curvature
- As valleys become more sharply incised downstream, subsurface transmissivity decreases, which helps stabilize flowing stream length
Plain Language Summary
Although stream networks are represented as fixed blue lines on maps, the actual extent of flowing water dynamically adjusts as landscapes become wetter and drier. This is an old observation, but one without a satisfying physical explanation. Intuitively, flowing streams extend during wetter periods, as smaller parts of the landscape are able to supply enough water to support streamflow. But the supply of water is only part of the story, because some parts of the landscape may have greater capacity to move supplied water through the subsurface without streamflow, affecting where water ultimately emerges. In this study, we use observations from 17 mountainous landscapes to show that topography can be used to predict both the supply of water and the capacity to move that water through the subsurface. Consequently, topographic maps can tell us how much a stream network will extend as its surrounding landscape becomes wetter. This helps us predict how dynamic (or, conversely, stable) stream networks will be during rainstorms, droughts, and longer-term climatic shifts.
