Evapotranspiration components and its driving mechanism in a sandy shrubland

• The improved S–W model significantly enhanced the simulation accuracy of evapotranspiration (ET). • ET, evaporation (E) and transpiration (T) were primarily influenced by precipitation and vegetation conditions. • T/ET was mainly controlled by leaf area index (LAI), and its influencing effect enhanced when LAI exceeded 1.6. • The water balance was mainly influenced by precipitation characteristics. Accurate characterization of evapotranspiration (ET) and its components in sandy shrublands and understanding its driving mechanisms are essential for desertification control and water management in desert regions. However, considerable limitations remain regarding the estimation accuracy of ET and its components in sandy shrubland, as well as the driving mechanism of the proportion of each component. Using long-term (2015–2022) in situ observations from a typical Caragana microphylla shrubland in the Horqin Sandy Land of China, this study improved canopy surface resistance and soil surface resistance in the original dual-source ET model and integrated random simulation algorithm to optimize empirical parameters. The improved model significantly outperformed the original dual-source model, with the coefficient of determination (R 2 ) value increasing by 20 % and root mean square error (RMSE) and mean absolute error (MAE) decreasing by 55 % and 31 %, respectively. During the growing seasons from 2015–2022, ET ranged from 0.02–6.38 mm/d with the average of 1.73 mm/d at daily timescale, and the dynamic of ET was primarily driven by the precipitation and vegetation conditions. The annual ratio of ET to precipitation (P) (ET/P) ranged from 0.71–0.83, with ET being the primary component in precipitation allocation. The ratio of T (vegetation transpiration) to ET (T/ET) varied between 0.22 and 0.67 at monthly timescale, peaking during the vigorous growth stage compared to the early and late growing stages, primarily controlled by the Leaf Area Index (LAI), and its influence on T/ET became more pronounced when LAI exceeded 1.6. The Caragana microphylla community exhibited a water surplus, with the difference between annual P and ET (P-ET) ranging from 80.77–142.07 mm, and it was mainly governed by precipitation characteristics. ET dominated the water balance, and played a more significant role during drought period. This study indicated that water and vegetation conditions jointly regulated the distribution process of P and ET, which was of great significance for water management and ecological restoration in desertification regions.