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ARS Home » Plains Area » El Reno, Oklahoma » Oklahoma and Central Plains Agricultural Research Center » Livestock, Forage and Pasture Management Research Unit » Research » Publications at this Location » Publication #389525
Research Project: Integrated Agroecosystem Research to Enhance Forage and Food Production in the Southern Great Plains

Location: Livestock, Forage and Pasture Management Research Unit

Title: Vegetation index-based partitioning of evapotranspiration is deficient in grazed systems

Author
item RAGHAV, PUSHPENDRA - University Of Alabama
item Wagle, Pradeep
item KUMAR, MUKESH - University Of Alabama
item BANERJEE, TIRTHA - University Of California Irvine
item Neel, James

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/2022
Publication Date: 8/22/2022
Citation: Raghav, P., Wagle, P., Kumar, M., Banerjee, T., Neel, J.P. 2022. Vegetation index-based partitioning of evapotranspiration is deficient in grazed systems. Water Resources Research. 58(8):e2022WR032067. https://doi.org/10.1029/2022WR032067.
DOI: https://doi.org/10.1029/2022WR032067

Interpretive Summary: Evapotranspiration (ET) plays a significant role in water and climate cycles by affecting the energy and water balance over the land surface. ET is composed of two primary components i.e., direct evaporation (E) and plant transpiration (T). Partitioning of total ET into its individual components (E and T) is of significant importance for better assessment of both regional and global water budgets. One of the primary approaches to partition ET over large areas is by using satellite-derived vegetation indices (VI), which indirectly capture plants' biophysical state. This approach has been used to partition ET in different landscapes, but its efficacy has not been tested in disturbed (e.g., grazed) systems, which cover a large fraction of earth's vegetated area. The effectiveness of this VI-based ET partitioning approach was assessed in disturbed (i.e., grazed) wheat systems. The VI-based ET partitioning introduced large errors in disturbed systems. Further investigation identifies conditions that can be used to filter-out regions where the VI-based partition is likely to be more (or less) effective

Technical Abstract: Partitioning evapotranspiration (ET) into its primary components, i.e., evaporation (E) and plant transpiration (T), is needed in a range of hydrometeorological applications. Using vegetation index (VI) to obtain spatially resolved T:ET ratio over large areas has emerged as a promising approach in this regard. Here, we assess the effectiveness of this approach in differently managed wheat systems. Results show a weak relation between T:ET and VI in disturbed (i.e., grazed) systems. Flux partitions based on a canonical T:ET vs. VI relation or one derived in a neighboring undisturbed wheat system introduce large errors in disturbed systems, thus underscoring the limits on the translatability of the VI-based ET partitioning approach. The effectiveness of the VI-based approach is found to be related to the strength of correlation between VI and vapor pressure deficit and/or radiation. This correlation metric can help identify settings where the approach is likely to be effective.