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| Titel |
Disentangling the response of forest and grassland energy exchange to heatwaves under idealized land–atmosphere coupling |
| VerfasserIn |
C. C. van Heerwaarden, A. J. Teuling |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 21 ; Nr. 11, no. 21 (2014-11-13), S.6159-6171 |
| Datensatznummer |
250117673
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| Publikation (Nr.) |
 copernicus.org/bg-11-6159-2014.pdf |
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| Zusammenfassung |
This study investigates the difference in land–atmosphere interactions
between grassland and forest during typical heatwave conditions in order to
understand the controversial results of Teuling et al. (2010) (hereafter T10),
who found the systematic occurrence of higher sensible heat fluxes over
forest than over grassland during heatwaves. With a simple but accurate
coupled land–atmosphere model, we show that existing parametrizations are
able to reproduce the findings of T10 for normal summer and heatwave
conditions. Furthermore, we demonstrate the sensitivity of the coupled system
to changes in incoming radiation and early-morning temperature typical for
European heatwaves.
Our results suggest that the fast atmospheric control of stomatal resistance
can explain the observed differences between grassland and forest. The
atmospheric boundary layer has a buffering function therein: increases in
stomatal resistance are largely compensated for by increases in the potential
evaporation due to atmospheric warming and drying.
In order to disentangle the contributions of differences in several static
and dynamic properties between forest and grassland, we have performed a
virtual experiment with artificial land-use types that are equal to
grassland, but with one of its properties replaced by that of forest. From
these, we confirm the important role of the fast physiological processes that
lead to the closure of stomata. Nonetheless, for a full explanation of T10's
results, the other properties (albedo, roughness and the ratio of minimum
stomatal resistance to leaf-area index) play an important but indirect role;
their influences mainly consist of strengthening the feedback that leads to
the closure of the stomata by providing more energy that can be converted
into sensible heat. The model experiment also confirms that, in line with the
larger sensible heat flux, higher atmospheric temperatures occur over forest.
As our parametrization for stomatal resistance is empirical rather than
mechanical, our study stresses the demand for a better mechanistic
understanding of physiological processes in plants. |
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