Critical comparison of actual evapotranspiration estimates using ground based, remotely sensed, and simulated data in the USA

Abstract

Agriculture is a major consumptive user of water through evapotranspiration (ET). Quantification of actual ET (ET_a) is of significant interest to better address water management and improve decision making in the agricultural sector. Many methods to estimate ET are available. However, due to the increasing need of validation of estimates of ET from various techniques, there arises a call for a critical comparison of ET_a estimated from a combination of methods. This research presents a critical comparison of ET_a estimates obtained using ground based (eddy covariance), remotely sensed (ET ensemble), and simulated data (a crop-soil-water balance model, SIMETAW#). The study focuses on experimental sites in Nebraska, Oklahoma and California (USA). Results show a relatively small and consistent variation between the three methods. The results are relatively close giving a reasonable impression of the expected ET_a at a site including variability which is useful to address agricultural practices. The estimates from remote sensing deviate from the other two methods since the method used is relatively new and requires further research to improve measurements and ET estimation. This study offers water managers at the sites new information for reliable, multi-source ET estimation for water resources planning and the study is in principle replicable at different locations.