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| Titel |
Variably-saturated flow in large weighing lysimeters under dry conditions: inverse and predictive modeling |
| VerfasserIn |
Sascha Iden, Daniela Reineke, Jeremy Koonce, Markus Berli, Wolfgang Durner |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250109347
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| Publikation (Nr.) |
 EGU/EGU2015-9251.pdf |
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| Zusammenfassung |
| A reliable quantification of the soil water balance in semi-arid regions requires an accurate
determination of bare soil evaporation. Modeling of soil water movement in relatively dry
soils and the quantitative prediction of evaporation rates and groundwater recharge pose
considerable challenges in these regions. Actual evaporation from dry soil cannot be
predicted without detailed knowledge of the complex interplay between liquid, vapor and
heat flow and soil hydraulic properties exert a strong influence on evaporation rates during
stage-two evaporation. We have analyzed data from the SEPHAS lysimeter facility in
Boulder City (NV) which was installed to investigate the near-surface processes of
water and energy exchange in desert environments. The scientific instrumentation
consists of 152 sensors per Lysimeter which measured soil temperature, soil water
content, and soil water potential. Data from three weighing lysimeters (3Âm long,
surface area 4Âm2) were used to identifiy effective soil hydraulic properties of the
disturbed soil monoliths by inverse modeling with the Richards equation assuming
isothermal flow conditions. Results indicate that the observed soil water content in
8 different soil depths can be well matched for all three lysimeters and that the
effective soil hydraulic properties of the three lysimeters agree well. These results
could only be obtained with a flexible model of the soil hydraulic properties which
guaranteed physical plausibility of water retention towards complete dryness and
accounted for capillary, film and isothermal vapor flow. Conversely, flow models using
traditional parameterizations of the soil hydraulic properties were not able to match
the observed evaporation fluxes and water contents. After identifying the system
properties by inverse modeling, we checked the possibility to forecast evaporation
rates by running a fully coupled water, heat and vapor flow model which solved the
energy balance of the soil surface. In these numerical simulations, atmospheric
measurements of temperature, humidity, and wind speed were used as transient boundary
conditions. |
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