Exploring the components of evapotranspiration (ET) is essential but challenging because of the difficulties in ET partitioning. This study aims to improve the accuracy in partitioning ET under farmland and apple orchards by the hydrological model HYDRUS-1D constrained with isotopes, and further identify the effects of land use change on soil water balance (SWB). In particular, the long-term average SWB was first decoupled by combining multiple isotopes (δ²H, δ¹⁸O, and δ³H), and then used to constrain HYDRUS-1D to improve model performance. With the isotope-based partitioned SWB, some hydrological model parameters difficult to be obtained experimentally were inversely optimized. Consequently, the performance of HYDRUS-1D in ET partitioning was greatly improved. Specifically, with the isotope method as a reference, the HYDRUS-1D with optimized parameters had errors of 20%±2.1, 4%±2.0, and 6%±0.8 for evaporation (E), transpiration (T), and ratio of transpiration to evapotranspiration (T/ET), which were much smaller than those from the model with default parameter (171%±34.5, 57%±5.8, and 58%±5.8). The apple orchards increased T by decreasing other SWB components. The framework of optimizing hydrological model by isotope-based SWB decoupling is promising in improving model accuracy, and the partitioned SWB components can be used to promote our understanding of ecohydrological processes.

探索蒸散发 (ET) 的组成部分至关重要，但由于 ET 分配困难，因此具有挑战性。本研究旨在提高同位素约束的HYDRUS-1D水文模型对农田和苹果园ET划分的准确性，并进一步识别土地利用变化对土壤水平衡（SWB）的影响。特别是，长期平均SWB首先通过组合多种同位素（δ ² H、δ ¹⁸ O和δ ³ H）进行解耦，然后用于约束HYDRUS-1D以提高模型性能。利用基于同位素的分区SWB，对一些实验难以获得的水文模型参数进行了逆向优化。因此，HYDRUS-1D 在 ET 划分方面的性能得到了极大的提高。具体而言，以同位素法为参考，参数优化后的HYDRUS-1D蒸发量（E）、蒸腾量（T）和蒸腾量比值的误差分别为20%±2.1、4%±2.0和6%±0.8。与蒸散量（T/ET）的关系，远小于默认参数模型（171%±34.5、57%±5.8、58%±5.8）。苹果园通过减少其他 SWB 成分来增加 T。基于同位素的SWB解耦优化水文模型的框架有望提高模型精度，并且分区的SWB组件可用于促进我们对生态水文过程的理解。