Daily underlying water use efficiency for AmeriFlux sites

Water use efficiency (WUE) is a crucial parameter to describe the interrelationship between gross primary production (GPP) and evapotranspiration (ET). Incorporating the nonlinear effect of vapor pressure deficit (VPD), underlying WUE (uWUE = GPP · VPD0.5/ET) is better than inherent WUE (IWUE = GPP · VPD/ET) at the half-hourly time scale. However, appropriateness of uWUE has not yet been evaluated at the daily time scale. To determine whether uWUE is better than IWUE, daily data for seven vegetation types from 34 AmeriFlux sites were used to validate uWUE at the daily time scale. First, daily mean VPD was shown to be a good substitute for the effective VPD that was required to preserve daily GPP totals. Second, an optimal exponent, k*, corresponding to the best linear relationship between GPP · VPDk* and ET, was about 0.55 both at half-hourly and daily time scales. Third, correlation coefficient between GPP · VPDk and ET showed that uWUE (k = 0.5 and r = 0.85) was a better approximation of the optimal WUE (k = k* and r = 0.86) than IWUE (k = 1 and r = 0.81) at the daily scale. Finally, when yearly uWUE was used to predict daily GPP from daily ET and mean VPD, uWUE worked considerably better than IWUE. Comparing observed and predicted daily GPP, the average correlation coefficient and Nash-Sutcliffe coefficient of efficiency were 0.81 and 0.59, respectively, using yearly uWUE, and only 0.59 and −0.83 using yearly IWUE. As a nearly optimal WUE, uWUE consistently outperformed IWUE and could be used to evaluate the effects of global warming and elevated atmosphere CO2 on carbon assimilation and evapotranspiration.

[1]  R. Valentini,et al.  A new assessment of European forests carbon exchanges by eddy fluxes and artificial neural network spatialization , 2003 .

[2]  M. Battaglia,et al.  Constraints on transpiration of Eucalyptus globulus in southern Tasmania, Australia , 2008 .

[3]  H. Fallahi,et al.  Water Use Efficiency of Wheat , 2013 .

[4]  T. Vesala,et al.  On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm , 2005 .

[5]  Markus Reichstein,et al.  Mean annual GPP of Europe derived from its water balance , 2007 .

[6]  Josep Peñuelas,et al.  Twentieth century changes of tree‐ring δ13C at the southern range‐edge of Fagus sylvatica: increasing water‐use efficiency does not avoid the growth decline induced by warming at low altitudes , 2008 .

[7]  J. Nash,et al.  River flow forecasting through conceptual models part I — A discussion of principles☆ , 1970 .

[8]  S. Niu,et al.  Water‐use efficiency in response to climate change: from leaf to ecosystem in a temperate steppe , 2011 .

[9]  Josep Peñuelas,et al.  Increased water‐use efficiency during the 20th century did not translate into enhanced tree growth , 2011 .

[10]  Tim R. McVicar,et al.  Prediction of crop yield, water consumption and water use efficiency with a SVAT-crop growth model using remotely sensed data on the North China Plain , 2005 .

[11]  Gianni Bellocchi,et al.  Sharing knowledge via software components: Models on reference evapotranspiration , 2006 .

[12]  C. Peng,et al.  Evaluating the effects of future climate change and elevated CO2 on the water use efficiency in terrestrial ecosystems of China , 2011 .

[13]  Ge Sun,et al.  Model estimates of net primary productivity, evapotranspiration, and water use efficiency in the terrestrial ecosystems of the southern United States during 1895–2007 , 2010 .

[14]  F. Woodward,et al.  Global response of terrestrial ecosystem structure and function to CO2 and climate change: results from six dynamic global vegetation models , 2001 .

[15]  Li Yingnian,et al.  Carbon Dioxide Exchange Between the Atmosphere and an Alpine Shrubland Meadow During the Growing Season on the Qinghai-Tibetan Plateau , 2005 .

[16]  Motoko Inatomi,et al.  Water-Use Efficiency of the Terrestrial Biosphere: A Model Analysis Focusing on Interactions between the Global Carbon and Water Cycles , 2012 .

[17]  R. Norby,et al.  Elevated CO₂ increases tree-level intrinsic water use efficiency: insights from carbon and oxygen isotope analyses in tree rings across three forest FACE sites. , 2013, The New phytologist.

[18]  Guirui Yu,et al.  Effects of vegetation control on ecosystem water use efficiency within and among four grassland ecosystems in China , 2008 .

[19]  E. Gutiérrez,et al.  Long tree‐ring chronologies reveal 20th century increases in water‐use efficiency but no enhancement of tree growth at five Iberian pine forests , 2011 .

[20]  A. Porporato,et al.  The hysteretic evapotranspiration—Vapor pressure deficit relation , 2013 .

[21]  Di Long,et al.  Remote estimation of terrestrial evapotranspiration without using meteorological data , 2013 .

[22]  Bofu Yu,et al.  The effect of vapor pressure deficit on water use efficiency at the subdaily time scale , 2014 .

[23]  Nuno Carvalhais,et al.  Characterizing ecosystem-atmosphere interactions from short to interannual time scales , 2007 .

[24]  Donatella Zona,et al.  Carbon and water vapor fluxes over four forests in two contrasting climatic zones , 2013 .

[25]  Markus Reichstein,et al.  Temporal and among‐site variability of inherent water use efficiency at the ecosystem level , 2009 .

[26]  Hans Peter Schmid,et al.  Increase in forest water-use efficiency as atmospheric carbon dioxide concentrations rise , 2013, Nature.

[27]  X. Mo,et al.  Responses of crop yield and water use efficiency to climate change in the North China Plain , 2010 .

[28]  P. Abbate,et al.  Climatic and Water Availability Effects on Water‐Use Efficiency in Wheat , 2004 .

[29]  I. R. Cowan,et al.  Stomatal function in relation to leaf metabolism and environment. , 1977, Symposia of the Society for Experimental Biology.

[30]  X. Shao,et al.  Long-term trends in intrinsic water-use efficiency and growth of subtropical Pinus tabulaeformis Carr. and Pinus taiwanensis Hayata in central China , 2014, Journal of Soils and Sediments.

[31]  Markus Reichstein,et al.  Cross-site evaluation of eddy covariance GPP and RE decomposition techniques , 2008 .

[32]  G. Farquhar,et al.  13C discrimination during CO2 assimilation by the terrestrial biosphere , 1994, Oecologia.

[33]  A. Rigling,et al.  Increased water-use efficiency does not lead to enhanced tree growth under xeric and mesic conditions. , 2014, The New phytologist.

[34]  Atul K. Jain,et al.  Forest water use and water use efficiency at elevated CO2: a model‐data intercomparison at two contrasting temperate forest FACE sites , 2013, Global change biology.

[35]  Michael Grabner,et al.  Long‐term increases in intrinsic water‐use efficiency do not lead to increased stem growth in a tropical monsoon forest in western Thailand , 2011 .

[36]  C. Priestley,et al.  On the Assessment of Surface Heat Flux and Evaporation Using Large-Scale Parameters , 1972 .