Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2021
Publication Date: 4/27/2021
Citation: Wagle, P., Skaggs, T.H., Gowda, P.H., Northup, B.K., Neel, J.P., Anderson, R.G. 2021. Evaluation of water use efficiency algorithms for flux variance similarity-based evapotranspiration partitioning in C3 and C4 grain crops. Water Resources Research. 57. Article e2020WR028866. https://doi.org/10.1029/2020WR028866.
Interpretive Summary: Partitioning of evapotranspiration (ET) into evaporation (E, unproductive water use) and transpiration (T, productive water use) has numerous important implications. Several recent studies have reported a good performance of the Flux Variance Similarity (FVS)–based ET partitioning method. The FVS partitioning requires estimating leaf–level water use efficiency (WUE). A comparison of different WUE algorithms for the FVS partitioning in different crops is lacking. In this study, we compared five WUE algorithms for the FVS method to partition ET using high frequency eddy covariance data for carbon dioxide and water vapor during peak growth in wheat, canola, soybean, maize, and grain sorghum. Considerable differences in FVS algorithm performance and partitioned fluxes (E and T) for different WUE algorithms illustrate that the choice of WUE algorithm can lead to large discrepancies in partitioned E and T fluxes.
Technical Abstract: Flux Variance Similarity (FVS)–based partitioning of evapotranspiration into evaporation (E) and transpiration (T) requires estimating leaf–level water use efficiency (WUE) if measurements are not available. The WUE can be estimated from eddy covariance (EC) data for carbon dioxide and water vapor, plus (usually) a parameterized model for the intercellular carbon dioxide concentration (ci). Despite the high sensitivity of FVS partitioning to WUE estimations, relatively little work has been done comparing ci models and WUE algorithms. We tested four ci parameterizations (Constant ppm, Constant ratio, Linear, and Square root) and one optimized WUE approach. All models were evaluated using high frequency EC data during peak growth for three rainfed C3 grain crops and two irrigated C4 grain crops. The tested models yielded considerable differences in FVS algorithm performance and partitioned T:ET ratios. The results illustrate that the choice of WUE algorithm can lead to large discrepancies in partitioned fluxes.