Using satellite data to improve the leaf phenology of a global terrestrial biosphere model

[摘要] Correct representation of seasonal leaf dynamics is crucial for terrestrialbiosphere models (TBMs), but many such models cannot accurately reproduceobservations of leaf onset and senescence. Here we optimised thephenology-related parameters of the ORCHIDEE TBM using satellite-derivedNormalized Difference Vegetation Index data (MODIS NDVI v5) that are linearlyrelated to the model fAPAR. We found the misfit between the observations andthe model decreased after optimisation for all boreal and temperate deciduousplant functional types, primarily due to an earlier onset of leaf senescence.The model bias was only partially reduced for tropical deciduous trees and noimprovement was seen for natural C4 grasses. Spatial validation demonstratedthe generality of the posterior parameters for use in global simulations,with an increase in global median correlation of 0.56 to 0.67. The simulatedglobal mean annual gross primary productivity (GPP) decreased by~ 10 PgC yr⁻¹ over the 1990–2010 period due to the substantiallyshortened growing season length (GSL – by up to 30 days in the NorthernHemisphere), thus reducing the positive bias and improving the seasonaldynamics of ORCHIDEE compared to independent data-based estimates. Finally,the optimisations led to changes in the strength and location of the trendsin the simulated vegetation productivity as represented by the GSL and meanannual fraction of absorbed photosynthetically active radiation (fAPAR),suggesting care should be taken when using un-calibrated models inattribution studies. We suggest that the framework presented here can beapplied for improving the phenology of all global TBMs.

[学科分类] 地球化学与岩石