Using satellite data to improve the leaf phenology of a global terrestrial biosphere model
Correct representation of seasonal leaf dynamics is crucial for terrestrial biosphere models (TBMs), but many such models cannot accurately reproduce observations of leaf onset and senescence. Here we optimised the phenology-related parameters of the ORCHIDEE TBM using satellite-derived Normalized D...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-12-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/12/7185/2015/bg-12-7185-2015.pdf |
| Summary: | Correct representation of seasonal leaf dynamics is crucial for terrestrial
biosphere models (TBMs), but many such models cannot accurately reproduce
observations of leaf onset and senescence. Here we optimised the
phenology-related parameters of the ORCHIDEE TBM using satellite-derived
Normalized Difference Vegetation Index data (MODIS NDVI v5) that are linearly
related to the model fAPAR. We found the misfit between the observations and
the model decreased after optimisation for all boreal and temperate deciduous
plant functional types, primarily due to an earlier onset of leaf senescence.
The model bias was only partially reduced for tropical deciduous trees and no
improvement was seen for natural C4 grasses. Spatial validation demonstrated
the generality of the posterior parameters for use in global simulations,
with an increase in global median correlation of 0.56 to 0.67. The simulated
global mean annual gross primary productivity (GPP) decreased by
~ 10 PgC yr<sup>−1</sup> over the 1990–2010 period due to the substantially
shortened growing season length (GSL – by up to 30 days in the Northern
Hemisphere), thus reducing the positive bias and improving the seasonal
dynamics of ORCHIDEE compared to independent data-based estimates. Finally,
the optimisations led to changes in the strength and location of the trends
in the simulated vegetation productivity as represented by the GSL and mean
annual fraction of absorbed photosynthetically active radiation (fAPAR),
suggesting care should be taken when using un-calibrated models in
attribution studies. We suggest that the framework presented here can be
applied for improving the phenology of all global TBMs. |
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| ISSN: | 1726-4170 1726-4189 |