Determination of crop evapotranspiration of table grapes in a semi-arid region of Northwest Mexico using multi-spectral vegetation index

The main goal of this research is to develop and to evaluate a relationship established between Normalized Difference Vegetation Index (NDVI) and crop coefficient (Kc) for estimating crop evapotranspiration (ETc) of table grapes vineyards (Vitis vinifera L., cvs. Perlette and Superior) in the semi-arid region of Northwest Mexico. Two consecutive growing seasons (2005 and 2006) of continuous measurements of ETc with the eddy covariance system were used to test the performance of the Kc–NDVI relationship. An exponential relation relating Kc to NDVI (R2 = 0.63) is proposed and tested here as the basis for calculating ETc. The obtained results indicate that the Kc–NDVI approach estimates ETc reasonably well over two growing seasons. The root mean square error (RMSE) between measured and derived ETc from NDVI during 2005 and 2006 were respectively about 0.45 and 0.76 mm day−1. Some discrepancies between measured and simulated ETc occurred when NDVI saturates at high values, causing the under-estimation of evapotranspiration.