article published yes Jakob Zscheischler author Simone Fatichi author cf8e546b-a9b0-11f0-a43b-aa89ed1b56d6 Sebastian Wolf author Peter D. Blanken author Gil Bohrer author Kenneth Clark author Ankur R. Desai author David Hollinger author Trevor Keenan author Kimberly A. Novick author Sonia I. Seneviratne author Ecosystem models often perform poorly in reproducing interannual variability in carbon and water fluxes, resulting in considerable uncertainty when estimating the land‐carbon sink. While many aggregated variables (growing season length, seasonal precipitation, or temperature) have been suggested as predictors for interannual variability in carbon fluxes, their explanatory power is limited and uncertainties remain as to their relative contributions. Recent results show that the annual count of hours where evapotranspiration (ET) is larger than its 95th percentile is strongly correlated with the annual variability of ET and gross primary production (GPP) in an ecosystem model. This suggests that the occurrence of favorable conditions has a strong influence on the annual carbon budget. Here we analyzed data from eight forest sites of the AmeriFlux network with at least 7 years of continuous measurements. We show that for ET and the carbon fluxes GPP, ecosystem respiration (RE), and net ecosystem production, counting the “most active hours/days” (i.e., hours/days when the flux exceeds a high percentile) correlates well with the respective annual sums, with correlation coefficients generally larger than 0.8. Phenological transitions have much weaker explanatory power. By exploiting the relationship between most active hours and interannual variability, we classify hours as most active or less active and largely explain interannual variability in ecosystem fluxes, particularly for GPP and RE. Our results suggest that a better understanding and modeling of the occurrence of large values in high‐frequency ecosystem fluxes will result in a better understanding of interannual variability of these fluxes. https://creativecommons.org/licenses/by-nc-nd/4.0/ American Geophysical Union2016 eng 2169-8953 2169-8961 2777436710.1002/2016jg003503 12182186-2198 yes Zscheischler, J., Fatichi, S., Wolf, S., Blanken, P. D., Bohrer, G., Clark, K., … Seneviratne, S. I. (2016). Short‐term favorable weather conditions are an important control of interannual variability in carbon and water fluxes. <i>Journal of Geophysical Research: Biogeosciences</i>. American Geophysical Union. <a href="https://doi.org/10.1002/2016jg003503">https://doi.org/10.1002/2016jg003503</a> Zscheischler, Jakob, Simone Fatichi, Sebastian Wolf, Peter D. Blanken, Gil Bohrer, Kenneth Clark, Ankur R. Desai, et al. “Short‐term Favorable Weather Conditions Are an Important Control of Interannual Variability in Carbon and Water Fluxes.” <i>Journal of Geophysical Research: Biogeosciences</i>. American Geophysical Union, 2016. <a href="https://doi.org/10.1002/2016jg003503">https://doi.org/10.1002/2016jg003503</a>. Zscheischler J, Fatichi S, Wolf S, Blanken PD, Bohrer G, Clark K, Desai AR, Hollinger D, Keenan T, Novick KA, Seneviratne SI. 2016. Short‐term favorable weather conditions are an important control of interannual variability in carbon and water fluxes. Journal of Geophysical Research: Biogeosciences. 121(8), 2186–2198. Zscheischler J, Fatichi S, Wolf S, et al. Short‐term favorable weather conditions are an important control of interannual variability in carbon and water fluxes. <i>Journal of Geophysical Research: Biogeosciences</i>. 2016;121(8):2186-2198. doi:<a href="https://doi.org/10.1002/2016jg003503">10.1002/2016jg003503</a> J. Zscheischler <i>et al.</i>, “Short‐term favorable weather conditions are an important control of interannual variability in carbon and water fluxes,” <i>Journal of Geophysical Research: Biogeosciences</i>, vol. 121, no. 8. American Geophysical Union, pp. 2186–2198, 2016. Zscheischler, Jakob, et al. “Short‐term Favorable Weather Conditions Are an Important Control of Interannual Variability in Carbon and Water Fluxes.” <i>Journal of Geophysical Research: Biogeosciences</i>, vol. 121, no. 8, American Geophysical Union, 2016, pp. 2186–98, doi:<a href="https://doi.org/10.1002/2016jg003503">10.1002/2016jg003503</a>. J. Zscheischler, S. Fatichi, S. Wolf, P.D. Blanken, G. Bohrer, K. Clark, A.R. Desai, D. Hollinger, T. Keenan, K.A. Novick, S.I. Seneviratne, Journal of Geophysical Research: Biogeosciences 121 (2016) 2186–2198. 225742026-07-27T12:30:24Z2026-08-03T13:57:54Z