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B. Mueller¹, M. Hirschi¹, C. Jimenez², P. Ciais³, P. A. Dirmeyer⁴, A. J. Dolman⁵, J. B. Fisher⁶, M. Jung⁷, F. Ludwig⁸, F. Maignan³, D. G. Miralles⁹, M. F. McCabe¹⁰, M. Reichstein⁷, J. Sheffield¹¹, K. Wang¹², E. F. Wood¹¹, Y. Zhang¹³, and S. I. Seneviratne¹

 

¹ Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland;

² LERMA, Observatoire de Paris, Paris, France;

³ LSCE, UMR CEA-CNRS, Gif-sur-Yvette, France;

⁴ George Mason University, Fairfax, Virginia, USA;

⁵ VU University Amsterdam, the Netherlands;

⁶ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA;

⁷ Max Planck Institute for Biogeochemistry, Jena, Germany;

⁸ Wageningen University, Wageningen, the Netherlands;

⁹ School of Geographical Sciences, University of Bristol, UK;

¹⁰ Water Desalination and Reuse Center, King Abdullah University of Science and Technology, Kingdom of Saudi Arabia;

¹¹ Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey, USA;

¹² College of Global Change and Earth System Science, Beijing Normal University, Beijing, China;

¹³ CSIRO Land and Water, Canberra, Australia.

 

ABSTRACT

Land evapotranspiration (ET) estimates are available from several global datasets. Here, monthly global land ET synthesis products, merged from these individual datasets over the time periods 1989–1995 (7 yr) and 1989–2005 (17 yr), are presented. The merged synthesis products over the shorter period are based on a total of 40 distinct datasets while those over the longer period are based on a total of 14 datasets. In the individual datasets, ET is derived from satellite and/or in-situ observations (diagnostic datasets) or calculated via land-surface models (LSMs) driven with observations-based forcing and atmospheric reanalyses. Statistics for four merged synthesis products are provided, one including all datasets and three including only datasets from one category each (diagnostic, LSMs, and reanalyses). The multi-annual variations of ET in the merged synthesis products display realistic responses. They are also consistent with previous findings of a global increase in ET between 1989 and 1997 (1.15 mm yr−2 in our merged product) followed by a decrease in this trend (−1.40 mm yr−2), although these trends are relatively small compared to the uncertainty of absolute ET values. The global mean ET from the merged synthesis products (based on all datasets) is 1.35 mm per day for both the 1989–1995 and 1989–2005 products, which is relatively low compared to previously published estimates. We estimate global runoff (precipitation minus ET) to 34 406 km3 per year for a total land area of 130 922 km2. Precipitation, being an important driving factor and input to most simulated ET datasets, presents uncertainties between single datasets as large as those in the ET estimates. In order to reduce uncertainties in current ET products, improving the accuracy of the input variables, especially precipitation, as well as the parameterizations of ET are crucial.

 

PUBLISHED BY: HYDROLOGY AND EARTH SYSTEM SCIENCES, 2013, 17 (10): 3707-3720.

 

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