New Parameterization of a Global Vegetation Model for Steppe Ecosystem From Southern Siberian In Situ Measurements

Abstract

This article presents a new parameterization of the global vegetation organizing carbon and hydrology in dynamic ecosystems (ORCHIDEE) model, modifying the assimilation, allocation, and phenology processes for a steppe ecosystem. It aims 1) to improve the modeled growth primary production (GPP) based on both in situ CO2 flux measurements and remote-sensing data of the fraction of absorbed photosynthetic radiation, and 2) to evaluate how GPP improvement results in better-modeled fluxes for ecosystem respiration, net ecosystem exchange, and latent heat. This new parameterization leads to a realistic annual GPP (comparable to the data within 10%), and a realistic seasonal variability of GPP (R2 = 0.80). Further, we found that improving GPP into ORCHIDEE immediately brings ecosystem respiration and net ecosystem exchange fluxes into better agreement with the eddy-covariance data, both on seasonal but also on interannual time scales. This result suggests that the response of this steppe ecosystem to interannual climate variations can be well reproduced from the response to seasonal variation, and that biotic effects are not interannual. This indicates the potential ability to reproduce climate-induced changes in the carbon balance of steppes with the use of a generic process-oriented vegetation model such as ORCHIDEE.