Sampling strategies to estimate field areal evapotranspiration fluxes with a soil water balance approach

In this paper, we analyse the spatio-temporal variability of instantaneous and cumulated evapotranspiration (ET) fluxes measured during two long drying periods with a soil water balance approach on 28 point measurements located within a small maize cropped field. Then we test three sampling procedures to estimate field averaged ET and their associated uncertainty. Results of this study show that the ‘within-field’ spatial variability of the local scale instantaneous measured ET is large with coefficients of variation ranging between 15.5 and 46.3%. The corresponding cumulated ET for the first and the second period ranges between 39.4–107.5 and 30.3–55.7 mm, respectively. We show that this variability of ET fluxes can be related in some way to the measured spatially variable crop growth (2.2