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| Titel |
A missing piece of the puzzle in climate change hotspots: Near-surface
turbulent interactions controlling ET-soil moisture coupling in semiarid
areas |
| VerfasserIn |
Erfan Haghighi, Daniel J. Gianotti, Angela J. Rigden, Guido D. Salvucci, James W. Kirchner, Dara Entekhabi |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250142213
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| Publikation (Nr.) |
 EGU/EGU2017-5808.pdf |
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| Zusammenfassung |
| Being located in the transitional zone between dry and wet climate areas, semiarid
ecosystems (and their associated ecohydrological processes) play a critical role in
controlling climate change and global warming. Land evapotranspiration (ET),
which is a central process in the climate system and a nexus of the water, energy and
carbon cycles, typically accounts for up to 95% of the water budget in semiarid
areas. Thus, the manner in which ET is partitioned into soil evaporation and plant
transpiration in these settings is of practical importance for water and carbon cycling and
their feedbacks to the climate system. ET (and its partitioning) in these regions
is primarily controlled by surface soil moisture which varies episodically under
stochastic precipitation inputs. Important as the ET-soil moisture relationship is, it
remains empirical, and physical mechanisms governing its nature and dynamics are
underexplored.
Thus, the objective of this study is twofold: (1) to provide observational evidence for the
influence of surface cover conditions on ET-soil moisture coupling in semiarid regions using
soil moisture data from NASA’s SMAP satellite mission combined with independent
observationally based ET estimates, and (2) to develop a relatively simple mechanistic
modeling platform improving our physical understanding of interactions between micro and
macroscale processes controlling ET and its partitioning in partially vegetated areas. To this
end, we invoked concepts from recent progress in mechanistic modeling of turbulent energy
flux exchange in bluff-rough regions, and developed a physically based ET model
that explicitly accounts for how vegetation-induced turbulence in the near-surface
region influences soil drying and thus ET rates and dynamics. Model predictions
revealed nonlinearities in the strength of the ET-soil moisture relationship (i.e.,
∂ET/∂θ) as vegetation cover fraction increases, accounted for by the nonlinearity of
surface-cover-dependent turbulent interactions. We identified a (predictable) critical
vegetation cover fraction (as a function of vegetation stature and environmental
conditions) that yields the strongest ET-soil moisture relationship under prescribed
atmospheric conditions. Overall, the results suggest that ∂ET/ ∂θ varies more
widely in regions with tall-stature woody vegetation that experience higher rates of
change in turbulence intensity as the cover fraction increases. Our results facilitate a
mathematically tractable description of ∂ET/ ∂θ, which is a core component of models
that seek to predict hydrology-climate feedback processes in a changing climate. |
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