•The values of αc in the generalized nonlinear complementary relationship have shown both temporal and spatial variability.•The change characteristics of αc is closely correlated to aridity index (AI) and average NDVI during growing season in the Loess Plateau.•Climate change and revegetation result in evapotranspiration increase in the Loess Plateau. Evapotranspiration (ET) is a key component in terrestrial climate and vegetation interactions. A generalized complementary relationship proposed by Brutsaert (2015); Brutsaert et al. (2020) has been shown to be a powerful tool for ET estimation. As the single parameter in the generalized complementary relationship, it is generally accepted that αc has high spatial variability and is closely correlated to the land-surface conditions. However, understanding of the temporal variability in αc is also important in a changing environment. In this study, we investigated the impacts of climate change and revegetation on ET by establishing the relationship between αc and the climatic-vegetation factors in 14 catchments of the Loess Plateau. The results showed that αc presented both spatial and temporal variability, where the aridity index (AI) and the average Normalized Difference Vegetation Index (NDVI) during the growing season are two dominant factors that control the variability in αc. Furthermore, combing the generalized complementary relationship and the empirical model of αc proposed in this study, the impacts of climate change and revegetation on the ET increase were quantified in the Loess Plateau. The results show that climate change (mainly expressed by an increase in precipitation) contributed the most to the ET increase (approximately 68% on average), whereas revegetation (quantified by the NDVI increase) also played a dominant role (approximately 32% on average) in the ET increase, which suggests that revegetation planning management should pay more attention to the increased water consumption by evapotranspiration in the sustainable economic and ecological development of the Loess Plateau.