Reprocessing scintillometer data to describe evapotranspiration fluxes in a semi-arid region: analysis of the effectiveness of different theoretical methods

Abstract:

The Central valley of Chile is a semiarid region where water is crucial for agriculture and natural habitats. However, during the past few years it has faced a water scarcity problem due to droughts as a result of decreased precipitation and additional water loss through evapotranspiration (ET), which will become worse in the future due to climate change. Therefore, precise ET data are crucial for water security in this region and to face the challenge of sustainable practices in agriculture.

Agricultural fields that are over-irrigated present ET rates highly influenced by dry air advection during sub-hourly temporal scales. These rates have been seen smaller than those computed by remote sensing at spatial scales, but larger than those computed by traditional in-situ methods. In a previous study, ET water loss influenced mostly by advection was quantified in an irrigated vineyard in Pirque, Chile. An Eddy Covariance system (EC) and an optical-microwave scintillometer (OMS) were used to compute ET fluxes and surface energy balances. However, the OMS data were altered by wind currents overestimating fluxes and therefore, reprocessing the data is needed to make a proper flux quantification. In this study, OMS data were reprocessed through spectral analysis to eliminate unwanted contributions to the scintillometer signal due to wind currents. Once the signal was filtered, heat fluxes were calculated using four methods previously developed. The results of these methods are compared to those obtained by the EC system, concluding the effectiveness and accuracy of each one of them. A discussion is provided about the improvement of methods and how the accurate measurement of ET fluxes can promote sustainable practices.