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Abstract

A better understanding of the local variability in land-atmosphere carbon fluxes is crucial to improving the accuracy
of global carbon budgets. Operational satellite data backed by ground measurements at Fluxnet sites proved valuable
in monitoring local variability of gross primary production at highly resolved spatio-temporal resolutions. Yet, we
lack similar operational estimates of ecosystem respiration (Re) to calculate net carbon fluxes. If successful, carbon
fluxes from such a remote sensing approach would form an independent and sought after measure to complement
widely used dynamic global vegetation models (DGVMs).
Here, we establish an operational semi-empirical Re model, based only on data from the Moderate Resolution
Imaging Spectroradiometer (MODIS) with a resolution of 1 km and 8 days. Fluxnet measurements between 2000 and
2009 from 100 sites across North America and Europe are used for parameterization and validation.
Our analysis shows that Re is closely tied to temperature and plant productivity. By separating temporal and intersite
variation, we find that MODIS land surface temperature (LST) and enhanced vegetation index (EVI) are sufficient
to explain observed Re across most major biomes with a negligible bias [R² = 0.62, RMSE = 1.32 (g C m
2 d
1),
MBE = 0.05 (g C m
2 d
1)].
A comparison of such satellite-derived Re with those simulated by the DGVM LPJmL reveals similar spatial
patterns. However, LPJmL shows higher temperature sensitivities and consistently simulates higher Re values, in
high-latitude and subtropical regions. These differences remain difficult to explain and they are likely associated
either with LPJmL parameterization or with systematic errors in the Fluxnet sampling technique. While uncertainties
remain with Re estimates, the model formulated in this study provides an operational, cross-validated and unbiased
approach to scale Fluxnet Re to the continental scale and advances knowledge of spatio-temporal Re variability.