We apply and compare three widely applicable methods for estimating ecosystem transpiration (T) from eddy covariance (EC) data across 251 FLUXNET sites globally. All three methods are based on the coupled water and carbon relationship, but they differ in assumptions and parameterizations. Intercomparison of the three daily T estimates shows high correlation among methods (R between .89 and .94), but a spread in magnitudes of T/ET (evapotranspiration) from 45% to 77%. When compared at six sites with concurrent EC and sap flow measurements, all three EC-based T estimates show higher correlation to sap flow-based T than EC-based ET. The partitioning methods show expected tendencies of T/ET increasing with dryness (vapor pressure deficit and days since rain) and with leaf area index (LAI). Analysis of 140 sites with high-quality estimates for at least two continuous years shows that T/ET variability was 1.6 times higher across sites than across years. Spatial variability of T/ET was primarily driven by vegetation and soil characteristics (e.g., crop or grass designation, minimum annual LAI, soil coarse fragment volume) rather than climatic variables such as mean/standard deviation of temperature or precipitation. Overall, T and T/ET patterns are plausible and qualitatively consistent among the different water flux partitioning methods implying a significant advance made for estimating and understanding T globally, while the magnitudes remain uncertain. Our results represent the first extensive EC data-based estimates of ecosystem T permitting a data-driven perspective on the role of plants' water use for global water and carbon cycling in a changing climate.

A N Severtsov Institute of Ecology and Evolution Russian Academy of Sciences Moscow Russia

Basque Centre for Climate Change Scientific Campus of the University of the Basque Country Leioa Spain

Bioclimatology University of Goettingen Göttingen Germany

CEFE UMR 5175 CNRS Univ Montpellier Univ Paul Valéry Montpellier 3 EPHE IRD Montpellier France

Centre of Biodiversity and Sustainable Land Use University of Goettingen Goettingen Germany

CREAF Cerdanyola del Vallès Spain

Department of Atmospheric and Oceanic Sciences University of Wisconsin Madison Madison WI USA

Department of Biogeochemical Integration Max Planck Institute for Biogeochemistry Jena Germany

Department of Biological Sciences Macquarie University Sydney NSW Australia

Department of Earth and Environmental Engineering Columbia University New York NY USA

Department of Ecology University of Innsbruck Innsbruck Austria

Department of Environmental Systems Science ETH Zurich Zurich Switzerland

Department of Geography University of Colorado Boulder CO USA

Department of Geography University of Zurich Zurich Switzerland

Department of Landscape Design and Sustainable Ecosystems Agrarian Technological Institute RUDN University Moscow Russia

Department of Matter and Energy Fluxes Global Change Research Institute of the Czech Academy of Sciences Brno Czech Republic

Department of Sustainable Agro Ecosystems and Bioresources Research and Innovation Centre Fondazione Edmund Mach San Michele all'Adige Italy

Earth Institute Columbia University New York NY USA

Ecologie Systématique Evolution Univ Paris Sud CNRS AgroParisTech Université Paris Saclay Orsay France

Faculdade de Ciências e Tecnologia FCT Universidade Nova de Lisboa Lisbon Portugal

Faculty of Land and Food Systems University of British Columbia Vancouver BC Canada

Forest Service Autonomous Province of Bolzano Bozen Bolzano Bozen Italy

IKERBASQUE Basque Foundation for Science Bilbao Spain

Institute for Agricultural and Forest Systems in the Mediterranean Ercolano Italy

Institute for Atmospheric and Earth System Research INAR Physics Faculty of Science University of Helsinki Helsinki Finland

Institute of Agricultural Sciences ETH Zurich Zurich Switzerland

Institute of Bioeconomy Firenze Italy

Karlsruhe Institute of Technology Institute of Meteorology and Climate Research Atmospheric Environmental Research Garmisch Partenkirchen Germany

Laboratory of Geo Information Science and Remote Sensing Wageningen University and Research Center Wageningen The Netherlands

Lamont Doherty Earth Observatory of Columbia University Palisades NY USA

Michael Stifel Center Jena for Data Driven and Simulation Science Jena Germany

Southwest Watershed Research Center USDA ARS Tucson AZ USA

Universitat Autònoma de Barcelona Cerdanyola del Vallès Spain

Université de Lorraine AgroParisTech INRA UMR Silva Nancy France

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