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I'm trying to understand transpiration estimation methods. The FAO recommends a standard Penman-Monteith methodology for modeling evapotranspiration based on meteorological and vegetation parameters (ie. wind speed, leaf area index). Many eco-hydrology models make use of the Penman-Monteith equations, some with minor modifications.

I understand the Penman-Monteith equations, and modification thereof, are simplifications of complex processes. It would be impractical to measure actual transpiration in all conditions where that information is useful, so we model it instead. That said, field observations in the development or support of models is valuable for verifying knowledge gained through models.

My question is: what field studies have developed or supported Penman-Monteith equations (or modified versions of it)? In a sense there is indirect verification of the equations through field measurement verification of results from models that implement the Penman-Monteith equations. Are there any direct field measurements of (evapo-)transpiration that support (or even helped develop) the Penman-Monteith equations, to demonstrate the equations' validity in real world conditions?

cr0
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  • I changed my search methods and am having a little better luck finding field studies putting P-M findings to the test. I may come back and answer this myself sometime over the next week. For now, I'll comment with some articles that may be applicable. – cr0 Mar 17 '17 at 15:59
  • https://escholarship.org/uc/item/4q78h1tw#page-2 – cr0 Mar 17 '17 at 15:59
  • http://ccc.atmos.colostate.edu/ET_Workshop/pdf/2_Allen.pdf – cr0 Mar 17 '17 at 15:59
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    Are you interested in studies that demonstrate that the model parameters act in the way that they are incorporated into the model or in studies that compare Penman-Monteith to other estimation methods such as water balance estimates? Probably the best place to look for comparison to direct measurements is the literature on the global eddy-covariance flux measurements - https://fluxnet.ornl.gov/ – haresfur Mar 22 '17 at 00:01
  • I think the former - studies demonstrating that model parameters act in the way they are incorporated into the model. Really I am looking for comparison to direct measurements. I'll look into your suggestion, thanks. – cr0 Mar 22 '17 at 15:54
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    While not directly integrated in the official FAO documentation, a dense bibliography is appended at the end of it: http://www.fao.org/docrep/X0490E/x0490e0q.htm#b.%20et%20equations – Delforge Apr 20 '17 at 08:19
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    @Delforge I've converted your answer to a comment because it doesn't answer the question. – gerrit Apr 20 '17 at 13:14
  • @Delforge that bibliography looks useful but as I try to follow threads from it that sound like field studies, I'm not easily finding the cited sources. E.g. "Phene, C. J., dark, D. A. and Cardon, G. E. 1996. Real time calculation of crop evapotranspiration using an automated pan evaporation system. In: Camp, C. R., Sadler, E. J. and Yoder, R. E. (eds.). Evaporation and Irrigation Scheduling, ASCE: 189-194." does not appear to be accessible online. The search continues! – cr0 Apr 20 '17 at 13:46
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    @cr0 In addition, you may find useful references and some descriptions about experimental setups in a recent review: Crop Evapotranspiration (ET) Estimation Models: A Review and Discussion of the Applicability and Limitations of ET Methods. If you want to read Penman first paper (1948) [Natural Evaporation From Open Water, Bare Soil and Grass]where he described his field measurements, it is available online. – Delforge Apr 20 '17 at 14:24

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