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| Titel |
Emergent phase shift between diurnal transpiration maxima and stream flow minima during base flow as diagnostic of eco-hydrologic interactions in landscapes |
| VerfasserIn |
Stefano Zanardo, Arno Hilberts, Efi Foufoula-Georgiou, William Dietrich |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250098143
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| Publikation (Nr.) |
 EGU/EGU2014-13790.pdf |
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| Zusammenfassung |
| Diurnal oscillations in river base flow are frequently observed in hydrological datasets, yet
have only been examined in a few, exploratory studies. In this work we focus on the
oscillation shift between base flow and the forcing signal, which, in the case study at
hand, is essentially dominated by the tree transpiration oscillation. This quantity
characterizes the propagation time of the forcing throughout the river basin, and will be
referred to as Eco-hydrological Phase Shift (EHPS). In principle, it is reasonable to
hypothesize that EHPS depends on the combination of hillslope and channel characteristic
transport times, however it is unclear whether and how its value varies over a range of
spatial scales. This is the central question of the study. We analyzed base flow data
collected between 2009 and 2012 in 8 stations within the Eel river basin (Mendocino
county, CA), where the typical Mediterranean climate allows for long, undisturbed
summer base flow recessions. The drainage areas relative to each gauging station
span over four orders of magnitude, ranging from ~10 km2 to ~10000 km2. We
found that, despite the wide range of spatial scales, EHPS by late summer tends to a
remarkably narrow range of values, between 8 and 11 hours for all the stations
considered. This implies that the timing of diurnal oscillations is dominated by
hillslope rather than river network processes, even at large spatial scales. We then
propose a simple, conceptual model to explore the hillslope controls on EHPS. The
framework allows deriving analytical expressions for EHPS under different “behavioral
assumptions” for vegetation water-use. Results show that, within this framework, a delay
of 8-11 hours can only be observed if tree roots exclusively use water from the
unsaturated zone and variations within that range are due to different signal propagation
times in both the unsaturated and the saturated zone. This analysis demonstrates
that EHPS represents a scale-invariant signature of river basins and can be used to
further explore the eco-hydrological interactions between hillslopes and streams. |
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