Evaluating of simulated carbon flux phenology over a cropland ecosystem in a semiarid area of China with SiBcrop.

The cropland ecosystem in semiarid areas is sensitive to climate change. The accurate representation of crop phenology is important for predicting the carbon and water exchange process. The performance of a newly developed phenological model (SiBcrop) for simulations of carbon flux phenology in a semiarid area ecosystem was evaluated. The results showed that the SiBcrop improved the prediction for daily maximum gross primary production (GPP), and the days GPP reached the maximum value were closer to the observation, compared to SiB3. SiBcrop had a better prediction for both monthly total net ecosystem exchange (NEE) in the growing season than in the dormant season in semiarid areas. The day when the cumulative NEE predicted with SiBcrop became positive was closer to the observation. The observed start date of carbon uptake (CUstart) had a larger annual variation than did the end date of carbon uptake (CUend). SiBcrop had a better prediction for CUstart but poor for CUend, compared to SiB3. There was a longer carbon uptake period (CUP) predicted with SiBcrop than the observed results.