Effects of in-situ and reanalysis climate data on estimation of cropland gross primary production using the Vegetation Photosynthesis Model

摘要

Satellite-based Production Efficiency Models (PEMs) often require meteorological reanalysis data such as the North America Regional Reanalysis (NAAR) by the National Centers for Environmental Prediction (NCEP) as model inputs to simulate Gross Primary Production (GPP) at regional and global scales. This study first evaluated the accuracies of air temperature (T-NARR) and downward shortwave radiation (R-NARR) of the NARR by comparing with in-situ meteorological measurements at 37 AmeriFlux non-crop eddy flux sites, then used one PEM - the Vegetation Photosynthesis Model (VPM) to simulate 8-day mean GPP (GPP(VPM)) at seven AmeriFlux crop sites, and investigated the uncertainties in GPP(VPM) from climate inputs as compared with eddy covariance-based GPP (GPP(EC)). Results showed that TNARR agreed well with in-situ measurements; RNARR, however, was positively biased. An empirical linear correction was applied to RNARR, and significantly reduced the relative error of RNARR by similar to 25% for crop site-years. Overall, GPP(VPM) calculated from the in-situ (GPP(VPM(EC))), original (GPP(VPM(NARR))) and adjusted NARR (GPP(VPM(adjNARR))) climate data tracked the seasonality of GPP(EC) well, albeit with different degrees of biases. GPP(VPM(EC)) showed a good match with GPP(EC) for maize (Zea mays L), but was slightly under-estimated for soybean (Glycine max L.). Replacing the in-situ climate data with the NARR resulted in a significant overestimation of GPP(VPM(NARR)) (18.4/29.6% for irrigated/rainfed maize and 12.7/12.5% for irrigated/rainfed soybean). GPP(VPM(adjNARR)) showed a good agreement with GPP(VPM(EC)) for both crops due to the reduction in the bias of R-NARR. The results imply that the bias of R-NARR introduced significant uncertainties into the PEM-based GPP estimates, suggesting that more accurate surface radiation datasets are needed to estimate primary production of terrestrial ecosystems at regional and global scales. (C) 2015 Elsevier B.V. All rights reserved.