Vegetation index-based partitioning of evapotranspiration is deficient
in disturbed systems
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 transferability 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.