Simultaneous assimilation of satellite and eddy covariance data for improving terrestrial water and carbon simulations at a semi-arid woodland site in Botswana

[摘要] Terrestrialproductivity in semi-arid woodlands is strongly susceptible tochanges in precipitation, and semi-arid woodlands constitute an importantelement of the global water and carbon cycles. Here, we use the Carbon CycleData Assimilation System (CCDAS) to investigate the key parameterscontrolling ecological and hydrological activities for a semi-arid savannawoodland site in Maun, Botswana. Twenty-four eco-hydrological processparameters of a terrestrial ecosystem model are optimized against two datastreams separately and simultaneously: daily averaged latent heat flux (LHF)derived from eddy covariance measurements, and decadal fraction of absorbedphotosynthetically active radiation (FAPAR) derived from the Sea-viewing WideField-of-view Sensor (SeaWiFS).

Assimilation of both data streams LHF and FAPAR for the years 2000 and 2001leads to improved agreement between measured and simulated quantities notonly for LHF and FAPAR, but also for photosynthetic CO₂ uptake. Themean uncertainty reduction (relative to the prior) over all parameters is14.9% for the simultaneous assimilation of LHF and FAPAR, 8.5% forassimilating LHF only, and 6.1% for assimilating FAPAR only. Theset of parameters with the highest uncertainty reduction is similar betweenassimilating only FAPAR or only LHF. The highest uncertainty reduction forall three cases is found for a parameter quantifying maximum plant-availablesoil moisture. This indicates that not only LHF but also satellite-derivedFAPAR data can be used to constrain and indirectly observe hydrologicalquantities.

[学科分类] 地球化学与岩石