On temperature and water limitation of net ecosystem productivity: Implementation in the C-Fix model

Introducing water limitation and converting atmospheric temperature to apparent canopy and soil temperatures, significantly improves validation results based on EUROFLUX data. For pooled data, a final slope, intercept and correlation coefficient of the linear regression between C-Fix and EUROFLUX NEP values is 0.86, 0.09 and 0.64, respectively. When implementing full water limitation a reduction of 42% of the estimated NEP is obtained with respect to partially limited NEP. The error propagation by C-Fix for the partially and fully water limited cases and when applying temperature buffering, are similar. Respectively, an average daily NEP of 0.69 ± 0.4 and 0.40 ± 0.3 g C m−2 d−1. Due to the combination of simple semi-empirical approaches, inclusion of full water limitation into C-Fix enhances the application field of a remote sensing based model with potential in regional, continental and global dry matter estimations and in carbon uptake/release studies, although a more physically based support is recommended to convert atmospheric temperature to soil and canopy temperature and to estimate fAPAR.