Abstract
River networks are typically treated as conduits of fixed discharge conveyance capacity in flood models and engineering design, despite knowledge that alluvial channel networks adjust their geometry, conveyance, planform, extent and drainage density over time in response to shifts in the magnitude and frequency of streamflows and sediment supply. Consistent relationships between modes of climate variability conducive to wetter-/drier-than-average conditions and changes in channel conveyance have never been established, hindering geomorphological prediction over interannual to multidecadal timescales. This paper explores the relationship between river channel conveyance/geometry and three modes of climate variability (the El Niño–Southern Oscillation, Atlantic Multidecadal Oscillation, and Arctic Oscillation) using two-, five- and ten-year medians of channel measurements, streamflow, precipitation and climate indices over seven decades in 67 United States rivers. We find that in two thirds of these rivers, channel capacity undergoes coherent phases of expansion/contraction in response to shifts in catchment precipitation and streamflow, driven by climate modes with different periodicities. Understanding the sensitivity of channel conveyance to climate modes would enable better river management, engineering design, and flood predictability over interannual to multidecadal timescales.
Highlights
Alluvial river channels are self-formed by the sediment-laden flow they convey downstream, adjusting their geometry[1,2,3,4], conveyance[5,6], planform[7], network extent[8] and drainage density[9,10] dynamically over time to reflect prevailing streamflow regimes[11,12] and any changes in the sediment supply generated upstream[13]
Over multidecadal timescales across the USA, findings differ: some studies have found that climate anomalies, river flows[19] and flood events[29] are linked to slow variations of sea surface temperature driven by the Atlantic Multidecadal Oscillation (AMO); others indicate that the fraction of stream gages exhibiting a significant relation between flood magnitude/frequency and the AMO is no greater than would be expected by chance[30]
It is recognized that climate patterns have consistent effects on streamflow distributions in different regions of the world[25,26,34,35], that alluvial river channels adjust to reflect changing streamflow and sediment regimes[1,4,11,36], and that channel morphology can be influenced by large-scale climate modes[27,37], a systematic association between large-scale climate patterns and changes in channel conveyance has not been established in observational records
Summary
River networks are typically treated as conduits of fixed discharge conveyance capacity in flood models and engineering design, despite knowledge that alluvial channel networks adjust their geometry, conveyance, planform, extent and drainage density over time in response to shifts in the magnitude and frequency of streamflows and sediment supply. The longitudinal expansion and contraction of active stream networks[8,9,10,17] as well as shifts in channel conveyance (i.e. the ability of the channel to convey flow, measured in m3/s) and cross-sectional geometry[11,18] are expected to reflect the occurrence of wetter- or drier-than-average climatic conditions that alter the volumes of precipitation, runoff, streamflow, and sediment supplied to alluvial channels[8] (Fig. 1). Uncovering relationships between local climate and large-scale climate modes is challenging, because associations are notoriously non-stationary[31], reflect interactions between multiple modes[32] and are influenced by emerging anthropogenic climate change signals[33]
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