Evaluation of an empirical piecewise regression model in simulating GPP in the Northern Great Plains

For better understanding the carbon fluxes in the grassland ecosystems, an empirical piecewise regression (PWR) model was developed to estimate gross primary production (GPP) in the Northern Great Plains. The PWR model spatially scales up the localized flux tower measurements across an ecoregion at 1-km resolution. In this study, cross-validation was employed to evaluate the robustness of the PWR model. The PWR GPP developed from five flux towers and MODIS GPP were then compared with the tower-measured GPP. The GPP spatial maps from the PWR and MODIS models were also compared for grasslands for the entire study area. The PWR GPP was lower than, or similar to, the MODIS GPP in the east and higher in the west and south. Environmental factors that may contribute to the spatial patterns of the GPP differences between the two models were evaluated using a decision tree technique.