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| Titel |
Plant water-stress parameterization determines the strength of land-atmosphere coupling |
| VerfasserIn |
Marie Combe, Jordi Vilà-Guerau de Arellano, Huug G. Ouwersloot, Wouter Peters |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250123762
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| Publikation (Nr.) |
 EGU/EGU2016-3067.pdf |
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| Zusammenfassung |
| Land-surface models that are currently used in numerical weather predictions models and
earth system models all assume various plant water-stress parameterizations. We investigate
the impact of this variety of parametrizations on the performance of atmospheric models. For
this, we use a conceptual framework where a convective atmospheric boundary-layer (ABL)
model is coupled to a daytime model for the land surface fluxes of carbon, water, and energy.
We first validate our coupled model for a set of surface and upper-atmospheric diurnal
observations over a grown maize field in the Netherlands. We then perform a sensitivity
analysis of this coupled land-atmosphere system by varying the modeled plant water-stress
response from a very insensitive to a sensitive response during dry soil conditions. We first
propose and verify a feedback diagram that ties plant water-stress response and
large-scale atmospheric conditions to the diurnal cycles of ABL CO2, humidity and
temperature. Based on our undertanstanding of the diurnal coupled system, we then
explore the impact of the assumed water-stress reponse for the development of a dry
spell on a synoptic time scale. We find that during a progressive 3-week soil drying
caused by evapotranspiration, an insensitive plant will dampen atmospheric heating
because the vegetation continues to transpire while soil moisture is available. In
contrast, the sensitive plant reduces its transpiration to prevent soil moisture depletion.
But when absolute soil moisture comes close to wilting point, the insensitive plant
will suddenly close its stomata causing a switch to a land-atmosphere coupling
regime dominated by sensible heat exchange. We find that in both cases, our modeled
progressive soil moisture depletion contributes to further atmospheric warming up to 6 K,
reduced photosynthesis up to 89 %, and CO2 enrichment up to 30 ppm, but the
full impact is strongly delayed for the insensitive plant. Finally, we demonstrate
that the assumed plant water-stress parametrization can strongly shift the model
sensitivity to other environmental conditions that are coherent with a soil drying during
droughts (e.g. larger atmospheric subsidence, decreased cloud cover, etc). Our findings
thus indicate that the ability of coupled weather or climate models to represent
drought events is very much tied to the underlying plant water-stress parametrization. |
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