title: A high-resolution approach to estimating ecosystem respiration at continental scales using operational satellite data.
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.
authors.affiliation: Potsdam Institute for Climate Impact Research, RD 1: Earth System Analysis, PO-Box 601203, D-14412, Potsdam, Germany; Geography Department, Humboldt-Universität zu Berlin, Unter den Linden 6, D-10099, Berlin, Germany.
authors.forename: Jonas
authors.initials: J
authors.lastname: Jägermeyr
authors.forename: Dieter
authors.initials: D
authors.lastname: Gerten
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lucht
authors.forename: Patrick
authors.initials: P
authors.lastname: Hostert
authors.forename: Mirco
authors.initials: M
authors.lastname: Migliavacca
authors.forename: Ramakrishna
authors.initials: R
authors.lastname: Nemani
mesh_terms: D057486:Carbon Cycle; D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods*; D008962:Models, Theoretical; D063809:Satellite Imagery / Q000379:methods*; D013696:Temperature
keywords: FLUXNET; LPJmL DGVM; MODIS; RECO; land surface temperature; temperature sensitivity; terrestrial carbon flux; up-scaling