Assessing satellite-based basal crop coefficients for irrigated grapes (Vitis vinifera L.)

A combined methodology of basal crop coefficient (Kcb) derived from vegetation indices (VI) obtained from satellite images and a daily soil water balance in the root zone of the crop was proposed to accurately estimate the daily grape crop coefficient and actual evapotranspiration. The modeled values were compared with field measurements of crop evapotranspiration (ET) using an energy balance eddy-covariance flux tower and adjusted for closure using the measured Bowen ratio. A linear relation between Kcb and VI for vineyard was obtained, Kcb = 1.44 × NDVI-0.10 and Kcb = 1.79 × SAVI-0.08. The correlation of the measured crop coefficient (Kc) and modeled (Kcrf) exhibits a linear tendency, Kc = 0.96Kcrf, r2 = 0.67. Other derived parameters such as weekly Kc and daily and weekly ET show good consistency with measurements and higher coefficients of determination. The study of the soil water balance suggests the importance of soil water storage in grapes within the La Mancha region. These results validate the use of remote sensing as a tool for the estimation of evapotranspiration of irrigated wine grapes planted on trellis systems.