Abstract The accurate determination of land surface water fluxes at various spatiotemporal scales remains a challenge in hydrological sciences. It is intuitive that land surface net water flux (i.e., infiltration minus evapotranspiration) directly affects near-surface soil moisture. However, there exists no hydrological model suitable to calculate net water flux based on measured near-surface soil moisture data. This is a consequence of the mathematical structure of existing models that use ‘boundary conditions’ to determine ‘internal conditions’, whereas what is needed is a model amenable to use near-surface soil moisture data (an internal condition) to determine the surface water flux (a boundary condition). To pursue the idea of utilizing remotely-sensed or in situ (i.e., sensor networks) near surface soil moisture data for estimation of net water flux, we derived an analytical model via inversion of Warrick’s 1975 analytical solution to the linearized Richards’ equation for arbitrary time-varying surface flux boundary conditions. The applicability of the new analytical solution was evaluated based on actual water flux observations as well as HYDRUS-1D simulations for four vastly different sites in Arizona, California, Idaho, and Indiana. Our results demonstrate that the proposed model reasonably captures net water flux variations in natural settings, including layered and vegetated soils, especially at larger time scales (e.g., monthly). While the model works for a wide range of climatic conditions, the prediction accuracy is somewhat lower for extreme dry or wet conditions. A major advantage of the new model is that it does not require calibration, which provides an unprecedented opportunity for large scale estimation of land surface net water flux using remotely sensed near-surface soil moisture observations.

中文翻译：

---

从近地表土壤水分观测估算地表净水通量的分析模型

摘要 准确测定不同时空尺度的地表水通量仍然是水文科学面临的挑战。地表净水通量（即入渗减去蒸散量）直接影响近地表土壤水分是很直观的。然而，目前还没有适合基于实测近地表土壤水分数据计算净水通量的水文模型。这是现有模型的数学结构的结果，这些模型使用“边界条件”来确定“内部条件”，而需要的是一个适合使用近地表土壤水分数据（内部条件）来确定地表水的模型通量（边界条件）。追求利用遥感或原位（即，传感器网络）用于估算净水通量的近地表土壤水分数据，我们通过 Warrick 1975 年对任意时变表面通量边界条件的线性化理查兹方程的解析解的反演得出了一个分析模型。新解析解的适用性是根据实际水通量观测结果以及 HYDRUS-1D 模拟对亚利桑那州、加利福尼亚州、爱达荷州和印第安纳州四个截然不同的地点进行的模拟评估的。我们的结果表明，所提出的模型合理地捕捉了自然环境中的净水通量变化，包括分层和植被土壤，尤其是在更大的时间尺度（例如，每月）。虽然该模型适用于广泛的气候条件，但对于极端干燥或潮湿的条件，预测精度略低。