Climate and vegetation controls on the surface water balance: Synthesis of evapotranspiration measured across a global network of flux towers

Water Resources Research - Tập 48 Số 6 - 2012
C. A. Williams1, Markus Reichstein2, Nina Buchmann3, Dennis Baldocchi4, Christian Beer2, Christopher R. Schwalm1, Georg Wohlfahrt5, Natalia Hasler1, Christian Bernhofer6, Thomas Foken7, Dario Papale8, Stanislaus J. Schymanski2, Kevin Schaefer9
1Graduate School of Geography, Clark University, Worcester, Massachusetts, USA
2Max Planck Institute for Biogeochemistry, Jena, Germany
3ETH Zürich, Zürich, Switzerland
4Environmental Science, Policy and Management University of California Berkeley Berkeley California USA
5Institute of Ecology, University of Innsbruck, Innsbruck, Austria
6[Institute of Hydrology and Meteorology, Technische Universitat Dresden, Dresden, Germany]
7Department of Micrometeorology, University of Bayreuth, Bayreuth, Germany
8Department for Innovation in Biological, Agro-food and Forestry, University of Tuscia,Viterbo,Italy
9National Snow and Ice Data Center, University of Colorado, Boulder, Colorado, USA

Tóm tắt

The Budyko framework elegantly reduces the complex spatial patterns of actual evapotranspiration and runoff to a general function of two variables: mean annual precipitation (MAP) and net radiation. While the methodology has first‐order skill, departures from a globally averaged curve can be significant and may be usefully attributed to additional controls such as vegetation type. This paper explores the magnitude of such departures as detected from flux tower measurements of ecosystem‐scale evapotranspiration, and investigates their attribution to site characteristics (biome, seasonal rainfall distribution, and frozen precipitation). The global synthesis (based on 167 sites with 764 tower‐years) shows smooth transition from water‐limited to energy‐limited control, broadly consistent with catchment‐scale relations and explaining 62% of the across site variation in evaporative index (the fraction of MAP consumed by evapotranspiration). Climate and vegetation types act as additional controls, combining to explain an additional 13% of the variation in evaporative index. Warm temperate winter wet sites (Mediterranean) exhibit a reduced evaporative index, 9% lower than the average value expected based on dryness index, implying elevated runoff. Seasonal hydrologic surplus explains a small but significant fraction of variance in departures of evaporative index from that expected for a given dryness index. Surprisingly, grasslands on average have a higher evaporative index than forested landscapes, with 9% more annual precipitation consumed by annual evapotranspiration compared to forests. In sum, the simple framework of supply‐ or demand‐limited evapotranspiration is supported by global FLUXNET observations but climate type and vegetation type are seen to exert sizeable additional controls.

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Tập 48 Số 6

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