Improving North American terrestrial CO2 flux diagnosis using spatial structure in land surface model residuals

[摘要] We evaluate spatial structure in North American CO₂ fluxobservations using a simple diagnostic land surface model.Thevegetation photosynthesis respiration model (VPRM) calculates netecosystem exchange (NEE) using locally observed temperature andphotosynthetically active radiation (PAR) along withsatellite-derived phenology and moisture.We use observed NEE froma group of 65 North American eddy covariance tower sites spanningNorth America to estimate VPRM parameters for these sites.Weinvestigate spatial coherence in regional CO₂ fluxes atseveral different time scales by using geostatistical methods toexamine the spatial structure of model–data residuals.Wefind that persistent spatial structure does exist in the model–dataresiduals at a length scale of approximately 400 km (median402 km, mean 712 km, standard deviation931 km). This spatial structure defines a flux-tower-basedVPRM residual covariance matrix.The residual covariance matrix isuseful in constructing prior fluxes for atmospheric CO₂concentration inversion calculations, as well as for constructinga VPRM North American CO₂ flux map optimized to eddycovariance observations.Finally (and secondarily), the estimatedVPRM parameter values do not separate clearly by plant functionaltype (PFT).This calls into question whether PFTs can successfullypartition ecosystems' fundamental ecological drivers when theviewing lens is a simple model.

[学科分类] 地球化学与岩石