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| Titel |
Seasonal and spatial variation in broadleaf forest model parameters |
| VerfasserIn |
M. Groenendijk, M. K. van der Molen, A. J. Dolman |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250023712
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| Zusammenfassung |
| Process based, coupled ecosystem carbon, energy and water cycle models are used with the
ultimate goal to project the effect of future climate change on the terrestrial carbon cycle. A
typical dilemma in such exercises is how much detail the model must be given to describe the
observations reasonably realistic while also be general. We use a simple vegetation model
(5PM) with five model parameters to study the variability of the parameters. These
parameters are derived from the observed carbon and water fluxes from the FLUXNET
database.
For 15 broadleaf forests the model parameters were derived for different time resolutions.
It appears that in general for all forests, the correlation coefficient between observed and
simulated carbon and water fluxes improves with a higher parameter time resolution. The
quality of the simulations is thus always better when a higher time resolution is used. These
results show that annual parameters are not capable of properly describing weather effects on
ecosystem fluxes, and that two day time resolution yields the best results. A first indication of
the climate constraints can be found by the seasonal variation of the covariance
between Jm, which describes the maximum electron transport for photosynthesis,
and climate variables. A general seasonality we found is that during winter the
covariance with all climate variables is zero. Jm increases rapidly after initial spring
warming, resulting in a large covariance with air temperature and global radiation.
During summer Jm is less variable, but co-varies negatively with air temperature
and vapour pressure deficit and positively with soil water content. A temperature
response appears during spring and autumn for broadleaf forests. This shows that an
annual model parameter cannot be representative for the entire year. And relations
with mean annual temperature are not possible. During summer the photosynthesis
parameters are constrained by water availability, soil water content and vapour pressure
deficit. |
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