Developing a two-source evapotranspiration (ET) method is a major challenge of the accurate ET estimation. As a single source ET method, the performance of Non-Parametric (NP) approach is limited by the unavailability of conventional equation of equilibrium ET in the water-limited situation. To solve this problem, a two-source equilibrium ET equation derived from Penman–Monteith equation expressed using relative humidity (RH-PM) is introduced into the NP method, then a Two-Source Non-Parametric (TS-NP) method is proposed regarding vegetation and soil as individual source. The accuracy of equilibrium ET derived from two-source method has significantly improved in the bare-soil surface (relative error: 31.26 %; RMSE: 13.18 W/m2) compared with that of conventional equilibrium ET equation and surface flux equilibrium (SFE) theory. Validated by eddy covariance tower sites, the performance of TS-NP method on bare soil surfaces is satisfactory, involving a significant reduction (near to 1/2) in the ET estimation error (relative error: 49.45 %; RMSE: 16.15 W/m2) compared with that of NP, SFE-NP and RH-PM method. On the dense vegetation surface, the performance of TS-NP method (relative error: 8.44 %; RMSE: 17.44 W/m2) is also slightly better than that of the NP method, SFE-NP and RH-PM method. In addition, air temperature and surface temperature are the most sensitive input variables in the TS-NP method, particularly in bare soil surface. The ET derived from the combined TS-NP method shows the best performance in arid areas (relative error: 22.20 %; RMSE: 16.52 W/m2) and non-arid areas (relative error: 8.12 %; RMSE: 17.61 W/m2), and the combined TS-NP method has satisfactory accuracy on the heterogeneity of underlying. Therefore, the TS-NP method provides a simple but efficient two-source method for high-precision ET estimation.

中文翻译：

---

一种估计陆地蒸散发的双源非参数方法：涡度相关点的验证


开发双源蒸散 （ET） 方法是准确估计 ET 的主要挑战。作为一种单源 ET 方法，非参数 （NP） 方法的性能受到水有限情况下常规平衡 ET 方程不可用的限制。为了解决这个问题，在 NP 方法中引入由相对湿度 （RH-PM） 表示的 Penman-Monteith 方程推导的双源平衡 ET 方程，然后提出了一种将植被和土壤作为单个来源的双源非参数 （TS-NP） 方法。双源法得出的平衡 ET 精度在裸土表面显著提高（相对误差：31.26 %;RMSE： 13.18 W/m2） 与传统平衡 ET 方程和表面磁通量平衡 （SFE） 理论的比较。经涡度相关塔站点验证，TS-NP 方法在裸土表面的性能令人满意，涉及 ET 估计误差显着降低（接近 1/2）（相对误差：49.45 %;RMSE： 16.15 W/m2） 与 NP 、 SFE-NP 和 RH-PM 方法的比较。在茂密的植被表面，TS-NP 方法的性能（相对误差：8.44 %;RMSE：17.44 W/m2）也略优于 NP 方法、SFE-NP 和 RH-PM 方法。此外，空气温度和表面温度是 TS-NP 方法中最敏感的输入变量，尤其是在裸露的土壤表面。从组合 TS-NP 方法得出的 ET 在干旱地区表现出最佳性能（相对误差：22.20 %;RMSE：16.52 W/m2）和非干旱地区（相对误差：8.12 %;RMSE： 17.61 W/m2），TS-NP 组合方法对底层物质的非均质性具有令人满意的精度。 因此，TS-NP 方法为高精度 ET 估计提供了一种简单而高效的双源方法。