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| Titel |
Potential groundwater contribution to Amazon evapotranspiration |
| VerfasserIn |
Y. Fan, G. Miguez-Macho |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 14, no. 10 ; Nr. 14, no. 10 (2010-10-25), S.2039-2056 |
| Datensatznummer |
250012453
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| Publikation (Nr.) |
 copernicus.org/hess-14-2039-2010.pdf |
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| Zusammenfassung |
Climate and land ecosystem models simulate a dry-season vegetation stress in
the Amazon forest, but observations do not support these results, indicating
adequate water supply. Proposed mechanisms include larger soil water store
and deeper roots in nature and the ability of roots to move water up and
down (hydraulic redistribution), both absent in the models. Here we provide
a first-order assessment of the potential importance of the upward soil
water flux from the groundwater driven by capillarity. We present a map of
equilibrium water table depth from available observations and a groundwater
model simulation constrained by these observations. We then present a map of
maximum capillary flux these water table depths, combined with the
fine-textured soils in the Amazon, can potentially support. The maps show
that the water table beneath the Amazon can be shallow in lowlands and river
valleys (<5 m in 36% and <10 m in 60% of Amazonia). These water
table depths can potentially accommodate a maximum capillary flux of 2.1 mm day−1
to the land surface averaged over Amazonia, but varies from 0.6
to 3.7 mm day−1 across nine study sites.
We note that the results presented here are based on limited observations
and simple equilibrium model calculations, and as such, have important
limitations and must be interpreted accordingly. The potential capillary
fluxes are not indicative of their contribution to the actual
evapotranspiration, and they are only an assessment of the possible rate at
which this flux can occur, to illustrate the power of soil capillary force
acting on a shallow water table in fine textured soils. They may
over-estimate the actual flux where the surface soils remain moist. Their
contribution to the actual evapotranspiration can only be assessed through
fully coupled model simulation of the dynamic feedbacks between soil water
and groundwater with sub-daily climate forcing. The equilibrium water table
obtained here serves as the initial state for the dynamic simulation, and
together with the equilibrium potential capillary flux, will serve as a
baseline to evaluate the diurnal, event, seasonal and inter-annual dynamics. |
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