B31E-03
Short-Term Weather Variability is an Important Control of Interannual Variability in Carbon and Water Fluxes in Temperate Forests

Wednesday, 16 December 2015: 08:30
2004 (Moscone West)
Jakob Zscheischler1, Peter Blanken2, Gil Bohrer3, Kenneth L Clark4, Ankur R Desai5, Simone Fatichi6, David Y Hollinger7, Trevor F Keenan8, Kimberly A Novick9, Sebastian Wolf1 and Sonia I Seneviratne1, (1)ETH Zurich, Zurich, Switzerland, (2)University of Colorado, Boulder, Boulder, CO, United States, (3)Ohio State University Main Campus, Civil, Environmental & Geodetic Engineering, Columbus, OH, United States, (4)USDA Forest Service, Northern Research Station, New Lisbon, NJ, United States, (5)University of Wisconsin Madison, Madison, WI, United States, (6)ETH Swiss Federal Institute of Technology Zurich, Zurich, Switzerland, (7)USDA Forest Service, Durham, NH, United States, (8)Macquarie University, Sydney, Australia, (9)Indiana University Bloomington, School of Public and Environmental Affairs, Bloomington, IN, United States
Abstract:
Land surface models perform poorly for interannual variability in carbon and water fluxes, resulting in considerable uncertainty when estimating the land-carbon sink or making future projections. While many aggregated variables (e.g. growing season length, annual precipitation, growing season temperature, and phenology among others) have been suggested as predictors for the variability of annual sums in carbon fluxes, their explanatory power remains limited and uncertainties remain as to the relative contribution of each. Recent results suggest that the annual count of hours where evapotranspiration (ET) is larger than its 95th percentile (denoted as "good hours") is highly correlated with the annual variability of ET and gross primary production (GPP) in an ecosystem model (Fatichi and Ivanov, 2014). This suggests that the occurrence of favourable conditions driven by short-term weather fluctuations have a strong influence on the annual carbon budget.

Here we analyse data from 8 forest sites of the AmeriFlux network, each having at least 8 years of continuous measurements. We show that for ET and all carbon fluxes (GPP, ecosystem respiration and net ecosystem exchange), counting “good hours/days” (i.e., hours/days when the flux exceeds a high percentile) correlates well with the respective annual sums (with correlations generally larger than 0.8). By exploiting this relationship and classifying hours/days as good or not good, interannual variability in ET and carbon fluxes can be predicted well by climate variables. We explore the implications of our results for understanding the dominant processes responsible for interannual variability in carbon and water fluxes.

Reference: Fatichi, S. and V. Y. Ivanov (2014) Interannual variability of evapotranspiration and vegetation productivity, Water Resources Research, 50, 3275-3294.

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